Topic: Too much oil pressure?

[Random1111]

I have a 73 CB750 that was basically given to me. I got it running easily but on the first ride it developed a bad oil leak through the oil seal on the crank. I just recently replaced the oil seals, valve cover gasket and oil breather line from the top of the engine to the oil tank.

After starting the engine back up it started leaking oil bad through the valve cover. After shutting down the motor you can hear a hissing sound. I checked the bolts on the valve cover and they were all snug. If I run the engine with the oil cap off it doesn't leak near as much.

Should the CB750 have that kind of oil pressure? Any ideas on cause?

Rand

[trueblue]

Sounds more like blow by pressure building up in your crankcase, it could be either really bad rings, or your breathers are blocked or the hoses aren't hooked up properly, if it was the rings you would notice it because it would be blowing blue smoke out the exhaust, otherwise it more likely a breather issue.

[dave500]

i go for the breather,blocked maybe,do you get those wasps that build mud nests in little holes?,if you have or can borrow a compression guage check it,ive had those wasps mud nests in exhaust outlets of weed wackers so they wont start.

[Hinomaru]

I have a 73 CB750 that was basically given to me. I got it running easily but on the first ride it developed a bad oil leak through the oil seal on the crank. I just recently replaced the oil seals, valve cover gasket and oil breather line from the top of the engine to the oil tank.

After starting the engine back up it started leaking oil bad through the valve cover. After shutting down the motor you can hear a hissing sound. I checked the bolts on the valve cover and they were all snug. If I run the engine with the oil cap off it doesn't leak near as much.

Should the CB750 have that kind of oil pressure? Any ideas on cause?

Rand

Welcome to the forums.

The breather hose from your valve cover does not connect to your oil tank. This is probably what’s causing your crankcase to be pressurized resulting in leaking seals and the hissing sound.

See this thread for correct oil hose routing:

http://forums.sohc4.net/index.php?topic=95059.0

[ekpent]

+1 Hinomaru---Top vent hose off valve cover vents to the atmosphere and the lower hose of the back of the lower crankcase is attached to the oil tank.

[Random1111]

Thank you for the replies!

Hinomaru I think has the right answer with the hose routing being the problem. I feel very relieved to have an answer to this and I am really looking forward to going for a long ride.

Rand