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Smoking Commando on idle #795754 01/16/20 2:02 pm
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SteveT Offline OP
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Any thoughts regarding my 850 Commando smoking when idling from both silencers in equal measures, the smoke is blue so I’m presuming that’s oil burning,
So the symptoms...... start it up fine, let it idle and it will start smoking a lot, give it some revs and it will clear, back on idle and it will start smoking again.
The diagnosis so far...... rebore completed, I think it was +20? New genuine Hepolite rings, new stem seals fitted. I didn’t do this work which I left to a local bike mechanic , the rebore was done at a very experienced engineering shop and all looked good.
The symptoms are a bit different before the above work but similar, the mechanic who did the work suggested running it for a 100miles or so to let things bed in? My thoughts with this is that they didn’t smoke when new regarding running in etc Im just reluctant to put some miles on it and possibly causing damage. YOUR THOUGHTS?
Anything else which would cause the smoking?
Thanks, Steve

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Re: Smoking Commando on idle [Re: SteveT] #795761 01/16/20 2:48 pm
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When you say new genuine hepolite rings is that NOS from years ago or the latest Wassell offerings.

What spec grit was used for honing, eg 150 or say 220.

As soon as you started bike for the first time did you leave it idling, if so how long before you actually got it out and under load ie pulling up a hill.

You need to get then engine under load for short periods to get pressure in behind the rings to force them to wear in on the honing on the bore. If you do not get this done quickly the bores glaze and you need to get it rehoned and new rings, course grit 150 to 180 for honing for cast iron rings.

Re: Smoking Commando on idle [Re: kommando] #795770 01/16/20 4:23 pm
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SteveT Offline OP
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Thanks for the reply, Im sure the honing was good, regarding running it under load, that’s a no, it’s a John Player and it didn’t have the full bodywork on so didn’t get the chance, suppose a plan will be as soon as the weather warms up 😱 give it a good run out under load and hope? The rings are new old stock genuine Hepolite...

Re: Smoking Commando on idle [Re: SteveT] #795777 01/16/20 5:45 pm
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kommando Offline
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Don't assume the honing was good, ask what hone grit was used, even good machinists forget to change the stones over. All modern rings use a much higher number grit as both the bore and the rings are already round so the honing machine is likely set up wrongly for old cast iron rings 95% of the time.

Re: Smoking Commando on idle [Re: SteveT] #795779 01/16/20 6:00 pm
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Following a re-bore and new rings, the bike needs to be started and immediately ridden on the road for a good 10 miles or so including runs up steep hills in second gear with plenty of throttle.

The idea is that in the first few miles the rings need to bed in against the cylinder which should have has a coarse hone as already mentioned. This window of ring bedding opportunity is often missed if the bike has been started and idled in the garage whilst the owner proudly blips the throttle. Whats needed is instant riding with throttle applied so that the cylinder pressure will force the rings to bed in.

The other possibility is that the oil pump isnt working too well and not scavenging enough from the sump, whats the return oil flow to the tank like?


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: Smoking Commando on idle [Re: SteveT] #795782 01/16/20 6:45 pm
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SteveT Offline OP
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The oil pump/return is a poss considering its showing similar smoking problems to before the rebore etc I’ll take a look when I get the chance......

Last edited by SteveT; 01/16/20 6:46 pm.
Re: Smoking Commando on idle [Re: SteveT] #795792 01/16/20 9:12 pm
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htown Online Content
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What oil are you using for break in?


1978 Bonneville T140E
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1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
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Everything will be alright in the end. If its not alright, its not the end.
Re: Smoking Commando on idle [Re: SteveT] #795848 01/17/20 9:46 am
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SteveT Offline OP
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20w50 mineral oil

Re: Smoking Commando on idle [Re: SteveT] #795861 01/17/20 3:58 pm
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If its rated SG and not SL or SM that should be okay.


1978 Bonneville T140E
1974 Trident
1970 BSA Thunderbolt
1971 Norton Commando
1972 Norton Commando
1973 Norton Commando
1974 Norton Commando
2018 Kawasaki Z900RS


Everything will be alright in the end. If its not alright, its not the end.
Re: Smoking Commando on idle [Re: SteveT] #795902 01/18/20 2:47 am
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I've noticed everyone preaches to immediatly get the bike out on the road. Does anyone set the tiimig first????????


Rich (last remaining member ThreeMustGetBeers)
"It's not always about going fast. Sometimes it's nice to slow down" (Wendy E.2016)

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Re: Smoking Commando on idle [Re: Richrd] #795922 01/18/20 7:19 am
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Depends. If you still have points, it's relatively easy to get very close without strobe timing. But if you have solid state ignition, the initial setting may be quite a few degrees off from what you want. I wouldn't feel very comfortable riding a new motor with EI without checking first.
Cheers,
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Re: Smoking Commando on idle [Re: SteveT] #795925 01/18/20 9:55 am
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I work on the basis that anyone complaining of a smoking exhaust on a rebuilt running engine had already checked the timing, if they hadn't then they have other issues.

Re: Smoking Commando on idle [Re: SteveT] #795941 01/18/20 5:13 pm
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Usually when an engine does most of it's smoking at idle the problem is in the head.
Bad guides or seals, too much oil supplied to top end or oil drain back restricted.

Re: Smoking Commando on idle [Re: SteveT] #796069 01/20/20 12:04 pm
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SteveT Offline OP
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Just wondering if the following gives a clue?
Last year after been stood over the winter I took the sump plug off to save any wet sumping, it didn’t just empty the sump it continued on to emptying the tank as well, just a thought, at the time it seemed strange? I went to empty the sump a sometime after this and all normal with just the normal amount of oil from the sump..... any thoughts...

Re: Smoking Commando on idle [Re: SteveT] #796070 01/20/20 12:16 pm
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That is normal behaviour for a Norton and is discussed ad infinitum since people stopped riding their bikes daily, it wet sumps when standing through the clearances in the pump, the bigger the clearances the faster the wet sumping. If it empties the oil tank in a week or 2 then the pump clearances need attention but none of this explains the smoking on idle unless the sump was full when drained.

Re: Smoking Commando on idle [Re: SteveT] #796140 01/20/20 11:32 pm
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Villiers Offline
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I’m with RWEB. Sounds more like a cylinder head issue, valves, guides, etc, and not something I’d particularly obsess about. It was designed a lifetime ago in a different world. I think sometimes we worry too much. Riding it is the answer.

Re: Smoking Commando on idle [Re: SteveT] #796166 01/21/20 2:20 am
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Rohan Online Content
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They shouldn't smoke at idle though.
ESPECIALLY after having it rebored and new pistons.

If you have checked via removing a rocker cover or 2 (or 3) that the top end is well oiled,
I'd be tempted to blank off the rocker feed for a wee while and take it for a short spin, and see what happens..

If the smoking ceases, its obviously in the top end.
If it continues, then it needs to be explored deeper.


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