86 K100RS front brake master non ABS rebuild

[zipster68]

Hi,
Where do you guys buy your front master rebuild kits for a '86 BMW RS non abs?  Beemer Boneyard is out of non-ABS kits.  Is it just a straight $80 for just a piston from Maxbmw #32722302356 ?
[/size]Cheers,
[/size]Ray

[Martin]

Zipster I have been trying to find a replacement for the OEM kit. I believe either one from a Ducati or one from a Guzzi should fit. I have approached local Brisbane dealers but they don't want to know about it. I would try pulling the M/Cyl apart and take it into your nearest Ducati or Guzzi dealer they might be more approachable than our two. If you do manage to get a replacement kit part # there is a cheap source of Ducati kits in So Cal   https://store.bevelheaven.com/index.php?p=home. If you manage to get a number and model out of them could you please post it.
Regards Martin.

[zipster68]

Brembo and Magura 13mm kits look significantly different. 

[The Mighty Gryphon]

Gee, that Brembro kit has more parts, I bet it costs a ton more than the BMW Magura kit. 

R-i-i-i-i-i-g-h-t...

[Martin]

It's a pity but you would think (hope) that there is a cheap replacement out there somewhere. Considering the amount of motorcycles fitted with Brembo and Magura and copies of them there must be something that will work. I have a mate also chasing kits and I am not giving up at this stage.
Good hunting regards Martin.

[zipster68]

Gee, that Brembro kit has more parts, I bet it costs a ton more than the BMW Magura kit. 

R-i-i-i-i-i-g-h-t...

It's only $32.

[The Mighty Gryphon]

It's only $32.

Thank you, that was my point.  Best price I know of for the BMW part$ is $80.

[bmwpyro]

do we really have to replace the entire piston or can we source the rubber bits elsewhere?

[The Mighty Gryphon]

Even if you could find the rubber bits elsewhere, you would need a tool to install them.  I've used those tools and would guess that the tool would cost about as much as a piston. 

Trying to install the seals without the tool is almost guaranteed to ruin the seal.

[zipster68]

This might be it.  Out of stock. 13mm cup seal for master.
http://italianmotorsusa.myshopify.com/collections/brake-hardware-and-seals/products/13mm-locking-seal-5-pack

[zipster68]

Or these guys
http://www.fastech-racing.com/brake-seals/

[Martin]

Gryph I have an image in my head for the tool needed to replace the cups. Very interested to see if what you used is the same, a description would be great a picture would be very exciting.
Regards Martin.

[The Mighty Gryphon]

The tool we used was for installing o-rings on valve bodies.

It is a long bullet shaped affair with a hollow end with an inside diameter that is a sliding fit over the piston.  The other end has a taper to a rounded point, the seals would be slid up over the taper and down to the other end.  The other end tapers down to a thin edge.  The surface of the tool is polished and lubricated with a film of oil or grease to allow the seals to slide over it easily.

The end of the tool is positioned on the piston so it aligns with the edge of the groove the seal is supposed to be installed in.  When the seal is pushed off the end of the tool it drops into the groove.  Because the inside diameter does not have to travel over the edges on the piston there is no danger of damage to the inside surface of the seal.  Also because of the shape of the tool, the stretch of the seal is controlled.   

Hope this makes sense.

[Martin]

 :2thumbup: Thanks Gryph pretty much what was rattling around in my head. I have something that might be able to be machined to fit, might have a go at it later in the year.
Regards Martin.

[zipster68]

You guys think o-rings would work?  These are lip seals, widely used in master assemblies on pistons. 
-Ray

[The Mighty Gryphon]

O-rings won't work.  I was only describing a tool I used to use to install o-rings and seals in hydraulic valve assemblies.

[wmax351]

The tool we used was for installing o-rings on valve bodies.

It is a long bullet shaped affair with a hollow end with an inside diameter that is a sliding fit over the piston.  The other end has a taper to a rounded point, the seals would be slid up over the taper and down to the other end.  The other end tapers down to a thin edge.  The surface of the tool is polished and lubricated with a film of oil or grease to allow the seals to slide over it easily.

The end of the tool is positioned on the piston so it aligns with the edge of the groove the seal is supposed to be installed in.  When the seal is pushed off the end of the tool it drops into the groove.  Because the inside diameter does not have to travel over the edges on the piston there is no danger of damage to the inside surface of the seal.  Also because of the shape of the tool, the stretch of the seal is controlled.   

Hope this makes sense.

Sounds like a tool that is ripe for 3d printing. When it comes time to rebuild my Master cyldinder, I'll have to get my friend to print one for me.

[wmax351]

https://www.ecstuning.com/b-genuine-bmw-parts/piston/32722302356/

Here's the OEM one for $70, shipped, from the US. I've bought a decent amount of parts from these folks, they're reliable.


Other option is to take advantage of geopolitics altering exchange rates. Right now, the UK is probably going to be the best deal.




Motobins has one for 39 GBP. Thanks to Brexit, that's only 49 dollars, and it's small enough shipping will be cheap.

Venhill has one for 30 GBP.
https://www.venhill.co.uk/Controls,_Levers_&_Handlebars/MOTORCYCLE_CONTROLS/HYDRAULICCONTROLS/OTHER_MAGURA_MASTER_CYLINDERS/317217_MASTER_CYL___REPAIR_KIT_13mm__700_11EM.html

[The Mighty Gryphon]

Yes, would be a candidate for 3d printing, but be aware the wall thickness has to be pretty thin to avoid overstretching the seals when they are pushed over the body.  The tools we used were made from thin wall brass tube that was spun to a small diameter at the tapered end where the seals were slid on. 

This resulted in a wall thickness of the tool being something on the order of .010" with a sliding fit on the valve bushing.  The brass was necessary to prevent scratching the polished surface of the valve. 

Wish I had a photo to show here.

[zipster68]

make out something like this

[Laitch]

The tool we used was for installing o-rings on valve bodies.
It is a long bullet shaped affair with a hollow end with an inside diameter that is a sliding fit over the piston.  The other end has a taper to a rounded point,

Like these?

[The Mighty Gryphon]

Yep!!!  That's the ticket!

[Martin]

I was going to make them out of  aluminium.  Taper up and then taper down where it slides onto the piston to get the required strength.
Regards Martin.

[zipster68]

Beemer Boneyard has the 13mm Maguras back in stock for 2v K100 bikes for $69.  I snagged one.

[lmiklosy]

To answer zipster58's original question from 18 February 2017, if you're in a pinch yes you can make your own plastic bits, I tried it and it works. Boneyard didn't have a master cylinder and the OEM is pricey so I disassembled my 12mm Magura (ABS) master cylinder to see what was going on. Photo shows the outboard piston seal is worn out and leaks, the inboard seal is ok. Cut a 5mm piece from a Goodyear composite fuel line, spun it on a 1/4" mandrel and square-up the cylinder sides till you get 4mm. Use brakefluid and slip the new seal over the piston till it seats, use the assembled piston as a mandrel in a lathe or drill and shape the new seal with an emery board to look like the original.  The shape is important particularly for the inboard seal, the seal must be compliant enough to touch and seal the cylinder bore. You want an interference fit on both the piston and the cylinder bore. Clean dry and reassemble with a dab of Brembo silicone grease in the master cylinder bore and reassemble the rear brake, bleed and check the action. I did this a month ago and no leaks, brake action like new, cost 2-hours of garage time. My control group of seals are soaking in brakefluid on the shelf, no signs of swelling.   My gold brake master cylinder from China is sitting on the shelf as back-up.