A10 plunger sprocket hub

[Von datoh]

Well well the plot thickens!,got an eBay “bargain” I thought bsa part no:67-6150 42t drum sprocket all seemed good until I came to fit the hub bearing the Id is 50mm and not the supposed 57 I think I can get it on my lathe and bore it out to the right size it’s got enough edge landing in there to do so,what do people think?Im assuming it’s the reason I got it cheap,if a smaller bearing could go in I’m
Not sure the plunger dummy spindle will fit?.

[Minto]

I think you might've got that from the same seller as I had one from.
Stupidly, I assumed it was right without measuring it and tried pressing the bearing in with a heavy duty hydraulic press which resulted in it fracturing at the bearing boss, not such a bargain after all, it turns out.

[muskrat]

G'day Vd.
This might answer your question.
https://www.bsaownersclub.co.uk/bsaoc_forum/index.php?topic=12957.0
Cheers

[Von datoh]

Muskrat,morning *smile*or evening there
That part no:67-6149 I think is for the swingarm a10 according to dragonfly website.would make sense though what a pickle,I was gonna make stub axle anyway hmmm I have bearing and circlip to fit plunger sprocket or do I bore it out?

[muskrat]

G'day Vd, 2pm now.
67-6150 is what you need.
https://draganfly.co.uk/shop/75468/rear-sprocket-rigidswinging-arm-42t/#67-6149 rigid & s/a
We don't know if there any other minor differences that may come into play if you bore the small hole to suit the bigger bearing.
Cheers

[Von datoh]

I’ve emailed the seller see if I get a reply!,indeed it looks like it is for a rigid model then,much digging needed to get through the information haze.

[Swarfcut]

 Look closely at the central boss. Plunger drum has a large  centre hole and a more rounded profile to the edge. S/A drum is a sharper profile.....bit like a Scotch Pie compared to a Steak and Kidney Pudding.  Easy mistake to make. 42 Teeth for a Solo lie very close to the edge of the drum.....anything else is more suited to sidecar work.

 The same basic Plunger drum is also used on other contemporary BSA models. They will all interchange...BUT  the number of teeth differ, as does the width of the teeth, being narrower for lower powered ranges. Care needed, as you have found.

 Swarfy.

[Von datoh]

Swarfy the profile on edge of drum near the teeth is sharp not rounded is that why you mean?Also aside from some remachining of bearing bore do you see any other issue using this sprocket I will count the teeth when home but pretty sure it’s 42 and supposed to be for the larger chain ?!,It was so cheap on eBay I couldn’t believe I got it now I do !!! I expect the return postage back to India will be more than I payed for it:))))live and learn 1 step forward 2 back

[Swarfcut]

 No, it is the profile and shape of the centre boss which is the quick means to identify, not out by the teeth. Pictured side by side the difference is clear between the two parts, plenty of images on the web. Reckon you have the S/A 42 teeth drum, which should be easy to move on.

 Now you know what you're after,  look for the right drum and do not waste your time and effort on an ex oil tanker scrap metal meltdown...

 Swarfy.

[Von datoh]

Those closing remarks really bought a tear to my eye :))),however in my defence I would gladly buy the part from someone manufactured locally but most that i see currently for sale are either made in India,from India or imported over to uk seller made in India originally!sprocket made from an old cruise ship there’s a thought(probably true)attached hopefully is pic of sprocket

[Von datoh]

Another pic

[trevinoz]

Just a nitpick, I think that you all will find that the rigid drum is not the same as the plunger.
The rigid has the same bearing as the swinging arm drum.

[muskrat]

G'day Trev.
Yes the Drags site says rigid/swingarm, https://draganfly.co.uk/shop/75468/rear-sprocket-rigidswinging-arm-42t/#67-6149
67-6150 is for the plunger only.
Cheers

[Swarfcut]

 Reckon you're right there Trev. A painful trawl of the 1949 parts catalogue (all models, all parts in one place) shows a different spindle arrangement for the rigid frame A7 running alongside the newly introduced Star Twin with Sprung (Plunger) Frame.

 Here are a few pics of a well worn 42 Teeth Plunger sprocket/drum, along with a later backplate having the welded in bracing bar and fixed centre  bearing support spacer. Note the large centre hole and more smoothly domed centre boss compared to the S/A version.

 Swarfy.

[Von datoh]

Fair play for looking that lot up,I can see the difference,I’ve contacted the seller on eBay told they’ve sent me the wrong one you never know something may come if it or like you say I’ll sell it on.Here is pic of my backplate I think it’s a later one like you say with reinforcing plate and spacer built in?thanks again. Von.