oil leak rear head

[philg100]

Hi All. Following rebuid last year my 900ss has an irritating oil leak from the rear head. Having removed the head to fix this issue it seems that the O rings in the return passages are not very compressed. Having measured everything, it is not holding up on the oil spigots but it looks as if the head is sealing on the top of the liner and leaving too great a clearance between the faces where the o ring will seal. Any thoughts for reducing this gap to create a better seal??

[wdietz186]

Phil, Reducing the clearance between the head and cyl. would involve either milling the top of the cyl. sleeve or machining the relief in the head a bit deeper.Assuming the head didn't leak before you took it apart I would look carefully at the locating sleeves that the o-rings fit around and see if there are any burrs that would hold the head up or allow oil past on the inner dia. of the ring. Also are the rings the correct thickness?

[Geoff]

Are you absolutely sure the leak is from the O rings in the head and not oil weeping out of the exhaust header at the nut? I had the same problem and my first diagnosis was the same as yours. After screwing around for a while I figured out (with help) that the leak was weeping from that place, with some additional evidence visible at the balance pipe - drips of oil there. The leak tracks around the head sealing area and is easy to confuse with blown O rings.

The oil 'leak' at the exhaust nut area was caused by either the valve guide seals being shot or the need for a deglaze hone on the bores and new rings (I had had the top end off and replaced with original rings and no hone). I renewed the guide seals (pain in the ,,,), degalze honed, new rings and she was clean again.
Cheers
Geoff

[Lumpy]

Solid words Geoff. Beware of oil leaks that are exposed to wind. They can be tricky to spot the source. Trouble being that when you pull it all to bits the evidence is gone and your back to square one. Make absolutly 100% sure you have sussed it before you break out the spanners. I generally wipe her clean, ride 2 k`s down the road, check, ride another 2 k`s, check, till i get the very first sign off weapage.

[philg100]

Hi guys thanks for the steer. I have replaced everything with new seals now so if it still leaks I will start looking closer to the front of the head.

[ScottyDucati]

I just put my 750 roundcase back together and all was clean and perhaps even a "sterile" working environment, as well as the proper 30ft lbs of torque.... Add oil and fuel, fired right up.... and oil leaks from both heads at the o-ring junction.

I purchased an entire engine gasket kit from bevelheaven [gskt/seal-RC-comp] and all seemed well.... except the five o-rings in the oil passageways from the head to jug.... they looked too small to me. Like, thinner, than the green ones I removed, and were'nt going to work.... but I figured... nah.... these gotta be right, these guys know these machines.

Well... they leak.

Now perhaps it's just a variation in the Ducati manufacuring process, as there are known to be many, but the little grooves surrounding the perimeter of the alignment dowels seem to totally envelope the o-rings provided in the kit, not allowing enough of a 'squish' to form a proper seal. This is a '72 GT750 with a springer head. The cylinder compression chamber seal is fine. BCM Ducati in NH sourced my last set of gaskets and o-rings, and I never had as much as a drop of oil on the exterior of the motor.

So now, I've got a source for the thicker o-rings, from Ducati, and I'm not blaming or flaming anyone, but I've gotta drop the engine and pull the heads again for $5 worth of o-rings [I guess your's are ten bucks]. I should've gone with my guts on this one and opted for a better fitting set of O-rings.

As an aerospace mechanic and machinist... I guess I should've trusted me. But as a word to the wise, be sure to check your seal fittings during re-assembly.

Regards,

Scott