Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

  A newly acquired 5hp 70’s Ariens snowblower started fairly well over several days with test starts and running the engine for a minute.  Then it started a bit harder and just barely putted along having very week combustion after 10-to 16 cycles and died.  It’s been about the same every since then.  It won’t start easily now with gas through the carb.  I can get it going with gas through the plug but it only sputs along for about 10 cycles, very faintly and dies.

   It has 60psi compression after 5 pulls cold.  There was no to  very faint spark so I replaced the points which were pitted.  The spark is good but the same thing of running faintly for a short time and dies.

   My test of the coil was a little fuzzy so I replace the coil but the same thing happens.  It only starts by dumping gas through the plug and it does so in an unusual but consistent way.  I have to pull about 10 times and I hear a faint put or two with a slight breath of smoke.  The next pull or two a few more puts, the next pull about 6 to 10 puts, the next a couple then nothing.  I can do that over and over.  What’s unusual is that it never fires quickly but takes many pulls. 

   If I change the plug often it does not change things.  I check the spark and it seems very fine. I have a plug with the arm cutoff so the spark jumps to the rim.  I test the tester on other machines and their spark is about the same as on the 5hp. 

   Gas is not an issue, spark is not an issue, air is there.  I pulled the head and the gasket is fine.  The valves look ok.  The intake lightly covered with black carbon, the output a light brown ash.

   The timing is set as best I can set it.  The points gap is correct.  I don’t have a dial indicator so guessing BTDC, take off the point wire and use an ohmmeter so just get the points to open at BTDC.  I’m sure I’m at the right cycle as I’ve checked it over and over with a flashlight through the plug watching the valves and watching the key turn on the crank. I’m probably not on the money for BTDC but think I’m close enough.

   The only thing I can think of is if there was a compression leak from a wall crack or rings.  With 60 psi I think I should be running with no load fine.  It should at least run and sound like a good motor even it did not have any power. 

    I’ve obviously missed something so the reason I’m posting.  This business of running fine then within a few days very hard to start or no starting with running only for a short period and with very week combustions has happened before with a lawnmower and a chainsaw.  All very quickly deteriorated to non-starters unless gas was dumped into the plug.  When they did catch and only after many pulls they ran only for a short time and very weakly.  Since it’s happened three times it must have happened to someone else and be a fairly common thing but I’ve never seen a write-up on the web similar.

trouts

You've done so many things all at once, it will be hard to isolate the problem.  Particularly if you have adjusted the timing   Not sure what the advance is on one of those things.  The two stroke engines I've been working lately have an advance setting of 2.3 mm before TDC by measurement with a dial indicator.  Before diving into major and complicated settings, it's best to knock off all of the easy stuff, one at a time.  If you're making settings changes, you need a reference point.  That is if you make carb adjustments and they don't work, you must set them back to original settings.  Same with everything else.  Have you checked to see if you have water in your fuel?   By the way, 60 psi is fairly low for compression.  Carbon on the intake valve tells me that exhaust gas is flowing back behind it.  Your problem might just be valves.    

Maybe by write up was no so clear. The machine has only been around for a few weeks. It has a carb problem but I flushed the tank and line, pulled the carb and cleaned it. The thing worked fine.

After a week of test starts it went to this mode of very week combustions and dying. From that point on I bypassed the carb and have only been putting in gas through the plug. I don't expect it to run more than 20-30 cycles before dying but they should be strong healthy sounding like the week before. They were not. The combustions are wimpy like 1/10 normal. There's no sharp exhaust sound.

On looking at the spark the spark seemed weak or non-existant so I changed the points. It would not start. I changed the coil and got spark back. I'm at this time still putting gas in through the plug and changing plugs often just in case - all known good.

Spark came back but it still had very wimpy combustion. I pulled the head to check the gasket and it seemed fine. The weird part was the buildup on the intake valve, not much but there. There was a little more around the valve walls. The exhaust valve had a whiteish brown ash and no carbon around. I thought there would be carbon pretty much evenly around so confusing.

60psi is boarderline but should be enough to run well without load. It did a week before so it's the sudden change which is a puzzle.

I've tried to isolate so eliminated the gas system and only going through the plug. The spark was fuzzy before but always there when I check now. It's very hard to make the gas through the plug fire and takes several pulls. It catches and gives a short run of very week combustions.

I don't know much about valves but they don't seem to have hotspots. The intake is evenly covered with carbon. The exhaust evenly covered in brown white ash.

I described this to a guy today and he suggested pulling the head to see if the piston moves around at all which would suggest rings.

Borat - you suggested exhaust swirling aound the intake causing the carbon which might be happening. Maybe the intake is not seating fully and causing that. I don't know if the valves are ok underneath, seating properly.

The issue seems like valves or rings but how could that possibly happen in a week? I don't think it can be valves or rings but the symptoms say it's probably is. ??

if you try starting the engine without putting fuel does it start or sputter at all?, if not pull the plug and see if theres fuel on it, if there no fuel on it sounds like a carb problem. with 60 psi cold it should start and run just fine. does the engine backfire at all?  just wondering how you adjusted the timing because as far as l know there not adjustable.

It was not starting using the fuel system and the spark was weak at first so I wanted to isolate things. I have been putting gas in through the plug to eliminate the carb to focus on spark.

It does not start quickly with a pull or two with gas through the plug as most motors do. I did this many times changing plugs often. I changed out the points and coil and have decent spark now but won't start quickly.

When it does start it barely fires and goes like this. After 5-6 pulls it gets a whispy combustion or two. The two to three after another pull or two. Then several on the next pull or two, then nothing - the gas is used up. I don't care about running continually off the gas system. I'm looking for a healthy combustion. I think weak combustion must be due to either the timing being off, valves or rings.

