Valve cover leaking

[JParty]

Hello,

I know this is a highly covered topic on forums, but I want to ask for specific advice regarding the o ring like valve cover gasket on the CB400F

Prior to a rebuild, I have oil coming out of this gasket causing a fair amount of oil smoke and mess. When I pulled the gasket off it was flat and looked quite old. I installed a new gasket from an aftermarket gasket set



I still have plenty of oil coming from the top end here. I also get lots of oil smoke as the oil burns off (you can see it bubbling on the top fin) which doesn’t inspire much confidence from me or other motorists (aside from making a mess).

I’m guessing this suggests I need to deck the head and top valve cover as they must be warped. However I really want to use this bike before the weather turns so I was wondering if any of you have found any other solutions.

For reference, I lightly oiled the o ring type gasket and followed the torque down procedure in the manual supplement. I wasn’t sure if I should pack anything in with the gasket but couldn’t see any mention so didn’t.

Thanks for your help,
Jaden

[Bryanj]

You cant machine the top of the head or the bottom of the cover as you would loose cam bearing clearance. Usual problem is O ring slipped out or damaged

[McCabe-Thiele (Ted)]

It might be worth trying again with a new gasket & some Blue Hylomar.

Are you sure the crankcase is venting okay - on a car I've had similar leaks caused by excess crank case pressure.

[paul G]

It might be worth trying again with a new gasket & some Blue Hylomar.

Are you sure the crankcase is venting okay - on a car I've had similar leaks caused by excess crank case pressure.

I’ll second this one. Once got the pipe kinked made a right old mess.
Kink removed no more mess 

[JParty]

The vent you are referring to is the breather on top of the valve cover? I can see this tube venting when it’s cold so I don’t think it’s pressurizing. Not sure if I’m missing something with a separate crankcase vent though. Thanks! 

[paul G]

This one should go from the valve cover to the bottom of the air box

[Piki]

I have the same problem in my 400 Four and I still have not solved it ... some time ago I bought the original gasket and I am waiting to put it on but I think that a little oil coming out of the cover gives a touch of class to the bike, right?

[Erwin83]

I've had the OEM and aftermarket gasket (from a gasket kit) side by side, and there is a clear difference in size (thickness)...
Therefore, the fairly expensive OEM gasket seems to be worth the investment.