Topic: My other last question about twindiscs

[timtune]

Ok so I have the speedo drive turned down and pinned. I understand the need to shim the mounts to get the pads parallel with the disc.

I've read most of the twin disc posts and nobody mentions the problem I have which is the mounting surfaces for the discs are not symmetrical about the centerline of the spokes on the hub. In other words the outer face of the disc is about 3mm from the fork tube on one side and about 7mm on the other. Because the caliper, fork tube and brake arm are either mirror image or identical both calipers are the same distance from the fork tube. One article mentioned removing material from the fork tube mount but that was more of the shimming operation I thought - he talks about removing some material from one mount to reduce the shimming on the others.

Also I want to flip the forks (calipers behind forks) does present special problems??

[MauiK3]

First, a few photos might help, are you saying the disc is not equidistant from the fork top and bottom? The casting of the fork lowers is not conducive to such a measurement, it wouldn't be the same.
The measurement you need to check is how the caliper drops over the disc, you can use feeler gauges to help check for irregularities, try to duplicate what you have on the other side. Some simple washers can often adjust the alignment. Mine were off a bit and I had some bad squealing until I re-did the washer spacing. I imagine the sizes may vary by bike and I don't remember the thicknesses I used. Others here may be able to provide that.
Swapping the forks around can be done with some benefits in weight swing but there is the matter of when brakes are applied it can cause some fork stiction due to the flexing from behind. I'm not smart enough to describe how it is different from the stock arrangement other than that the force comes from the opposite side and has a different effect on how the forks work. Our forks are marginal by today's standards so I always like to keep things as gentle as I can on the forks.

[timtune]

No the disc is closer to the fork tube on one side than it is on the other. The discs are not equally centered between the fork tubes. The calipers are equally centered. To make it right one caliper needs to move closer to the fork tube. No one has mentioned this (that I've read)
If you look closely at the front hub you can see one face is pretty much flush with the spokes at the hub and on the other side that face is about 3mm beyond the spokes.

Sorry no smart phone so pics are a pain.

[scottly]

The right side disc mounting surface on the hub is 3mm further from the fork. If you want the discs to be symmetrical, you need to add a 3mm spacer between the disc and the hub, have no spacers on the top two mounts on the right side fork, and machine 3mm off the lower mount on the fork leg (You could also machine 3mm off one side of the head of the mounting pin instead of the fork leg). Note: this may cause problems with the speedo drive.
If you want to flip the calipers to the rear, the right side fork gets moved to the left side, so the 3mm difference in the fork leg will need to be addressed to align the caliper with the left disc.

[Kaze]

I would very much like to see photos.

The brakes weren't symmetrical when I did mine either, and I rode all over Washington State for a couple years like that. It was great. I never experienced any sort of uneven handling, or strange weight issues or leaning. Bike was awesome at freeway speeds and beyond.

Also, I didn't shim anything, so I'm not sure why anybody thinks that's necessary. I had to grind my speedo drive plate, but that was the extend of my suffering. I wish I knew what bike I got the longer hub bolts from. GL1000?

If you haven't bought your brake lines yet, I recommend looking for the type of braided lines that go from your (double) banjo bolt at the in-line brake switch, directly to the calipers. Don't faff around with those stupid bent metal tubes. That part can at least be symmetrical if you go with those sort of lines. I'll put a pic to illustrate what I mean. Good luck. Pics please?

[scottly]

Also, I didn't shim anything, so I'm not sure why anybody thinks that's necessary.

The stock fender brace acts as a spacer for the top two mounts on the right side. (I tend to forget that since I don't use a stock fender. )

[Kaze]

OOOoooooh. Glad you brought that up Scottly. I'm into those double front fender bracers.

[scottly]

OOOoooooh. Glad you brought that up Scottly. I'm into those double front fender bracers.

Looking at your pic, it doesn't look like the fender brace is between the fork leg and the caliper bracket like it should be?

[timtune]

The right side disc mounting surface on the hub is 3mm further from the fork. If you want the discs to be symmetrical, you need to add a 3mm spacer between the disc and the hub, have no spacers on the top two mounts on the right side fork, and machine 3mm off the lower mount on the fork leg (You could also machine 3mm off one side of the head of the mounting pin instead of the fork leg). Note: this may cause problems with the speedo drive.
If you want to flip the calipers to the rear, the right side fork gets moved to the left side, so the 3mm difference in the fork leg will need to be addressed to align the caliper with the left disc.

Scotty,
Those mounts in your pic, are they stock or did you grind one down?

[scottly]

Those are the stock mounts. The ruler is sitting on the upper mounts, which are the same on both sides. The taller lower mount boss is the right side fork leg.

