Smoking

[Manga]

After a ride on Sunday, my mates summoned the courage to tell me Tuesday that the 996 is smoking on acceleration.

I warmed it up yesterday on the side stand plus a bit of wood to get near upright and when cold there is a steady white puffing - probably condensation from a cold engine. At 40 C and above this dissapears. However, when blipping the throttle, a jet of white smoke is emmitted from the horizontal cylinder exhaust can.

I realise this could be down to a lot of different ailments but just thought I'd post up here anyway for some thoughts.
looks like the inside of the exhaust can from the horizontal cylinder is more dirty than the vertical.

Bike has been for sale at the dealers since at least March 2010 and apart from a few test rides it has been laid up there that long till I got it last week.

As the clutch is so worn & noisy I cant tell if the engine sounds abnormal - not that I would know anyway so I shall pop over to BikeTech in tamworth to let him have a look at it before I take it back to the dealers for the clutch

I've put some petrol treatment in the tank to see if it makes any difference - poss injector dirty.

On another matter, how much if any oil should a 24,000 mile engine use?

[Manga]

I warmed up the bike and when at just under 80C, you can make out a little smoke on blipping the throttle.

http://www.facebook.com/?sk=lf#!/photo.php?v=2149197043412&set=vb.1050922085&type=1&theater

Anything to worry about?

[Manga]

61 views and not one comment?
Come on, anyone - is the smoking abnormal????

[RickyX]

All I can say is that I have never experienced any kind of smoke issuing from my 748 or 916 exhausts - apart from condensation when bike hasn't been run for a while.
Suggest a compression check would give an indication of valve or piston ring wear.

R

[Manga]

Bike has been collected today with a list of defects - smoking from horizontal cylinder, clutch worn and noise from generator.

Roll on the return.

[skidlids]

Hope they sort it for you
One point about the opening post, you refer to vertical and horizontal exhaust cans. On all the exhaust systems I have come across the intemediate pipe between the downpipes and the Silencers conatin a cross over that links the two pipes together, so that they are not independent of each other

[Manga]

Hope they sort it for you
One point about the opening post, you refer to vertical and horizontal exhaust cans. On all the exhaust systems I have come across the intemediate pipe between the downpipes and the Silencers conatin a cross over that links the two pipes together, so that they are not independent of each other

Thanks for the help - wonder why the smoke only appears from one can then? Looking at the rear of the bike, it is the right hand pipe and the outlet is much sootier than the left.

[smilo006]

If there is a link pipe then have you tried it with the can off to confirm which cylinder it is coming from. Great excuse to try it too. Had 3 and never had that problem.

[Manga]

Turns out the 'smoking' is unburnt fuel so all is good.

[skidlids]

And as the unburnt fuel isn't expanding like the hot exhaust gasses it tends to head straight down the pipe and out of the end can without expanding through the hole in the link pipe

[smilo006]

unburnt fuel is ok? unburnt fuel = less power = less fun!

[antonye]

unburnt fuel is ok? unburnt fuel = less power = less fun!

Presumably by "ok" he means it doesn't require new cylinders, pistons and rings ;)

[Manga]

Presumably by "ok" he means it doesn't require new cylinders, pistons and rings ;)

Correct

[Manga]

Turns out I dont think this is unburt fuel now.

One mate thinks its a valve stem seal.

So, I may have a stem seal damaged as the bike is smoking on part throttle.

Does anyone know if the stem seals can be changed without taking the cylinder head off?

I don't have an exploded drawing showing the arrangement.

If the stem seals are pressed into the valve guides then I would think the head has to come off.

[antonye]

Here you go....

[Manga]

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

[antonye]

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.

[Manga]

I have had the airbox off and apart from some small oily mess diectly under the crankcase breather return hose, there was no oil in the box.

I took the plugs out but they look fine.

Someone suggested I do a leakdown test but as I don't have a compressor I can't go ahead.

[Ian 748]

Just re read my post and “oil in the air box” is a bit vague. Mine threw up this much oil every 100 miles of spirited riding but nothing when pottering around. As I say both tests showed ok (done at service centre) but the cause was certainly blow by.
Just thinking it’s a little presumptuous for me to say it didn’t smoke, how would I know? I was going the other way at erm…say…60? So I’d better say I wasn’t aware it was smoking.