Help wanted - mystery oil leak

Just started up the 850 after a two week lay-off to go for a ride and have got a large oil leak dripping down the front of the engine (only when it is running). It seems to be coming from about 3 fins above the cylinder head gasket but I can't see exactly where from.

It was fine last time it was running with no sign of a leak. Any ideas where this can be coming from? All the top oil lines are ok and none of the rocker covers are leaking. Never had this one before.

mystery oil leak

Hey mike, the oil leak in question is probably in the area of the front cylinder head bolts, oil will find it's way up the threads of the bolts and out onto the cylinder head and down the front of the motor. The usual fix is to remove the bolts, apply thread sealant -- NOT Loctite!, and reinstall the bolts to the correct torque.Good luck. James.

Ok thanks for that james. I'll get the bolts out and seal the threads with some silicone- that's a simple one to sort out.

The bit I don't understand is how come it was fine when I last ran it then I start it again two weeks later and its pis***ing out? Weird :?

As James said check the bolts and the nuts under the exhaust ports. If these have loosened you can try sealant and re-torque.

If you are getting a lot of oil dripping as you mention, it is probably the gasket has been damaged and it is allowing oil to seep out of the push rod tunnels.. The only answer here would be to pull the head and replace the gasket.

If James suggestion does not stop the leak, I would pull the head, check the studs on both the head and the barrel for tightness and if necessary seal them. Then use a new flame ring gasket with a light smear of gasket sealer around the pushrod tunnel holes on both sides of the gasket. Usually original gaskets will seal without this, but some aftermarket do not. I don't know about current Andover supply, so I don't risk it and use the sealer.

Third fin up is where any oil from above finds its way down through the casting to the front edge, often leaving little visible evidence on the way.

Before dismantling, I would re-check and seal rocker covers (especially the rear one and including the fixing nut). I would also check rocker feed banjos and lines as well as spindle end plates.

79x100 said:

I would also check rocker feed banjos and lines as well as spindle end plates.

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Looks like you nailed it on the spindle end plates - score 11 out of 10 for that one.

Had already checked the front head bolts and no probs there but just had another look after reading your post and noticed a spindle end plate gasket has half blown out on the LH inlet side. The oil has run into the head and is coming out third fin up on the front.

Just got to get a couple of new gaskets and with a bit of luck that should sort it - a nice very simple and inexpensive fix for a change. Cheers :lol:

Good call 79X100! Mike916SP, had you disturbed the rocker spindle covers? There usually isn't enough pressure there to "blow out" a gasket. Maybe the bolts loosened?

Ron L said:

Good call 79X100! Mike916SP, had you disturbed the rocker spindle covers? There usually isn't enough pressure there to "blow out" a gasket. Maybe the bolts loosened?

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No not touched a thing since I rebuilt the engine from the barrel up about 4 thousand miles ago

Glad to be of service Mike !

It looks as if the gasket was damaged on assembly. I can't imagine it being forced out there if everything was in order. Are the stainless end plates new ?

I remember that the set I bought years ago were far from flat and needed stoning before use (actually, it was the fat bloke with a beard who sold them to me who needed stoning )

I can't see any risk of blocking oilways so at the risk of bringing the anti-bath sealent brigade down on me, I would suggest a smear of silicone on reassembly.

There old end plates. Have been on since I bought the bike 3 years ago. I will check there flat before reassembling though.

Can't remember catching the gasket last time I put the head back together - but always a possibility.