Topic: Rear Comstar Swap Help

[sethmcalister]

Hey All,

I just fitted a 78 GL1000 front end on my bike.  While this is the more uncommon swap due to the comstar, it was available and I seem to be really digging the comstar on the front.  For consistency, I'd like to swap a comstar on the rear of the bike.  My two options seem to be a rear comstar off a 750A or a comstar off an F1 or F2, correct?  The trouble with the latter is that the supersports were rear disc brakes.  The 77-78 750A's, however, were spokes and not mags. 

Can you guys offer your opinions up on what you think would be the best option for the swap and why?

[70CB750]

I seem to be missing what your goal is  - do you want disc in back?

[sethmcalister]

The goal is a mag wheel in the back to match the comstar now on the front, I don't necessarily care if it's a disc or drum.  It would seem that more work would be involved to convert to disc though, from what I've read on the forums.

[70CB750]

Of course, I am slow, sorry 

I done the comstar with disc for my K3F project.  You would need late swingarm to accomodate the wider wheel, extend the rear left top shock mount, install a rear master cylinder and resolve the brake pedal.

[madmtnmotors]

Or lace your front Comstar hub to a spoke rim?

http://motosynthesis.blogspot.com/p/products.html

[sethmcalister]

Of course, I am slow, sorry 

I done the comstar with disc for my K3F project.  You would need late swingarm to accomodate the wider wheel, extend the rear left top shock mount, install a rear master cylinder and resolve the brake pedal.

I have a K8 now, so the swingarm should be good, right?  Why extend the left rear top shock mount?  What did you do for the rear master cylinder and brake pedal on your conversion?

[sethmcalister]

Or lace your front Comstar hub to a spoke rim?

http://motosynthesis.blogspot.com/p/products.html

Thanks, Wilbur.  I prefer the look of the mags though.

[madmtnmotors]

Of course, I am slow, sorry 

I done the comstar with disc for my K3F project.  You would need late swingarm to accomodate the wider wheel, extend the rear left top shock mount, install a rear master cylinder and resolve the brake pedal.

I have a K8 now, so the swingarm should be good, right?

The K8 swingarm should be wide enough (I would have to measure, I've got both 78 "F" and 78 "K" models), but the mounting point for the F2 disk brake caliper stay arm is on top of the swingarm on the "F" model. The brake hub stay arm on the "K" model attaches to the bottom of the swingarm.

[70CB750]

Of course, I am slow, sorry 

I done the comstar with disc for my K3F project.  You would need late swingarm to accomodate the wider wheel, extend the rear left top shock mount, install a rear master cylinder and resolve the brake pedal.

I have a K8 now, so the swingarm should be good, right?  Why extend the left rear top shock mount?  What did you do for the rear master cylinder and brake pedal on your conversion?

In that case, you should be fine  refer to Wilbur, I never saw K8 in my life

Here is the brake pedal:

http://forums.sohc4.net/index.php?topic=115305.250

The master cylinder is somewhere earlier  in the project, basically a flat bar welded on the frame.  I used cylinder from newer Honda, it was used on many later bikes, this one is from 900RR if I recall correctly.

[madmtnmotors]

The 1978 CB750A had a rear comstar with a drum brake:

http://www.sohc4.net/cb750a-model-guide/

[sethmcalister]

I thought I had seen somewhere the 78 750A's were comstars.  As I started looking today, I found a reference article to the 77 and 78's being spoke though.  Thanks for pointing that out. 

That being said...is the 78 750A a direct bolt up to a 78 750K?

[madmtnmotors]

Well..... a quick reference to the parts fiche reveals that the 78K and the 78A share the same part number for the rear swingarm...

52100-405-000ZA

[sethmcalister]

Wilbur, 

Did you pull that from cmsnl or do you have a different reference point?

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[madmtnmotors]

I find this link to Service Honda's parts lookup pretty user friendly:

http://www.servicehondapsn.com/fiche_select1.asp?cat=Motorcycles&mfg=Honda

[trueblue]

The 650's were comstar and drum brake

[cb650]

The 650's were comstar and drum brake

Yed but different style.

[trueblue]

The 650's were comstar and drum brake

Yed but different style.

Not all

[cb650]

No but not many like your in the states right?

[trueblue]

I've seen a number of the 650 standards with the normal comstars on them advertised over there. They may not be the most common but they are there and an option.

[cb650]

I have yet to see one.  Even the Canadian models are like the US ones just with KPH speedos.   the "standards" here have wire wheels.   No standard in 79Z's only the one model.

[sethmcalister]

So it would seen that the best and easiest solution would be to find a rear 750A wheel?

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