I have a 1950 M21 and need to replace the primary chain. It has a 19 tooth engine sprocket. The bike currently has a 69 link chain but I see that it is supposed to have for this size sprocket a 70 link chain. I am wondering if the 70 link chain was shortened to take up wear or is 69 links correct?

Bruce

EDIT: My mistake, the engine sprocket is 20 teeth not 19. But still need to know how many links the original chain should be.

Bruce

AFAIK

Sprocket 15/16 T = 68 links
17/18 T = 69 links
19/20 T = 70 links

Cheers

Pete

email (option): petercomley@web.de

Bruce, a standard WM20 has a 19T sprocket and 69 links. I had to up mine to 70 links when I went up to 600cc and fitted a 21T spocket. I've now gone down to a 20T sprocket and still on 70 links. Ron

email (option): ronpier@talk21.com

According to the "useful Information" in the technical section,the standard sprocket is 18 teeth

email (option): petercomley@web.de

The technical Section has the engine and gearbox sprockets listed the wrong way round, with an 18T engine and 19T gearbox...

It should be a 19T engine and 18T gearbox...

Those are the sizes for a WDM20...

On the other hand, the standard engine sprocket size for a solo 1958 M21 is 20T..(1949-58 BSA parts list)....Ian

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

and I have a tatty parts list showing M20 as 18T and M21 as 20T (albeit for solo 1955 models)- confusing sometimes.

Did the civvy and WD models have different gearing?

Cheers

Pete

email (option): petercomley@web.de

You have to remember that WD models had different gearing to civvy models so the correct parts list has to be referred to...Ian

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