Hello all. I've a '71 CB350 I picked up a couple months ago that I've been tinkering with in the garage. After diagnosing a few small issues, I have a big issue with the left crankcase cover leaking oil that I cannot seem to rectify.
Quick back story...
I first realized the leak from the lowest point of the cover after about 10 miles of riding. I parked the bike and noticed a decent amount of oil around the kickstand. Essentially, the oil is leaking from the cover, hitting the frame, and running down the kickstand. If the bike is cold, nothing leaks. The bike only leaks once it has warmed up and is running (both while running and after it is cut off). It seems like it is a combination of thermal expansion and pressure buildup from the crankcase causing the leak.
Assuming a bad gasket, I picked up a Honda OEM paper gasket. After cracking the cover, I see it is all RTV or similar - no paper to be found. I do the normal checks and cleaning and reinstall in a "star" pattern. I "torque" the phillips down using a manual impact driver without going too nuts. All surfaces are smooth and free of debris. I crank it up and ride a couple more miles - leaking worse than before.
Okay... So I tear it back apart and use the black RTV in combination with the paper gasket. This time I spend about 2 hours or so replacing this gasket to make sure I'm not overlooking something. Zero debris left on any faces, all surfaces are straight with no apparent deformations. I reinstall and tighten a bit past finger tight to allow the RTV to cure slightly for ~15 minutes or so then I crank down in the "star" pattern once again. Let the bike sit about 24 hours before I fill up with oil and crank it up. It is essentially raining oil out of this cover now. The leak seems to be coming more towards the clutch cover side instead of the lowest point of the crankcase cover. I've given a video to show just how bad the leak is.
https://youtu.be/SPnEK8eAD8I
I'm at a loss. Has anyone else experienced this? My final guess is the alternator wiring which goes through its rubber grommet on the cover. With that said, the rubber is in good shape and is fitting in the cover just fine. As I understand it, this cover isn't necessarily an oil reservoir whilst running, but more of an expansion tank. Is this true?
Another set of eyes or opinions on this would be great. What are your thoughts? First "obvious" problem causer would seem to be mismatched surfaces, but it all seems true.
Thanks!
-Tyler
