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

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.