Oil Leak from Exhaust Headers?

[Guest]

Hi, Am coming near to the end of a full bike rebuild from scratch (would be finished if not for this oil leak!!) - 1979 GS850GN
Engine has had new gaskets (head and base) and Orings. Has been torqued to spec, ridden and re-torqued. Valve shims done. New spark plugs, coils, leads, reg/rec, total re-wire, battery. Managed to get an original airbox in good shape - new air filter, new rubbers (carb to airbox and carb to engine with o-rings). Carbs cleaned/Jetted. 4-into-1 Exhaust.
Bike starts and runs a lot better than when I got it several years ago.
The problem I have now is that after it starts and warms up, oil seems to start coming from the No 2 Exhaust header lower stud bolt and no amount of retightening seems to stop it.
Is there an oil channel behind the exhaust studs? If so and the stud has gone in too far - can this be fixed. Or could the problem be from somewhere else (RHS of engine is dry)

IMG_20190302_103900_edited.jpg

[Burque73]

Valve cover gasket maybe? Those drain holes on top of the engine let oil out in weird places.

[LAB3]

I've seen that happen when an engine is old and in need of a rebuild. How does the plug in that cylinder look?

[Guest]

Have you done the "baby powder diag" yet? This helped me hunt down a leak like yours, and it wasnt leaking anywhere near where I thought it was...

[bwringer]

The oil is mostly likely running forward from somewhere further back.

For that particular stud, I'm pretty certain there's no oil passage back there.


I have seen a case of oil escaping via an exhaust fastener involving a botched thread repair, where some long-ago tool twiddler drilled too far and entered an area containing oil. However, this was one of the upper bolts; poke too far with one of those and you can get into the cam area. For the lower ones like yours, I don't think this is possible.


99.999% of the time oil leaks around the cylinder head are not coming from where you think they are at first. That stuff migrates in odd ways.

[jwhelan65]

Valve Seals are shot

[Guest]

Thanks for the info.
Valve gasket looks to be dry.
plugs in all cylinders look good (if anything, #4 looks a bit richer).
powder diag not done yet - should be able to do it this week

[Grimly]

You stripped it to repair base gasket leaks, I assume?
I don't see any mention of new rings or a cylinder head overhaul.

[Guest]

There was indeed a base gasket leak.
engine overhaul included base gasket and o-rings, cylinder rings, head gasket, timing chain o-ring, re-shim, new cam bolts, new studs with copper o-rings, valve gasket.
cylinder head had a spark plug thread repair on #4
compression testing gave a range between 110-130 on all four cylinders.

[Grimly]

Looks like you needed to take the head apart and replace the valve stem oil seals, lapping the valves in for good measure as they could probably do with a touch anyway.
As jwhelan65 said, I'd be dead suspicious of the oil seal on #2 exhaust - it's probably shot, and they're all 40 years old now; rock-hard and not sealing much.
Bite the bullet, take the head off and do it again with new (or Viton) oil seals, checking valve guide wear as you do so.