The timing has been gone over several times but I don't have a dial indicator to stick through the plug. I'm guessing BTDC. What I don't know is how much leeway there is in settting BTDC. If it's got to be exact then I can't do that. If it can be very close and off but still give a healthy combustion then I don't have that. If it can be close but slightly off then I've got a valve or ring problem. (The head was pulled and the gasket ok).

I did a wet test today which was 80 so I think that says valves and the motor hosed. What I don't get in all this is how it can go from running strong and a week later a wimp. ??
trouts2

first of all squirting fuel in the spark plug hole is not gonna give you a reasonable combustion (air to fuel mixture) and in some cases the engine wont fire at all. 80 psi of compression cold is pretty good last time l checked and if compression increased when you added oil its the rings are worn and not the valves, you need to fix or replace the carb to diagnose probally, but as l mentioned crank the engine several times and pull the plug and see if its wet, if not you need a carb, or check and make sure you dont have a cracked intake manifold or a large intake leak. and the only way you can adjust the timing is buy the gap of the points which isnt adjustable, when you set the gap to .020 then your set., so if you got good spark/ points are set/ good compression then your only missing (air to fuel mixture) (fuel) hopefully this will help keep us posted.

>>first of all squirting fuel in the spark plug hole is not gonna give you a reasonable combustion (air to fuel mixture) and in some cases the engine wont fire at all.

What you say sounds reasonable but I've always gotten solid combustions with healthy engines even if they were not 100%. This engine is way off the mark. It's barely catching.

>>80 psi of compression cold is pretty good last time l checked and if compression increased when you added oil its the rings are worn and not the valves,

It's 60 dry and 80 wet. I don't have a lot of experience with compression tests but 60 is usually enough to run and toss snow so healthy combustions but not on this engine. An engine at 30 can at least sound healthy even if it gushes oil out of the breather tube. For rings I would expect a much higher reading for wet.
My net reading suggests that low close wet and dry readings are due to valves. I've had two engines that were pushing oil through the breather and their wet and dry readings were greatly seperated so I thought rings.

>>you need to fix or replace the carb to diagnose probally, but as l mentioned crank the

I have a clean spare I could put on but thought it a waste of time. This is an older Ariens and there's no bulb prime. It's got a push in cover that goes over the carb throat. Going through the plug should get healthy fires even if not peaked.

>>the only way you can adjust the timing is buy the gap of the points which isnt adjustable, when you set the gap to .020 then your set., so if you got good spark/ points are set/ good compression then your only missing (air to fuel mixture) (fuel)

I set my .02 on the peak of the dwell then loosened the ignition component frame so it could be moved to fix the opening of the points while at BTDC with a multimeter. I wound the engine through several cycles while looking through the plug hole to insure I'm at the proper place. I know I'm not on the money but I think it's close enough to fire well which does not happen.

Your understanding can only come from my subjective description about the firing being weak. The firing is like a repeated dying last gasps. The difference between a usual sequence of combustions (with gas through the plug) with a healther engine and this engine is like night an day. It's not small or off a bit it's huge. Gas dumped in through the plug will explode. It's just barely firing, just barely getting the crank around.

After reading about your problem.. a few thoughts!
Are you sure that your exhaust valve is not hanging up..  perhaps due to carbon on the stem or in the valve guide ??  Also, has the air temperature changed dramatically during the run and no run time ??
An engine which runs well in the summer will not always run well (if at all) in the winter without increasing the fuel flow. Did you say that you did replace th coil ?  I have had a few cases where mice, etc.
have chewed the coil wire causing a weak or no spark !!  Finally, some TEC's have a jet in the carb. which have an almost imposible to see hole in it which can plug up very easily !! Even seasoned mechanics have been known
to miss this one !!

>>Are you sure that your exhaust valve is not hanging up..
I'm not sure about that at all and don't know how to check that. I've watched the valves cycle many times by hand and they were opening and closing ok. When I removed the head I scrapped off all the surface buildup and tried to get under the valve and clean the seat as best I could. They opened and closed but I'm not sure it was properly.

This all happened in the last two weeks here in Massachusetts and the temp difference might have ranged between 50 and 75.

The points were replaced with no improvement. The coil was then replaced with no improvement. I've got the old coil back on now and it's the same. The spark jump outside the engine looks passable but not the best. It looks better than other engines that run fine though so I'm pretty confident the spart is ok. There are several new plugs around so I'm swapping and cleaning them constantly to insure I'm using a clean dry working plug.

>>An engine which runs well in the summer will not always run well (if at all) in the winter without increasing the fuel flow.

This is not about trying to run smoothly or well so much as going from health combustions to extremely weak combustions in a matter of days.

If I remember right this carb has a fairly large hole close to the base of the nut. I've seen some that have one or a few very tiny holes and always check for them.

I think I'm bypassing the carb altogether by dumping gas into the plug. Based on niper88's post I did some more tests. The older machines do not have a rubber button push prime. They had a spring loaded bakelite button attached to a carb throat cover. The manual says to get a prime you push the cover onto the throat and pull the start cord through a compression cycle.
I had a few engines like this and they were a bit tougher to start than engines with the soft rubber primes. I put gas directly into the throat and then tried starting. The machine got a couple of very wimpy puffy combustions a tad weaker than dumping gas through the plug but basically the same thing.

I'm under the impression that I could remove the carb altogether and still test the combustion part. I think if I removed the carb I should still get healthy sounding explosions from the engine. By dumping gas in the plug I should get a short run of decent explosions and I can't get that with this engine.

The explosions sound very weak like the combustion is happening way off BTDC or TDC. May this started happening as you suggest because one of the valves is not closing properly so it can't get a full combustion. When I had the head off I looked for cylinder wall and head cracks but did not notice any.

