Blue smoke

pitrat101

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Hi Guys, Been asked to post from an old boy who I know, He has a 1981 R100. The bike blows blue smoke on start up, then has a blue haze when on tick over and warm. He has had the heads off and changed the rings but still the same, he says he can see oil in the bore (using a endoscope) and the top of piston looks wet. I don't really know much about the old bikes except the liners are coated and the clearance is quite tight, but my gut feeling is saying valve guides? is there a hard and fast way to check? Any other areas to consider? Any help appreciated.

Thanks

Steve.
 
Hi Guys, Been asked to post from an old boy who I know, He has a 1981 R100. The bike blows blue smoke on start up, then has a blue haze when on tick over and warm. He has had the heads off and changed the rings but still the same, he says he can see oil in the bore (using a endoscope) and the top of piston looks wet. I don't really know much about the old bikes except the liners are coated and the clearance is quite tight, but my gut feeling is saying valve guides? is there a hard and fast way to check? Any other areas to consider? Any help appreciated.

Thanks

Steve.
A general rule,

Put teaspoon of oil in through plug hole, and do a compression test if it increases, rings.

If not, guides.



Sent from my SM-N910F using Tapatalk
 
Update from Dave, valve guides were done 5000mile ago, (not sure where) left cylinder was slightly smoking on start up but all the rest has started since he done push rod seals. Done compression test cold today and got 85psi both cylinders, done again when warm and up to 115psi both sides. I've asked him to it again tomorrow with the teaspoon of oil, will this find the worn piston ring grooves? Hope that sheds some more light on things.
 
Might have broken the rings when doing the push rod seals, or fitted the oil rings wrong.
Ring grooves can be recut , at one time replacement ring sets included a spacer to take up the slack after the recut, looked like one part of a 3 part oil ring -----.
 
a couple of things

If he has only recently changed the rings they will need time to bed in

and is it simply overfilled with oil?? a lot of folks keep these bikes topped up to the top level and they simply burn it off to a level and it can stay there to next service

he should drain off the oil and see how much is in there and recheck his year or manufacture and amount I recall a difference between twin shock and monoshock (and I think his is a mono with the plated bores) but don;t have the books here something like 0.4 litre

Also check the crank breather pipe and breather valve in case its stuck open and blowing fumes straight into the carb area, a good indicator would be the left side carb intake pipe being much oilier that the right side
 
Thanks guy's, have passed info over, wait to see what outcome is.
 
Well, spoke to Dave and he's already done comp test at warm and he getting the same both times even with the teaspoon of oil, 110psi right and 95psi left, backed the valve clearances off to eliminate tight valves but still the same, could be as simple as valves not lapped in properly when new seats fitted?
 
Sounds like a closer looksee is needed,
New rings will never bed in to a worn or polished bore,nicasil can only be honed with a diamond hone,using a carborundum one will more than likely pick up and score it.
in any case there is notalot of point honing a worn bore.
IIRC the clearance on the ring lands is between 0.05 and 0.12mm max
The valve seats need checking as well, some wd40 and a high pressure blow gun up the intake and exhaust ports will show any leaks
 
Is he removing the carbs to do the compression tests?

DrF mentioned bedding in the rings, which could also be the cause.
Modern motorcycle oil is wonderful stuff but it might simply be too good to let the rings break in, particularly if synth is used initially.
Running in oil used to be available, it lacked the additives designed to protect the motor from wear and let it bed in nicely, but I haven't seen it for years.
Nearest thing to it you are probably going to find is probably a cheap and obsolete SF/SG/SH Dino Auto oil , and it can be found if you look hard enough.
But dont leave it in too long, 500 km will be long enough, then dump it and fill with a good motorcycle MA2 20/50.

And running in techniques have changed a lot too- the motor needs a fair few hard pulls to bed things in so find a long step hill and give it some stick1
 
I don't know the compression figures offhand, but they sound very low to me. Besides that, they are off the specced 10% tolerance between each other.
 
If you really think diamond grit is needed to deglaze a nicasil bore diamond grit abrasive sheets are not hard to find, and could be cut into narrow strips the make rats tail hone.
The OE bores are reputedly cleaned up after honing with diamond impregnated " Scotchbrite" which is harder to find.
Aluminium oxide Scotchbrite is easier to find and a couple of thicknesses around 100mm in dia fixed to an arbor and pushed through the barells and back at slow speed in battery drill have let me bed in rings any tine I have fitted them.
https://www.mcmaster.com/#sanding-abrasives/=1bq1esc
 
If you really think diamond grit is needed to deglaze a nicasil bore diamond grit abrasive sheets are not hard to find, and could be cut into narrow strips the make rats tail hone.
The OE bores are reputedly cleaned up after honing with diamond impregnated " Scotchbrite" which is harder to find.
Aluminium oxide Scotchbrite is easier to find and a couple of thicknesses around 100mm in dia fixed to an arbor and pushed through the barells and back at slow speed in battery drill have let me bed in rings any tine I have fitted them.
https://www.mcmaster.com/#sanding-abrasives/=1bq1esc


If the original hone marks are no longer visible its because they have been worn away.
A proper parallel hone won’t even touch the worn parts of the bore.
Deglazing may well help to bed a new set of rings but it’s never going to be best practice not to even measure the bore properly is it?
I’ve lost count of the number of times I have been brought bikes,supposedly had top end rebuilds only to find new piston rings in worn pistons or buggered bores,
New guides fitted in heads with worn seats,
New valves fitted in heads with worn guides and seats.
I’d just start back at the beginning and check everything again.
After all,it’s not exactly difficult to pull the heads and barrels back off is it?:nenau
 
Spoke to Dave today and passed info over, heads coming back off and a good looking at. He has option of loaning a good set of heads to see if if we can eliminate bottom end totally. So think this may be the way forward. Will keep updated as we progress.
 


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