Topic: Where does oil overflow come from first? CB750

[michrobi]

There are overflow spouts on the rear of both halves of the case, and one under the oil tank. Which one will generally spew overflow first/most?

[BlackMax]

Hmmmm, what year?  Mine has only a breather on the valve cover and one on the back of the trans case.  On mine, the one on the back of the trans case will spew oil if overfilled......by 3 or more quarts.  Don't ask....

[bucky katt]

the one on the tank should be connected to the one on the rear of the engine case

[michrobi]

That's right, one off the case, one of the valve cover, and the oil tank one. Are you sure about the oil tank connecting to the case breather? They've always just had a hose that ran from each one to the ground. I have looked at the service manual everywhere I can imagine that it might speak about the breather hose placement, but no joy.

My bike leaks a little oil after every ride that ends up dripping from the end of the swingarm and down the center-stand. There is also motor oil buildup on the leading edges of both side covers after each ride. The engine is dry as a bone but the lines from the engine breathers both have fresh oil residue at the ends. I did overfill the oil by somewhere between 1/2-1 quart, but just like I have done for 15 years and never had leakage.

[MCRider]

That's right, one off the case, one of the valve cover, and the oil tank one. Are you sure about the oil tank connecting to the case breather? They've always just had a hose that ran from each one to the ground. I have looked at the service manual everywhere I can imagine that it might speak about the breather hose placement, but no joy.

My bike leaks a little oil after every ride that ends up dripping from the end of the swingarm and down the center-stand. There is also motor oil buildup on the leading edges of both side covers after each ride. The engine is dry as a bone but the lines from the engine breathers both have fresh oil residue at the ends. I did overfill the oil by somewhere between 1/2-1 quart, but just like I have done for 15 years and never had leakage.

Many threads on this topic. Glad I wasn't the only one.  Definitely the crankcase breather behind the tranny goes to the oil tank. You've been lucky, that breather can spew enough oil to make your tire very slick. It is not open to the atmosphere. THere is a thicker vent tube from the back of the oil tank to the atmosphere. That would be the only "overflow" though it should never happen.

There is no reason you should have oil anywhere on the sidecovers. The valve cover breather vents to the atmosphere and should not have oil on it, unless the engine is tired and pressurizing the crankcase, which in turn pressurizes the valve cover area. There could be minimal moisture on the end of the breather tube, but not enough to make a drip.

Later bikes vent the valve cover into the airfilter housing, to close the loop.

[michrobi]

Wellsir, when you're right you're right. Connected the oil tank with the case breather and went for a long hard ride
not even a drizzle of oil on the swingarm, center stand or side covers.

Thanks again!

[MCRider]

Wellsir, when you're right you're right. Connected the oil tank with the case breather and went for a long hard ride
not even a drizzle of oil on the swingarm, center stand or side covers.

Thanks again!

Ta Da!