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

[Treve]

Hi PeWe
I see in picture no. 4 that you managed to get the bleed nipple in the front hole on the right side as well. How did you manage this?

[PeWe]

I ordered the right side caliper from Yamiya.
It was "cheaper" back then.
I'm sure people here know how to remove it and put it back again without harming it.

I saw somewhere that small thing was for sale. Maybe Yamiya750.com

[Treve]

I have all the stuff here and have started assembling it all. In other words, it should be possible to unscrew the cone and change places. Yes, there are challenges in life and this is another one.

I have seen nice pictures on your conversion in another tread "How to make your CB750 stop like a modern bike" back in may 2016. Reply #52. Those pictures are telling me allot. Thanks.

[MauiK3]

I had an extra left side caliper and I tried to move the bleed nipple to the other port. It was corroded in or stuck in some way, no luck. I got a Yamiya caliper for the right side along with the Monel pipes to hook them up. Nice thing about the Monel is it doesn't really corrode much, it just gets a little darker. Very subtle. I can't remember how I got the speedo drive to go on but I don't recall that it was difficult, I guess I'll take a look at it to refresh my feeble memory.

[newday777]

I had an extra left side caliper and I tried to move the bleed nipple to the other port. It was corroded in or stuck in some way, no luck. I got a Yamiya caliper for the right side along with the Monel pipes to hook them up. Nice thing about the Monel is it doesn't really corrode much, it just gets a little darker. Very subtle. I can't remember how I got the speedo drive to go on but I don't recall that it was difficult, I guess I'll take a look at it to refresh my feeble memory.

What is  "Monel pipes"?

[bryanj]

More often called Kunifer, as the name suggests a copper/nivkel alloy easy to flare and easy to bend without kinking and special tools