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Offline timtune

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Twin disc conversion question
« on: April 16, 2023, 04:46:02 PM »
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?
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Offline bryanj

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Re: Twin disc conversion question
« Reply #1 on: April 16, 2023, 05:20:45 PM »
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
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Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline bryanj

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Re: Twin disc conversion question
« Reply #2 on: April 16, 2023, 05:23:39 PM »
Look in the documents section under c500 twin disc conversion
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Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline PeWe

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Re: Twin disc conversion question
« Reply #3 on: April 17, 2023, 07:03:39 AM »
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.
« Last Edit: April 17, 2023, 07:35:53 AM by PeWe »
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CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline MauiK3

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Re: Twin disc conversion question
« Reply #4 on: April 17, 2023, 09:17:06 AM »
Yamiya sells the parts you need.
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1973 CB 750 K3
10/72 build Z1 Kawasaki

Offline PeWe

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Re: Twin disc conversion question
« Reply #5 on: April 17, 2023, 10:10:35 AM »
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.

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CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline bryanj

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Re: Twin disc conversion question
« Reply #6 on: April 17, 2023, 11:44:51 AM »
That Yamiya part looks like it needs the two flats on the hub
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Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline PeWe

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Re: Twin disc conversion question
« Reply #7 on: April 17, 2023, 09:03:40 PM »
Quote from: bryanj on April 17, 2023, 11:44:51 AM
That Yamiya part looks like it needs the two flats on the hub
Yes it does.
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CB750 K6-76  970cc (Earlier 1005cc JMR Billet block on the shelf waiting for a comeback)
CB750 K2-75 Parts assembled to a stock K2

Updates of the CB750 K6 -1976
http://forums.sohc4.net/index.php/topic,180468.msg2092136.html#msg2092136
The billet block build thread
http://forums.sohc4.net/index.php/topic,49438.msg1863571.html#msg1863571
CB750 K2 -1975  build thread
http://forums.sohc4.net/index.php/topic,168243.msg1948381.html#msg1948381
K2 engine build thread. For a complete CB750 -75
http://forums.sohc4.net/index.php/topic,180088.msg2088008.html#msg2088008
Carb jetting, a long story Mikuni TMR32
http://forums.sohc4.net/index.php/topic,179479.msg2104967.html#msg2104967

Offline timtune

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Re: Twin disc conversion question
« Reply #8 on: April 18, 2023, 10:59:02 AM »
I have a lathe. It's more than turning it down though , isn't it? Will I need to refabricate the tabs?
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Offline bryanj

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Re: Twin disc conversion question
« Reply #9 on: April 18, 2023, 01:59:56 PM »
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
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Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!
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