It's evening now and I just went out and checked the spark and it's great. Nice whitish blue thick jumps and I can hear the air snaps. I put in a fresh plug and unfortunately it did not tighten to a stop so the threads are now hosed. I've got to pick up a helicoil kit.

   I feel a bit defensive about gas through the plug given some of the posts above returning me to a possible carb problem.  I’ve picked up number of snowblowers from people who want to get rid of their machine so give them away or sell them for $50.   

 

  Today a person was selling an older Toro 724 for $25.  Those were very well made and dig into the end of the driveway pile very well unlike the lighter new machines.  Chances are always high if the engine is ok the rest can be made to work very easily and without much expense.   Today was a good example of using gas through the plug as a fast check on things. 

 

   The first thing I do when I get something like this home is check for spark and I do that quickly by dumping gas in the plug.  People generally are dumping these because they don’t start or run well because of carb problems.  Most have been sitting around for a few years and never had proper maintenance.  The gas in the tanks is usually old or dried up.  The carbs generally have varnish crud buildup or white cake buildup.  The carb jets are usually screwed up from tinkering so there’s no sense in pull starting till my arm falls off or heating up the starter until it melts trying to start the thing.  Dumping a bit of gas in the plug lets me know there’s spark and the thing can usually be made to run if it fires up well.  As long as I get a healthy sounding combustion there’s hope to go further. 

 

   If I get a short run of good fires it’s very positive.  I used to at this point put gas into the tank and try to run.  Over time I’ve found that sometimes some of these things would run but very soon develop gas related problems.  It was sort of a waste of time to put gas in the tank as I’d have to later drain the bowl, line and tank which is messy.  I found it was better to assume dirt everywhere so now if I get a machine to fire well I just take off the carb and clean it.  If the gas tank has a lot of crud I’ll drain the line and tank and flush it out with a garden hose. 

 

     I should add that I did a compression check right after I got the run of good combustions which on this machine was a not so great 75 cold by the hand pull.

 

   I’ve found the majority of these machines don’t need a rebuild kit, just a through cleaning.  So today after getting a short run of good combustions I pulled the carb and gave it a good cleaning along with the tank and line.  I put the carb back on and it ran rough and hunted for several minutes but settled down and ran fine. 

 

   I got in the habit of using gas through the plug often as a quick check I guess because I’m always worried about spark and the pain in the neck of pulling the covers and removing the flywheel to get at the ignition area.

 

   Today’s combustions with gas through the plug were similar to the usual I get with an engine that is healthy.   They were quite different than the stubborn 5hp that has the wimpy combustions.  I’ve pretty much given up on that unless I can figure out how to check for a sticking valve which was suggested.  Other than that the only thing I can think of is to take out the valves and inspect the underside and the seats.  So it’s sidelined for consideration. 

 

    I’ve got another just like it, another old Ariens ST520.  It was a free rig as it would not start for the owner.  It got the gas through the plug treatment and it’s compression test was 145 so impressive.  I pulled the carb right away and cleaned it along with the gas tank and it been a great starter ever since.  It also had healthy combustions on it’s initial test. 

Tecumseh engines have a compression release, don't wory about the compression.

Take the bowl off the carb, the bowl nut is the inlet for the main jet,  take a piece of wire from a wire brush and clean the holes out with it, top and sides, then blow through it with carb cleaner.  I think that is all it needs.  timing is nonadjustable on 95% of the engines that TECUMSEH makes.

just put it back together. and run it..  let me know what happens.

Good luck

Friiy

   Most second hand older engines I've seen don't have compression release.  The ones that do test around 45psi but I'm not sure how consistant that is.  What is consistant is wet and dry test the same on the ones I've tested with compression release.

   Maybe you did not read the top posts.  I'm just giving a test to the engine and not looking ot make it run.  The carb may be all screwed up.  What I'm looking for is healthy combustions by dumping gas directly into the plug.  That should happen.

Almost all engines have compression release.   One type is a mechanical release that is spring loaded to pull aside at certain engine speed.

The other is un-noticeable rise ( intake side ) in the camshaft just before top dead center,  The second also is very critical to valve clearance.  Have you ever noticed that a engine with very little  Valve clearance is easy to pull over and a engine with too much clearance his hard to pull throught  (jerks back)..

Good luck,

Friiy

triiy,
>>One type is a mechanical release that is spring loaded to pull aside at certain engine speed.

What gets pulled aside?

I don't understand compression release so I'll have to dig into that.

>>The other is un-noticeable rise ( intake side ) in the camshaft just before top dead center, The second also is very critical to valve clearance.

When trying to imagine what's going on it always seemed a problem that once the engine fires the compression release could have to be disabled to close things off to maintain pressure. ??  Something obviously has to disengage this after the engine fires but I don't have a clue to what that is.

>>Have you ever noticed that a engine with very little Valve clearance is easy to pull over and a engine with too much clearance his hard to pull through (jerks back)..

This is pretty interesting if we're both on the same page here on the jerking back part. I think you're saying the pull out locks or tries to pull back the other way. On this engine that happens all the time. On some engines it's occasional but this one very often. It would make sense if the valve clearance being to much causing jerk back would also cause so low compression that an engine would not fully fire like a healthy engine resulting in  very weak combustions. Is that expected?
trouts

mechanical compression release is wieghts attached to the camshaft with springs so when the engine fires it reaches rpm and the wieghts fly out and disengage the mechanism, which closes the vavle. some of the old engines had a rod which you pulled out or pushed in to to achieve the same result. any how your tecumsech 5 hp does not have a compression release. as for the engine pulling back  when cranking (out of your hands) thats not a valve clearnace problem, its more likely a sheered  flywheel key which sounds like it could be causing pre ingition which in return will pull starter out of your hand when your cranking. and if so your timing will be off and is probally causing you all your problems.     ie good sounding compression.

niper99,

    The flywheel shear pin is ok.  The flywheel has been off a few times for replacing the coil and points.  As mentioned above I set the timing after installing the points at BTDC with a multimeter.  The point gap of .020 was set on the peak of the dwell then the crank rotated several times to get to the proper place in the stroke BTDC.  The point housing was then loosened and the points gotten to just open at BTDC.   

