What caused this

[jimj]

A 20,000 mile since rebuild engine and the exhaust was getting smokier and smokier until clouds of it. Expecting a holed piston or ring problem the engine was stripped. No piston problems, ah! a valve guide slipped but no, everything on the head was fine, crack tested, perfect. All the valves were thick in burnt oil so the problem wasn`t with just one cylinder. Engine rebuilt and running fine but................what was it?
Jim

[cocky]

My Plus Two would on occasion put out clouds of whitish smoke - lots of it. One day I jumped out of the car into the smoke cloud and smelled brake fluid. I concluded that the servo was allowing BF to be sucked into the engine from time to time and burning it. I replaced the servo and the problem never recurred.

[hatman]

A 20,000 mile since rebuild engine and the exhaust was getting smokier and smokier until clouds of it. Expecting a holed piston or ring problem the engine was stripped. No piston problems, ah! a valve guide slipped but no, everything on the head was fine, crack tested, perfect. All the valves were thick in burnt oil so the problem wasn`t with just one cylinder. Engine rebuilt and running fine but................what was it?
Jim

Overfilled with oil and crankcase pressure blew the excess into the airbox?

[jimj]

Wouldn`t the airbox be dripping in oil then? It wasn`t.
Jim

[rgh0]

Jim

You have any photos of what the head and valves and piston top looked like when stripped before rebuild would help understand the cause

Also what needed replacing when rebuilt and why.

cheers
Rohan

[jimj]

I didn`t take any photos but the valves and pistons all looked black and tarry. Apart from a hot spot in one bore we couldn`t find anything awry. Weird!
Jim

[rgh0]

Black and tarry says a lot of oil getting into the cylinders so the question is where from. Only 3 possible sources given no major catastrophic failure.

1. Up the bores - due to oil rings not working
2. Down valve guides due to excessive clearances
3. In the air intake due to oil carryover via the breather.

Each of these is diagnosable via careful examination of the engine as you dismantle. Hardest to diagnose is oil rings letting to much oil to pass but if you exclude the other 2 which is relatively easy then this is left as the reason.

cheers
Rohan

[ElanSeries2]

But, if all cylinders/pistons/valves were rougly the same, its unlikely to be coming either up the bores or down the valve guides, as you'd expect one bore/guide to be worse, and one to be best.

I'd have to say, its likely coming through the airbox, as it seems the only way you'd get an even distribution.

This kind of issue would be much worse on full throttle, as the vacuum in the airbox would be highest (therefore sucking most air through out of the crank case). Is that what you saw? There wouldn't necessarily be loads of oil in the airbox, as most of it would be sucked through into the engine.

[jimj]

Yes, the most surprising thing to me was that the problem was with all 4 bores so I think Sherlock Rohan is right to exclude the impossible and be left with the answer, no matter how unlikely.
Thanks chaps.
Jim