Slow cooking - R100/7 twin-disc conversion at last

[Mal S7]

This might be the most drawn out project since melvilles!

I picked up a complete running R100S spares bike about 5 or 6 years ago.
Nice pair of new grimeca discs from motobins ... hmm maybe 3 years back, plus pads and seals and gaiters and all.



I guess I have been happy enough with the single disc on the /7 ever since I fitted the handlebar M/C and steel braided hose. Not scary at all.
But two has gotta be better than one don't it? And the parts are just sitting there.

So, a year ago I got all excited, had the lower legs grit blasted, pulled the old /7 forks apart and dammit found the chrome was worn off at the base of one fork tube.



So motobins gets my money again, I bought a new italian made fork tube. By the time it arrived, I was already riding.

So now, a month ago, I tear the front end down again. Finding a bit of time here and there to make progress. New fork tube fits up nice, mess about with pre-load spacers, new seals and a bit of a polish up. And I shouted myself a present ...



Bought off ebay, a bargain at $120 (plus lots o' postage) from SJBMW. It took two and half weeks to arrive, I was starting to worry. I am skeptical about the handling benefits but it sure is a nice bit of bling. In any case there be nary a curvy road for 100 miles so it may be some time before I can report back on that. Roundabout race anyone?

I considered the TT brace but thought they looked a bit overengineered, at least in photos. The CC brace is subtle, it looks like it belongs. I haven't sized it up yet, but it slipped on neatly. No I haven't done the fork alignment thing YET ..., my dial indicator is awol, and I get lost hunting on ebay, from the States you can get some beautiful old machinists sets for not much more than some junky new dodgy brandname indicator. http://www.ebay.com.au/itm/Vintage-Star ... 500wt_1414

But time, there is time for that.... I popped the calipers apart, I now have three ATE 40mm pistons and they all look like this.



and that's after a good wire brushing. This one was from the /7, it was working fine with well worn pads, but new pads mean them craters will have to slide past the seal. So, mo' money from the wallet. $240 plus post from UK for two. And I have a couple of weeks now to wait for them to arrive, so will clean and polish and align.

Back on the road by April though.

Cheers
Mal

[Major Softie]

You only need a dial indicator to align the forks with the old style top plate. With a top triple clamp, the distance between the tubes is dictated by the clamps, so you only need a flat surface like a piece of glass to make sure the tubes are in a single plane.

(weird how topics appear in different strings at the same time - i.e. lelocp's thread)

[Mal S7]

(weird how topics appear in different strings at the same time - i.e. lelocp's thread)

Yeah I noticed that.

Thanks for the advice MS. A piece of glass I can do.

Why isn't someone out there making pattern caliper pistons for $40 a pop, that's what I want to know. Liability? You are all quite safe in china and vietnam and you know it!!

Mal

[DucatiPete]

sjbmw cnc'd top triple tree... drool... I'll havta check 'em out...

I have two 40mm ATEs up front on the RS (with H/B M/C and braided lines)... would not inspire confidence in any roundabout race... but prolly better 'n having just one of those old relics.

Looking good Mal...

pete

[ME 109]

You only need a dial indicator to align the forks with the old style top plate. With a top triple clamp, the distance between the tubes is dictated by the clamps, so you only need a flat surface like a piece of glass to make sure the tubes are in a single plane.

Would it be fair to say that the maximum specified fork runout of .01mm (?) is impossible to achieve with a top triple clamp, and impossible to alter?
And if so, does that bring into question the need for such a close tolerance?
I realise that cnc machining is/can be of very close tolerances, but I'm wondering can such accuracy be achieved?

[barryh]

Would it be fair to say that the maximum specified fork runout of .01mm (?) is impossible to achieve with a top triple clamp, and impossible to alter?
And if so, does that bring into question the need for such a close tolerance?
I realise that cnc machining is/can be of very close tolerances, but I'm wondering can such accuracy be achieved?

In numbers I can visualise that's 0.4 thou which would be impressive. If my R65 type yokes are that good I don't think they are any better. How likely is it that both stanchions are straight to that tolerance which would be one way of compensating.

Logically to avoid binding the stanchion alignment tolerance should not exceed the forks running clearance which BMW give as 2 to 4 thou. Due to the multiplying effect of the stanchion length that would suggest the yoke alignment would need to be something like 3 or 4 times less so maybe the yoke bore spacing does need to be accurate to 0.5 thou.

[ME 109]

Due to the multiplying effect of the stanchion length that would suggest the yoke alignment would need to be something like 3 or 4 times less so maybe the yoke bore spacing does need to be accurate to 0.5 thou.

That's what I was thinking. I can't see it happening.

[Mal S7]

Its a good practical Quality assurance question Jeff.

Machining tolerances shouldn't be a problem, given good machining gear and tooling that's well calibrated, set-up and maintained. CNC just makes reproducing that accuracy more economical (i.e. cheaper but that sounds bad)
But accurate to what? How close were BMW tolerances kept for production of all those lower clamps, that's at least half the problem.

Most accurate way to ensure alignment would be with the top and bottom blanks machined while clamped together. Thats' OK for small jobbing runs but probably not realistic to have matched pairs go through a factory production run.

I'd still like to check alignment of my forks just to see. I never did understand, from Randy Glass's article, how pressing the forks (i.e. distorting the lower clamp) back into alignment would help anyway. If the top plate holes aren't aligned with the bottom plate holes, it will all just get mis-aligned as soon as you bolt up. And vice-versa of course.

Am I missing something?

[barryh]

So the outfits that are making after market top triple clamps must be machining them with a bore spacing accurate to 0.5 thou of the origninal lower clamps and all the original lower clamps are exactly the same ? I'm pretty sure that even my my original R65 type upper and lower clamps are not both exactly the same.

Makes you wonder if there wasn't some merit in the original top plate design as far the potential for accurate alignment was concerned even if it wasn't as rigid.

[Mal S7]

So the outfits that are making after market top triple clamps must be machining them with a bore spacing accurate to 0.5 thou of the origninal lower

Lets hope so. 0.5 thou should be no problem, its not a remarkable tolerance. Your point that BMW may not have consistently achieved it is a different matter. Make the same part, tens of thousands of units, for year after year and ALWAYS keep to that. Thats a difficult but common problem. Bread and butter though for BMW, and Honda and ....

I too would like to know how well they did in the 70's