motor still smokes

I had to bore my 1976 850 over .020 after the head gasket blew and scored the cylinder wall.Installed new jap pistons and rings, reassembled, still smoked.
tore back down and installed new valve guides and seals and reground the valves, reassembled, still smoked. Tore back down and removed the pistons. Took the jugs back to the machine shop and had the cylinders rechecked. Clearance checked out okay with a .003 clearance between pistons and cylinders walls. Shop did not check for tapper or out of round, should have!! Shop suggested to hone cylinders a bit and install new rings and reassemble. I ordered new rings which were of the one piece wiper type compared to the orginal type of the three piece wiper. Reassembled, still smokes. Trouble has to be in the head , so I removed a good head from another 850 that I have and installed it on the motor that smokes. Reassembled, still smokes!! Disgusted!!! Out of things to try. When I say smokes it,s pretty bad. After about a minute after start up it,s hard to see behind the exhaust but gradually gets better as the engine warms up but never does quit smoking. Both cylinders smoke about the same. Swaping heads did not make any difference in the smoking but the second set of rings did make some difference. Could it be the jap pistons, something to do with the oil pump maybe putting to much oil in the sump? I did check the sump oil after the bike sat for 24 hours and drained one pint of oil, not bad. I tried draining the sump befor start up and it still smokes. The only thing I know to do is tear it back down and have the jugs rechecked at a different machine shop. ANY BODY WITH ANY IDEAS!!!!

Was the end gap checked on the rings?

How many hours was the motor run before pulling it apart? Rings need time to bed in so the smoking could be the result of first few starts and all the oil in the cylinders from fitting. I assume of course you used oil to fit the pistons in the jugs. Sounds like you looked at all the possible suspects. Did you ensure the ring gaps were aligned about 120 degree's apart?
Cheers
Steve J

Did you double check the rings to see if they were put on right side up. I used jpn piston and rings, with them it doesnt matter because there sqare.

The first you should do is relax, Back in early 80s I took my head off 4 times in one day trying to find what I thought was a oil leak from my head.

It would only leak once it got warmed up. It turned out to a pinhole from my rocker feed line(it was a steel line,must have been taken off a atlas)

Once I found out I felt relieved and stupid at the same time. If you can try a different carb give it a compression test, leak down test and go from there.

good luck

ludwig said:

' Listen very carefully , I will say this only once ..!" ( actually I 've said it a few times before ) :
Disable the oil feed line to the head .
Ride the bike for 5 minutes .
let it cool for 15 min .
Ride it again for 5 min .
This way , you will KNOW whether the oil is coming from up or down .
Stop guessing . Make a proper diagnosis BEFORE taking things apart !

Click to expand...

Take Ludwig's advice (then you probably will find out trouble isn't the head). What exactly did your pistonrings look like after you took them out again?? (close up picture)
Avoid one piece oilrings, two piece with expander is fine, three piece with expander (like standard Norton Hypolite) even better.

ludwig said:

Stop guessing . Make a proper diagnosis BEFORE taking things apart

Click to expand...

How about stop f!@#ing with stuff you know f##$ all about.
0.003 is a tad tight. the most likely cause is not enough honing allowance and you still have horizontal boring marks in the cylinder, that is if you assembled the rings around the right way, if the steps in it's up if it;s out it;s down :lol: :lol:, with good components and done correctly it shouldn't smoke from the moment you first get it up to temperature.

nortonspeed said:

ludwig said:

' Listen very carefully , I will say this only once ..!" ( actually I 've said it a few times before ) :
Disable the oil feed line to the head .
Ride the bike for 5 minutes .
let it cool for 15 min .
Ride it again for 5 min .
This way , you will KNOW whether the oil is coming from up or down .
Stop guessing . Make a proper diagnosis BEFORE taking things apart !

Click to expand...

Take Ludwig's advice (then you probably will find out trouble isn't the head). What exactly did your pistonrings look like after you took them out again?? (close up picture)
Avoid one piece oilrings, two piece with expander is fine, three piece with expander (like standard Norton Hypolite) even better.

Click to expand...

This is excellent advice - take it.
I've posted the same advice myself in the past but I always get the feeling it falls on deaf ears.

Presume you are using a multigrade oil.

hi all,my {un educated guess} would be the jap pistons and rings,high in silicone and low expansion,as you allready tried a known head with no improvement i would rule that out ,why not try the barells and pistons from the known motor

One other item I had thought of is did you confirm the oil way to the cylinder base is clear (rear by right hand intake valve down through barrel into cases). I have seen this blocked with gasket sealer and this prevents the oil from draining in the head. It will drain through the pushrod tunnels but by then the oil is up to the top of the guides and it can be pumped in the guides. Also another thing although it is hard to screw up is the rocker spindles if removed must be inserted correctly to prevent excess oil in the head. With the spindle covers off the slot should cover about 20-30% of the oil feed hole coming in from the rocker feed line. If it is open all the way the oil feed to the head will be excessive. Don't give up and don't get frustrated.
As far as those discussing removing the feed to the head and riding around, this I personally would not recommend. Perhaps others have done it but it doesn't take much to cause excessive wear when there is no oil flow. Perhaps you could try this with the bike idling in the shop but I for one wouldn't ride it around. Any part that is close tolerance would expand very rapidly as the exhaust temp would heat the head rather quickly and the lack of oil flow to assist in cooling it down would be begging for more problems than an exhaust smoke.
Let us know what else you've looked into
Cheers,
Steve J

Swapping head out eliminated the problem being in the head including the rocker spindles letting in too much oil.

