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

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.