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6 hp air cooled engine

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PAUL161

PAUL161

Great Pumpkin
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Nothing to do with cars, but I thought I'd post it here to tap into your minds for a possible solution to a problem I've had/have with this little engine.
I have a 6hp Tecumseh vertical shaft on a Sears mower. It started blowing oil out the crankcase vent, which is the later style with the vent on the top and rear of the case and vents into the carburetor. Since I thought it was because of piston blow by over pressurizing the case, I rebuilt the engine, new rings etc. The cylinder was in perfect condition. I also replaced the vent valve assembly in the block. Started it up and it is still blowing oil out the vent tube. Anyone have a cure for this? Don't say get a new engine, that's out of the question, I'll buy a new mower first! There is a reason for this and I would like to know what it is. I bought this mower new and it's only ever been used for trimming, so it's never been worked hard. Any help would be appreciated. Oh yeah, I didn't cross hatch the cylinder before installing the piston, which might have been a mistake making seating the new rings take much longer. PJ
 
Try a break-in oil in it then break it in to see if the pistons are still in blow by mode. Smooth bore, new rings, might not break-in.
 
Agree with Larry. Run it while and see if things improve (although I'll admit......I'm not sure what "break-in oil" is?). On that engine, the only other place I can think of for crankcase pressure to come from would be a loose exhaust valve guide.
 
I have had experience with 3 different mowers with 5hp Tecumseh engines on them. One caught fire, one leaked everywhere, and the third blew lots of smoke. All of these happened within a year of purchase. All three were out-performed by a twenty year old 3.75hp Briggs & Stratton. I have never been impressed with them and replaced them.
 
I thought this was going to be a post on how to increase the HP in your MG. That said you should have honed the cylinder wall, can't imagine the rings seating well in a smooth bore. Oh and I agree with Nial about the valve guides being the only other place where blow by could be coming from in that engine.
 
New rings, and no cylinder hone? They may never seat properly. I'd hone that cylinder along with the break-in oil already suggested.
The only other things I can think of is a possible restriction in the exhaust, or a blockage in the intake causing extra vacuum on the vent tube.
 
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