Britbike forum Forums British Motorcycle specific Brands Norton bulletin board Right Exhaust on Mk3 Smoking After Shutdown

I have a 75 Commando Mk3 that runs really well. While riding there is no visible smoke out of either exhaust. It idles great and runs very smooth with good power. The bike uses no oil and has excellent compression. However, when I shut down the engine after it has been running more than 2 - 3 minutes, a large amount of smoke comes out of the right exhaust. No smoke comes out of the left side. It is a very light-colored smoke which continues to come out for about 3 - 5 minutes. I'm at a loss as to the cause.

Gary -

Just so I understand ... when you say "shut down the engine", do you mean go down to idle, or cut off the ignition and the engine is stopped?

And volumes of light colored smoke come out of the right exhaust for 3+ minutes after the engine is "shut down"?

Lannis

Have you sniffed at it - the smoke ? (!!)
Does it smell oily ?

What are the histories of these mufflers ?
They were well used ?
In a previous life, the bike they were on was a real oil burner. ?
Or one cylinder was ..

I say this because a project 850 I bought came with the mufflers SOOO full of oil,
they refused to rust while the mufflers sat in the corner.
They needed some serious washing out with kerosene before they could be used.
The engine was somewhat worn in the piston rings dept.

Also, have you (carefully) compared the temps of each muffler while they are doing this. ?
A quick touch-and-go may be required - to avoid burnt finger tips !
If one is getting hotter than the other, they may otherwise smoke in unison. ??
Esp if the bike in question had an exhaust balance pipe still.

Just a random thought...

OR, it could maybe be that the mice have dragged Aunt Edies favorite little doll into yer muffler,
and it is slowly being cooked.
I have had the rags I jammed into the muffler exits disappear, and on investigation they were inside.
The mice were the only thing I could put it down to - the joys of farm life ...

When I say shut down the engine, I mean cut the ignition and the engine is stopped. The smoke comes out of the right exhaust after the engine stops running.

The smoke does not smell oily and actually burns the nose when breathing it. I have no idea on the history of the mufflers because I purchased the bike several months ago with the mufflers installed. However, I never had the issue with the smoke until recently and I've put close to 500 miles on it since I got it. I've actually touched both mufflers and exhaust pipes with my hands after starting from cold with the engine idling for approximately 2 minutes. Both sides were obviously very hot but appeared to be equally hot. If I can't come up with a cause, I might remove the muffler and see if it still smokes. I should have also mentioned that both plugs look perfect when removed - no oil on right side plug.

Something plastic hasn't got inside the muffler has it ??
Or header pipes.


Think you need to think outside the square here. ?
This ain't normal, by any stretch of the imagination ?

Parked on sidestand?
LH exh valve drains into engine, RH valve/spring retains oil
A bad RH guide to head clearance leaks oil into hot exh port/pipe and will smoke the oil until used up or cooled down...no oil in combustion chamber!!!

would not happen so much when normal running.

Only really good way to see smoke is for friend to follow at night and have headlights illuminate the smoke that you will NOT see in daylight.

If the smoke doesn't smell 'oily', where does that take us ?

Radiator fluid

Commandos leaking radiator fluid is not even in my Commando fix-it manual !! ?

Vaccuum fluid!! I would go with the valve guide idea. If you pull it down find someone in your area that is proficient at sleeving guides!!

850 Commandos have valve guide seals on them - perhaps one has 'fallen off' like one of mine did.
If it was wear, you'd expect both cylinders to be more or less equal.
(depending on sidestand use ?).
Worn valve guides are usually very visible at starting time - huge clouds of blue smoke is a dead giveaway. !


BUT, continuing on along the radiator fluid theme, if it doesn't smell oily, perhaps the 'white smoke' is merely steam.
Could one muffler have got water in it anywhere. Could someone have tipped a coke - or beer - down one ??

I ended up taking the bike on a long hard ride through the mountains, around 100 miles and then to a rally yesterday. There is no longer any smoke coming out of the right exhaust after shutting down the engine. I'll just have to wait and see if the problem stays gone. At least I had a good time riding in the mountains! I'll be riding it to the 'British In The Blue Ridge Rally' in Hiawassee, Georgia again today and entering it in the bike show. The Commando really does run great.