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Smoking Commando

Classic Norton Commando Motorcycles.

Smoking Commando

Postby Michelle Norton » Mon Sep 11, 2017 1:55 pm

Hi everybody. I have `72 Combat. It has a single carb with a Boyer. It leaks no oil and starts and runs ok{though slightly rich dark brown and sooty on the surround , no sign of oil at all on plugs} Oil return is good and has an Holland anti sumping device. I keep the oil{SAE 50} just above minimum on dipstick. I do have an oil pressure gauge fitted{running of the rocker feed]. When cold at idle its around 40 running up to 50 plus at 4000rpm. When hot it drops right off{unlike my BSA oily frame Lightning which maintains pressure never dropping below 40 to 50 . The feed is taken of the front crankcase . The bike has an SRM conversion with end feed]
The above is really for background as I know pressure gauges and anti wet sumping devices are contentious! The problem is that after a run of 10/15 miles{Commando} there is whitish smoke with slightly more on the right hand side. There is none that I can see on start up. It is not a huge smoke trail and seems worse at tick over and clears slightly with throttle blipping.
If any one has any ideas I would welcome input. Some moons ago I had a MK2a which never had this problem.
Many thanks

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Re: Smoking Commando

Postby Mike B » Mon Sep 11, 2017 2:10 pm

Sounds like oil is getting past the exhaust guide.

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Re: Smoking Commando

Postby RoadScholar » Tue Sep 12, 2017 5:31 am

How many miles and years does your engine have on its' valve guide seals, rings?

How many miles do you get out of a pint of oil?

Have you checked the torque on the head fasteners recently?
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Re: Smoking Commando

Postby Michelle Norton » Tue Sep 12, 2017 1:30 pm

I will take the head off over winter{ no doubt all will be revealed!} The bike is a recent {ish} purpose with about 28,000 miles on it so not sure about rings and pistons. Not checked head torque settings but there are no weeps anywhere. Compression is good and the plugs are not at all oily.
Ta for replies.

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Re: Smoking Commando

Postby Steves » Tue Sep 12, 2017 2:07 pm

I have a 72 combat. I have a problem of oil getting into the right chamber. A while back it would billow white smoke on start up then become a 375cc bike as the plug would oil up. I found a work around which was to do what you did, anti wet sump valve and pressure gauge. This (I think) stopped the head being flooded with oil on start up and then finding its way by means unacertained at present into the combustion chamber. Also I put a grade hotter plug in. Plan was to take the head off over the winter, however last week the gearbox broke.
So I am in the process of taking apart both items.
I am just hoping I don't dind a crack. I did a valve seal replacement a little while ago using the old rope trick and some home made tool. Made no difference, fact was the seal I took off was good.
When I take the plugs out and turn the engine I can hear a sucking noise. When I remove a rocker cover it disappears (noise), the noise is just from the right side.
Might look into putting a breather on the intake rocker cover when I reassemble as the head does seem to pressurise quite a lot. If the head is good will check the bore and rings. My money at the moment is a problem in the valve guide area.
Will report back in due course.

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Re: Smoking Commando

Postby DevonNorton » Tue Sep 12, 2017 2:22 pm

Michelle Norton

Worth trying some of the suggestions here?
http://www.nortonownersclub.org/support/technical-support-common/smoking-engine

My '72 Roadster had the problem of oil leaking past the valve guide causing smoking.

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Re: Smoking Commando

Postby Michelle Norton » Tue Sep 12, 2017 3:26 pm

Hi Andy and thanks. I suspect guides . So if is guides is it normal for the smoking to get worse as the engine warms? There is none on start up.

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Re: Smoking Commando

Postby batrider » Tue Sep 12, 2017 4:29 pm

My bet is a loose fit between the guides and the head. Usually it is not valve seals either but oil getting around the outside of the guide. If someone has done a guide replacement by the manual at home then the head has probably lost some aluminum in the guide bore. Sometimes the guides will just fall out. Oversize guides are available for this. There are not many shops that know how to do this job right or have the capability. It does seem to get worse as it warms up and there is a distinct nasty smell to the exhaust.
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Re: Smoking Commando

Postby RoadScholar » Tue Sep 12, 2017 6:30 pm

DevonNorton: Excellent article although I'd be quite reluctant to run the engine without an upper oil feed, and I'd be anxious about withdrawing the rocker shafts worrying about the spring washer falling into the head, but I am not nearly as dexterous as I was years ago. I like the idea of making a small hook (out of safety wire?) to probe for the oil hole in the rocker shaft

If the valve guides are to be removed they should be machined out; if you drive them out you run a strong risk of enlarging the bore.
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Re: Smoking Commando

Postby Matt Spencer » Wed Sep 13, 2017 2:34 am

Restriction in the return ?

Oil should be 40 bar Calif Summer 100 + type weather , then 50 . 30 if snow .

Should have 10 pis per 1000 rpm , 10-15 MINIMUM at idle .
Can be internal pressure leak . Somewhere . Faulty by pass / relief set up .or sticking .

Sounds like its wet sumping a bit . Does it kick some smoke out on start up ? .
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Re: Smoking Commando

Postby Matt Spencer » Wed Sep 13, 2017 2:37 am

ALSO theres a rubber grommet / seal in the timing cover , which would explain things , if kaput / absent .
Or a nicked / tired crank end oil seal in the timing cover , or if the circlip there isnt .

Its the BSA with the End Feed THING I take it .

In my opinion the Norton oil pumps fine. on a 16H .

Theyre a ' blueprint clearances ' thingo . if some forign matters gone thru it , they can be overly weak .
Which rthey were anyway . Down Sulby straight the crank centrifuges it out as fast as the pump supply .
Guage = Zero , as does top end cooling feed . Which suzuki invented with the GSX :roll: .

If its under 25 psi hot highway < Id pull the timing cover & inspect the relephant entities .
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Re: Smoking Commando

Postby Steves » Thu Sep 14, 2017 1:46 pm

So I got the head off tonight. Good news no cracks, valve guides look in good nick, valves look good, no sign of oil upstream of intakes or downstream of exhaust. A little play between valve stems and guides but what I would think is normal. Oil definitely getting burnt in the right cylinder. I think the culprit is oil from intake return line (which as we know just goes from right intake valve Spring area). Copper head gasket which I think is reusable.

Any tips anyone before I put it back together? Sorry if I have hijacked your thread Michelle but might be of interest.

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Re: Smoking Commando

Postby Torontonian » Thu Sep 14, 2017 5:27 pm

New intake seals.
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Re: Smoking Commando

Postby cjandme » Thu Sep 14, 2017 5:32 pm

Torontonian wrote:New intake seals.

+1 on new seals (try getting the ones with the little spring around it) what is the Holland anti sump valve ? If it is an in line valve on the supply line you might want to consider getting rid of it. Cj
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Re: Smoking Commando

Postby Steves » Thu Sep 14, 2017 9:12 pm

Thanks the valve stem seals will get replaced, probably don't actually need to though. I think oil is getting into the right cylinder from the oil way which connects through the head gasket. Copper gasket or eyelletedgasket? Think was there was no external oil leak round the joint between head and barrel. Maybe more torque required, it difficult to get a socket round some of those nuts.

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