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Tecumseh Engine Lacks Power


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#16 HowardsMF155 OFFLINE  

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Posted June 11, 2012 - 12:10 AM

Got into the engine some today. While the valves have some play, it looks like there is not enough. The exhaust valve is between .006 and .010 ( I wasn't checking too closely, didn't know specs at that time.) and the intake is around .006 . Specs call for .020 for exhaust and .010 for the intake. Am I reading correctly that you have to grind off the end of the valve to maintain proper clearances? I suppose that this would be a good time to lap the valves to renew the seat? Sorry, no pictures to post. Not too much carbon built up in the combustion chamber, but I'm sure this would be a good time to remove that as well. Head gasket looked OK, I think I'll have to reuse it. I did also find the float on the carburetor was set too low, probably why it needed a touch of choke at idle. I saw in a trouble shooting guide that a clogged muffler can cause lack of power and overheating, so I'll be checking, perhaps replacing that.

TIA

#17 MH81 ONLINE  

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Posted June 11, 2012 - 02:45 AM

IDT I have ever seen a set that grew longer. Normally, I'm finding I'm on the high end of the tolerances due to wear.

Yes, the book does say to manually shorten them, but watch the compression release isn't messing your readings up.

:anyone: remember how to compensate for this?
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#18 HowardsMF155 OFFLINE  

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Posted June 17, 2012 - 09:39 AM

Pulled back into this a few days ago. To avoid the ACR, manual says to have the piston at TDC on compression, so I did. Clearances were definatly off, so I "rented" a valve compressor from my local Advance Auto and went to work. The intake valve was in good shape, so I lapped it, then ground very lightly on the bottom of the valve shaft until I had just about .011 clearance. The exhaust valve actually had some carbon built up in the seat, plus it lacked proper clearance. I cleaned the valve with a brass brush, then lapped it into the seat. The clearance at this point was only .005, so I ground the end ot the valve until I reached .020 clearance and put it back together. I used a copper gasket spray on the head gasket since I was re-using it, and torqued down the head bolts. After I reassembled everything, I found that the starter relay decided to die, so I still have to get that fixed.

#19 olcowhand OFFLINE  

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Posted June 17, 2012 - 10:05 AM

.005 is pretty tight for these engines. It may have been closing that gap when up to temps. Hope this is your fix.

#20 HowardsMF155 OFFLINE  

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Posted June 17, 2012 - 09:21 PM

Installed the new start relay today and was able to crank and test the engine. A short test run showed it doing pretty much the same, it sounded like it was running well, but lacked power. One thing I had looked at while I was under the cooling tin was the ignition setup. I checked the gap to the tallest pin and it was OK, but with an eye to trying to check ignition timing in the future, I looked at the flywheel and found that one of the mounting holes for the debris sheild was close to being aligned with the taller ignition pin. There was a noticeable distance from the tall "cranking" trigger pin and the shorter "running" trigger pin. So before I had reassembled it from the valve job, I marked that particular boss so I could throw a timing light on it. After the disappointing test run, I took my timing light and checked the position of that boss while running. It was at the ignition position of the tall pin, so that told me that for some reason the short timing pin was not firing the ignition. I removed all the tin, pulled the flywheel and looked the pins over. The shorter pin had somehow been driven in too far, so it was not triggering the ignition properly. I carefully drove the pin out until it was at the specified 3/16ths (it was more like 1/8th). I then reassembled the engine and cranked it back up. A check of the timing light showed that the ignition was now firing at an advanced position! I then took the tractor for a short spin and I think the issue is solved. I won't know for sure until the next time I cut grass, hopefully in a few days.

#21 olcowhand OFFLINE  

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Posted June 17, 2012 - 09:43 PM

Good detective work! I've never had an issue with the pins, so didn't figure them to be an issue. But the valves did need attention, so nothing done in vain.
I bet she runs like a champ now!

#22 HowardsMF155 OFFLINE  

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Posted June 17, 2012 - 09:54 PM

Good detective work! I've never had an issue with the pins, so didn't figure them to be an issue. But the valves did need attention, so nothing done in vain.
I bet she runs like a champ now!

The bizarre part is that I never really heard it running badly, just lacking in power. I'll have to give the grass a chance to grow to be certain, but it certainly had at least those two problems.

#23 MH81 ONLINE  

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Posted June 18, 2012 - 08:15 AM

Howard, good news you found that issue. The taller pin will run it, but timing is so far retarded that it would have virtually no power at all. 17 degrees is a long way off.

