Help with a Rotor Swap - Rotor Dims Needed

[cinco]

Hey guys,

I need some help with obtaining the dimensions to the stock XS400 rotors. I was hoping someone could measure the stock rotor for me (see below).

I'm in the middle of contemplating/doing a mag swap onto my drum equipped XS400. From a parts search I found on a 1979 that the front and rear rotors are the same part number (1L9-25831-00).

So I've got a Suzuki GS850 parts bike that has some usuable drilled rotors. This being a cheap skate build - it could save me about $60.

Suzuki GS850 Rotor Specs:
- Outside Diameter = 275mm (10 3/4")
- Inside Diameter Hole = 55mm (2 3/16")
- 6 hole mounting bolt pattern is the same
- Offset (with rotor laying so it looks like an upside down bowl - measurement from rotor surface/desk top to top of mounting flange) = 20mm (13/16")

Stock XS400 Rotors Specs?:
- Outside Diameter = ?
- Inside Diameter Hole = ?
- Offset from Rotor Surface-to-Mounting Surface = ?

What goes here - a spacer? When I put the Suzuki rotor on the wheel it would sit on a ledge (see pic). If the rotor (Suzuki or XS400) were to sit flush against the bolt holes the amount of material surrounding the rotor mount holes would be dangerously thin - thus, I assume a spacer goes b/t wheel and rotor.

If I go forward, I plan on doing a write up to help others. It'd include parts lists, pix etc.

Thanks a bunch guys

 

[cinco]

Here's the "stepped ledge/collar" that the rotor sits on...

 

[cinco]

Well as I was looking through my Chilton manual I find this info:

Front Disc Brake Diameter:
- All UK Models = 267mm (10.5")
- XS400 SG (3F9), SH (4R4), SJ (14V) = 267mm (10.5")
- All other US Models = 257mm (10.1")

HOWEVER, a parts search does NOT back this information up. Every year from '78-'81 show the exact same front rotor (#1L9-25831-00) and the "78-'79 show the same number for the rear rotor.

So back to square one.... Can someone still measure their rotor for me so this can at least be cleared up? And oh yeah can anyone shed some light on the need for a spacer b/t the wheel and rotor as shown above in post 1 and 2?

On a bad note - no love on my straight across GS rotor swap... Oh well, a little more learned.

 

[drewpy]

no spacer on the wheel, the stock rotor sits flush on the bolt holes. The susuki rotor won't fit without modfication!

 

[cinco]

Thanks drewpy

Yeah, I think I'm gonna just drop the Suzuki swap idea. Just was hoping to save a few bucks here and there... Its easy for a few bucks/quid here and there having a way to add up in a sneaky sort of way

I'm kinda surprised the rotor sits flush to the bolt holes as there did not appear to much material that would surround the bolt hole Like around a 1/16th" or a couple of mm...