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Re: Primary Cover (outer) - Are there more than 1 type?

From my experience there are at least two types for the various periods of M20 and quite a few more from other models that look similar. I would rather spend some time or money repairing your original. Ron

email (option): ronpier@talk21.com

Re: Primary Cover (outer) - Are there more than 1 type?

Brad, this is probably not the whole story but here are a few things to be aware of.
There are quite a few BSA primary covers that look right at a glance - here are a few I just pulled from the shed.


From the left they are:

1. Post war (I think after 1948 but I'm not sure offhand. This has a pert number stamped on the inside just below the inspection hole of 65-7584. This will fit the WM20 but has two obvious differences - the flanged section at the front and the smaller inspection hole (1 7/16" compared to 1 3/4" on the WM models.

This photo shows the size difference of a genuine inspection plug sitting beside the smaller 1 7/16" hole. This is also missing the cush drive cover section.


2. This was fitted to a basket case WM20 I bought and at the time I was caught out thinking it was correct because it didn't have the clutch fitted.
Looking at clutch dome profile you can see it is a little lower so I think that suits the pre-war clutches that are on shorter main shafts. It has also had the foot peg mounting hole butchered up to move it back to suit a WM20. This is stamped 65-7560 and I think this is from a pre-war B model. It does physically line up with the mounting holes on the inner cover of a WM20 just to be confusing.



3 & 4. These are the real deal for a WM20 and are stamped 66-7503 (the parts lists show 66-7502 - very normal BSA for the actual stamped/cast part number to be 1 digit different). The right-most one is a NOS one I chanced on at a swap meet. These have inspection holes that are 1 3/4" and no added flange on the edge.
One is fitted with an alloy inspection hole plug and the other with the brass version - as I understand it the alloy type was not on the wartime bikes but perhaps on the very early ones? I'm sure someone will know.

Unless your crack is really terminal I would get it welded but make sure the welder knows their stuff as these can distort very easily with gung-ho welding and if that is anywhere near the edges you might introduce sealing problems.
If you are going to buy a replacement make sure you see what the stamped part number is. I have seen some really rusty covers and the stamped part number has been at least partially visible - it would have to be skanky to not be visible.

email (option): rays54@hotmail.com

Re: Primary Cover (outer) - Are there more than 1 type?

Wow. Lots to take in here, and thanks Ray for all the info.

I have a split in the primary drive side cover (on the top of the dome) caused by a loosely secured spring retaining Nut.

In the interim, I have JB Weld Putty'd the cover, and will file/sand it smooth. This will fix the split, but also build up the dome a bit too in case it is thin anywhere else I do not know.

I have found a few on ebay, but they are all beat up or rusted out, or prohibitively expensive - but I will seek out a replace/spare just in case my repair fails down the road.

Part of being in Canada is it is a fair bit more difficult to find parts for these. We don't have the "jumbles" you guys do.

Thanks,

Brad F

email (option): You can look me up in past posts :)

Re: Primary Cover (outer) - Are there more than 1 type?

There are a seemingly infinite number of steel cases from prewar and post war BSA models for the B, C and M Ranges and Rays observations hint at that.....

I've had BSA singles for about 45 years and still can't definitively identify all of them (not that I really tried to, concentrating mainly on the features of the ones I need)...I think it would be possible to write a fairly hefty tome on the subject...!!!....One observation, the post 48 cover shown on the left of Rays photo won't fit a WD M20 as the 'flange' around its edge interferes with the crank case breather casting on the crank case. 1948 on models had the breather on the other side of the engine in the timing cover...

Another point is the cases are very prone to damage over time and in curing one problem you may inherit another...I'd tend to follow Rons' line of thinking...If your cover is basically good go with a careful repair to that....Ian

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

Re: Primary Cover (outer) - Are there more than 1 type?

Interesting point Ian, I have seen those fitted to supposed WM20's but wrote them off as 'that's not right' and didn't pick up on the breather missing issue. :wink:
Wouldn't be the first time I missed something hidden in plain sight.

email (option): rays54@hotmail.com

Re: Primary Cover (outer) - Are there more than 1 type?

I realised the 'flanged' cover didn't fit a long while back after I'd spent a few days preparing, spraying and lacquering one to go on the 1947 Girder fork M21 I was building at the time....Doh!!....Ian:laughing:

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

Re: Primary Cover (outer) - Are there more than 1 type?

I have a spare “flanged” primary cover destined for a Bitsa M20; it appears that it would be simple enough to cut the flange flush with the cover lip and have a good fit. (?)

I’m assuming someone has tried this at some point as the flanged covers are more readily available.

Any comments?

email (option): teladelujo@msn.com

Re: Primary Cover (outer) - Are there more than 1 type?

The flange is spot welded to the cover...Drilling out the welds would allow it to be completely removed though the resulting small holes would have to be welded up afterwards...

If the flange was cut back to the edge of the cover that would leave a thin strip of material the thickness of the flange still welded to it..Though visible I shouldn't think the remaining piece would be at all obvious with a little filler applied before painting...Just keep away from rivet counters...:laughing: ...

If the bike isn't to standard specification the cover can be fitted with the flange only partially cut away to clear the breather casting on the crank case...Ian

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

Re: Primary Cover (outer) - Are there more than 1 type?

This one looks good:

Gerade bei #eBayKleinanzeigen gefunden. Wie findest du das?

https://www.ebay-kleinanzeigen.de/s-anzeige/bsa-b31-primaerkettenkasten/1476738106-306-370?utm_source=sharesheet&utm_medium=social&utm_campaign=socialbuttons&utm_content=app_android

The seller did send me some extra photo's, see below. I am not that interested, I already have enough of these. Price is also ok, IMO.

IMAGE-1596560754239-4240188970756164444

IMAGE-1596560754301-1783681221693490852

email (option): wdmotorcycles@gmail.com

Re: Primary Cover (outer) - Are there more than 1 type?

I have had more than a few genuine WW2 WD M.20 outer chaincase covers over the years, some with damage and others appearing good. The general comment from those whom I have asked to repair holes in some has been the metal is extremely poor quality steel. I had one in particular that looked good but discovered it was porous with a constant film of oil on the outside of the chaincase.

I suppose that is how it was at the time - if it did not require top quality material you did not get it.

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