Author Topic: Twin disc caliper modification?  (Read 4820 times)

Offline sprinta

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Twin disc caliper modification?
« on: February 10, 2020, 05:19:58 PM »
I am considering doing a twin disc conversion on my 73 CB750 K2 and currently looking at all the parts I would require to do the modification.

On looking at the caliper whilst it it is straightforward to fit to the RH side they are handed in the sense that the nipple will now be closer to the fork tube and the hydraulic pipe now furthest away as the seats for the nipple and hydraulic pipe are different with the nipple using an inverse cone shape and the pipe a raised cone seat.

On looking at the relevant parts book page, see attached, there is an unnumbered part that looks to be some sort of olive insert above the pipe connection position.

Can anybody advise if this a push in seat that can be removed or if there is a relatively simple process so the nipple and hydraulic can be fitted as a mirror image of the LH side with the hydraulic pipe close to the fork leg?
« Last Edit: February 10, 2020, 05:22:21 PM by sprinta »

Offline Trigger

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Re: Twin disc caliper modification?
« Reply #1 on: February 10, 2020, 07:28:35 PM »
Yes, it is a press fit. You will destroy the old one getting it out. I think Yamiya do the caliper and spacers for the 750 conversion  ;)

Offline sprinta

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Re: Twin disc caliper modification?
« Reply #2 on: February 10, 2020, 11:57:26 PM »
Yes, it is a press fit. You will destroy the old one getting it out. I think Yamiya do the caliper and spacers for the 750 conversion  ;)

Thanks for the reply.


Offline Trigger

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Re: Twin disc caliper modification?
« Reply #3 on: February 11, 2020, 12:23:56 PM »

Offline 71 V12

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Re: Twin disc caliper modification?
« Reply #4 on: February 11, 2020, 03:05:17 PM »
Hi Sprinta,

I am in the process of gathering the parts to add a right disc to my 750 K4. A second hand Caliper and arm cost me £50 and a disc £20. The Yamiya Caliper and arm is £350 ish plus shipping and duties and looks like K0/1 type to me.

There is a olive of some type in the Caliper in the pipe location. I have removed it by threading it and pulling it out with a screw. I am planning to make brake pipe with a bubble flare and a long M10 tube nut. Hopefully this will seal.

The other issue I can see is securing the steel brake pipe to flexible to the mudguard. The left side has a correctly bent wire welded to the mudguard. Not sure yet what to do for the right side. Maybe a K0/1 type bracket can be adapted.

The conversion is far from straight forward. Where are you at with the job?

Cheers,

Kevin




Offline Trigger

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Re: Twin disc caliper modification?
« Reply #5 on: February 11, 2020, 03:14:19 PM »
A K0, K1 and K2 are not that straight forward as the later ones. They share the same caliper but, not the same arm or lower forks  ;)

Offline sprinta

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Re: Twin disc caliper modification?
« Reply #6 on: February 11, 2020, 03:45:42 PM »
Thanks for the link Graham and your comments Kevin.

Yes at around £350 plus p & p and import cost it is a rather expensive way to go.

Whilst having the correct handed parts makes for an easier and neater conversion I can't really justify that sort of cost. Having to stretch the hydraulic pipe a bit will not match the LH side, but you can't see both side at the same time?

Perhaps there may be a way to modify the seats so that the nipple and hydraulic connections can be reversed?

I believe that there is also a handed brake pipe/hose brk available, but again if you can find one it is bound to be fairly expensive?

Andy
« Last Edit: February 11, 2020, 03:48:39 PM by sprinta »

Offline sprinta

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Re: Twin disc caliper modification?
« Reply #7 on: February 11, 2020, 04:25:13 PM »
Hi Sprinta,

I am in the process of gathering the parts to add a right disc to my 750 K4. A second hand Caliper and arm cost me £50 and a disc £20. The Yamiya Caliper and arm is £350 ish plus shipping and duties and looks like K0/1 type to me.

There is a olive of some type in the Caliper in the pipe location. I have removed it by threading it and pulling it out with a screw. I am planning to make brake pipe with a bubble flare and a long M10 tube nut. Hopefully this will seal.

The other issue I can see is securing the steel brake pipe to flexible to the mudguard. The left side has a correctly bent wire welded to the mudguard. Not sure yet what to do for the right side. Maybe a K0/1 type bracket can be adapted.

The conversion is far from straight forward. Where are you at with the job?

Cheers,

Kevin

Hi Kevin

You say that you have removed the 'olive'. Do you have a close up photo of it and what sort of seat is left in the caliper after removal?

Andy

Offline 71 V12

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Re: Twin disc caliper modification?
« Reply #8 on: February 11, 2020, 04:39:54 PM »
The seat is the same as the bleed valve side. As I mentioned I am hoping that a bubble flare will seal without the need for the unobtainium olive.

Offline Bryanj

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Re: Twin disc caliper modification?
« Reply #9 on: February 11, 2020, 04:47:16 PM »
The op1 flare,or bubble as you call it, should work and you can get lont brake pipe nuts but make sure you have the correct thread as there ar two BUT you  will have to remove the end two or three threads on the nut as the threads in the calliper dont go all the way down.

Offline 71 V12

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Re: Twin disc caliper modification?
« Reply #10 on: February 11, 2020, 06:26:18 PM »
The internal dimension of the brake line inlet on the Caliper is identical to bleed nipple inlet except the port to the piston chamber is approx 0.5 mm larger. As Bryan mentions it is not threaded all the way. The thread is 1.25mm pitch.

Photo of the olive below.



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Offline 71 V12

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Re: Twin disc caliper modification?
« Reply #11 on: February 11, 2020, 06:33:46 PM »
This is brake pipe flare and long M10 x 1.25 tube nut I will try.

Offline Bryanj

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Re: Twin disc caliper modification?
« Reply #12 on: February 12, 2020, 01:06:59 AM »
Id sooner see kunifer not steel pipe

Offline sprinta

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Re: Twin disc caliper modification?
« Reply #13 on: February 12, 2020, 10:27:11 AM »
The seat is the same as the bleed valve side. As I mentioned I am hoping that a bubble flare will seal without the need for the unobtainium olive.

Hi

Olive is available from Yamiya. The attached photos from their site.

It is always possible that you could cut the appropriate nipple seat into the existing olive whilst still in place? It might rotate during the process and have to be removed? A new olive insert could be machined with the necessary seat for the nipple and then pressed in?

The suggested reverse flare on the hydraulic might work in the existing nipple seat face?

You can also increase the depth of the thread with the appropriate bottom tap

Offline 71 V12

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Re: Twin disc caliper modification?
« Reply #14 on: February 12, 2020, 12:01:28 PM »
I would like the conversion to look as near as possible a mirror of the left brake. I therefore hope to use the rear Caliper inlet for the brake pipe on the new right side brake, if that makes sense.

Plan A is to try a long brake tube nut that is not fully threaded as in the image above with the OP1 (bubble flare). If this seals great, job done.

If not

Plan B drill the rear Caliper port on the right Caliper and fit the removed olive which will clean up and use the OE brake nut and OP2 double flare.

Not sure why Bryan has a preference for cunifer, Honda used steel as do all other vehicle producers to this day. I think the surface coating may be better these days to prevent corrosion.

Anyway still at the parts gathering and refurbishing stage. I have most of the parts and fixings now except the brake line wire fixing bracket, but I will leave this until I’m into the job and can review the viable options.

 

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