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Oily exhaust


Sorry to keep on throwing questions to the board but I'm still getting to grips with my latest toy.

Timing is now sorted (37deg BTDC thanks to advice here), and this morning it started literally first kick.

But I'm afraid it is laying down a smoke screen. I fear a broken oil control ring. I'm hoping someone may say something brilliant about crank case ventilation (which one of the items I need to read up about).

It smokes waiting for lights, and there is a big cloud on pulling off. I can't believe valve guides are the issue since they've done so few miles.

It had a few misfires on the way to getting it sorted. Could that have been the issue? Piston clearance is on the wide side (I believe 8 thou) but I can't detect piston slap.

I fear I shall have to remove the barrel. Bother!

Any words of wisdom out there  please?

It goes very well. Great fun...although the notorious oil leaks have thoroughly wetted my boots.


I know nothing of singles except they are likely to have no valve seals.If excess oil is supplied there will be smoke.Close off the oil supply to the head and run it for a few miles,won't hurt it,but if the smoke subsides then you know a lot more.


That's a thought, Robert. As you thing at a time. I fear I'd worry about disconnecting a pressured pipe.

I've now been looking at breathing. My engine is early... Sept 1932. I don't see the non-return crank case breather on the left. Only a vent pipe behind the lower bevel box. I assume that just pumps in and out, so would benefit from a non return valve which it does not seem to have at present. Unless there is something else somewhere that I haven't found.


... is usually excess oil reaching the combustion chamber via the piston / rings, so the cylinder oil feed adjustment would be my first port of call. If it's guides then usually you get a puff when opening the throttle after being on the overrun when the lower combustion chamber pressure sucks the oil through the guides.

Having said that I know nothing about OHC engines......


Thanks engine is just an engine...the rear cylinder feed screw is a bit less than half a turn back. So if anything it is on the mean side.

Pics of the breather are attached. One shows it in place, with the drilled dome nut. The second shows the little alloy shuttle under it, in the position it reaches when fully pushed out. Anyway I removed it entirely this morning but no opportunity to test yet.

The PO used to race (cars) so there is lock wire all over the place...


Good question, Ian. Sadly I might never know. I don't know what its supposed to look like! I'll search his copious notes  but they are just as likely to tell me what the oil tank level was on a random day in 2010.

I gave it a trial run today. Only about 2 miles each way (down to show it off to Les at Russell Motors). Without the shuttle in place it does seem better  thankfully. On Sunday there was so much castor oil in the air at traffic lights I was beginning to worry about its laxative properties! I'll use it a bit, as it"s great fun. Ear plugs are of course vital. Probably advisable for nearby pedestrians. Now I have to worry about noise cameras, as if life isn't complicated enough.


The standard breather arrangement on a long-stroke ohc Norton is a drilling through the drive side mainshaft.  It exits laterally (between drive side case and the primary drive), and is shrouded on the upper half, so that it is open when the crank case volume is reducing.  There is also a pair of little ball valves, one in the rear of the drive side case, and another behind the cam drive.  They actually are far too small to have any real effect.

The breathing is not good enough to keep the motor unpressurized (a flap valve on the chamber at the front of the drive side case is a good start), but you should not be getting heavy smoke.  I would check how much oil is being fed into the cylinder wall.  If that is not excessive, look to rings



I think you are probably right about rings, Paul.  Based on a small but growing majority opinion.  The engine has done very few miles since the new piston.  Compression is very good, and there is a 'haze' on acceleration but not more.  (I once had an Austin Maxi, and I know what smoke looks like when it emerges from a worn engine working hard up hill!)  So I wonder about oil control ring.  But I wonder why?

The rear screw adjusted is only out half a turn.  I don't want to close it more in case I starve it of a place where it is under oiled!

It should be with Surrey NOC at the Ryka (Dorking) on Sunday morning 8th Sept, after a 17 mile run through mostly busy roads.  I'll have nothing to do apart from search out other opinions.  And anyway - the town centre in Epsom has so many slow changing traffic lights, I'll take positive pleasure out of filling their streets with blue smoke!

It looks like 'simply' changing the rings on an Inter isn't too difficult (compared with, say, a Dommie), as long as I don't lose the timing (which should not happen if I take care).  I'll see how I get on on a rather longer trip than 2 miles down the road.  Fingers crossed it might settle down.  But I've never known an engine to get better of its own accord.

And now I need to find a speedo.  Meanwhile it will have to be coloured dots on the rev counter.  Cameras everywhere near me.




May I suggest trying a bicycle speedo?

Don't cost much, simple to use (during the daytime anyway), are accurate providing that you measure the circumference well and you don't need to modify anything on your bike. Just make sure that you get the magnet as close to the hub as you can.

Regards, George. 



