1961 Slimline M-50 gearing

I have a 1960 model 50 engine in my slimline. Some books say a 17 tooth engine sprocket but another says 18. I use an 18 and glad I do. It just about pulls away OK and doesn't start reving hard until around 60mph.

The main thing with engine sprockets is to ensure you have the correct offset. A halfway house from a 17 tooth engine sprocket would be to fit a 20T gearbox sprocket.

I assume you are using 19 inch wheels. There is no std choice with rear sprockets.

Hi Steve,

I agree with Neil, although I can't confirm the engine and clutch size as I have a M Hemming belt drive fitted (via Mike P) after a short while I realized it was overgeard and had to go two teeth DOWN on the gearbox sprocket, (from 19 to 17 ) to compensate It now performs similar to Neils, a bit slow to start, but performance (for a 350 ) acceptable. I am hoping when I fit my 'spare' head just back from Mike P with new seats,valves etc it will improve my non existence compression, and therefore performance. Enjoy the bike for what it is. My M50 is one of the first slimline ones, andwas first registered on 12 Oct 1960, and is very original,apart froma TLS front brake, (safety) and 'Goldie silencer(sound !) see pic on Yorkshire branch site.

Regards John O

Thanks for keeping us posted Steve. If that 17T came with the engine as original I suspect it will be the correct offset, there are 3 and the Late George Cohen defied anyone to find logic to it. I understand there were even different offset engine sprockets on the Mk 3 Commando.

This must be a well used model 50, I'm not surprised, they are a lovely bike to ride if you are not in a hurry and my favourite. My Alpha went back with the rod as it was FAR too tight, I guess you were lucky with that, being down under. Hopefully it was just me getting a duff one. It came back perfect.

Good Luck.

G'day, Steve,

We have bikes in common. I also have a WD 16 H and a 650SS though not original (Earlier single carb cylinder head for a start) and I'm sure they are not supposed to rattle and knock like mine but after 440 miles it is no worse. My mate is getting a probe you can drop down the plug holes to check the bores. A bit like key hole surgery!

Anyway, back to the Model 50. As well as my existing Slimline I'm putting together a 57 Model 50 but mine will use a 59 engine, same as yours. Ian R in Victoria had some plates made for me (& a set for the club) after waiting 8 years. He also loaned me his 57 parts book to copy too. A good bloke!

So, you had the same issue with your Alpha bearing. A good job you know some precision engineers. I bought a new old stock big end for my ES2 and that of course was no problem. But I also bought a Wassell big end for my Poor Man's Manx (ES2) and that was no problem either. Of course there is some nut machining to clear the cases for the Model 50. I suppose as a low stress motor there is less demand for specific Model 50 set ups and they are a rarer machine anyway, made even rarer by those putting a different engine in the frame...Buggers!

As for the judder, I only had one front wheel hub pulled out of true and I was fortunate that a Late old engineer I knew, knew another old chap who had a rig set up to skim certain drums, thankfully Norton full width 8 inchers were one of them. There are plenty of hubs about though. Check your steering bearings Steve and also the slot in the RHS fork slider for the front anchor. The alloy wears but a bit of shim does the trick. Wheel balance is the other thing, more critical at the front.

Your Model 50 will go a long long way before it needs taking apart again. I have done 5,000 miles so far (8,000K's) with only oil changes on mine and never missed a beat. The old chap I bought my 55 19S from in 1975 told me that of the three singles the Model 50 was the best of the lot. Having ridden all three he was dead right. But as I said, as long as you are not in a hurry.

Having said that, Bob in NZ races a Model 50 so if you want to go a lot faster it is possible but I get 80 mpg out of mine and happy with the nice handling and smooth motor. I'm sure this pre F/bed version will be just as nice. This will have an 18T engine sprocket and 20T on the gearbox as an experiment, along with the 19" wheels. BTW, my Slimline Model 50 runs on 18" wheels so that lowers the ratio slightly.

Way past my bed time. Have fun.