CB550 1977 F2 twin disc conversion

[Sesman]

WARNING. There exists multiple conversion guides on this topic. The most popular one advises that to retain the original Speedo drive you need to machine the Speedo drive ring flat and secure it to the hub using flat head screws.   I have the round hub. Beware, this doesn’t work on the 1977 F2 hub as firstly the screws need to be located towards the perimeter of the machined drive plate and secondly the Speedo drive will foul the drive ring unless the screws are countersunk flush. I’m not sure if a small shim between the Speedo drive may help. Advice welcome….

I found this out when I assembled the axle; the Speedo drive became locked solid with the Speedo drive ring! It’s bit of a dangerous oversight in my view

Or what did I do wrong?

[Bryanj]

The way with the round hub is to machine the back of the disc holder to accept the ears on the speedo drive

[Sesman]

Disc holder? According to the guides on this forum there are three parts: dress ring, Speedo retainer and Speedo drive.

Can you expand on the machine piece please?

[Sesman]

Sorry, do you mean the actual disc rotor itself? The guide in Alladiins cave recommends for the round hub machining  the retainer flat and securing it with screws. Which I’ve found to be bollocks.

Spare retainer drive anybody please?

[Nurse Julie]

Sorry, do you mean the actual disc rotor itself? The guide in Alladiins cave recommends for the round hub machining  the retainer flat and securing it with screws. Which I’ve found to be bollocks.

Spare retainer drive anybody please?

Have a look through Grahams post, I'm not sure if the forks on his Mongrel are the same, or similar to yours but it may help a little.
He's done a twin disc conversion to this bike and so far, he is totally unimpressed and says 2 discs don't give any superior braking than 1 disc.
http://www.sohc.co.uk/index.php/topic,20419.0.html

[Bryanj]

I mean the alloy disc carrier or holder that the disc is riveted too and is bolted to the hub.
Machining the drive flat and securing it withcountersunk screws will work but you have to get it exactly central you dont use the chrome plate and the drive must fit inside the hole of the disc carrier

[Sesman]

Ok, thanks both. Surprising there is no improvement over 1 disc….at least logically if not practically! Obviously I’m a novice on braking physics.

I now need a new Speedo drive as the flat retainer theory will not clear the drive body with pan head screws. Any decent second hand sources, DS and CMNSL is prohibitive.

Oh Lordy.

[Sesman]

Hi Julie.

Iv’e drilled down Trigger’s build and it seems that he has used the earlier symmetrical hub with flat sides rather than the later asymmetrical ‘round’ hub design. So his solution won’t work On a ‘round’ hub unfortunately.

Think I’ll shim the Speedo drive by 0.25mm to clear the slightly raised heads on the countersunk screws, but if I can get my hands on a new retainer I’ll opt for Bryanj’s solution and machine two small indentation’s on the back of the disc carrier to accept the original retainer drive tabs.

So finally, anybody know of a non mainstream course for a new retainer?

Cheers

P

[Sesman]

Hi, Oddjob.

That really is weird as the knock pin heads would touch either the drive seal or the Speedo drive body. I know cos I tried it.

My boy is a 550 F2 with the later asymmetrical ‘round’ hub. When tightening the axle the Speedo drive binds on any protuberances on the drive ring. The clearance is very small indeed, probably less than 0.5mm, but I’ve yet to measure it. I didn’t notice when I tightened the axle, but all became clear when I tried to roll the bike .

Promise I’ll,, not mention a replacement drive ring again….

[Bryanj]

 The drive is same on 750/550/500(4 and twin) and i think 400&350

[Sesman]

Thanks Oddjob. The bearing is driven slightly below the hub housing so I don’t think it could be a contributory factor.

I’ll try to source another drive and give it another go.

[murdock]

Since we are talking about brakes, could someone tell me what is the size and pitch of the banjo screw that the caliper threads, I want to put a hose directly to the caliper and avoid the rigid tube

[Bryanj]

M10x1.5 i think but not a lot of thread for a banjo bolt, i use an adaptor to a swivel fitting

[murdock]

tank you , I will look for something to adapt

[murdock]

tank you , I will look for something to adapt

I have to ask again, I have looked below on the caliper without disassembling it and yes, it looks like 10 x 1.5
The one above, the one with the master cylinder is also like this?