    I don't have a gauge to measure BTDC so it's a guess.  The timing will not be per spec but I think should be close enought to get a heathy combustion.      

   The pullback is very stong.  It's tough to say exactly but it's like an immediate lock up of the cord so it gets ripped out of my hand.  I don't hear any combustion or see any smoke out of the muffler so don't think it's firing slightly but it might be.  The timing could be off and the problem.  I've set it and gone over it a number of times but when you've missed something you don't always catch it on a recheck.  It's been raining for a few days so on the next decent day I'll go back over the timing and possibly adjust the vales.  As I remember valves in a car engine there was a nut and the valve could be screwed in or out then locked down with the nut.  I'm not sure how to adjust on a small engine so will have to look into that also. 

   The picture is of the 5hp valves.

I beleive the points are to be set AT top dead center,  What color of flywheel key does this have (gold or silver)..

Good Luck ,

Friiy

trouts2,

when l set points l do it this way, the rod that open the points make sure its fully extended out (points fully open) which should be TDC, then take your feller guage (.020) and move the capacitor up tight to the feller guage then tighten down the bracket, and that should do it. theres nothing that l can think of that  would cause the engine to pull back other than pre igintion and if you want to test if its the igintion system take the plug wire off and turn engine over serval times and see if it pulls back. and as far as valve adjustments there isnt any (non adjustable). 

friiy,

It's silver. ? Never saw a gold one.

niper99,

There is no "rod that open the points". The points are opened by an enlarged portion of the camshaf, at the peak of the dewll. The .020 was set there at the point of the enlarged portion that opens the points the most.

The capacitor is mounted on the coil and has a lead running outside the points housing. It's not near the points so impossible to make touch the feeler gauge. You must mean the movable part of the points bracket which the point arm attaches to and is moved by loosening it's holding screw.

The Tecumseh manual says get the .020 set at TDC then move the piston to BTDC. That position backs the points arm off the peak of the dwell and the place where the points should just open.

The ignition holder (not the points) then gets untightened and moved until a lead connected to the points and ground reads a break of resistance with a mulitmeter. That will cause a break in the field and excit the secondary of the coil. That's supposed to be what happens but given the way the thing runsI have something wrong in this. The spark is fine. It's got gas and air and does fire but not strongly. Compression is leaking someplace. Hopefully it's not the rings.

So, no adjustment for the valves. Maybe they need cleaning on the underside or refitting.

trouts

trouts2,

l'm sorry my example was on a briggs stratton, l would set the points when the camshaft opens the points the most (that should be close to TDC) then set  to .020 try that. the timing (DWELL ) can be changed a little by using a bigger gap or setting the gap a little early or late, it sounds like you have it a bit early which explian the pull back.

The Tecumseh manual says get the .020 set at TDC then move the piston to BTDC. That position backs the points arm off the peak of the dwell and the place where the points should just open.

if you set your points to the peak of the dwell (TDC) then your points will start to open just before before TDC and come off just after. the points if my opinion cannot start to open at BTDC its to early, you could check and see if the points are open before TDC because if they are its gonna spark. 

Niper99 wrote:

>>The Tecumseh manual says get the .020 set at TDC then move the piston to BTDC. That position backs the points arm off the peak of the dwell and the place where the points should just open.

 

Above, Yes.

 

>>if you set your points to the peak of the dwell (TDC) then your points will start to open just before before TDC and come off just after. the points if my opinion cannot start to open at BTDC its to early, you could check and see if the points are open before TDC because if they are its gonna spark.

 

Above, No, at lest not as I understand things.  The first paragraph conflicts with the second.

 

   The points opening at BTDC is what is called for so although early is not early enough to cause pullback. 

 

   To get the points to open right at BTDC there is a process to do that.  The metal enclosure that houses the points and is bolted down by two bolts.  The bolt holes are not round but oval and oval enough that the housing can be moved about 20 degrees.  The points are screwed to this housing so moving the housing affects the points. 

 

   After the .020 is set at the dwell the crank is rotated to BTDC and that is the spot the points should open not TDC.  To insure that happens the bolts of the housing can be loosened and the housing rotated slightly to get the point to just open at BTDC.  A mulitmeter is used to monitor the points.  The housing is rotated and just when the mutlimeter indicates the point opens is when the timing is right.  That’s at BTDC and when the start of the process of firing the fuel happens. 

 

   The spark creation is instantaneous with the opening of the points but the firing of the gas is not.  As the firing occurs in time the piston moving fast with a lot of mass.  Having the spark at BTDC is just the start of the explosion, not the middle, or finish.  They happen later.

 

  The explosion takes time and after the ignition spart the piston moves past BTDC.  There is still compression going on as the piston moves from BTDC to TDC.  The gas is starting to ignite but not completely ignited.  The piston gets to TDC, the compression complete and the gas completed exploding enough to drive the piston down for the power stroke. 

 

   That’s what should happen but since there is a lot of pull back something is wrong.

trouts2

All I know is that kick-back of the motor when starting is wrong,

Try top dead center, this engine only runs at 3500 rpm max, it does not need any advance anyway... it's not a  2002 Kawasaki cycle with smog junk on  it.

Do you have any Tecumseh motors that have been made in the last 20 years?  Maybe you can try one of the cdi units off of it, and put this painfull chapter behind us.