...what oil are you using?  if  you have gone modern your rings will take some bedding in.  You report good compression and no abnormality in sound or movements; plenty of excess from the usual spots so good oil flow.  Pressure relief valve set ok?   The return to the tank is double scavenged so its intermittent flow is normal.  Is your cam tunnel sound? 

I would be inclined to run with the oil spray turned way down /off to eliminate it, its surprising how sensitive it is. The temp you run on the road and with the low mileage it wont harm, and as soon as you recognize it worked (or it didn't) you can re set it to a more optimum position during the road test.    

With regard to thought of broken ring, roll the motor over TDC with plug out,  you may hear the loose tail of the ring click at it changes direction....  but explore all possibilities before you disturb the build; unless you are unhappy with the quality of it.


Good luck



Based on my time in a car garage, another possibility occurred to me.  If the bike has been burning oil for a long time, oil can build up in the exhaust system.  It then smokes for a long time even after the engine is running cleanly.  The cure is a long hard run to burn the excess oil out of the exhaust.  Worth thinking about anyway.


... more fun than messing around with cylinder wall oilers!

I had a bicycle speedo on my Sunbeam and it worked well. It was one with a cable rather than wireless and cost less than £10.


Good stuff - thanks, all.

George and Ian - I mounted a cycle speedo and it gave random numbers!  I'll test the reed switch resistance with a meter, and maybe try a new speedo.  I was maybe too clever by half and used a small neodimium super magnet glued to the spoke just as it reaches the hub, using silicone sealant, because it's not easy to arrange a 3mm gap from magnet to sensor.  It's hard to find somewhere to glue the magnet. I'll try again.  Maybe the magnet is too strong, and keeps the reed switch closed too long.  Or the speedo is not working. As you say, they are cheap enough.

Jonathan - I've only just read up about the pressure relief valve, (buried behind the mag chain cover at the back of the case I think?).  Don't know what to do with it - someone says to use a manometer and get 8" of water head in the oil line to the cam box!  When you say 'oil spray', where do I turn that off?  I thought I might remove the two small copper external valve lubricating tubes and block them temporarily.  Is that what you are suggesting?

The cylinder walls are well oiled judging from the state of the plugs.  So although the wall oiler screw is less than half a turn out, maybe I can shut it altogether at least for a short time.  That's easy to do (and to undo) at the roadside.

Regarding the cam tunnels - they seem to be uninspectable without first removing the cam box, and then taking it apart.  That sounds like fun for a winter's evening.  Unless one side can be removed?  But the drive tube and top bevel would need to come off.

Oil is  Morris R40  castor oil.  PO used Castrol R, and I did not want to strip it all to change oils.  Maybe I should have bought R50,

Christopher - maybe the simple fact that long hard runs are difficult to indulge in near London that is part of the problem.

And maybe I need to follow someone else's to find out how smoky others are.  But I've been to plenty of Brooklands events where hot bikes line up at the test hill, and they are seldom all that bad.

Having removed the breather cap, I need to re-test it good and hot before doing something drastic.

Thanks to all, and I'll keep you posted!

It should be at Surrey NOC at Ryka on Sunday 8th Sept.


that the wireless speedos don't like being near magnetos (or probably any ignition system).


Further news/ideas - and thanks to all whom I have not already thanked.

I removed the non-return shuttle valve from the breather that runs sideways straight into the primary chain case, and it is much better.  I'm no longer in danger of choking on the fumes!  But plugs are still filthy and black, and starting is reliably easy only with a freshly cleaned plug.  I see one Norton company publication saying that correct plugs should look like polished ebony (and definitely not grey...), so maybe I'm worrying too much.  Judging by the fact that the Inter has direct oil feed pipes in half way up both valve guides, the company took no chances about under-lubrication!  Incidentally - are those pipes really needed?  It's not as though the top of the engine has no oil splashing about!

I see on this site, John Hudson told Commando owners to detach the top end oil feeds and ride 15-20 miles without it.  Then they could positively isolate whether blue smoke was from rings or valve guides.  It would do no harm (he said).  But I'm not sure I'd fancy doing that for more than a couple of minutes with the cams not being properly and continuously fed.

I'll turn off the rear cylinder lubricator completely next.  Most bikes don't have them anyway and rely on splash I think.  Again, I assume Norton erred on the side of over-oiling - very sensible for an engine intended to be run safely at 6000rpm for over an hour at a time (allegedly).

Next also to try hotter plugs.  At least it might then be easier to start from cold.  It's fine when hot.  I don't really know which plugs to use at present. 

And the final (?) plan is to rig up a small temporary fuel tank, and run the engine exposed to the sunshine.  Then use my fancy mobile phone Super Slow Motion option and film the rockers thrashing around - and find out what actually happens up there!  If it is interesting enough, I might put it on YouTube.


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