Topic: 1975 Honda CB750F Engine Case Damage

[RodSOHC750]

I noticed a small piece missing from a stiffener in the lower case next to the center main bearing support and directly under the valve chain sprocket.  I don't think this will have any impact on engine performance or reliability.  Looking for other opinions before I continue with assembly. 

[HondaMan]

Someone let the cam chain get real loose. Then, during a hard downshift, the slack all went to the back of the chain and clipped that little casting right off. It is supposed to be an oil separator to reduce the amount of oil that travels back up the cam chain, lest it carry so much up to the top that it causes an oil weep from vaporized oil. This weep will appear around the top oil breather cover (middle of the top of the engine) if yours becomes a problem, but I doubt it will. This happens when the oil is too light (like 10w40) and the engine is run hot: it collects oil in the breather cover at the top, then dribbles it out the breather tube.

[RodSOHC750]

Thanks for your feedback.  I'll take the risk and reassemble the case.  I don't think this will affect the main bearing support or case strength.  If I thought about it earlier, I probably should have taken my Dremmel and cleaned off the rough irregular surfaces to help prevent crack propagation.

[RodSOHC750]

I went ahead and removed the rough surfaces.   

[HondaMan]

You're certainly not alone in this! I myself have rebuilt more than 6 engines that I remember that casting lip being broken off (and probably more than I don't remember). A couple of times, I even found the piece, which had been laying inside for so long that the crankcase 'gunk' had fastened it to the bottom of the cases.

[Jerry Rxman Griffin aka MuthaF'er]

You're certainly not alone in this! I myself have rebuilt more than 6 engines that I remember that casting lip being broken off (and probably more than I don't remember). A couple of times, I even found the piece, which had been laying inside for so long that the crankcase 'gunk' had fastened it to the bottom of the cases.

Yeah, it is a WTF moment when you find that mystery piece in your oil pan LOL