The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Gearbox, Clutch, Primary => Topic started by: Daftmate on 25.10. 2015 07:45
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I am replacing the gearbox casing on my 1956 A10 plunger because of a cracked mounting boss on the bottom mount. I sourced a replacement from Newark auto jumble but have noticed some differences in the casting and internal machining. Does anyone know when the cases were modified and whether my original '56 internals will fit and finally any special points to watch on rebuild.
Attached are some pictures, spot the differences ! The 'original' case is on the right.
DM
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The one you have bought from Newark looks as though it has been beefed up a bit. maybe BSA had noticed a few issues with the earlier casting, particularly cracking around the bottom bolt mounts - common problem. I'm sure the parts are interchangeable.
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Interesting stuff; just had a look at the four spare cases I have, and with regard to the mounting boss all are like the one on the left, including the box that came on my '52....Not to say that it's original stock. ... But the box that I'm currently running is Like the one on the right, which I believe is an earlier box, as it came with a flat kick spring, and corresponding peg and maybe even part Number?
Re the layshaft constant-mesh gear 'relief', dunno until I dissect them again.... On that basis, you may have an early box as 'original', and have acquired a proper 'original' box as spare.... Either way it'll work but depends how fussy you wish to be with originality. .. *dunno*
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Thanks Dutch that's kinda what I wanted to know. If they had problems with mounts breaking it looks to me that the left hand one is the later box with the 'buttressing' around the bottom mounts.
When did they stop making A10 plungers, guess they carried on for the sidecar brigade for a few years with production alongside the s/a model ?
Mine is '56 and I've no reason to think the gearcase isn't original as it's a matching numbers bike (well at least with the original Buff log book) I know engine and frames nos are different ! So the 'buttressed' one would be later than '56 and I guess continued to the end of plunger production yes ?
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Did ^that^ on the phone, so just changed a couple of bits; Either way it'll work but depends how small (fussy) you wish to be with originality. .. *dunno*
and "fixed gear to "constant-mesh"...
Spares books say the Plungers were made to '57, but I'm no expert on this, and am basing my comments on my own observation/misadventure *eek* , like I don't remember noticing that difference-- even though it needed helicoils in those lugs...good spotting
Might be worth considering any measurement difference between the bushings/overall cluster length on the layshaft with regard to the milling around the bushing area, and thrust 'collar' thickness of the bush, might be a bit more end float? *dunno2*