Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > Smoking

[Manga]

Thanks for the drawing.
It doesn't answer my query regarding replacing the stem seals only - ?

[antonye]

Originally Posted by Manga

Thanks for the drawing.
It doesn't answer my query regarding replacing the stem seals only - ?

Alright Mr Picky!!

[final_edition]

I think he maens the rubber valve stem seals rather than seats or guides.

[Manga]

Yes thats it, the rubber seals.

But I wonder if I should just take the engine out & check the rings as well?

I suppose a compression test will show which cylinder but won't tell me if its valves or rings?

[skidlids]

Need a Leak down test done
Then if the pressure drops you can listen for the air leak

[Ghost]

Valve stem seal problems usually exhibit themselves on startup. Oil trapped in the upper chamber can leak down onto the top of the piston, resulting in smoke at startup.

Smoke whilst running usually indicates rings, Nicasil bores are very cruel to rings and you can end up with almost 3mm ring gap instead of 0.3mm.

[Ian 748]

Do you have oil blown up into the air box? Although not smoking, a while ago I used to get oil in the air box and so had compression and leak tests done. Both showed no problem but I decided to change the rings to be completely sure and bingo…no more oil.
So on this occasion I found that although everything, even the old rings were within tolerance it still wasn’t good enough.