Good Luck,

Friiy

trouts2,

just wondering if you had a update on 5hp.

niper99

   Nothing further has been done but it's certainly not forgotten.  Next on the list is doing a quick valve tune,  probably just checking clearances and a lapping to insure a good seat.  I don't have the tools to do that so the holdup. 

   I put a wanted ad on Craigslist for small engine rebuilding tools 8 weeks ago and got a response.  The guy said he had lots of tools, needed time to get them out,  had everything needed, and would outfit me with a good set.  It's been 7 weeks now.  I've contacted him a few times and each time it's a list of excuses.  Yesterday he said no problem, give him two more weeks.  Time at first was not an issue as I'm still learning so getting information online. 

   A friend has the compresser so I may borrow his or get one from Jacks.  Cleaning around the cellar the other day I unearthed a dial face micrometer with a long stem like used for checking piston hight and valves.  Unfortunatly it does not have the second short arm which goes to the valves.  It probably can be used for getting BTDC though.  Friffy suggested just setting the timing at TDC.  That might be useful.  Doing that would at least eliminate any slip-ups from rough figuring BTDC.  If there is not a good fire at TDC then the problem is even more likely to be valves. 

   Within a week hopefully I'll round up enough tools to do a semi-valve job that will tell me if the problem is really the valves.  The other thing that was iffy was just what tool to use to check the seat clearance.  I have the basic feeler gauges but for checking the seat to valve clearance I think I would need a round set.  Still confused about how people check the valve clearance and piston clearance. 

trouts2

 

you check valve clearances between the valve stem (end of valve) and the lifter. and for checking piston gap you can use a feeler between the piston and cylinder wall.   hope that helps

Hey Touts'

I think you are going the wrong way on the valve job, A  snow machine works in a controlled work enviroment.. (lot- a -snow ,  not much dust and grit).  a lot of the engines we preform valve jobs on were mowers in dirty areas (grit eroding the valves, mostly intake),  or mowers that had plugged cooling fins that overheated the block and tipped the seats or pounded them into the case, (mostly exaust side)... or  floor buffer propane motors that would build large deposits in the chamber that break and lodge on the valve seat (ex side),   cheap generators that only run at full speed ALL the time do have valve and guide wear issues.  Other than the odd situations of throttle shaft screw ingestion, most valves on a aluminum bore engines outlast the most of the motor, sometimes they need to be adjusted  and lapped.  But  97% of the time they are just fine.

I would think before you had a worn valve, you might have a gummy intake stem..old gas varnish slowing down the intake valve when you crank it over. this can be unnoticeable when the engine is apart and you are turning it over by hand slowly.   So spray some type penetrating oil on the stems if you still have it apart and turn the valves to wash any sticky gas goo away.

Please, please, please,  pretty please set the points only at TDC.

Always best of luck,

Friiy

P.S.  If you are going to lap the Valves, in the field I have hot glued a wooden dowl to the valve face instead of valve lapping tool, and used a sharpie pen instead of Prussian Blue.. At very least it will show you the shape your valves are in.

niper99,

  

    OK, on the clearance check being between the valve stem end and its lifter.  I’m still fuzzy on what gets worked to change that distance.  I suppose when I get in there it will be obvious.

 

    The cylinder wall piston check is the part that confuses me.  I have a wide and thin set for plug gap checking.  They are flat and the wall curved so the I can’t see how jamming in a flat feeler would give an accurate measurement.  It seems a round gauge would have to be used.  I’ll have to google around for that.

 

 

friiy

 

>>I think you are going the wrong way on the valve job,

  That’s a high possibility.

 

>>a lot of the engines we perform valve jobs on were mowers in dirty areas (grit eroding

  OK, a lot of interesting info.  The high likelihood is not valves but if valves then not burnt but other issues.  The gummy stem is a new one for me.

 

>>Please, please, please,  pretty please set the points only at TDC.

 

   This is really my next step before messing with the valves.  I have just not gotten to it yet.  It seems that if it’s set to TDC and the valves or rings are marginal I should still get healthy combustions.  My readings were 60 dry and 80 wet.  I think that’s enough to get a proper sounding fire even if there is no power. 

 

  In a post above I mentioned not knowing just how much leeway there was in setting BTDC before poor performance becomes noticeable.  For example if I’m 5 thousands off or 20 thousands off where is the breakpoint for noticeably degraded performance?  I figured by setting to TDC I could eliminate any BTDC error so it’s on the top of the list.

 

   Bare with me I’m still learning a bunch.  This past year I’ve picked up a number of older snowblowers with mostly carb and gas related problems and learned a bunch.  Getting a non-starter or stumbling dog going by stripping the carb, flushing the tank and line and have a machine starting and running reliably in about 20 to 30 minutes.  This forum has a lot of good current and prior posts which I search all the time for info.  It’s been a big help.

 

   Some of these engines, like the current 5hp, have issues that possibly could be cleared up without too much work or expense.  I’m still learning how to deal with those things.

 

   The 5hp has an issue with valves or rings given the compression tests.  It should be able to fire though and before I go further with valves or rings clearing up the firing problem seems the first thing to do. 

trouts

Hey Touts,

You grind the stem of the valve  to adjust clearance of the valves ( a little goes a long way,  start slow - finish slow. Try to grind flat /square.)

Good Luck,

Friiy

    No luck on the timing adjustment.  The engine is a HS50 67008 and the BTDC setting .035.   I finally found a dial indicator with a long enough leg to take a reading. I found the timing set at .1 BTDC so .065 before BTDC.  The timing was reset  to.010 BTDC. 

 

   The flywheel was spun many times with a multimeter attached to the points arm to check over and over that it was on the compression stroke and the points were opening at .010 BTDC.

