So this is a track bike project bought on the cheap with a non-running engine. I figured best case it's something easily fixed and worst case we have to buy a used motor for $500 and put it in the bike. Looks like it might be worst case! Currently the bike will fire but it won't keep running when you let off the start button. Almost but not quite and there's oil spitting out the exhaust. But before I go and pull motor I wanted to pick the brains of the beeb to get an idea of the likely cause just so I know where to look first. Any ideas? Thanks, Timm
A longshot but open up the airbox and check if there is oil in it. Bike could have been in a tip over or crash and oil got in through the breather hose.
Oil out of the exhaust has to be something bad. Rings, valves. If it won't start it could have no compression and could explain the oil. I would get another motor for sure but I would also suggest taking that one apart and see what's up. Even a bad motor can have tons of good parts in there that are worth saving
I'm with the tipover assumption. Bad rings or valve seals blows smoke, raw oil is something else. It could be bad rings causing the crankcase to pressurize and pump oil out the breather and into the intake, and the fact that it's not hot enough to burn the oil is possible. Also, raw oil coming out of the exhaust is a long path, is it really engine oil or dirty gas? Pull the plugs and do a compression check if possible.
Another possibility is a failed valve guide seal. Pull the plugs and the exhaust system and see which cylinder is oiling the exhaust. You can R & R the heads “in the frame”, but you need to loosen up all of the engine mount bolts to do it. Make SURE you tighten the engine mount bolts in accordance with the manual, or you risk a cracked frame ... and the crash that can accompany that failure.
Well, the bike did have a bunch of oil in the airbox along with a pretty good sized collection of nuts and grass, all of which were removed prior to the attempt to start. The rear plug did have just a little black residue on it but otherwise looked good. I think I'll see if I can find a compression pressure gauge to see if there's a difference between the cylinders. Thanks for the input so far. I'll post on the results.
Has the PAIR valve been blocked off? If not done correctly it can cause issues. It's been a long time since I looked into that so I don't remember exactly the symptoms but something maybe worth looking at.
if the o-ring for the pair valve under the valve cover is missing. It will suck oil straight into the exhaust.
