Purchased project ATV. It wouldn't start, and the guy said it was leaking oil like crazy.
I replaced MOST of the gaskets, the cam shaft, both rockers, both valves, the top timing chain sprocket, and timing chain tensioner. and rebuilt the carb. Afterwards, it ran good, did not leak any oil, but the clutch slipped, and it smoked.
So I took it apart, replaced primary, and secondary clutch, piston and rings. Afterwards, it starts quickly, doesn't smoke, runs good, and clutch doesn't slip. But it started to leak oil from the alternator cover gasket, which I had NOT replaced before. I removed the oil fill screw while ATV running, and found it has relatively high positive crankcase pressure. It was the first time I had removed the oil fill screw while engine running, so I don't know what is normal. But it seems like it has excessive positive crankcase pressure. I checked the vent hose attached to the timing cover and it is NOT blocked. I replaced the Alternator cover gasket, and it runs great, but now leaks from around the rubber grommet that the sensor wires feed through from inside the crankcase to the wiring harness. I think it is related to high crankcase pressure. The spark plug does not have oil on it, so it is not passing oil, so I cant figure how the crankcase has excessive pressure or blow by. Any help would be much appreciated.

 

A 250cc single cylinder engine has to blow out 250cc of crankcase air at every downstroke and suck in 250cc of air at every upstroke. This makes them very susceptible to oil leaks. Some, like Briggs & Stratton have a one way breather that allows the air out on the first downstroke then seals on the upstroke, leaving a vacuum in the crankcase. However Honda, Kawasaki, etc, seem to go for big breather pipes and baffles, long enough to ensure oily crankcase air blown out by the downstroke, doesn't get to the end of the breather pipe before it is being sucked back in on the upstroke.

 

Thank you, VERY much for your reply, THAT is good info.

 

I went to Kawasaki repair shop and talked with the guy regarding my leak and where it was, and about the fact that the engine has SOOO much positive crankcase pressure while running, He echo'ed what the "merryman" said, these engines do have a large amount of positive air pressure, which is causing my oil leak. He sold me some "silicon gasket" in a tube. It is NOT your normal silicon in a tube, he told me to remove the alternator cover, and clean with brake cleaner REAL well, the rubber grommet that was leaking inside and out, and apply silicon, that should fix it. I will provide and update tomorrow, and let everyone know if it was successful.

 

The "Threebond" 1211 silicon liquid gasket worked like a charm preventing oil leak today. While I was putting everything back together it occurred to me, I had already checked to make sure the vent line that runs from top of timing chain cover was not blocked, but it has a "Tee" in the line, one side connects to the bottom of air breather, the other side of "TEE" was blocked, by what appears to be a factory rubber cap, held in place by a factory spring clamp. I removed this small rubber cap and noticed a lot of crankcase pressure coming out, so I left it off, in an effort to prevent blowing out any gaskets or seals. The open end of tube is under the fuel tank, so I cant think of a down side to this mod. I did purchase a breather element to mount in the place of the rubber cap, to prevent debri from entering crankcase, mainly while the engine is not running, because while it is. running, their is air exiting this tube, preventing anything from entering. So far so good, what do you all think? It seems the bayou, is prone to oil leaks, so anything that can be done to prevent challenging the gaskets or seals can only help.

 

As I wrote above, as well as shoving out 250cc of air on the downstroke, it sucks in 250cc of air on the upstroke, so a filter may be a good idea.

 

1999 Honda TRX300A FOURTRAX 300 Frame | Ronnie's Mail Order

 

Look at photos in them you will see number 22 joint,number 9 in duck bib value that on honda trx300 to help vent down stroke[ let air off and the duck bib will close on up stroke \this may help you issue

 

THAT is an AWESOME idea, I am ordering them today, they are very cheap, and better than keeping an open line. Thank you, VERY much.-Doug

 

Thank you VERY MUCH, you have a GREAT help.-Doug