Crankcase pressure

[alpinadude]

Our 05 RMZ250 is dumping 1/2 quart of oil out the crankcase vent at each race. 4 moto's 125B and 125jr. This engine has 25hrs on new head with all new O.E.M. valve train parts, rod, crank bearings,gaskets etc.Just had new cylinder,piston kit installed 3hrs ago.I put new clutch cover gasket and kickstart shaft seal in last race after noticing weeping from each. Kickstart seal is pushing out and clutch cover leaking slightly again. Any ideas on what is causing this excessive pressure? Did our shop assemble something wrong? Where should I start looking. Oil is not overfilled. Drained and measured each time bike is run. Very nervous about running low, not to mention the mess on swingarm. Thanx for listening

 

[Rich Rohrich]

It would be worth doing a leakdown test, or at the very least a compression test. It sure sounds like the compressin ring (there is only 1 ) isn't sealing properly.

 

[alpinadude]

Will most certainly do that Rich,just thought new piston,rings, cylinder would eliminate that. Replaced 125hr components with above by reputable mechanic,only one real way to prove the ring seal like you said. Thanx

 

[Rich Rohrich]

You need diamond tooling to hone an RMZ cylinder and at 125 hours that bore is likely to need it. It's unlikely that anyone but a high end performance shop would have a diamond stone hone. Most guys who are racing regularly just toss the barrel at that many hours, and use a new one.

 

[alpinadude]

Rich this is going on with a new cylinder. Borrowed a Motion Pro leakdown tester but the step in the head at the plug hole wouldn't let me thread the adapter in. Going to pull clutch and make sure the crankcase breather is not partly blocked or plugged until I find a different adapter for the tester. Thanx for your advice