engine blowby?

[Raptor22]

hey everybody. I have a go kart with a 12hp tecumseh ohm120 engine on it and has some pretty serious blowby but I did a compression test on it and got normal levels. What's causing the blowby then? Thanks for all the help

 

[OzFab]

Sorry, I'm not familiar with the term "blowby", can you explain?

 

[Doc Sprocket]

What are your symptoms, and what are your compression readings? What is the compression spec for your engine?

 

[Raptor22]

I don't know if blowby is the correct term but that's when compression from the combustion chamber is leaking into the crankcase. I got 115 for the compression test, I don't know what it should be but I checked some snowmobiles and they were getting 120 so I figured it was fine. I have oil coming into the air filter from the little tube that goes into the side of the case. Sorry I don't know what's its called. I was told that I might has gas mixing with the oil and that might cause it but I changed the oil and it still did it right off the bat. Thanks for the replies.

 

[Bluethunder3320]

http://www.perr.com/phpBB3/viewtopic.php?f=14&t=9201
The engine uses a mechanical compression
release on its camshaft....so start-up compression readings will
usually be around 80-90 psi. If MCR is not working, readings can
be 120-140 psi.

not sure if this is the exact same engine you have. i believe if you crank it over backwards the compression release wont be kicking on.

similar story... i have a brand new tecumseh HM100, put it on my mini bike. it ran great the day i first started it. after a couple hours of riding, it was overheated and gasoline/oil was pouring out the blowby. i never rode it again, i pulled off the engine and its been sitting ever since.

when i get some time i will try to figure out whats wrong with it. but i dont understand how a brand new engine (0 hours!!!) could get the symptoms of an old, worn out engine

 

[anderkart]

I have oil coming into the air filter from the little tube that goes into the side of the case.

Something real easy you could try first is to replace that short breather hose with an 18" or 24" long one, and then rough/secure that hose into a loop-shape (pointing upwards) way up above the engine. This would still let the crankcase breathe fine, It'd just help stop the oil from pumping out.

 

[Raptor22]

ok, that's a good idea. I'll try that today. That other article said the breather might be upside down so the oil doesn't drain back into the engine. I'll check both of these and let you know how it goes. Thanks for all the responses.

 

[anderkart]

Cool, let us know if that fixes your issue or not. I've got some other remedies you could try if needed.

 

[Raptor22]

So I took it apart and when I loosed the screws it was full of oil and it fell out. I took it out and sure enough it was upside down and the drain holes were pointing up. I flipped it around and put it back together but now it won't start...

 

[Raptor22]

Ok, so I have a little problem. I tried to start the engine and nothing was working. I have spark and air is moving through so I cleaned the carb again. Didn't do anything. I pulled the head and check the valves and they work fine so that isn't a problem. I tried turning it over again and air is being pulled in through the exhaust and gas is shooting OUT of the carb. So i figured the timing is wrong and pulled the crankcase cover off and as far as I can tell the timing is fine. You just match up the dot on the crankshaft and the groove on the camshaft right? That's how it is. Any ideas?

 

[youtheotube2]

Have your piston rings worn down to a level where gas can blow by the piston?

 

[Raptor22]

no the rings are fine. I did a compression test and it was ok

 

[Swabbster]

lol its not because your engine is messed up, it is a single cylinder not a multi cylinder it is just the piston creating a vacume and compression as the piston strokes, being as the air pulsating in the pcv or any other opening

 

[Raptor22]

so nothing is wrong? Sorry, I didn't really understand that.