 

  The result was the same.  It would only start to fire after 8-10 pulls, very weakly, with one or two fires.  Then on the next few pulls a string of 2-4 weak fires.  No strong combustions so the same behavior as it has been before the new points, condenser and coil change.  It had the same behavior after the incorrect timing setting of .1 BTDC.  And the same behavior after setting .010 BTDC.

 

    My guess is it’s the valves or valves and rings.  The engine was hanging around for a long time.  I wonder if it was possible to have a wall or ring buildup that would seal the chamber for a while but get burnt off causing the apparent quick demise over a week.  Possibly some carbon got burnt off the valves which opened things up more all of a sudden. ??

    Valves are next then rings.

trouts2

trouts2 wrote:

trouts2,

just wondering if you set the timing to TDC yet ?. anyway l think your making this diagnose way to complicated stick to to the basics, SPARK/FUEL/COMPRESSION u need those three things before the engine will run, you have compression so l dont understand why u think its valves or rings?, and as far as timing goes l have never if my life set points with a multi meter or dail indicator ever, did you put another carb on this engine or repair the orignal one?, if the engine is pulling back while cranking then u have a timing problem period not maybe for sure,  any how elimanate one problem at a time make sure u have fuel then check compression then spark and as far as the valves go there non adjustable other than maching as fitty menthioned.

Niper99

 

>just wondering if you set the timing to TDC yet ?.

  No,  .010 BTDC is fine, close enough. 

 

>>l have never if my life set points with a multi meter or dail indicator ever

 

   Neither have I.  The points were set with a feeler gauge.  The timing was set with the multimeter and dial indicator.  You use the mulitmeter set to ohms to check continuity of just when the points open.  That place is located with the dial indicator. 

 

The process of setting the timing is:

 

1.      The points are gapped at .020 with a feeler gauge at the peak of the cam dwell.

2.      The points are isolated by removing the coil and condenser wires.

3.      An ohm meter (multimeter set to ohms) is connected to the point arm and ground.

4.      The piston is then rotated to .010 BTDC.  The dial indicator is used to tell where that spot is while rotating the crank.

5.      The points are located in a holder which can be rotated.  The length of rotation is just enough to allow the points to move on the cam dwell a small amount, about .40. That allows the timing to be adjusted from TDC to way before TDC. 

6.      You set the timing by rotating the holder to the place where the points just open as indicated by the multimeter. 

7.      That sets the timing.

  

   So the process is set the points(feeler gauge), get the piston at whatever BTDC you want(dial indicator), then make sure the points open at that spot(multimeter). The timing is then adjusted. 

 

   That is the process described by the Tecumseh Technicians Handbook, “3 to 11 hp 4-Cycle L-Head Engines”.

 

>>you have compression so l dont understand why u think its valves or rings?,

 

   Your right.  I would think that 60 dry and 80 wet would be enough to get healthy combustions so I’m not sure what’s going on. 

 

   There is air, a healthy spark, and gas.  It does run but weakly.  I’m guessing that it’s weak because of valves or rings. 

Hey Touts,

Niper is right,  all you have to do is put the engine at TDC and set the points at .020  .

I have NEVER used ohm meter for that.

I think you're reading more into this than is needed.

I know this flywhell is a pain tin the A$$ to take off, but please do this for us.

All the engine requires to fire is fuel, spark and compression.

You have compression,  you have been bottle feeding it,  all you need is set your spark.

Good Luck,

Friiy

hey trouts2,

i didnt mean to affend you in any way if did,  just trying to help u get your engine running l know the tecumseh manual say that about setting the timing that way, but lve never set the timing that way before and l never  had a problem, l'm just concerned about pull back while cranking and what could possiably cause that and the only things that l could think are (timing to far advanced/ flywheel key sheered/ camshaft timing marks not aligned) but l was thinking and l'm not sure about this but when you replaced the points u probally replaced the condensor and l just thought maybe u got a bad one and its causing the pull back or inconstant spark if u still got the old one maybe u could try it and see what happens.

I have read every post to double check the most important thing. You may have several pieces of OPE equipment that may run fine on the gas you are using because the compression is better and/or spark is better BUT....your problem engine engine may DEMAND the freshest gas beause of weaker spark or weaker compression.

Is your gas fresh?

I have had problems with starting if the gas I use goes just slightly stale.

niper99 & newjerseybt,

The pull-back bugs me also. Given the weak reading of 60 dry 80 wet I think it should be firing ok so I’m stuck. Now that it's on .010 it should be fine for timing unless I've just plain old missed the boat and am off 180. But I did go over the position of TDC many times and also checking the spark often.

1. The timing should be ok.
2. There may be an issue with the plug and compression. Above I mentioned the plug being cross threaded when I got it. Today I'm going to put some talcum powder around the plug and see if there is any blow-by on pull starting. I'll be checking for a healthy spark again today.
3. The flywheel has been off more than debutants underwear and the key is fine.
4. I don't think the timing marks have jumped but it's imaginable. There has never been any grinding or metal crunching sound to indicate something internally has moved.
5. If the condenser is bad I don't think I'd get a healthy spark. It was replaced so new.
6. There could be an intermittent with spark and greatly reduced when it finally catches causing weak fires but not likely.
7. I'll have to check for pullback again provided I can pull many times. My back went out and just coming around again.
8. The gas is fresh gas. There are a number of small engine machines here and I buy a gallon and a half at a time. The tests have all been done with gas that was at most two weeks old and the last run a few days old.

1. Today I'm going to check for leak in the plug threads.
2. Reckeck the spark.
3. Recheck the wet and dry compression.
4. Order a valve spring compressor. Given the input above I'm leaning to the valves might make a difference but overall not the cause of the problem. Probably the rings are worn also but not the cause of the weak fires. I've have engines whose compression readings are worse and pump oil out the breather but sound fine.
5. There is the head gasket which I think is ok = "think" is ok

I think I've found it. Talcum powder was put around the plug and on pulling it puffed away from the plug with fairly strong puffs. Its leaking compression through the threads.