Trying new rings with different type of oil ring seems to eliminate rings being the problem unless not run enough to seat. However most rings seat pretty quick without much obvious oil burning.
A leak down test could show if way out of spec but I doubt it's needed.

Hard to imagine why the fit of the pistons at .003" would cause smoking.
Is the smoke blue? If yes its coming up past rings or in through intake guide.
If smoke white it may be coming in through exhaust guide and heating of exhaust causes it to be white.
If coming in through intake guides Nortonman70's comment on blocked cylinder base drain hole a possibility but since you swapped heads I wouldn't suspect the guides themselves.

Since you said the smoke starts after about a minute Nortonman70's thought on blocked cylinder base drain hole from intake valve box a real possibility since it will take a short while for the oil to accumulate at the base of the guide.

Possibility of boring lines deep enough to hold quite a lot of oil like Splatt says but did it really look that rough? Although if so why would it take a minute of warm up to show.

Checking cylinders for taper and out of round may be needed.
If out of round the rings will not seal. Not sure how a boring machine could really make an out of round though.
If taper a problem it would have to be pretty severe and any machine shop should have checked for it.

Other route of oil into combustion chamber is thru carb.
Any chance you have the engine vent terminating at carb intake and its blowing enough oil mist out to cause the smoke?

Is it possible that the crankcase vent is blocked causing enough pressure inside the case to push oil up past the oil rings.


Good luck
Bob

Blocked oil drain is easily checked by removing oil feed, hard to think you would block it twice.
76, mark 111?, don't they have a breather onto the inlet manifold? it hasn't failed allowing oil straight into the motor, if the breather was blocked you would be blowing oil out of every orifice, try disconecting the breather off the motor.Although out of round and taper arn't good they shouldn't cause clouds of smoke, any boring marks left in the bores will cause oil consumption as the ring have to pass over them.If you have already pulled it apart post a photo of the bores.

Have you considered the oil you are using? A tech article in a recent Norton news stated that to get a good breakin on new rings you must use an older oil without all the modern additives. The modern oils create a film on the cylinder walls that that keeps the rings from touching the walls. Ok for water cooled motors not so good for air cooled. Older style oils let the rings touch the walls and bed in without the walls glazing and promotes better cooling. There was other recomendations on washing the barrels in Dawn dishwasing soap before installing and not to flood the pistons with to much oil during install.
I am in the process of putting new pistons and rings in my 750 and contacted the US distributor for Morris oil from the UK. He agreed with what was in the tech article and reccomended a straight weight breakin oil that is formulated for air cooled motors like our older britt bikes. I am going to give it a try when I put my motor back together.

If you want the rings to seat, keep the oil under the bench when you assemble the rings and pistons. Make certain the cylinders are oil free, too. Dry is the word. If you don't believe me, talk to any competent engine builder.

That was one of the first things I tried, still smoked. Sometimes you have to tear something apart to diagnosis the problem!!

Rich_j said:

nortonspeed said:

ludwig said:

' Listen very carefully , I will say this only once ..!" ( actually I 've said it a few times before ) :
Disable the oil feed line to the head .
Ride the bike for 5 minutes .
let it cool for 15 min .
Ride it again for 5 min .
This way , you will KNOW whether the oil is coming from up or down .
Stop guessing . Make a proper diagnosis BEFORE taking things apart !

Click to expand...

Take Ludwig's advice (then you probably will find out trouble isn't the head). What exactly did your pistonrings look like after you took them out again?? (close up picture)
Avoid one piece oilrings, two piece with expander is fine, three piece with expander (like standard Norton Hypolite) even better.

Click to expand...

This is excellent advice - take it.
I've posted the same advice myself in the past but I always get the feeling it falls on deaf ears.

Click to expand...

If you read the factory manual it calls for a clearance of .003 to .004. The cylinders were honed properly and the rings were installed with the mark T,wich stands for TOP, upwards and the end gaps of the rings were spaced according to the manual. As for not knowing what the f##k I,am doing, I,ve worked on engines on and off all my life and have found that one can always learn something new!! I have also found that a little less arrogance and a little more compassion go better in life!!!

splatt said:

ludwig said:

Stop guessing . Make a proper diagnosis BEFORE taking things apart

Click to expand...

How about stop f!@#ing with stuff you know f##$ all about.
0.003 is a tad tight. the most likely cause is not enough honing allowance and you still have horizontal boring marks in the cylinder, that is if you assembled the rings around the right way, if the steps in it's up if it;s out it;s down :lol: :lol:, with good components and done correctly it shouldn't smoke from the moment you first get it up to temperature.

Click to expand...

sent you a private message,

One other possibility I've not seen mentioned yet is having the tappets in backwards. If the chamfer isn't toward the front oil won't drain from the head leading to excessive smoking.

Hi Nortons3
Are the Rocker spindle positioned correctly. Make sure that the flats all face in the correct direction. check to see if you are flooding the cylinder with too much oil.
Regards, I like Ludwigs comments to diagnose before tearing down.
CNN

I have two storys about misdiagonosed problems.
Man goes with his buick funny knock in the back of his car underneath, 3 shops later still not fixed,finally goes to a gm dealer turned out to be a golf ball trapped somewhere in the back wheel well.

Man has been driving his car(again a buick) for last year and has run like shit most of the time 4 or 5 garages later no fix.Finally finds he had the wrong dipstick( to much oil)

Moral of the story is after you check for golf balls, and the dipstick go from there.

Never overlook the simple shit.