Author Topic: Another B31  (Read 165 times)

Online flashblack

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Another B31
« on: 09.11. 2020 18:37 »
I promised to treat myself to a new toy this year and this is what turned up. It's great fun as an alternative to the A10, a lot more leisurely but a huge amount of fun. Just about everything needed attention, but it rides really well now, and it will get cosmetically restored as money allows  *smile*
1959 golden flash
1949 B31 plunger

Offline Swarfcut

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Re: Another B31
« Reply #1 on: 09.11. 2020 19:47 »
  Flaskback.  Well, how good looking is that!!? Thanks for posting that pic.

    I am currently sorting a pile of BSA Gearbox Internals, some of which turn out to be pre'48 B & M. If it's all working I'd say leave that gearbox well alone!   Compared to the later A10 Plunger/S/A boxes it looks like the designer was paid by the hour and spun the job out. Talk about complicated, over engineered and a production engineer's worst nightmare, but you can see where the Orientals got the idea of selector forks on a rotating stick.  And you need three hands to put it back together......The later design is certainly a cost cut exercise, and far simpler in terms of design and the number of parts required.

 You machine is indeed a nice survivor and something a little different.

 Swarfy.

Online flashblack

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Re: Another B31
« Reply #2 on: 09.11. 2020 20:03 »
Hi swarfy, it's funny you should mention the gearbox as it was really rough specially in third, i bought a secondhand donor box and used the best bits and the box is now much better but it still has quite a whine in third because the only part i couldn't replace was the badly worn layshaft bush, nobody makes them apparently! I'm going to have to get a bush made up i think, definitely something to look at before long.
1959 golden flash
1949 B31 plunger

Online KiwiGF

  • Last had an A10 in 1976, in 2011 it was time for my 2nd one. It was the project from HELL (but I learned a lot....)
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Re: Another B31
« Reply #3 on: 09.11. 2020 20:29 »
Hi swarfy, it's funny you should mention the gearbox as it was really rough specially in third, i bought a secondhand donor box and used the best bits and the box is now much better but it still has quite a whine in third because the only part i couldn't replace was the badly worn layshaft bush, nobody makes them apparently! I'm going to have to get a bush made up i think, definitely something to look at before long.

3rd gear is never great on these bikes I’ve heard, mine has extra neutrals both sides of it  *eek* but which can be avoided with practice.

One thing I learnt the hard way is to be careful to keep the gearbox oil level right, a worn box leaks a surprising amount from the various shaft seals, and the selector forks suffer badly with lack of oil.

My pic shows the sidestand I made up recently, as I have a couple of older fellers who borrow it and the main stand (not actually fitted) is too hard to use for many.

New Zealand

1956 A10 Golden Flash (1st finished project)

1949 B31 rigid “400cc hot rod” (2nd finished project, + favourite bike)

GL1800 Goldwing, well, the wife likes it

KTM 950 ADV, cos it’s 100% nuts

1952 Armstrong Siddeley Whitley for rainy days (with wife)

Online RDfella

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Re: Another B31
« Reply #4 on: 09.11. 2020 20:59 »
Those singles boxes weren't the greatest. Try to hurry changes - especially 2nd to 3rd - and you end up with neutrals everywhere. Not ideal for competition! Back when I was competing a B31 (60's - 70's) I fitted close ratio gears to reduce the jump between 2nd and 3rd and shimmed everything to reduce all slop. Was better, but not great. I learnt not to hurry the change too much, and keep pressure on the gearlever whilst letting the clutch out and even for a second ot two after. Unlike today's bikes, where just a light touch on the lever guarantees the next gear.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Online flashblack

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Re: Another B31
« Reply #5 on: 09.11. 2020 21:04 »
Rdfella,
          What you just wrote reminds me of my gearbox *smile*
I am getting used to it though!
1959 golden flash
1949 B31 plunger

Online ironhead

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Re: Another B31
« Reply #6 on: 10.11. 2020 03:23 »
  Flaskback.  Well, how good looking is that!!? Thanks for posting that pic.

    I am currently sorting a pile of BSA Gearbox Internals, some of which turn out to be pre'48 B & M. If it's all working I'd say leave that gearbox well alone!   Compared to the later A10 Plunger/S/A boxes it looks like the designer was paid by the hour and spun the job out. Talk about complicated, over engineered and a production engineer's worst nightmare, but you can see where the Orientals got the idea of selector forks on a rotating stick.  And you need three hands to put it back together......The later design is certainly a cost cut exercise, and far simpler in terms of design and the number of parts required.

 You machine is indeed a nice survivor and something a little different.




I've found these gearboxes easier to assemble than the later types. Assemble all 3 shafts to the sandwich plate ( inner cover) then slide into the main housing ( similar to A65's ).

 
SA

Online Butch (cb)

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Re: Another B31
« Reply #7 on: 10.11. 2020 10:36 »
... and keep pressure on the gearlever whilst letting the clutch out and even for a second ot two after. Unlike today's bikes, where just a light touch on the lever guarantees the next gear.

A technique I have to use on my 70s and 80s Guzzis.
Warning - observations made by this member have a 93% unreliability rating.

Of Bikes; various, including ...
'58 Iron Head Flash Bitza