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#44702 - 10/26/05 9:01 pm BSA B31/B32  
Joined: Oct 2005
Posts: 1
minesak1 Offline
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minesak1  Offline
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Joined: Oct 2005
Posts: 1
Nottingham
I have a 1950 B32 which I am trying to sell (restoration project). I have been told that the B32 is not as "popular" as the B31, because B31 can be converted to Gold Star spec. Also, that the B32 motor is exactly the same as B31. I think both these statements are sus, but can anyone please give me a definitive answer. Thanks

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#44703 - 11/08/05 1:04 am Re: BSA B31/B32  
Joined: Sep 2001
Posts: 2,766
Gordo in Comox Offline
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Gordo in Comox  Offline
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Joined: Sep 2001
Posts: 2,766
Comox BC Canada
There are always variations but from what I have seen the B32 and B34 engines are the same basic engine as the B31 and B33. The crankcases do not have a bearing support plate and the crank has the thinner shaft with the smaller roller bearing on the drive side and the oil flinger disc. As well the bigend bearing has smaller nuts and the locking rings to keep them tight. It could be that the 32/34 have better flywheels but they do not seem to have the GoldStar flywheels unless someone has made changes. I mentioned variations because I am of the opinion that anything is possible coming out the the factory. I have the remains of what appears to be a genuine ZB34GS engine that was built with the weaker cases and bottem end even though it is stamped ZB34GS. As well I have a good ZB33A bottem end built with the stronger GS cases, bearing support plate and flywheels.

I would think that the B32/34 differed from the B31/33 in the tuning; pistons, C:R, and cams to match the job to be done, trials or scrambles.

Gordo


Without frequent roadside repairs there is no fun in riding!
#44704 - 11/08/05 9:23 pm Re: BSA B31/B32  
Joined: Aug 2001
Posts: 1,850
dave - NV Online content
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dave - NV  Online Content
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Joined: Aug 2001
Posts: 1,850
Elko, Nevada USA
Gents ... You are discussing a very interesting topic to me regards the differences in various BSA single lower ends. I have a long term wish to build up a hot rod, "Iron engine", and I've accumulated an assortment of B31 and B33 engines. I also have a couple of olde ZB34 engines to perhaps use pieces from.

It sure would be handy to have a "What Fits What", listing of BSA parts/pieces. The older HD engines and bikes were very slowly evolved over the years much like our BI bikes. They too were built up 'from the parts bin'. Because of this, there was a nice little book printed on the HDs years ago, "What Fits What", with a wealth of information for the HD builders. hmmm

Anyhow .. I might add some info on the subject of using B31 cases. Phil Pearson in England modifies B31 'alternator' engine cases for many of his Gold Star customers to build up engines. Many of the big bore/stroked 604 cc engines he builds use these cases and we have a set he built for us in our 500 cc GS racer.

Per Phil: The '57 - '59 B31 crank mounted alternator battery ignition engines were very low stressed so there are no fatigue crack issues plus BSA added extra material in the main bearing area in these engines that allow modifications.
He bores the drive side case to accept a pair of crank roller mains side by side to mate up with his over sized crank axle.
Including the timing side cam support plate with the needle roller bearing, the lower end then has a 5 main bearing supported crank. The whole design issue is to have a lower end with maximum crank shaft support to prevent the crank flex common to nearly all Brit Bike engines from The Era especially at high rpm. Used in conjunction with the Pearson pressed up cro-mo steel cranks and nice Carrilo or GM speedway rod, you have a very nice lower end.

Questions for you regards the iron motors:
I'm told there is a drive side roller bearing that will fit OEM DBD crank axles and fit the B33 cases. Does anyone have the bearing number for me?

As I and many other GSrs have 'usable'(?) OEM DBD cranks laying about we'll not be using, I could use one to build a 'short rod' iron motor with a shortened barrel and push rod tunnel. I know it's been done by others but I don't have contacts with any of the builders. I really hate to "reinvent the wheel"!

How large oversize can the B33 cylinder be safely bored? Sourcing a modern design custom made piston is not an issue.

I find it interesting there are no small bolts, pins or dowels locating the B33 iron cylinders on the cases. Is this an issue to be concerned about?

Are the B31 cylinder heads made from the same thickness castings as the B33s? I'm asking as I want to use a B31 head with the smaller chamber and fit as large a intake valve as possible with modified angle and larger pressed in intake tract.
How large can the B31 intake valve seat area be bored to install a seat?

Why go to all this trouble especially as I have 'spare' DBD engine pieces on the shelf? I guess it's kinda like asking a mountain climber, "Why"? But then it would be a large giggle/grin to keep up with my pals on their Goldies riding a "Iron Motor" BSA. heh


dave - NV
#44705 - 11/09/05 9:20 pm Re: BSA B31/B32  
Joined: Sep 2001
Posts: 2,766
Gordo in Comox Offline
BritBike Forum member
Gordo in Comox  Offline
BritBike Forum member

Joined: Sep 2001
Posts: 2,766
Comox BC Canada
Dave: Great idea to compile info on these engines. It does raise the question about for example when is a Gold Star not a Gold Star? B31/33 cases? B32/34 cases? B13/32/33/34 flywheels? Iron barrel and head? My 350 will have B31 flywheels and cases but the barrel, head, rockerbox, cams and frame are pure GS. I might not want to race it but if looked after I should get some service out of it before I have to buy a Pearson crank. I remember how hard my brothers Alloy Clipper (B34A) was raced with head work, GS piston, GS cams and TT carb. I figure if it works just do it and enjoy.
Gordo


Without frequent roadside repairs there is no fun in riding!

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