Topic: Twin disc conversion question

[timtune]

Adding a second disc to a CB 750 of about 73-74. I have extra fork legs with "mirror image" mounting of brake mounting arm.
My question is the speedo driver. It's too big with the second disc installed. I've seen where they were turned it down and then read about using a CB550 drive.

Can anyone shed some light on this?

[bryanj]

I am getting fed up of this myth, the 500/550 drive is exactly the same as the 750 drive, you need a hub with the two flats and a very early cb750 drive or you need a lathe and some acurate machining

[bryanj]

Look in the documents section under c500 twin disc conversion

[PeWe]

I used this setup.
Longer bolts and speedo gear.
https://www.ebay.com/itm/363581717279?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=FAFPPfGgRUK&sssrc=2349624&ssuid=XgCEg0CPSya&var=&widget_ver=artemis&media=COPY

Then you need to add spacers under right caliper to make it to be parallel to brake disc.

My upper 2 M6 have 5mm distance + fender bracket.


Lower bolt has 5mm distance + M8 washer.


Closer to lower spacer + washer



I see now that my last 240km ride a few days ago (Saturday) made it dirty!



This wheel has the later hub without 2x milling flat on right side. K0 part will not fit then.

I think this hub can use the K0 speedo gear.


The bolt on gear will fit all. You need to drill for M4 tap when centered wich need measure twice before punching, drilling tapping.

[MauiK3]

Yamiya sells the parts you need.

[PeWe]

It was the Yamiya K0 version I meant.
https://www.yamiya750.com/index.php?main_page=product_info&cPath=246_251_184_87&products_id=373
I have one I ordered before just for sure.
Their longer bolts for dual discs on the short side with very thin nuts.
Replaced them with Honda stock for dial discs.

[bryanj]

That Yamiya part looks like it needs the two flats on the hub

[PeWe]

That Yamiya part looks like it needs the two flats on the hub

Yes it does.

[timtune]

I have a lathe. It's more than turning it down though , isn't it? Will I need to refabricate the tabs?

[bryanj]

The tabs wont work, you will have to turn it so it is a flat disc the fits tightly inside the disc carrier then drill it and also drill and tap the hub to fix it