# Newbie with a Tecumseh compression problem



## Fowler

Hi Ladies and Gentlemen,
I'm new to the list and I apoligize if something is wrong with my post. I searched as best I could on the site but I didn't find this discussed before.

I have a ~1994 vintage MTD 38" riding lawnmower. The engine is a Tecumseh XL TEC12; OHV12-202701A ser2325A

During a recent cranking attempt I noticed that the cranking rpm suddenly increased. It didn't appear to have exhaust flow out of the muffler by holding my hand over the exhaust. I checked the valves and one rocker had loosened and had moved out of position (don't remember if it was an Intake or Exhaust valve). I located Top Dead Center on the compression stroke and set the valve clearance to .012" to .013" on both valves. Still the engine wouldn't start or if it did, it wouldn't start the next time.

I have rechecked the valves and they are still at the clearances above but the engine has no compression. I "feel" this by sticking my finger into the sparkplug hole while cranking. You can feel the cylinder breathing but there is basically no compression pressure. I know that some of these OHV engines have a "starting compression release" but I don't know if this model does or doesn't
I am "jump starting" the lawnmower from a running car so the battery voltage and cranking speed is OK.

From what little I can see through the spark plug hole the piston appears to be OK, at lease in the center.

The last time it cranked it ran well with no noticable problems.

What to do? What to do?

Thanks in advance Fowler


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## Rentahusband

Head gasket failure or a valve sticking??


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## usmcgrunt

Hello and Welcome to Hobby Talk.I agree with Rentahusband,sounds like a head gasket problem.The valve clearance should be set to .004 on each valve,although this is not your problem right now.Here is a link to the service manual for your engine.Let us know what you find,and we will all be happy to help you.
http://www.barrettsmallengine.com/manual/tecumsehoverheadvalvemanual.pdf


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## Fowler

*Thanks for the comments*

Thanks to you and rentahusband for the replies.

If it is the head gasket, that should be an easy fix. While the head if off I will check the valves for sticking and for sealing at the seats. I've seen some people use gasoline for this valve leak test.

That compression release mechanism is a "Black Box" to me. Can it cause this symptom? Is there a method to confirm that it is not the cause of the lack of compression during cranking?

Thanks again and best regards
Fowler (Charlotte, NC)


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## Fowler

*Tecumseh compression problem*

You gentlemen were close but no cigar for you today. My son-in-law, who became the proud owner of the non-running mower yesterday, took the head off tonight.

He found that the head gasket was OK but that the exhaust valve seat was lose and cocked out of position. I'll send a photo if I can figure out how to.

He was able to depress the valve and get the seat back into position and he said that now the compression was good (finger test in the hole again). 

He's going to try to get it to crank but I doubt if it will run a minute.

I have heard of some people using JB Weld to hold valve seats in place.

Do you guys (& gals) have another method to try before buying a new head & valves, & etc.?

Thanks again
Fowler


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## 30yearTech

I doubt that you would have any success using JB Weld on a valve seat due to the extreme temperatures in the combustion chamber. 

You may be able to peen the seat in place by using a center punch to expand the aluminum around the seat. Start with a punch at the 12:00 position, then one at 6,9 & 3, then the rest of the way around at 1, 7, 2, 8, 4, 10, 5 and 11:00 positions. Be sure to place the punch in the aluminum near the seat, so when you tap the punch with a hammer, the metal expands and pinches against the seat. You may have to have the seat cut if you don't get the seat in place straight. I would do this with the valve installed so the spring is holding pressure against the seat.

Best of Luck....


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## Fowler

*Thanks for the suggestion 30yearTech*

Center punching around the seat or staking it sounds like a reasonable idea.

I know this method is used on gas turbines to prevent some screws some from backing out.

Thanks again
Fowler


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## duffer72

This procedure is shown in a briggs manual somewhere, Have used too many times to remember and never had one fall back out, I also agree with the idea of doing it with the valve installed to hold it in place.


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## Fowler

*Tecumseh compression problem solved*

Many thanks to Duffer72; 30YearTech; USMCGrunt; and Rentahusband for all contributing to the problem identification and to the solution. Yesterday my son-in-law used the staking procedure submitted by 30YearTech on the loose exhaust valve seat. I didn't get to see the job but he had it running last night. Many thanks.

Local overheating likely caused the loose seat. I had had a weeping gasket on the valve cover and that accelerated the accumulation of oily grass in the area of the cooling fins near the exhaust valve. I guess I shouild clean that area more than once every 15 years.

Thanks again Fowler


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## duffer72

FYI it is not an uncommon problem and have seen it happen on engines less than a year old, glad we could help


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## usmcgrunt

Congratulations on the successful repair and thank you for posting a follow up on the outcome.


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## duffer72

For those that may search for this topic in the future here is a link showing how to reinstall the valve seat. The only thing I disagree with is the use of a flat punch, I have always used a pointed punch or larger center punch for the job. 

http://www.perr.com/tip7.html


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