Motorcycle Repair: Oil leak between head and barrels, aftermarket gasket, oil seepage

Question
Hi Bill, I hope you can help me.
Here in the UK I have a 1970 CB250K2 I have just pulled the motor to fit a new camshaft and when I pulled the Cyl head off
I found the head gasket saturated in oil. This ties in with the fact that I have had a small leak between the head and barrels.
I know the oil travels up the rear outer studs to the head and cam
bearings but the hole in the head gasket is far larger than the stud dia. Should there be a seal fitted to both sides to stop the
contaimination of the head gasket but still allow the oil flow.
I have looked in the previous gasket set but can't find anything.
What's confusing is that the Honda manual shows nothing but the
Clymer manual does touch on this subject but the picture is so small to see. I'm sure you will know the answer and would be very grateful for your advice. Thank you Gary.

Answer
Gary, after over 40 years, the head gaskets do get some oil migration laterally through the gasket material, which eventually causes some oil seepage/leaks on the external surfaces.

While I don't see them shown in most parts illustrations, Honda has typically used a small o-rings to seal around the knock pins which carry oil from the bottom end to the top. If you have purchased an aftermarket gasket kit, you may find the o-rings included in the kit. A quick search on gasket kits seems to indicate that they are not included, however if I was putting a motor back together and there is space around the knock pin holes in the gasket for an o-ring, I would install one that had a cross section just slightly thicker than the head gasket material.

Found this discussion..

http://www.cmsnl.com/classic-honda-forum/350twinnew_f20/reoilleakbetweenhead_t15...

http://www.m3racing.com/graphics/parts/c2_lg.jpg indicates that they don't have leaks with this maker's product.

While we are on the subject of gaskets, make sure that you replace both the clutch cover and dyno cover gasket with updated parts. The originals will get brittle and fail, causing bits to come loose and float up to block small oil passageways, which starves the top end for oil.

The front oil return holes are not under pressure and shouldn't need to be sealed up, but it is always better to be safe than sorry. If you can't get o-rings around the oil feed areas of the gasket, get some 3 BOND crankcase sealer and smear some gently inside the edges of the gasket holes and allow it to setup before installation.

The other potential issue is that the head gasket surfaces on the head and cylinder may not be flat and true, so have them checked and flattened out so there are no distortions between the two surfaces.

Bill Silver