Can't wait for the report on the trial run. Go water the grass ;)

#24 HowardsMF155 OFFLINE  

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Posted June 19, 2012 - 07:31 PM

Can't wait for the report on the trial run. Go water the grass ;)

All I can say is, you must have the ear of the man upstairs! On a day which was supposed to be sunny with a 20% chance of rain, we had a short but heavy shower withing 1/2 hour of you posting this :confuse: . So tonight I got out and ran the tractor and cut some grass, not tall grass, but enough to be throwing clippings. The engine did a decent job of keeping up RPMs and moving uphill at at least a fast walk. It did bog down when I went full speed, but that is sort of beyond designed parameters. There is NO question that the engine had more power than before, so I will see how things go in the future. I may need to try mowing at twilight and see if the muffler still glows. I may also tear down the carb because I don't think it is working correctly quite yet, it was running ok the other night, then was slobbering rich tonight. Still, it is progress, because that is a minor problem if it will run the mower deck while moving at a good clip.
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#25 sacsr OFFLINE  

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Posted June 19, 2012 - 08:30 PM

Sounds like you are going in the right direction. Glad you figured the pins out......I would never have gone in that direction either.
Good job!

#26 DH1 ONLINE  

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Posted June 19, 2012 - 08:59 PM

Good stuff on trouble shooting the lack of power problem with your engine, glad you got it running better.
An engine that is running with the ignition timing retarded will run hotter than it should and you might find that adjusting you high speed jet will make it run even better now with the right timing.
I bet the muffler still glows in the dark, more so closer to the exhaust port.

#27 HowardsMF155 OFFLINE  

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Posted June 19, 2012 - 09:14 PM

Sounds like you are going in the right direction. Glad you figured the pins out......I would never have gone in that direction either.
Good job!

All I can say is that it was a moment of inspiration. There are no timing marks on this motor, and the way it is set up you shouldn't ever need them. All I can say is that as I was putting it back together after the valve job, I wasn't convinced that they were the whole problem. So I looked for a way to see if the timing was advancing as it was supposed to, because I figured it was either timing or bad rings, and rings are a far bigger problem than timing.

#28 HowardsMF155 OFFLINE  

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Posted June 19, 2012 - 09:24 PM

IDT I have ever seen a set that grew longer. Normally, I'm finding I'm on the high end of the tolerances due to wear.

Yes, the book does say to manually shorten them, but watch the compression release isn't messing your readings up.

:anyone: remember how to compensate for this?


I hadn't mentioned this before, but the exhaust valve had a nice chamfered end on the bottom, as if it were factory new. I suspect that with the engine having such an obscure ignition fault, someone may have replaced a suspect exhaust valve but didn't know enough to get the clearance right. I also now think that this is part of the reason why the last owner was selling this and up-grading to a small full-size tractor, as it must have been dis-heartening to have the engine running but not have good power. I know the previous owner was using this mainly for sleeve hitch work, and had another lawn tractor he used for grass.

#29 HowardsMF155 OFFLINE  

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Posted December 17, 2012 - 02:31 PM

Wanted to revive this thread, cause I'm having another problem with this engine, perhaps more than one. After the events chronicled here, I proceeded to use the tractor a number of times cutting my grass. Power was greatly improved. However, I was hearing a bit of a knock when under heavy load, so I decided to return the mower deck to the "dump" Massey with the new engine. It used less gas and has plenty of power to muscle through anything I can throw at it. I let this tractor sit a couple of weeks, then wanted to use it to start plowing my garden under in the late fall. When I cranked it up again, the exhaust blew HEAVY smoke, enough to blanket the ground for several yards all around. I let it run thinking it would clear up, and while it did diminish somewhat, it continued to smoke heavily. Now, the last time I used it regularly, the exhaust had a slight haze to it, but nothing really bad. I haven't had much time to look at this, but I cranked it up again today, and it does the same thing, HEAVY smoke on start-up, then thins out a bit but still a real smoker.
So,
Question 1: Does the knock under load mean I have connecting rod problems?
Question 2: Any thoughts on why the engine is smoking so badly, esp. at start up?
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#30 chris m OFFLINE  

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Posted December 17, 2012 - 03:37 PM

Howard 1st off sorry to here you are still having issues with this :(

What your engine is doing is the same as the 2 I am rebuilding right now. Both smoked heavy and more so at start up and both had a knock under load.

I pulled the head on both engines and there was a puddle of oil sitting on top of the piston on both.

So far I stripped one of the blocks and the connecting rod on this one was out of spec.

After checking the bore and the ring end gaps on the stripped motor, The bore is to large and the ring end gaps were huge, when I say huge I'm talking close to an 1/8".

So... it is sounding like you may be having the same issue as me.

Tec engines seem to have rod problems more often than others, usually form not having the oil level full and or the oil not changed when it should have been.

I wish I had better news for you! But I think a rebuild may be in order :(




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