After a lot of help from you guys I have finally got this conversion done and went out on it today for a very cold 20 miles.
Even though I am running it in the 350 OHV engine is much nicer than the 500 SV, with more flexibility and punch, although I think I need to go up one tooth on the crankshaft sprocket.

I know its a deviation from original, but I like it and it makes the bike more usable while still looking like a WW2 bike, and I get the girder/rigid experience. I think it will keep up easier with my mates Norton ES2 than the SV did.

I can rebuild the old engine at my lesuire and its an easy swap to put it back should I want more originality later.

So thanks to everybody for their helpfull advice especially Dave Plumb for rebuilding the crankshaft, Mick Holmes for help with the Dragonfly catalogue, and Ian Write for spending what must have been a lot his own time explaining things on this exelent forum

email (option): Gasboy@btinternet.com

HI Peter, what was the cause of the bleu smoke?
I'm interested in it, because I've the same problem.
Regards from Belgium, Eric

email (option): ericvangils@skynet.be

Hi Eric.
What bike have you got? Is it an OHV or SV?

I know Ian will hate me for this, but I have a shut off valve in the feed to the engine from the oil tank on my B31.
I started my engine and it was smoking badly, then I shut off that oil valve, knowing the engine would run for a long time without oil. I watched the oil return to the tank until I saw it stop and the exaust was clean, so that I knew then that the crankcase was empty. I then turned the oil valve back on and the engine has been ok since, doing that 20 mile run.

The reason I ask if you have an OHV or SV is if its an OHV, shut off the oil to the valves, then if the smoke stops the problem is oil getting by the valve stems or over oiling at the top end.

This might sound a bit risky, but I know a few people in the Norton Owners Club who have done this diagnose smokey Commandos

email (option): Gasboy@btinternet.com

Hi Peter, I'm still confused..what caused the smoking in the first place?..I'm assuming you have a 'tap' in the feed line as you were able to turn it off..So does that mean you left the bike without turning off the tap and the non functioning anti drain valves in the engine allowed the cases to overfill?...Ian

email (option): ian@wright52.plus.com

During the initial start up which lasted about 20 minutes while I set the carb, advanced and retarted the ignition a bit to see how it sounded, tested the decompressor was working, revved it a bit, the engine smoked for a minutes then stopped. The oil return to the tank looked ok.

I closed to the oil tap on the engine feed, and left the bike for two days.

When I went back to it, the oil was still in the tank.

I started the bike with the oil tap open, and it was ok at first, but got smokier as I ran it, until it filled the garage and street so much it was emabarasing. At this point the engine also had a strange noise which I thought was the flywheels going through the oil in the crankcase.

I turned the engine off and posted the problem here (and got your exelent responses)

Next day I went out, and restarted the engine with the oil tap off. The engine ran a long time with oil returning to the tank and the smoke got less. When the oil stopped returning to the tank the exaust was clean, and I turned the tap on. The engine has been perfect ever since.

I cant work it out, but I hope someone can, and that it helps Eric

email (option): Gasboy@btinternet.com

Hi, Peter and Ian, thanks for your interest in my problem and thanks for your responses.
I hope there are not to much problems with my English language to explain my problem.(I live in Belgium).I'll do my best:
I have got an M20. I bought it 12 years ago and changed the engine 4 years ago by an overhauled M21 engine. I like that bike and I'm very interested in the mecanic.
At this moment I did about 6000 km with this engine (in summer) and no problems.
The only problem is the oil in the sump when the bike is parked in the garage for more than 1 week. (In summer when I use the bike daily there is no problem).
2 years ago I made a second drain plug ( in the sumpplate) to drain the oil out of the cranckase: I welded a nut and made a hole into the iron sumpplate and by a small bolt of 8 mm I can drain of the oil. I think this is easier and stronger than to remove the BSA plug in the allu cranckase.?????(sometimes weekly)
Last week I started to cure this problem.
-The first thing I did was 'reseating the ball in the timing cover' with a punch and a tap of a hammer,a new spring and a new ball.(thanks Ian)
After this job I tested the valves for leaking: removed the drainplug an put a tin under it: the next morming NO drop. I thaught that's OK ????
- I schrewed in the drainplug (I'm sure there was no oil in the crankcase) and started the engine.
The oil return to the tank looks OK: a 'spit and bubble' return. When I gave some revs it changed to a spit.All seems OK. After about 5 minutes at iddle speed (and sometimes a bit of revs) I stopped the engine.I removed the drainplug and placed a tin onder it.I was surprised to see the amount of oil that was in the crankcase: 25 cl !!!!!Is this normal at iddle speed? is the return capacity of the pump very low at iddle speed?
-Today I can't test it on the road (at more speed and more pump revs)due the cold and the snow at the moment in Belgium.
-now my question: is it normal that the capacity of the return of the oilpump is to low at iddle speed?
Personaly I think when the revs are higher (on the road), the pump 'll spit the oil into the tank.(and drain the crankcase)
I hope somebody can help me
Eric

email (option): ericvangils@skynet.be