Author Topic: Rear Hubs - Plunger and Rigid  (Read 204 times)

Online Nourish

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Rear Hubs - Plunger and Rigid
« on: 23.10. 2019 20:49 »
So basically you could have ordered your BSA twin back in 1949 till 1957 with either a rigid or plunger rear frame section - did these bikes share the same rear brake apart from the back plate - I ask as they only mention the plunger in the spares lists and the only rigid brake being the 1947/48 interchangeable type.
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Online trevinoz

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Re: Rear Hubs - Plunger and Rigid
« Reply #1 on: 23.10. 2019 21:18 »
I think that from 1949 the rear wheel and drum were the same as those used on the later swinging arm bikes. Brake plate obviously different.

Online Nourish

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Re: Rear Hubs - Plunger and Rigid
« Reply #2 on: 23.10. 2019 22:02 »
So looking back to through the threads the S/A models had a threaded bearing retainer on the spline end only and the plungers had two - one each end.

Offline duTch

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Re: Rear Hubs - Plunger and Rigid
« Reply #3 on: 24.10. 2019 00:25 »
 
Quote
So looking back to through the threads the S/A models had a threaded bearing retainer on the spline end only and the plungers had two - one each end.

 Yep- seems same hub but with the 1/4" of internal thread cut off- I had one on my Plunger before I knew they're different., but out still worked except for the late 60's chainwheel/ drum.... also the axles are different, rigid?& Plunger have a long through axle with short chain wheel stub, S/A has shorter main axle that screws into the stub and different hub bearing spacer... *pull hair out*

Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Offline Swarfcut

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Re: Rear Hubs - Plunger and Rigid
« Reply #4 on: 24.10. 2019 08:59 »
Nourish, there are probably few folks on this forum with first hand knowledge of the mix'n match possibilities of these early frames and brakes. The early Longstoke Parts List are available in the Forum Literature section, but before 1949/50 were published in a format to include all current models, so it will be a real test of character to wade through the information. At least you can compare what fits what. These lists have the individual parts well illustrated, rather than the exploded schematics of later publications.

 The rear wheel hubs of rigid, plunger and early S/A models have the same drive splines and wheel bearings, so the wheels will fit, custom spacers may be required depending on the frame used. As noted, plunger hubs have two bearing retainers, S/A just one. The basic pressings are the same, just machined for one or two retainers. Dust cover is more convex on a plunger hub, flat on S/A, so you can tell the wheels apart with a quick glance. Later A65 type can also be adapted, and can run a rear speedo drive, which brings the option of a cheaper modern speedo, rather than the gold standard chronometric type.

 The chainwheels are slightly different. They are similar, but have subtle differences for the unwary. As duTch says, the plunger spindle goes through the axle stub, which is bigger O.D. than the S/A type. This requires a larger bearing for the rigid/plunger chainwheel, so the center is machined out larger to suit.  The S/A hub bearing is the same as the wheel bearings. Drumside boss on the plunger chainwheel is rounded, S/A has a sharper edge, smaller central hole.

 Anything is possible, whatever the choice of parts they can be made to fit with a bit of thought, skill and a machine shop.

 Swarfy.

Online Nourish

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Re: Rear Hubs - Plunger and Rigid
« Reply #5 on: 24.10. 2019 10:39 »
I'm sure the more I read this the more I'll understand except "14" of internal thread cut off" - not sure about that?
Thanks for the replies

Online Greybeard

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Re: Rear Hubs - Plunger and Rigid
« Reply #6 on: 24.10. 2019 10:44 »
I'm sure the more I read this the more I'll understand except "14" of internal thread cut off" - not sure about that?
Thanks for the replies

Does he mean 1/4"?

Offline duTch

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Re: Rear Hubs - Plunger and Rigid
« Reply #7 on: 24.10. 2019 14:23 »

 
Quote
.....except "14" of internal thread cut off" ....
Quote
Does he mean 1/4"? 

 Yep- approximately (I'll edit that)
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia