mag swap

what all's involved in swapping the mags off my 78 650d parts bike to my 79 650b? will i need a new chain or any other parts i don't aready have? i know i'll have to fab a bracket for the rear master cylinder but if anyone has any wisdom to impart, i'm listenin.

Im assuming the B is a wire wheel with a drum brake? If so take the whole swingarm and just remove and replace. Then start looking at how to mount the master cyl. On mine I have the it mounted near the rear pedal and the resevior is mounted on a bracket that runs across the frame in front of the battery. Its rigged, but it works very good.

yeah i'm tired of the skinny meat out back. like the vintage look of the wires but the whole point of a cafe is cheap performance like a rat rod, right? that and i pulled a TOP GUN with barbedwire fence at a 3 way stop in the rain the other day.

I dont think you will get more width out of it. The swingarms are basically the same except the mounts for the rear disc, and the arm that the caliper attaches too.

I'm pretty sure the swingarms are exactly the same as I actually bought one from a KZ650B when I switched to wire wheels, hoping it would be wider. The only difference is the brackets for the respective braking systems.

when i measured it, my mag is wider (1/2" i think) than my wire. that won't allow me to fit a wider rear tire than i currently can?

r1ng3l78 wrote:

when i measured it, my mag is wider (1/2" i think) than my wire. that won't allow me to fit a wider rear tire than i currently can?

The aluminum mag is thicker than the steel rim, so measuring the outside to outside width is not the way to do it. Either measure it bead to bead on the inside, or just look at the size imprinted on the rim, it will be something like 2.15x18 (maybe 2.50x18) or 3.00x16.
The 78 being an SR should have a 2.15x19 front wheel (wider than yours) and a 3.00x16 rear wheel (again wider than yours because yours is probably an 18").

Post edited by: steell, at: 2006/06/03 09:54

don't have an sr. i'm currently runnin a 79 b with a single disc front and drum rear. the donor bike is a 78 D (can't remember if it's single or dual disc front, it's at the shop). if it helps i'll get some more details measurments. i'm just wondering if i'm gettin into something more complicated than mounting and plumbing the master cylinder and resovoir and bolting in a new swingarm.

The D model is also known as an SR.

'79 KZ650B stock rear tire size = 400-18 (roughly translated is a 120-18)
'78 KZ650D (SR) stock rear tire size = 510-16 (roughly translated 130-18).
I'm no rocket scientist, but isn't 510 wider than 400? :huh:

And yes, the KZ650D (SR) models did have dual front disc brakes.

If you wanted to keep the stock rear wheel height of 18" that you have on your B model, you could swap the rear wheel (mag) and swingarm from a KZ650C (Custom).
That's exactely what I did, and a 130 fits perfectly without rubbing the swingarm - the plastic chain guard however needs to be "notched" (it's very easy to do) where the outermost edge of the tire meets it or it will rub and force the guard into also rubbing on the chain.

Granted, if you wanted to go wider than a 130, the D model wheel and swingarm might be capable of fitting a 140 (if that size is available for a 16" wheel that is).

Be aware, tire and/or wheel profile (height) will affect how the bike will perform at diff speeds.
Generally a lower profile tire/wheel aids in quicker, more responsive turning/cornering, but at the expense of higher speed stability.

Post edited by: RetroRiceRocketRider, at: 2006/06/03 11:03

the bike came with a 110-90 cheng sh!@. it's not much bigger than what's on my mountain bike and i keep waiting on it to break out from under me in a turn

r1ng3l78 wrote:

the bike came with a 110-90 cheng sh!@. it's not much bigger than what's on my mountain bike and i keep waiting on it to break out from under me in a turn

Personally, I like that size on a 2.15 650SR rim on the "Front" but it's entirely to small on the rear for anything larger than a KZ440

I think a 130/90/18 rear tire works nice on a 2.5" rim on the rear, but I think the KZ1000P is the only one that possibly had the regular KZ mag in that size.