Cb750 K5 rear disc conversion ??

[bluemouse1006]

Hi

Anyone ever converted their K5 SOHC rear brake into a disc , mine has a F2 front end with front drilled discs and looks great !!
I have been lucky enough to get hold of a full rear end including rear wheel with rear disc and calliper etc and swing arm . When I offer the swing arm up the alloy bracket looks like it might catch the rear foot peg hangers and the tube the rear Brake pin goes through . Other than that it looks like it might fit although I'm missing a rear brake master and reservoir if any out there has a spare ?
It seems that I might have to chop those pieces off but don't want to wreck the frame if it's not going to fit .
I can add photos if any one has any ideas

Thanks

Amos 

[Waggles]

Not done it, and don't know anyone who has.

Think the F1/2 swing arm is a bit longer than the Ks, might cause an issue if its by a lot, ( rear chain length, mudguard etc? ) also not sure but I think the swing arm bearing differs a bit too so I would check all out carefully before you start cutting stuff.

Pics would help .....

[bluemouse1006]

Waggles

Yes your right ,it's a touch wider as well ,the pillion foot peg bracket on the frame gets in the way,  which will need chopping off and frame cleaning up so it looks like it was never there .
Also the rear brake pedal tube on the frame gets in the way so again will need cutting
I'm leaving it till the winter so I can strip it all out and test fit every thing and not miss out on this lovely weather we are all having ha ha. The side pedal frames will all need cleaning and chroming.
The exhaust might be a problem as I think it's too close to the pedal frame when offered up

I'll keep u all updated with the progress over the next few months and I'll see if it's feasible at a reasonable cost

I'll add some photos when I start the process

Thanks
Amos 

[Waggles]

Yes exhaust could be a problem but you could fit the studs to the head instead of the tubes and an F1 4 into 1 might then fit, then that might involve re jetting a bit? although the four pipes are much nicer the 4 into 1 is probably a bit more efficient ( something about one cylinders exaust pulse helping to suck the next and so on )

[bluemouse1006]

Hi 

Thought id put some photos on to see what you all think and see if you think it going to be worth all the hassle?





Thanks Amos

[Waggles]

See comments in other thread re that wheel!

Personally, overall, I wouldnt bother. The rear disc is nice I admit, but hardly essential, its more the front brake that needs improvement. I guess it depends on why you want to do it?

If you have the standard K5 front set up I would try and find an F1 rear wheel as it wasn't Comstar and would match the front but all in all it looks like a lot of work. Also bear in mind parts for the rear caliper are rare NOS, I could only get one half! the other smaller half is unobtainable. ( Seals, pistons etc are OK though )

[bluemouse1006]

Thanks

I have a twin disc conversion on the front with drilled discs I wanted to have a matching rear disc (drilled) as well. Will be worth it in the end I think ,I have all the parts to complete but will have to swap the centre hub around from my comstars ( see the other topic)

I'll keep you all updated when I do start the job

Amos

[hairygit]

The later DOHC 750K had twin disc on front and drum on rear, why complicate what you already have? The rear disc set up is not much better than the drum,and worse in the wet   but it's another master cylinder to leak, and another caliper to stick/sieze/bind, and it would seem to be a lot of aggro if you have to butcher your frame to fit the relevent swinging arm etc. Just out of interest, have you asked your insurers what they think of the idea? I figure they wouldn't be too happy about it, and you would need a detailed engineers report to satisfy them (expensive!) that's if they wanted to insure it. Please don't think of not telling them, as if some idiot car driver hits you, and they don't have insurance, your insurers would say "undeclared modifications" and refuse to pay out

[Bitsa (Ralph Wright - RIP)]

Plus 1 with hairygit why bother with all that aggro?
Bitsa

[mick]

Just my 2 penneth worth in my opinion there are some better looking aftermarket wheels out there that would look better than comstars on your bike 

[bluemouse1006]

Managed to get another comstar for the rear after I mistakenly stripped the one I had !!!  ( see other topic)
Been looking at photos of CB 750 f1 and it seems that the rear master and bracket are a lot smaller and with out cutting the frame ( the rear pillion peg brackets)
Anyone got the bits hanging about ? Don't mind paying a bit if it helps me not to start chopping the frame .
Any
 Ideas

Cheers
Amos

[bluemouse1006]

Hi me again

Had a go at seeing if the parts would fit my bike today ive attached some photos see what you think. Think Ive managed to track down a rear master cylinder/bracket/pedal and slave for a F1 it seems that would be a lot easier and no frame cutting ?

Anyone know if F2 chain and sprocket is a lot chunky er than the K5 if i buy a kit with chain and sprockets will they fit and is the
chain longer ? as when I fitted the rear arm etc with the hub all the way forward its three links too short !!

ill keep you all updated but i can see it will take some time and money as well !

Thanks Amos

[UKROBK7]

I think the F2 chain is the larger 630 chain ( the same as the K7).  I don't think the engine sprocket will fit as I believe the output shaft is different.

Rob

[mick]

102 links is standard for the F1,  the front sprocket is held on differently for the  K'S & F1 than the F2

[bluemouse1006]

cheers that answers my question ill look for a longer chain than the on i have now instead of messing with the sprockets (even more messing i should say !! )

Amos