Bottom yoke holes thread size.

[Mark]

Hi all.
Here’s an obscure one for you.
There are a few threaded holes on the underside of the bottom marzocchi yoke.
The two that concern me are at the front and are I think 7mm. They go right through the yoke.
I fancy making myself a bracket or two to support my new brake lines at this point on their way up to the m/c.
Does anyone know what pitch they are, ie, 1mm, 1.25mm etc?
I’ve tried a couple of options but as the holes are a bit grubby after 40 years I don’t want to use the wrong tap or bolt and ruin the thread.
Anyone

Cheers.

[George 350]

Hmmm. Interesting. .
On my 1978 single disc bikes they are blind, ie not going through. However, I have a set of K1 forks as spares and on those the front holes are untapped and are drilled through. (This is where the twin disc 'splitter/brake switch' bracket was fitted.) An M7 bolt will not pass through these holes in either yoke or bracket, suggesting M6 was used. All other holes on the underside are tapped M6.

For info, M6 is 1mm pitch, as is M7. 1.25mm pitch only comes in at 8mm, (and for Asian bike brands 10mm too).
Regards, George.

[Mark]

That’s an interesting reply George, because my yoke is indeed on a K1 (1982/3) and it raises another question.
I’ve heard before of the splitter on the twin disc bike and found this set up was assumed if ordering brake lines for a twin disc Morini 350 from HEL.
My confusion is that I have two 350K1’s and neither have a splitter fitted, both came to me with identical setups (so logically original fitments), twin lines uninterrupted from calliper to master cylinder.
What exactly was the splitter/switch arrangement?
Could it have been fitted to the K but not the K1?
Both these bikes were originally registered in Italy - would that explain anything?

Re the original question, I agree all the other holes are M6.
An M6 1mm pitch is too small for these holes (goes straight through) and an M7 was a bit tight but did turn in 3 or 4 turns by hand before any resistance was felt, making me think it was maybe just grime in the threads. Mystery!

[George 350]

You might be lucky and find someone who has an unmodified 500/K1/K2 and can photograph the splitter, but I seem to remember it was a 'generic' sort of part used on many bikes of the period, like this:

s-l400 (1).jpg (11.4 KiB) Viewed 7552 times

.
It was attached across the bike, to the underside of the yoke by an angled bracket.
George.

[Mark]

Ah yes, I can see how that would work.
Thanks for the photo.
I’m wondering why a 2 into I arrangement would be used rather than just running 2 lines.

[George 350]

My guess is legal - need for a front brake light after (1982)? - there was a single brake line 'splitter' also available at one time. Or simply packaging. I must say that on my Sport the bar/lever position for best comfort for me is with the banjo bolt from the master cylinder almost touching the speedo, so having a longer bolt and a second line would compromise something, possibly thumb yo tank on full lock?

[robint]

Those tapped holes are also used to mount the base of the cockpit fairing though as the (1978 cast/single disc) bike is in the depths of the garage and under covers I can't easily get at them, but M6 rather than M7 as I used handy lying around bolts when fixing the cockpit and M7 I don't have lying around......

[norbert]

My Rocinante, which is originally a K from ´81 was updated with dobledisc an has that splitter (without stoplight switch) which is mountod on the top of the lower yoke as mentioned. I don´t rememer the pitch. But when you can turn the 7mm bolt one or two turns in an than not further, for me it seems, that it is a 7 mm but with another pitch. The sport forks have mounted the steering damper at this yoke as well. I suppose it will be the same bore and pitch. Maybe on sunday I can have a look at the bike.

[JonD]

On my twin disc 1979 sport the two holes for attaching the splitter support plate on the bottom yoke are are drilled through and not tapped. The plate is held on by two 6mm nuts and bolts. I belìeve the bike was twin disc from new, it still had old Pirelli rubber brake hoses fitted when I acquired it..

[Mark]

I rechecked today and as people have mentioned here, the holes are 7mm but untapped. No wonder I couldn’t get a bolt to thread in, it was just minutely cutting into the bore making me think it was threading in - duh!

What I don’t get though, is both my K1’s came with identical period rubber hoses and no splitter, and the Grimeca master cylinder on both is modified from earlier ones in that it has a 2 spade electrical connection for the brake light switch.
It seems unlikely that both bikes would have been modified identically so I have to presume that by 1982-3 the splitter/switch had disappeared and maybe the holes were used for fitting a fairing, although neither of mine came with one - was that a factory extra?

As George has pointed out, the longer banjo bolt required for both lines means it’s quiet close to the clocks.
I’ve just fitted raised bars to one bike which I’ve found amplifies the problem to the extent that I may have to use a different m/cyl with a forward facing outlet.
All part of messing about with old bikes I guess!

[norbert]

If you want to place a stoplight switch as well you have to look for this. It should be awailable at allmost all hydraulic (brake) shops.

4fachm10x1 Verteiler.jpg (9.79 KiB) Viewed 7477 times

[3potjohn]

On my K1 the twin brake lines go from the master cylinder to each caliper directly.There is no splitter. The fairing is long gone. The stop switch screws into the lever perch and abuts the rear of the lever.
I think there is a new and unused splitter in my box of bits in the garage.
Just checked underneath, I have 2 threaded holes towards the rear, likely M6 One is vacant, the other retains a cable holding bracket.At the front are two holes passing right through which are >m6 <m8.They appear to be untapped.
John