I'm just working on a 1940 BSA M20 which could do with a replacement Inspection Cap, is the one shown in the photo correct?


Or should it look more like my 1945 M20's bikes brass version.



The thread on the 1940 bike is 1.48" x 19tpi (60 degree form), whilst the thread on my 1945 bike is 1.13/16" x 18TPI (60 degree form).
The thread isn't the issue so much it's just what is the correct external profile for the cap, shouild it be in brass with a hex or plain as is?

Kind regards,

Julian

email (option): 79aust@sky.com

Not sure which is the correct one but be aware the one that draganfly BSA is currently selling is in the brass style, but made from aluminium.....

email (option): tmuir12@gmail.com

Yes your brass plug is the correct one. Bantam John sells good repros. The ally one which is the same size and thread is for the timing cover that has the mag pinion inspection hole. Ron

email (option): ronpier@talk21.com

I thought the small one shown in the first picture was the postwar type?

Rob

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

Someone want to tell that to Draganfly as I ordered a chancase inspection cap thinking it would be brass and was most uset when a badly machined ali one arrived

email (option): tmuir12@gmail.com

The primary outer cover and inspection cap on the bike you are working on are both post war and from the Tele fork models...Ian

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

Just another query now that you've all very kindly identified what I need.

What is the size across the flats on the hex bolt stub for the 1940 inspection cap, on my 1945 larger brass cap it's 20mm across the flats, is it the same for the earlier model?

Kind regards,

Julian

email (option): 79aust@sky.com

Hi Julian...All the WD primary case inspection caps are dimensionally identical....Ian

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

The inspection cap on the first photo looks like
M20 late model gear clutch lever adjust/oil fill aluminium cap, painted. (?)

Noam.

email (option): noam10@gmail.com

Hi Noam...That is exactly what it is..Pre unit B Series bikes used these caps in the oiltank and gearbox from late 45 onwards and also the primary chaincase from 1947 onwards... Pre unit A series in the primary and oiltank, Tele fork M Series in the primary and gearbox..Tele fork Pre unit C Series in the oiltank and primary.....Oiltank caps for some years and models had the oil grades cast into them...Ian

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

There seems to be a few 20mm hex's on an M20. For which BSA supplied their own spanner. From memory:- The two plugs we are debating,the valve lift assembly nut in the barrel, Nut inside the timing case? And is it the front wheel nuts?? Ron

email (option): ronpier@talk21.com

Ian am I missing something here, what's the difference between war time and post war outer chain case covers apart from the fill and drain holes and plugs, By the way Ian I have just acquired an 250 cc OHV 1938 BSA B 21 the oil and fuel caps are plain screw on , and I believe they should be pie crust shaped also the handle bars are wrong, are they the same as an M20 ? if so do you have any left, Andrew .h.

email (option): warbikes@gmail.com

Hi Andrew,for want of a better picture,this ebay item shows the plug fitted to the bike in the first image on the post 260985499499.
cheers Rick

email (option): richardholt@rocketmail.com

Thanks Rik, That's a post war cap but Ian said the chain cases are different, I know the drain and fill caps are different but the tin ware is or looks the same as war time I think,Andrew.h

email (option): warbikes@gmail.com

There is a metal band spot welded around the edge of post war cases after 47..If you look closely you can see what's left of it on the photo posted (at the top/front of the cover). This is not present on wartime ones and it has to be cut away to clear the crankcase breather if fitted to earlier (Girder Fork) M Series bikes...Positions of the footrest holes and level plugs also vary from model to model....
On the inner case the position of the piece that the chainguard attaches is also different for various rigid and plunger models....Ian

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

Thanks Ian that sorts that out, Andrew.h.

email (option): warbikes@gmail.com

At some point in my M20's life, the cush drive nut has come loose and damaged the front cup. So I thought I'd just fit a better cover. Bugger me I looked at loads of them and actually bought three wrong ones!! There are so many variations of them.
In the end, Ian gave me a scrap cover with a perfect front cup, which I installed in my own cover. Nothing is ever easy Ron

email (option): ronpier@talk21.com