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Tecumseh Cam.. Shot?

1098 Views 7 Replies 6 Participants Last post by  Fcubman
Dad's Sears tractor with the 10hp Tecumseh started running horribly and had a 12" flame coming out of the glowing red hot muffler. Then it would start for a few seconds and quit. Turned over rather quickly like it had low compression.
I pulled the head and turned it by hand. As the piston travels up through the compression stroke the exhaust valve lifts off the seat slightly a couple times. Is there galling on the lobe? Or maybe the fitment of the cam in the block is loose. Anyone ever seen this? I haven't had the time to tear into the engine yet.
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maybe a decompression device that isn't disengaging?

That is a possibility, but CR devices usually fail the other way, they don't work when they're supposed to. Another possibility is a sheared flywheel key, although that event usually advances the timing, not retard it. If you can hear hissing in the exhaust when the engine is running, it is possible to have the problem you describe. If not, look at the key, it's a lot easier than taking the whole engine apart.
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Could an exhaust valve be stuck?
There is no decompression device.
I pulled the head and watched the exhaust valve lift off the seat as the piston is moving up the cylinder through the compression stroke. I could clearly see it lift up off the seat twice (maybe 3 times) as the piston was traveling up.
I would take the breather off and check the valve clearances on both valves. It is possible that the cam is worn,but check the valves before you tear the engine clear down.
Thanks Dave
I did take the breather off when I pulled the head but, didn't check any clearances. Mainly because I wasn't worried about a clearance issue. Because during the compression stroke the exhaust lifter should be riding around the heel of the cam thereby not lifting the valve. But, the opposite is happening. The valve is actually lifting a bit when it shouldn't be. Something is pushing on the lifter base when it shouldn't be. I may have to make the time to pull this thing down and look it over even if I don't do a re-build, just out of curiosity.
I've never opened one of these Tecumseh motors and don't know what the cams end journals ride in but, I'm thinking that might be where the problem is.
Thanks again for the input.
If I can "make some time", I'll tear it apart and post what I've found.
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If I can "make some time", I'll tear it apart and post what I've found.
My curiosity is really piqued! Please do!
I can't imagine what is causing this problem.
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