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Tecumseh 12hp OHV no compression!!


dalel20's Avatar
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08-01-07, 11:35 PM   #1  
Tecumseh 12hp OHV no compression!!

I had sold a Murray 12hp 40in deck mower to a woman and she used it "once" in a month in a half and it backfired and quit. We have had record rainfall here in the Spring and she only used it once. Ha Ha!! Anyway. It doesn't have any compression so I tore it down. The piston looked great but the exhaust valve guide popped out when I set the head on the bench. Is this why it backfired, or is it the result of the backfire? How do I put it back in so it is tight? The head gasket looked OK with some oil soaking around the bottom but no burn through. The cylinder wall looks good also? The exhaust valve doesn't look like it has the usual ring around the circumference like it was seating. But I don't think I would loose all this compression becuase of this? Please give me some ideas on where to start. Thanks so much. Dale

 
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08-02-07, 05:01 AM   #2  
Dale-that is exacly where the compresson is going.out the muffler.
I'm going take a stab at your problem,and asume that you mean the valve seat insdead of the valve guide.The valve guide is what the valve steam goes through.the valve seat is in the head under the head of the valve.

The valve seat can be put back in.Clean the head good,put it in the hole it goes in.make sure that it goes down all the way.Then ping a dimple all the way around the outside of the circumference on the Aluminum with a pin punch and a hammer.Starting at 12 & 6.Then 9 & 3.This will swall the Aluminum thigh around the valve seat and hold it in place.Then it would be best to do a complete valve job on it.Cut the seat and then lap the valve in.

 
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08-02-07, 06:26 AM   #3  
The better fix is to have a machine shop install a new valve seat where they will super chill it and install. This will be as good as new and then they can face the valves at the same time. Costs a little bit but worth it in the long run. But the old Murray with a 12 HP is getting up there where the peen job will get you by for a while.

 
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08-02-07, 11:24 AM   #4  
dalel20

Yes I did mean the valve seat. I guess I didn't check where the compression was going. I will try the peen job. That was my first choice 2nd was good old JB weld. I will try to get a machine shop to cut the valves and seats. Also is there a difference in the valve springs. I believe I mixed them up. I placed them side by side and they look identical. Also what are clearances between the rocker arm at TDC? Thanks for the help guys!!

 
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08-03-07, 06:23 PM   #5  
There used to be a differance in the valve springs on older engines (say pre 1979) the exhoust spring was stronger and a little taller.But now there are no differances I dont think.As far as the valve clearance's you'll have to tell us the model number of the engine B 4 we can give the correct specs.There's so many.

 
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08-04-07, 10:37 PM   #6  
dalel20

My engine model number is OVXL120 20204D Ser 1162D. Also does this engine have a decompression valve? Maybe I have a carb problem instead of valve issue besides the loose seat. Tell me what you think? I can spin the motor no problem with the palm of my hand. It will get a little tighter close to TDC but not much. I sprayed carb cleaner in the plug hole and got no pop or attempt. Thanks guys!!!!!!!!

 
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