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m20 chaincases & b31 are the same?

Hi there,
Iv'e checked the parts documentation regarding the primary chaincase for the m20. On the draganfly list there is 1 part number for the inner case. and 1 for the outer. Both numbers refer to m series models. I find no numbers for the b31.
Does anybody know if the inner and outer primarys are the same on m20 rigid as on b31 rigid?
I only ask because they often come up for sale for b series, Weather to buy is the question.
I have the m20 rigid with tele front
66-7601 inner
66-7502 outer.
Also judging from the part numbers i assume the footrests and shaft are all virtually the same

email (option): hutman80@hotmail.com

Re: m20 chaincases & b31 are the same?

There are so many varients of BSA chaincases. I doubt very much that a B31 is the same as M20. Ron

email (option): ronpier@talk21.com

Re: m20 chaincases & b31 are the same?

Unlike the war issue covers, my 1946 B31 has the extra front plating as the M20 from Post war. These were added post war to the M20s and can always be removed to adapt for a WM20 look alike.

email (option): unpob@yahoo.com

Re: m20 chaincases & b31 are the same?

For a rigid bike they should be the same as the footrests were in the same place as was the gearbox mainshaft and sealing method, the only differences really were that some had a kind of "skirt" around the top of the chaincase to tidy up it's appearance a little. The front mounting for the M20 and B31 were the same as, I believe the chainguard mounts were too. This applies to rigid models but there may be some small differences with the later models with the different clutch and plunger back end. I think in theory most will fit

email (option): davmax@ntlworld.com

Re: m20 chaincases & b31 are the same?

Mate I agree with Dave, as dad has a later primary cover set up on his m20, we think this is b31 as it has the sheilded area up front ,the only thing with this cover is unless modified it will interfear with the m20 breather.

email (option): cruiser@icisp.net.au

Re: m20 chaincases & b31 are the same?

What I have noticed during my search for a replacement cover for my WM20, was apart from the front shield! The foot peg hole can be in a different place. The oil fill plug is smaller and also different sizes of clutch bowl. I speak from the experience of buying three, only to find they were all different in some way. I ended up cutting the cush drive cup out of an old damaged cover that Ian gave me and replaced my damaged cup with it. Ron

email (option): ronpier@talk21.com

Re: m20 chaincases & b31 are the same?

As I'm making more of a "bitsa" then the added sheilding part is not of any concearn. I have an inner side from a plunger m20, I wondered weather I could just get any outer and use it with this. also as its plunger and my frame is rigid maybe it will differ. theoreticaly they should all be interchangeable, same engine, same gearbox alignment etc. cheers

email (option): hutman80@hotmail.com

Re: m20 chaincases & b31 are the same?

Oh I just read Your message. that's a beeatch. Exactly the sort of palarva I am trying to avoid.
Were the incorrect ones You bought b31 types? Or unidentified?

email (option): hutman80@hotmail.com

Re: m20 chaincases & b31 are the same?

Hi Maxwell. I bought two chaincases from different dealers by post, who both said they were WM20's and I bought one at a jumble that looked correct to me. The two from dealers were wrong in different ways. One I spotted was wrong straight away, the other one I stripped and primed before I realized. The one I bought at a jumble had the foot peg hole about 1/2 hole out(I also stripped and primed this one). I have no real idea what models they came from, and can only guess at different period M20's B31's. But I have also seen other variants that look nearly the same but aren't. Ron

email (option): ronpier@talk21.com

Re: m20 chaincases & b31 are the same?

Hi Maxwell...I probably have an outer case that is suitable for your special....will require a repaint etc...mail me direct if you are interested....Ian

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

Re: m20 chaincases & b31 are the same?

The odd ones are the C11 cases, so be careful with measurements.All rigid and plunger cases are the same, except for that front cowling. Think about it, the engine plates are the same so the footrests will be in the same position, the drive side cases will be in the same position and the gearbox in the same position. We have fitted an all alloy BB34 engine in an M20 frame with everything interchangeable.Thank you ladies and gentlemen!

Re: m20 chaincases & b31 are the same?

I thought about the engine plates, I figured m20 + b31 can potentially differ as they are 2 different frames.
as was said earlier, footrests could be positioned slightly differently and so forth. engines=same frames=different. If you say it's the same Ill take your word for it.cheers

email (option): hutman80@hotmail.com

Re: m20 chaincases & b31 are the same?

Well if Douglas says they're all the same! I guess I must be mistaken. Ron

email (option): ronpier@talk21.com

Re: m20 chaincases & b31 are the same?

Hi Douglas...The outer covers are not all the same. Postwar covers after 1947 have the smaller aluminium inspection cover as well as the 'shield' around the outside. As previously mentioned the 'shield' on post war types made after 1947 will interfere with the crankcase breather on earlier M Series bikes. There is also one version with both the 'shield' and the large inspection cover. The position of the oil level plug also varies with different types. M Series cases from 1960-63 were also modified to accept the alternator fitted to AA models and at least one type has the footrest hole in a slightly different position.
If B Series cases with the shield are fitted to an M Series bike the lower part of the shield also interferes with the frame on the underside...B Series bikes did not have lower frame rails in front of the gearbox like the M Series types...and then there are the C Series types with the shallower clutch dome to look out for as well, they are easily mistaken for the others..Ian

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

Re: m20 chaincases & b31 are the same?

Crikey. Thats some good chaincase knowledge. nice one.
Did You get my email regarding the case?
cheers

email (option): hutman80@hotmail.com

Re: m20 chaincases & b31 are the same?

Hi Maxwell..yes I got the mail...I'll get up in my spares loft over the weekend and mail you....Ian

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

Re: m20 chaincases & b31 are the same?

I apologize gents, but i was only referring to general dimensions. One could easily remove the front shield if desperate for cases. I must admit i did come across a set that had the hole for the footrests in a different position, they had me baffled. I just filled the hole and made a new one!

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