Hi guys,

Started to do a few jobs on the bike I purchased a few months ago. I only want it to work, I'm not looking for a show bike...

Brakes are non existent, to that end I removed the back wheel, sprocket and backplate.

The hub is a bit of a horror story, the bearing on the sprocket side is a rattling fit despite the numerous centre punch dots rained upon it, liner has a big lip of probably 2 to 3 mm and one of the bolts holding the sprocket on has been opened out to M10 or thereabouts.

I can repair the bolt holes, I can ally weld and bore the bearing diameter but the liner will be a pain.

Anyone have a maximum diameter for the rear drum? I'm hoping I don't need to make a new liner.

Also, if all of the above is possible I intend to do it without disassembly of the rim.

Am I wasting my time?

I really need a manual. (Or is it a Manuel being a Spanish bike?:))

Thanks in advance!

If I would be you I would look up EBay Gumtree or used parts motorcycle dealer for another hub or even better a complete wheel. You might too try to get a pair of Yamaha TY wheels so you have too the brakes sorted at once.

You can too use bits from Alpinas for example, do some research and look your way through offers.

 

My personal 2 cent opinion in cases where you just want a runner.

 

Edited February 23, 20188 yr by pschrauber

Excellent idea! Never thought about an upgrade. Thanks!

But, a used Yamaha TY hub could be just as worn, there's no guarantee they work any better. I've ridden Yams with dire brakes as well as good. My Sherpas have decent brakes using modern shoe linings machined to fit.  You could remove the lip from the hub and get the shoes relined with oversize linings, 5 - 6mm thick and then machine them down to fit.

Or there is an M49 wheel on ebay now after a dealer in Norwich broke a perfectly good bike for parts - utterly criminal in my opinion wrecking a perfectly good bike like that, especially the prices they're trying to get for the parts

 

https://www.ebay.co.uk/itm/BULTACO-250-SHERPA-REAR-WHEEL-BRAKE-HUB-B49-M49-BULTACO-PARTS-BREAKING-BIKE/282849801825?hash=item41db297661:g:VRwAAOSwXOVadfjW

Just seen the wheel on eBay Woody, can't believe they have broken the bike, such a shame, it looked good too. Cracking idea about the oversized lining! I'd still like to know the maximum permissible diameter, I have a feeling it's beyond that....

Madness to break that bike total greed.

For linings try http://villiersservices.co.uk or a wheelbuilder who can replace the worn brake drum possibly with the rim attached try Paul http://www.yorksclassictrials.co.uk/classified-ads/4543674651

I'm quite lucky in that I have a lovely big workshop full of metal and stuff to play , I mean work in.?... if it's doable while it's laced up I'm happy to have a crack at it.

Great resource this site,

Thanks again guys!

Have you spoke to Dave at Bultaco UK to see what he has and advice ? I'm sure he has manuals in stock as well.   

 https://www.inmotiontrials.com/

 

Edited February 23, 20188 yr by gasserguy

I'll phone him on Monday, I need guidance!?

Unless you are going to road register it, you can machine the drum out as far as you dare. The lining material is available up to 6mm thick so you have quite a lot of lattitude to play with. Bear in mind you don't have to machine out every last groove from the drum to get good brakes. Even something that is flat for 90% of the surface is way better than a drum with a surface that is uneven all the way across. The standard rear brake on them is quite strong by the way. Nothing like the little, lightweight Sherpa T rear hubs that came out in the mid 1970s

I'll brave the cold garage on Monday and have  a measure of the thickness. I Will be occasionally using it on the road so iĺl give it a good clean and inspect it properly. I'll phone up in motion as well...

Cheers!

Sherpas were fitted with four different hub types and there are quite a few more for other Bultacos. I'm not sure you'll find the tolerances / measurements you're looking for in a Bultaco manual, I don't think they were that detailed.

You can find some online if you google Bultaco manual

Thanks Woody, I'll look it up, failing any information I'll have to try common sense...?

Just had a look at that ad. I concur with everybody so far - that is outrageous breaking that bike.

6 hours ago, blueflag said:

Thanks Woody, I'll look it up, failing any information I'll have to try common sense...?

I checked my Haynes and Clymer manuals this afternoon but neither give any measurements. I don't have an actual Bultaco manual but I'm fairly sure they are just parts diagrams rather than instructional