[timtune]

Thanks. I must check mine. I thought those forks were identical.

[Kaze]

Scottly: Where the heck were you in 2001? I needed your help!

[Gamma]

The right side disc mounting surface on the hub is 3mm further from the fork. If you want the discs to be symmetrical, you need to add a 3mm spacer between the disc and the hub, have no spacers on the top two mounts on the right side fork, and machine 3mm off the lower mount on the fork leg (You could also machine 3mm off one side of the head of the mounting pin instead of the fork leg). Note: this may cause problems with the speedo drive.
If you want to flip the calipers to the rear, the right side fork gets moved to the left side, so the 3mm difference in the fork leg will need to be addressed to align the caliper with the left disc.

Agreed, very similar to my notes. I made a 2mm spacer for the extra disc (my wheel rim has been re-laced putting the hub in the centre, not sure if it was originally central) this put both fork legs 4.15mm from the discs,  then I very carefully filed approximately 2.5mm off of one of the fork lugs to get things lined up and symmetrical.  I am not using a cable drive for the Speedo (KOSO electric), so I just made new spacers for the wheel hub.

[Don R]

  It sounds like the K0 front hub may make a symmetrical situation since it is wider on the speedometer side. I just purchased the last one I need, so it won't matter to me if I create a run on them on ebay. L0L!
   My double disc project will use F1-K7 type calipers and either an F0 or late A hub, I need to pump out a couple pistons for inspection since compressed air didn't do it this morning. 
  This was allegedly my other last answer. 

[pekingduck]

Did any of the CB500, CB550, CB750 SOHC (except F2s) ever come standard with dual discs?  If not, doesn't it seem weird Honda would offer a right side fork leg for that purpose?  Maybe a different market?

I remember the early CB500 fours didn't have that provision, but a French or German company sold a clamp-around bracket that you could add a right side caliper bracket.  (Thank you Racecrafters).

[timtune]

OK so I checked mine and of course their identical to Scottys. Tempest in a teapot..

As well as adding a second disc I'm flipping them back behind the forks. Is there any way to do this and retain the speedo on the right side?
I couldn't figure out how to do that so I ground ( Very carefully) material away from both fork and speedo drive and I now have the speedo drive fitting above the axle on the left with the cable drive exitting to rear.

I thought this would be mostly a bolt on affair.......

[scottly]

As well as adding a second disc I'm flipping them back behind the forks. Is there any way to do this and retain the speedo on the right side?

The speedo drive stays on the right side!!! You don't flip the wheel, only the forks!

[Don R]

 Won't the speedometer turn backwards? Will it cause you to time travel? Will the bike be new after it zeroes out again?

[Mark1976]

Won't the speedometer turn backwards? Will it cause you to time travel? Will the bike be new after it zeroes out again?

   And I thought you could only do it with a Delorean.... who knew!!!

[HondaMan]

Won't the speedometer turn backwards? Will it cause you to time travel? Will the bike be new after it zeroes out again?

Yes! It's much easier than rebuilding everything.

A comment about the brake: the dual-disc mod fits well except on the K0 bikes made before 4/69 (and a few later than that). Those don't have the right-side of the hub machined off to accept a disc.

My other comment about flipping the calipers to the rear: I discovered, during a [quite rapid] descent from Mt. Evans, 14,259 feet high, that if it sleets and rains together while you're doing this, the pucks don't grab well until for 3 times longer than when the pucks are up over the top of the discs, in the rain. The following weekend found me in the garage, flipping them back to the top.

...just thought I'd mention it, just in case...

[timtune]

Scottly, how can I flip the forks w/o flippin the wheel? The discs are not centered and they need to meet up with the appropriate offset of the forks.

[Don R]

 Remove the fork tubes, swap them side to side, roll to face the brake brackets to the rear and install the wheel as always.
  I guess the bottom fork caps need the gap reversed (see your manual) Voila! Or Bob's your uncle, or you got this, or any other form of encouragement.   

  Or just face them to the front. I even cut up a pair of rotor fenders and made duals. Do not ask how, it is highly technical and a patented process. And I don't remember.
  I still contend it was the worlds only triple drilled disc F1 with dual rotor fenders. 

[scottly]

I thought this would be mostly a bolt on affair.......

It would be if you didn't try to flip the calipers to the rear. The off-set in the forks matches the off-set in the hub. It's like Honda planned a second disc from the start!!?? 

[Kaze]

PekingDuck: From what I have gathered, a customer could indeed buy that second disc all set up as an option.
http://forums.sohc4.net/index.php?topic=86255.0

[Kaze]

Is there a particular reason that someone would go against convention and face the calipers the opposite direction?