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OHV Problem


Jmaner1969's Avatar
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06-01-03, 06:40 PM   #1  
Jmaner1969
Tecumseh OHV problem

Hi Everyone. I have a tecumseh 12 hp OHV 120XL on a murray 26" rider. Started fine this spring, and after cutting grass for 1hr. I shut it off for a few minutes. When i came back to start it, it would not start for nothing. It only would backfire now and then.
I checked for spark. and fuel. Seems good. After much investigating i found out the valve seat inside the head is lifting up and then sticking in at a angle under the valve were it should be sealing when firing. Its the exhaust valve thats the problem. under both valves inside the head there's a ring thats were the valves seat when closed. Can anyone help me on what i need to do to get this running. Piston seems fine, no scourching. Thanks.

 
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Tcumcman's Avatar
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06-01-03, 06:59 PM   #2  
Tcumcman
Loose Exhaust Valve Seat

Heat makes the seats come out. Be sure to clean the cooling
fins around the cylinder and head before making this repair.
Also, have you by chance changed the muffler on the engine
recently? If so....a "non-original" muffler, or changing the
exhaust set-up will cause this overheating, too. You can
try and peen the seat back in by going around the outer edge
of the seat after properly installed back in the head. You're
looking to spread the metal a bit with a round punch so
that the outer edge of the head contacting the seat edge is
spread out a bit. It wouldn't hurt to spread a little JB Weld
on your peening and let cure for a day or so. Examine valve
and seat for damage. Sometimes valve can be bent when
this occurs and seat can get pitted/damaged when at an
angle like that. New head is expensive, around $134, unless
you can find a good used one lying around somewhere. Be
prepared to pay $40-50 for it, if shop knows the value of a
new one. Feel free to e-mail me if you need further help in
taking this apart, and ESPECIALLY....with putting it back together.
If your engine has a 2-screw valve cover....it WILL BE an....
"ADVENTURE" for a novice or part-time mechanic.

Tcumcman

 
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06-01-03, 07:16 PM   #3  
Jmaner1969
Thank you for the fast reply. Yes I had the head off and it is an adventure. This is how i started to understand what was happening. I tried tapping the seat into place, not too much just enough to make the seat stick in its place, then i put the head back on and she fired right up. about 15 minutes later it quit again and i notice one of the valves(exhaust) was not sticking out as far from the head again, which tells me, its not seating again so i'am assuming that round sealing area has moved again. Can i order a kit with new valves springs and pushrods. Maybe something is bent?

 
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06-01-03, 11:47 PM   #4  
Tcumcman
OHV Repair

You'd have to order the parts you mentioned (valve springs &
push rods) seperately. There's a "rocker arm kit", which comes
with rocker arms, O-rings, lock nuts, & rocker arm studs, BUT...
NONE of that addresses your real problem....a LOOSE VALVE
SEAT. The seat is NON-REPLACEABLE on those because it's
an integral part of the cylinder head. All you can do is try and
repair it...or replace the head. The seat is what the valve seals
to, and of course, MUST BE in place & secure or you lose
compression and engine won't run. The rocker arm kit for the
OHV with push rod tubes (old style OHV...OVM/OVXL120) is part
number 730221A. Head gasket is 35306A, and you'd need all
this IF...you're gonna attempt to repair vs. replace the head.
GOOD LUCK !!

Tcumcman

 
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06-02-03, 05:07 AM   #5  
merlin1965
Here is something for you to check before you go and buy all those parts. Have you checked the exhaust valve stem for carbon deposits, it sounds like the valve is just sticking that is why is will start after you have reseated the valve. once the engine is going there is enough motion for it to keep going but once you shut it off it sticks. So clean the valve stems before anything else. Thats what I would do first.

 
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06-02-03, 11:34 PM   #6  
Tcumcman
OHV Problems

Merlin,

Carbon could be present, certainly, but when the exhaust
valve seat comes out/loose, the only solution is to peen
back in, and "cross your fingers", or...replace cylinder head
with new one or good used one.

Tcumcman

 
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06-03-03, 02:39 PM   #7  
Jmaner1969
Thanks tcumsman, I have the head off and have been checking for anything that looks bad. Both valves look really good. The seats are nice and shiny. I think what happened originally is I had this mower for 2 years and never adjusted the valves. I don't think the previous owner checked them either. Finally this spring the lash in the exhaust valve got so bad and was creating heat on the head which resulted in the seat comming loose. Does this sound right to you? I can see on the head inside and out that the metal is brown by the exhaust valve area. I would guess from the heat. I hope I can pean it back in like you said. Whats that stuff that i might try. Do automotive shops carry it? Does it really work? Thanks again for the great advise. I never worked on these before but always wanted to learn about them.

 
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06-05-03, 12:17 AM   #8  
JB weld is available at any automotive parts store. I don't know if it works on valve seats or not...never tried. I don't trust any type of glue or epoxy around the heat of an exhaust valve. My neighbor tried using some on his muffler, but it melted when the muffler got hot enough, so I'm sure it would do the same on the valve seat. I would remove the valve and place the seat back in it's spot, and use a pointed punch and a hammer and peen the aluminum around the edge of the seat to hold it in place.


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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06-05-03, 10:51 PM   #9  
I just happened to be browsing on Ebay, and found a pic of a head that has had the seat re-installed by the peening method described. This is a link to the item, take a look at the picture, it will give you an idea of what you need to do.
http://cgi.ebay.com/ws/eBayISAPI.dll...category=20544

Hope this helps!


"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

 
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