head oil leak . pulling my hair out now . what's left of it

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Jun 1, 2007
I know this subject has been discussed before but i will take the 5th on it and ask again ...

74 850 Commando

have an oil leak from two fins up on the head ... leaks down on the front of the fins and then sprays around the cases ...

have done the following from good advice from here ...

removed the head and replaced the head gasket with a fibre (flame ringed ) gasket .... used threebond sparingly to seal her up .... the 3 studs at the front of the head i sealed the threads and put copper washers under the steel washers & nuts & Threebond to seal ....

cramped down in 5 stages as per manual order to 30FT Lbs .... ...

Fitted a PCV Valve to the breather near the oil tank ....

still i have oil comming down the fins ... two fins up from the head gasket ....

what's next ? ..... cracked head ?

oil leaks

Hi Steve,
Don't overlook the valve cover gaskets. I thought my head gasket was seeping, but, I finally traced it to the valve covers. They leaked in spite of the fact the gaskets were new, trimmed as suggested by the Norton Digest, and smeared with sealant. The problem was that the covers themselves had become slightly warped. I fixed it by lapping them on a piece of glass and a sheet of emery. Regarding finding the leak, one trick is to thoroughly clean the engine, let dry, then dust it with baby powder, goe for a ride stopping to check often for oily spots forming.
I had a similar leak on my 750. I could have sworn it was coming up the studs, but it turned out to be the left rocker feed banjo. There was an old copper washer stuck to the banjo bolt head that I had somehow overlooked and failed to remove. The old used washer plus the new washer added up to a leak, and the oil ran through the center area and collected at the front.

Replacing the two sealing washers with one new washer fixed it!

The baby powder sounds like a good idea. It can be hard to pinpoint where the oil is coming from.

Mine was the rocker spindle plates. Cleaned the head thoroughly and fired it up, ran for a few minutes and started dabbing around with a blue paper shop towel. Towel turns dark, there's the spot.


Kansas, America
Re: head oil leak . pulling my hair out now . what's left of

snibor said:
..... cracked head ?

Probably not cracked, but some Commando cylinder head castings are porous...unfortunately.
debby said:
The baby powder sounds like a good idea.

Try rather, a spray can of foot powder.....easier to aim, makes less mess, and a can lasts for years :wink:

PS... my messy head was the valve cover gaskets, removed gaskets and used red silicon in the tube instead, first time in 28 years the covers didn't leak... :D
I'm not saying this is the cause of your problem, but putting copper washers under head fastenings might not be a good idea.

You should try neoprene or viton rocker cover gaskets. No leaks and you can use 'em a few times.

I too am suffering from the same mystery leak - I too have a crank pvc valve, annealed washers, sealed head, tight valve covers, banjos etc.
I think the weak/leak point is the braided steel line/banjo junction - my clamps, although tight seem to leak on the primary side. Have yet to change clamps, but that is my current hypothesis.

Hewho: I like the foot powder method!
2nd breather does work


Been through all that too...the 1/4 breather on the inlet rocker cover finally cured it. Note, Commandos are known to have porous head and barrel castings. Excess crankcase pressure that the standard breather can't cope with overpressurises the top end and it leaks. Sounds weird, but believe me and others who tried, it can be stopped.

Could your tach drive be the source of your leak?

Imagine oil leaking from the tach drive and working its way up the cable as a result of air rushing over and around the front fender. And then, due to reasons I can't explain, the oil droplets release from the cable and splatter themselves against the front fins of your cylinde head.

I think it's possible under the right conditions.
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