# Tecumseh 12hp engine



## Serenissima (Mar 28, 2012)

Hi guys and gals,

I have a 12hp Tecumseh 4-cycle, single piston engine on my Troy-Bilt chipper/shredder. The model number is 224624B-OHM 120. The valves are overhead and part of the head of the engine. Recently, oil started leaking out of the air cleaner housing when the engine was shut off. In spite of that, the engine ran strong until a few days ago when it started sputtering followed by thick white smoke coming out of the exhaust. I immediately shut the engine off. A little later I started it up again and after 10 seconds or so the engine started sputtering again while shooting out thick white smoke out of the exhaust. I immediately shut it off again. A large amount of oil began flowing out of the air filter housing which led me to believe that one or more of the piston rings might have failed.
I pulled the head off yesterday and cleaned it up to check for any cracks. However, there was none. I also cleaned off what little carbon residue there was on top of the piston and cyllinder. The walls of the cyllinder felt mirror smooth except for one little section where there was very faint scoring but could only barely feel it. After rotating the piston both up and down through its full range of motion, I checked for any slack between the piston and cyllinder wall by attempting to wiggle the piston back and forth. There was very little play - not much more than 1/32" - and only when the piston was at the exteme top or bottom of its range of motion. I couldn't wiggle the piston at all while in the center of the cyllinder. So that leads me to believe that the piston rings are still in good shape.
Can anyone advise me on how to proceed from here? I figured that since I already have the engine pulled halfway apart that I should purchase a new +0.002" ring set, hone the cyllinder out and replace the rings but I'm not certain that it's necessary or not or whether that will even solve the problem of the oil leaking out of the carberator.
Anyone's expertise would be greatly appreciated. Thanks, Serenissima


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## Basementgeek (Feb 7, 2005)

Hi and welcome to TSF

First, just an FYI Tecumseh went out of business in 2009. Can't answer your question about the rings.

I would cleaner the breather well/make sure it is working. Also check/set valve adjustment. Best I can see they should Intake .010, exhaust .020.

If the air cleaner is full of oil it has to replaced.

BG


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## Serenissima (Mar 28, 2012)

Thanks BG.

According to PartsTree.com, I'll be able to acquire parts through them. They sent me a schematic of the engine and apparently a full parts list. All I have to do now is familiarize myself with such items as the breather and how to set the valve adjustments to the settings you specified since this is the first time I've pulled a small engine apart. There's a repair manual for this particular class of engine that Tecumseh put out a number of years back. It's priced on Amazon for under $12.00. I think that's definitely gonna be a must.
Thank you much for the tips. Serenissima


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## Basementgeek (Feb 7, 2005)

Send me a link for the manual. I have a couple stored on my PC. If I have the one you want, I will email it to you.

I don't think they were available on line until after they went out of business.

BG


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## Serenissima (Mar 28, 2012)

Hi BG,

Sorry I didn't get back to you sooner. Other things came up and wasn't able to get back to my engine repair until now.

I was able to locate and download the relevant repair manual for my engine and will research it this weekend.

Thanks again for your advice. If any other questions arise, I'll let let you know.

Thanks, Serenissima


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## k2skier (Sep 30, 2008)

A blown head gasket (or leaking) will casue this. Combustion pressure pressurizes the crankcase and pushes oil out the breather into the intake manifold. Replace the head gasket checking the block and head for warpage. Then get it tested with a leak-down tester, it will tell you where the loss of compression is coming from; rings, valves, head gasket.


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## Serenissima (Mar 28, 2012)

Hi K2skier,

I did pull the head off, cleaned and inspected it for cracks. There was none. Head gasket was in tact as well. I'm thinking that a ring must have failed. Placed my hand over the cylinder and rotated the flywheel. There was a significant amount of suction in the cylinder when the piston moved in the downward direction.
I did discover that there was an excess amount of oil in the crankcase so I'm gonna drain the old oil out and fill it to the proper level with new oil, place the head back on and test with a pressure gauge. I'll consult the technical manual for the proper pressure. Next I'll try to start it and see what happens. If it doesn't run, I'll consult with you on what to do next. If the pressure gauge shows a lack of pressure, then I'll assume that the rings failed and replace them.
Thanks for responding to my post.


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## k2skier (Sep 30, 2008)

Overfilled crancases will do it also, if it's more than 1" over the full mark, that's all it was.

PS-check to see if the oil smells like gas, a bad needle and seat will fill the crankcase up with gas and overfill it too.


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## Serenissima (Mar 28, 2012)

I'll do that. Thanks for your expertise.


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