front brake lever piston rubber parts?

[svejkovat]

1984 R65.
Any sources?  Any ideas?
Second time I've had to replace this.  Ok.  Maybe I didn't hone the barrel as perfectly as I should have before replacing the single 100 dollar (shipped cost) piston with rubber parts installed.
I'll hone it like a mirror.  But it pisses me off greatly to spend another 100 dollars on this damn part. 
Any other ideas on repair of this?

[svejkovat]

https://www.banggood.com/Motorcycle-Clutch-Brake-Pump-11mm-Piston-Plunger-Repair-Kits-Master-Cylinder-Piston-Rigs-Repair-Acce-p-1249741.html
I know, I know.   Ya gets what ya pays for... n all that.  And support your local parts dealer.  And so it goes.
But fer crissakes.

I won't be home from work till midnight.  Anyone know offhand what the OD and length of our piston is so that I might research an aftermarket fit?

Thank you soo much.

[Tony Smith]

I have bought pistons from a Chinese manufacturer in the past and then removed the cups intending to fit them to my BMW master cylinder. Except I then discovered the inner diameter of the cup was different. So I made a whole new piston from stainless steel to match the cups, except that by then I had removed and fitted the cups twice and ?I may not have been careful enough and tore one. At which point I sucked it up and bought the BMW replacement piston.

That said, next time I will just buy the cups and then make a piston to suit - I agree $100 for parts that cost BMW $0.25c is a bit much, even for BMW (Bring My Wallet).

[svejkovat]

Where are the intake and equalization ports on these master cylinders?  How accessible are they from without if I attempted to map/scribe them onto a sleeve inserted?

If I'm going to purchase a new cylinder from maxbmw for 200USD, and toss my old one in the trash, I may as well give this a try. 

I posted this question on a machinists forum and, as I rather expected, got a lot of blowback about the lunacy of attempting this without professional services or precision lathes.  I only have a good drill press.  But new seals don't give a rip (pardon the pun) about the precision of the rebore itself, but only the ID of the sleeve. Hell.. a hand held drill would suffice, no?  As long as a reasonable slip fit is achieved the sleeve is green loctited or epoxied in place and ports are cleaned up with a little fine polishing. The toughest part ought to be getting the ports mapped precisely enough.

It may even be possible that an appropriately sized sleeve could be found, perhaps linear bearing stock such as this...

https://www.pbclinear.com/Products/Round-Shaft-Technology/Simplicity-Precision-Sleeve-Linear-Plain-Bearings/PSM-Metric-Precision-Linear-Sleeve

Certainly adequate ID precision for this need. And relatively inexpensive.

[Tony Smith]

The replcement sleeve is usually seamless stainless steel tube. The finish standard on the ID is good enough to use with nothing more than a polish. A decent drill press will be good enough to bore out the mastercyclinder. You will need three things in addition to the drill press:

1/. A fractional drill as close as possible to the diameter of the tube OD (but smaller obviously).

2/. A hand reamer the correct diameter for the tube OD

3/. A Drill vice able to securely hold the master cyclinder during drilling/reaming.


Drill the master cylinder, then ream to size. Then press the tube into the master cyclinder using a fair amount of brake fluid proof sealant (Locktite green would work).

Drill the ports, polish the ID, refit the tank and you are good to go.

You will have to use sealant as without the massive bearings in a lathe or mill there will be a certain amount of "slop" in your drilling. The usual form of failure of re-sleeved master cylinders is fluid migrating out between the body and the sleeve OD - the reason why a high interference fit is aimed for when using machine tools - something you cannot achieve with a drill/reamer, but modern sealing materials may come to your rescue.

Good luck

[mrclubike]

You should be able to see the ports thru the fluid port after removing the reservoir
then just  redrill them after installing the sleeve