When I got the machine it was cross threaded but I thought just at the top threads. I must have put the plug in the wrong line a few times to open an air escape and cause the "quick demise".

The only fix I know for this is a plug kit which is about 45US. Uhg!

I have a 5hp with a broken rod which might match up.

Does this plug have a gasket on it?  I think you can go to an autoparts store and uy a thread repair kit cheaper than that..  I think your other 5 hp will fit most of the heads are the same, even from vertical to horizontal shaft motors..   I know on a electronic or cdi coil you want to make sure the coil is right side up,  make sure that when you changed coils you put it on the same way. 

Good Luck,

Friiy

   The plug repair kits I looked at were 40-50 bucks and the chances of me needing them after this job are pretty slim.  The head bold would not line up on three spare 5hp's I've got kicking around - hard to believe.  The local dealer has a spare 5 head which might match up though.  He's going to pick a 5hp snowblower he has and giving me the remains.  He also said he'd put a coil in the head for 5 bucks so I'll probably drop it off.

   The engine will still have the not so great compression so a good motor for me to experiment with.  Today I ordered the tools needed for a valve and ring job so will attempt it shortly.  If the job goes well I might attempt to put in a piston rod in another snowblower I picked for free. 

   The other snowblower is a Jacobson Imperial 526 which is a little weird.  It has light rust all over but the metal is in excellent shape.  The tractor section is like new inside.  The friction disk has the widest rubber I've seen on any snowblower.  It also has what must be it's original thickness given the light wear on the machine.  The engine on this one was 90psi but the rod broke.  If the engine was still good it would be hard to sell the snowblower because it looks so bad but it's a great snowblower.  So it's a good candidate for learning a bit more.

   On the 5hp, the compression leak was not noticable when it ran poorly.  There was no indication from sound or smoke.  The plug got changed a number of times but the plugs all had compression rings.  I know to be careful on overtightening plugs so the thread cross was probably close to completed when I got the machine.  The plugs were seating well after the "demise" so leaking before throughly broken through.  In a few days I'll have the dealer fix the plug threads and it should fire well again.

   A few comments about compression release.

 

   I’ve picked up more info on compression release mechanisms so now have a bit better understanding of what niper99 and friiy were mentioning in posts above.

 

   I now think many more Tecumseh snow engines have compression release than before and the reason is this.  From what I understand there are three basic types with variations. 

1. Mechanical, generally referring to a weight, springs and a pin or some other mechanism that finally lifts on or the other valves to release or lower compression for easy starting
2. Bump – a pump on cam intake or exhaust lob to push up one or the other valve.  I think this type is more sudden higher lifting than Ramp.
3. Ramp – like Bump only a slower rise to the lift and less lift.

 

    At lease that’s my take on the types for now.  I’ve gotten the impression from net reading and some testing on various machines that the amount of release can vary to give compression readings of 45 to 120psi.  

  

    The two newer motors I’ve tested and sure have mechanical release tested at 45.  Those were on snowblowers that had strong motors and tossed very well.  Some of the other motors I have which I think have bump or ramp have tested at 60 to 120.   It makes compression testing unreliable without knowing exactly what the expected value should be from the factory.  There could be a motor with a reading of 60 which would be expected because it’s the release point for that motor versus 60 on a motor that should read 120. 

 

    The conclusion is there are many more motors with compression release than I previously thought.  The motors that do have compression release have values but are a bit to difficult find out what they are.  Many of the motors I’ve tested test at 110 and above and I now think they had compression release – even motors that tested at 130 and 145.

 

   It would be a confidence builder to test an engine and get a reading of 100 to 145 but getting a 60-80 does not mean much other than the motor should be able to toss.  At a reading of 40 or below the motor can’t get up enough umph to rise about the compression release so a candidate for rework or scrap.

trouts

    Looking for any suggestions after working on the engine again.

    1. New points and condenser and getting a nice spark with the spark tester.  When I test with the plug to ground it gets a nice spark.

    2. Removed the head and lapped the valves.

    3. Put the head on a plate that .0005 flat over 17 inches and notices a slight irregularity in the head.  I could not measure it but possibly it might have been up to .003 diagonally across the head.  I ground it on the plate with 600 wet and removed the wabble. 

    4. Put on a new head gasket, Tecumseh not aftermarket.

    5. Torqued the head to spec and to the Tecumseh pattern.

    6. Rebuilt the carb just in case and installed a new gas line and filter.  I normally put in gas through the plug bit as it's been mentioned above I just wanted to eliminate as much as possible. 

    7.  The timing was reset with 20 point gap and the opening of the points happeneing as close to TDC as the points case allows for with rotation.  I don't think it's mechanically possible to get it closer to TDC than how it's currently set without changing the gap to a smaller gap.

   8.  The compression has stayed the same 60 and a poor 60 at that.  Real good engines I've tested go to 60 on the first pull and 90 on the second.  This engine goes to 30, 45, then 60 on three pulls.  Since I can't run the engine that's a cold reading.  The cold wet is 80 which made me suspect valves.

   9. There is no compression release of any type that I can see by watching the valves with the head off and turning the crank by hand.  There is no MCR in the drawings.  There is no valve movement other than expected with the 4 strokes.

  10.  On trying to start the engine it is a bit worse than before.  It's sometimes gets a few very faint fires.  The plug ends up wet all the time if it I keep cranking.  If I just have gas going through the plug for better control adding small amounts it will just barely fire once or twice.  If I keep pulling and testing the plug eventually gets wet.  I"ve done this a bunch of times with 4 new plugs. 

