Topic: Cb350f MAJOR oil leak

[nnichols211]

Don't even know if I can classify this as a leak or rather an explosion. Project was going well as I was finally able to start it tonight after waiting for a petcock. I had it idling for about 10 minutes as I was letting it warm up to sync the carbs. It was idling well and seemed to be running pretty well no weird noises or anything. While it was idling, oil shot out of the left side (front sprocket side). And I mean actually shot out, probably about 4 ft and it was definitely a high pressure failure. I inspected where it was leaking and it seemed to be at the gear selector shaft oil seal and that the seal blew out causing it to piss out about 2 quarts of oil.

I didn't have the front sprocket cover on because I was going to install a chain this week too. I thought maybe the side cover holds the shaft in but that didn't seem to be the case after I inspected the cover and the seal. Is this seal meant to contain high pressure and I just need to replace a seal? Seems like too simple of a part to prevent a potential catastrophic failure. Or do I need to look deeper? I never inspected the seal prior to this so I'm not sure if it was in all the way to begin with or not. Any help is appreciated.

[enwri]

blocked off breather building pressure in the cases? saw a compressor blow it's oil level inspection window out with similar results once.

[nnichols211]

Hmm okay ill check that out, I'm thinking you're right on point with that. So I guess in the case with these cb350f's and probably a lot of sohc's, if there's too much pressure in the cases, the shaft seal is the failure point?

[Bodi]

High pressure oil is basically only in the main gallery across the engine, in the cylinder block up to the head, and feeding the crankshaft bearings. Check the lubrication chart in the service manual.
Oil shooting out the gear selector oil seal is just strange. There's a second oil pump section that oils the transmission but I wouldn't expect it to have much pressure. That seal is not retained except by friction and any pressure would just pop it out, plus as I recall it just goes through the case with no oil supply to the seal area. I would suspect the crankcase is getting pressurized by a blocked breather tube?