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Hello all

Any advice please would be welcome on a recent problem. I have an 850 Mk1 which was rebuilt appx 6 years ago and has had regular use since then, standard except for a Boyer and recently new PVL colis.

Never any problems and has always ran very strong, started immediately and little oil use except for a bit of wet sumping when stood. Over the last 2-3 days though it's started to smoke on the right hand cylinder and misfired a bit until it's cleared, then it runs great as it always has. Looks like oil is getting into the combustion chamber but it still starts ok. Any thoughts from the wise and knowledgable?

Thanks

great topic, smoke and starting .oil can be leaking down a valve guide, but this happens over a period, sudden smoke ..well thats another story

Piston ring gaps have somehow all lined up in tandem.

I've looked at enough Norton run piston rings to see that gaps pretty much stay where first placed, but any thing is possible. My Trixie's sudden smoking after a few 1000 miles of smokeless turned out to be head gasket seal failing d/t too big of ring gap blow by, like over twice what is proper. I resisted tear down for 1000 more miles, not believing gaps could be the issue, till no choice when oilled so much misfiring began on way out to pavement. So suspect guides, lost intake stem seal, bore scores, ring gap, bad gasket seal, or crack in alloy casting or head fastener threads. Stock wisdom says rings smoke more on throttle and guides more off throttle, but did not apply to my very obvious extra ring gap issue as smoked about same either way, maybe more smoke on more exhaust flow increase is all I could see. Leak down testing is the classic method to determine where to spend to stop smoke, but its about impossible to do this effectively on a 360' twin I found out the hard way.

Yes ,listen to Hobot and pull the head. Rings stay in place if properly assembled . Usually guides, seals or head gasket.

Thanks for the replies, small update - rode to work yesterday and when starting it to go home, no smoke and ran as normal so it seems to be only when standing for a few days. I do use it regularly but sometimes a week might pass before riding again. Does this sound like worn guides and/or valve guide oil seals poorly?

well you did'nt say it had stood, If thats the case LEAVE IT ALONE!
A bit of ol weepage down the guide and a bit of wet sumping? thats OK.....so again LEAVE IT ALONE if you feel the need to do something,,change the oil. and leave it standing on its centre stand.

Spelky, that was similar to Trixie's smoking ring gap habit, kept me in denial as it tended at first to be intermittent and even switched sides. Could just be oil slowly weeping out guides that will self heal in time, if shoe eves don't take care of it first. Some day again you will be riding w/o smoking and forget all about what it took to do so...

Just a thought, when an aircooled engine is stopped the differance between engine heat can vairy depending how the bike was run.
If the motor had been pushed and then ticked over a while before stopping the head heat can be high, and the oil a lot thinner..increasing guide weepage.
But if the moter was cruised home last 5 miles [light throttle]and stopped quickly on a cool day the temp can be a lot lower, hence sligtly thicker oil.and less weep down the guide/past rings .

just a thought,

Ms Peel has monitored those conditions to find the Norton is a pretty good heat dumper, not heat soaker, so as soon as the fuel supply reduced the temps start dropping and don't increase on [ugh] immediate shut off from hi throttle temps, such as a lost belt or chain or electrical fault or surprise road blockage. The hotter the engine on shut off the quicker excreted oil can drip off. This year I found the hotter my gapped tooth Trixie - the less smoke was seen, a few minutes of hwy cruise, only left invisable orders and slight smoke on nailing her, which also kept me in denial longer hoping rings or guides would self seal with more use.

Classic diagnostic tool is a leak down tester test to listen for where pressure escapes, carb, exhaust or breather and how much, but just can't be applied to a 360' twin w/o special provisions of essentially impossible brutal counter force, as one part of the test is move engine off TDC to move rings off possible good seal area, yet as soon as you do its suddenly a Norton torque monster to hold back and can't be stopped at just a tiny bit off TDC but tends to move enough to open a valve which nulls the test. Norton drum brake sure ain't up to it. Object stuck through spokes gets hard trapped and removal lets piston free fall. A case of beer offered to first video of successful procedure on our type engines.

Only way I know is too take down to bottom then work back up renewing most likely issues, one at a time or all at once, depending on how much faith and time and money on hand. I resealed Trixie's head and barrel twice before finding ring gaps bad by me haste to assemble with eager friend helping. If ya ever hear yourself or others say, yeah they all do that...

Smoking on startup does sound like valve guides or guide seals.
I had a seal that 'fell off' somewhere somehow, a little while after on a rebuilt head.
Barely showed up, except a little smoke on startup, sometimes, and on the over run.
And a dirtier plug than on the other side.
Refiiting new guide seal = instant fix.

You may want to look inside the inlet valve cover after its been standing though, see if oil is pooling there for some reason, and not draining back down into the sump ?

Thanks all for the advice, I will certainly resist major surgery at this stage, oil change is due so start with that.

Yeah, I did that for a few 1000 miles vapor trail, only bit bullet when plugs began fouling-misfiring on throttle while leaving 1/2 mile drive way, going to work, so too pensive not to make it there, so took the cage and later took down Trixie. Too bad out of warranted sevicing period.