   11.  I"ve got gas and spark.  The valves have been lapped and look good along with the seats.  I"ve got a high power magnifier eye piece and the seats and faces look ok so I think from a compression standpoint the valves are not the problem.

   12.  The valves are not the problem.  The head and gasket are I think ok.  There was an issue with the spark pulg hold but it's been helicoiled and tested with talcum power around the base and seems fine. 

   13. It rained and a wind blew off the tarp covering the head.  The piston was down an inch into the cylinder so water gathered in the top inch and stayed there.  I drained the oil thinking there would be water but no water leaked down past the rings into the crank case.  I removed the oil to check.  It seems odd as there are ring gaps and I would have expected water to run through - but no water in the oil. ??

  14.  All the above seem to make me think the cylinder wall is cracked or the rings are bad.  Given that the engine ran fine not so long ago I don't think it's the rings or a crack.  ???  What have I missed?? 

   Since I'm confused about what's going on with the weak compressions and my thinking it's due to a compression problem I came up with a test which I think is valid.  I hooked up an air compressor through an adaptor to the spark plug hole.  I got the engine at TDC on the start of the power stroke.  Both valves should be fully closed.   40-50 psi of air was pumped in and there was leaking from the carb muffler area.  After taking off the carb and muffler, air was coming from the exhaust port.  On trying to block it off with my thumb there was significant pressure against my thumb. 

   After thinking about how that's possible I thought possibly the tappet might be lifting the valve.  There was 8 thousands clearance which is the max so ok.  There must be a poor seating between the valve face and seat.  I lapped the valves but did not pre-grind them.  I don't have the tools for that.  I figured a good lapping would be enough.  On inspecting the face and seat they looked ok with a magnifying glass.  ?? I guess not.  I think I've found the problem but if anyone has any comments about the test please let me know. 

  Will re-lapping be enough?

trouts

trouts2 wrote:

trouts

  Will re-lapping be enough? no, if there a that much of a leak u got a serouis problem, is this the same engine that would'nt run ?. check and make sure the seat isn't loose in the block, and when your have compressed air in the cylinder the engine sometimes wants to turn a bit make sure its staying on TDC u may half to hold.

Niper99

   If you were reviewing the job done by someone in your shop then you’d probably be right.  You could count on the guy that did the lapping to have done the job right.  I think I did not do the lapping right.

    The valve face was grayish.  It seemed smooth and even and the seats similar.  I figured since I still had a leak I might not have done the lapping well enough.  I tested them with water in the ports and there was water at the valves.   So poor lapping job.

    There was enough margin and lash to do them again so I did and decided to stay at it for a while and do a better finish also.  I’m using Permatex which is a course and fine together mix.  When you grind the compound breaks down to a fine grit and you finish with the finer broken down particles. 

 

   I ground quite a bit and got the same gray even looking finish.  I then did not add more compound but let it break down and ground with that for a long time. After a while the face top and bottom part started to get polished and reflective.  The middle of the face was gray still.  That told me the face was somewhat concave and the seat somewhat convex.  I ground more but slowly and evenly and eventually the whole face got ground and I think flatter and smoother than previously.  The full face ended up shiny and smooth. 

 

   I checked the job with water in the ports and no water leaked out of the valves.  So I think the lapping was ok this time.   I put the thing back together and it would not start.  Gas and spark were fine.  I took off the carb and muffler and put air in through the plug again with the cylinder at TDC (and a board to hold it there).  There was a lot of air coming out of the breather port.  I drained the oil and there was a lot of air coming from the oil check hole.  There was no air felt on my thumbs at the intake and exhaust ports now.  I think the valves are ok but I have a ring problem.  It was there all the time.  I think the motor had both a ring and valve problem. 

 

    I’m seat of the pants guessing at the air flow through past the rings because I don’t have a proper leak down tester.  At 50psi in it seems like a bunch leaking through the rings.  When I block the oil input there’s a lot of air blowing out the breather. 

  

   I ordered rings this morning, they’ll be sent out Monday and few days later installed and I’ll see what happens.  I’m still fairly new at engine internals so I’m pretty sure got the diagnosis wrong and the lapping wrong.  Hopefully I’m no the right track.

trouts 

Crew,

   There were a lot of problems with this engine and fairly difficult to deal with.  The carb was messed up, valve problems, and intermittent spark causing some confusing problems.  When this was posted I was still ramping up on rebuilding so this engine got put in the background several times.  Over time I’ve rebuilt 5 engines and finally got back to working on this engine again. 

    I relapped the valves, water tested them and put in rings.  It sill sucked, barely started and ran weak.  Since starting this thing I’ve picked up a leakdown tester and after testing this one last week found a big ring leak into the crankcase.  Evidently besides it’s other problems which were worked off it also has a worn bore.  You can’t win them all. 

    The good part was I’ve learned quite a bit and rebuilding and getting strong engines – aside from this one.  I’ve now ordered a decent bore gauge which should be here in a few days and prevent any false rebuilds in the future. 

     Thanks for all the help it’s very much appreciated.

Trouts2

I assume the bore was oval shaped.  This is a fairly common occurrence caused by piston wearing  as a result of poor lubrication.  When it wears, it begins to rock  in the bore usually wearing front to rear.  It's not a readily observable condition but, as you've learned, can seriously effect engine performance.  Was the cylinder beyond a re-bore or just not worth the expense.  I work on old 1970's two stroke motorcycle engines.  When originally produced, they were designed to be over-bored several times.  Max number of over-bores on the Yamaha RDs is eight (2mm).  Which is incredibly robust considering that you can get 10000 to 20000 miles per over-bore providing the bike is ridden sensibly and good quality oil used.      

What does you local machine shop charge to oversize the cylinder?   I have not done it in quite some time..   but if you fine a hungry machinist it can be done cheap..

Depends on you location and their workload, you may want to give them a call.

Friiy