I am now completely baffled! I bought a new primary chain for my BSA M20. The sprocket is 18T and the chain is 69 links.

I slacked off the gearbox bolts, as it states in the manual. I went to fit the chain and it seems to be 1 link too short, and even then it would be very tight. It's defo the right chain. And I double checked the number of teeth on the engine sprocket.

Would it be wrong to fit another link. Or can anyone tell me what I am doing wrong?

Thanks

Danny

email (option): dannyburt152@gmail.com

Danny you say you slackened off the gearbox bolts. Did you actually wind the gearbox forward with the adjuster at the rear of the gearbox on the kickstart side. Ron

email (option): ronpier@talk21.com

I am know completely stuck. Here is the tale.

I have gone to fit the clutch on my M20, it's now tight on the inner primary case. I have slacked off the gearbox plates and on the adjuster bolt.

I have removed the cush drive,clutch and brake pedal as the primary outer case does not fit. With the foot peg through the outer case it sits too high. To add, the correct length chain seems to be one link short.

I am at my wits end to be honest, and tried everything. Any help would be appreciated. If anyone lives near Barnard Castle, Durham, and willing to come up to the house to help as might be easier, or just laugh at my mistake. I can provide lots of tea!

Thanks

Danny

email (option): dannyburt152@gmail.com

Hi Danny
Could your problem be a poor fitting rear chainguard? It's attached to the inner chaincase & presumably helps to position it. If things were out there it would force the inner chaincase out of line.
No idea on the chain links though.

What size rear tyre are you running, a 400x19 reduces your chain lenght options.

And a half link in either chain is often essential.

Rob

email (option): robmiller11(a)yahoo.co.uk

Well that's a point Danny. Despite tyre size, your rear chain might be too short. Best disconnect it and sort the primary out first. Ron

PS. Would the rear tyre size make a difference?

email (option): ronpier@talk21.com

I stopped to help someone in Normandy who had broken his rear chain, he had a new chain with him that wouldn't fit, the rear wheel had a 400x19 tyre so was hitting the mudguard in either direction before all the adjustment could be used, I had half links for both chains with me and managed to get him going again.

Another possible problem could be the sliding plate in the back of the primary chain case, is it moving to its full extent?

Rob

email (option): robmiller11(a)yahoo.co.uk

Thanks all,

Here are some pics to try and explain it better. My rear tire size is 3.50x19, and the rear chain is really loose as not fitted it on correctly yet.

With the outer case and sprocket not fitting the chain, this might be connected.

email (option): dannyburt152@gmail.com

Indian Pattern parts?
I got a 16H field stand from India, an inch or two short......

email (option): jeremy@clogmaker.co.uk

There were different primary chain covers for different models, maybe one half is from a "C" range machine?

Rob

email (option): robmiller11(a)yahoo.co.uk

Rob,

You go top of the class, I scraped back the paint to see the part number, and looking at the forum posts, I found the following info that it's for a B series. There is very little difference. Alittle red faced.

Thank you for everyone's help. I will pop down a mates on Monday to see if he has the correct part.

The issue you mention Rob with the chain, is that common 1/2 a link?

Thanks

Danny

email (option): dannyburt152@gmail.com

I have often found 1/2 links to be needed, and new chains stretch after you fit them so sometimes you need to tinker again quite soon after you fit a new one.

Rob

email (option): robmiller11(a)yahoo.co.uk

Great, thanks Rob.

email (option): dannyburt152@gmail.com

Regardless of any wear issues requiring a half link, they are generally called for if altering gearing by one tooth on the sprocket.

If using, there is a correct way round to fit them.

Yes, B or C outercover, now we know you can also easily spot the shallow clutch dome. :upside_down_face:

I have learned the hard way, indeed!

Thanks again guys.

email (option): dannyburt152@gmail.com

Did you solve it?

I have exactly the same problem. My primary chain is 4mm too short with the gearbox all the way forward.

Did you use a 1/2 link?

email (option): darrylgubbels@gmail.com

Is the standard chain length not shown in the workshop manual ? WD Nortons with 18t engine and 42t clutch ran a 74 link primary...but every Renold chain spare parts tin included cranked half links. If you use one though, fit in the correct direction (so that it pulls together rather than apart).

Yes Rik. The standard WD 19T engine sprocket was fitted with a 69 link primary chain. Since I upgraded my engine to 600cc, I fitted a 20T sprocket and a 70 link chain. A 21T sprocket would require a 71 link chain.

I tried a 21T sprocket but found it to tall for my liking, so went back to the 20T. Ron

email (option): ronpier@talk21.com