BMW K bikes (Bricks)

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parky

parky
active member
active member
Hello team. This is my first post and this is my sin ...I am far too cheap to throw 600NZ$ (420US$) at a new complete right hand brake assembly and am now appealing to the masses who may have a novel fix to the cracked and weeping sight glass on my 20mm front master cylinder (16V 1991 K100RS)


  • I have considered welding a plate over the window hole but quite like the idea of seeing the amount of brake fluid in the sytem.

  • I have quietly siliconed up the crack, to little avail.

  • I have allowed the level get below the window in order to pass an inspection.

  • I even contacted Magura and ask if I could buy a replacement glass ...they said no.




Any insights would be greatly appreciated.

Cool.

    

K75cster

K75cster
Life time member
Life time member
I believe it's been done before.
Here is one from 2015.
https://www.k100-forum.com/t10024-wanted-k100-rs-16v-front-brake-master-cylinder


__________________________________________________
Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

duck

duck
Life time member
Life time member
I once replaced the front reservoir sight glass on a 4VRS with clear epoxy.  Worked surprisingly well and since I used clear epoxy the brake fluid level was visible.

1 - Remove from bike.
2 - Place tape over hole.
3 - Lay on side.
4 - Fill hole from inside with clear epoxy.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

Laitch

Laitch
Life time member
Life time member
Hi, parky. Please click your cursor on the Profile tab in the header of this page then click on the Signature tab that will appear. After that, enter the year of manufacture and the model of your moto then save it. The year and model of your moto will appear below each of your posts, helping readers understand what you are riding without their having to backtrack to find the information. Parts might vary year to year and model to model.


__________________________________________________
1995 K75 81,000 miles
Master (front) Cylinder Sight Glass Window (20mm 16V) Usa-lo10
    

parky

parky
active member
active member
Thanks for the ideas team. Ideally someone might know of a drop in aftermarket glass that fits the girl well and will provide years of maintenance free service. I shall keep hunting. Thanks again.


__________________________________________________
1991 BMW K100rs (16v)
    

K75cster

K75cster
Life time member
Life time member
Well mate all I can suggest is a trip to the bike wreckers and sus out all the sight glass master cylinders on Jap Bikes for one that's close


__________________________________________________
Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

parky

parky
active member
active member
Indeed, that's a good suggestion. I'm quite surprised that it has not been done and "threaded" in a forum. From what I can gather, there is a wee lip or step that makes this sight glass unique to the more ubiquitous (Jap) models. Motorbins has an exchange offer on such assembles where they recondition second hand units. My question is where do they get the glass to do this? So frustrating.


__________________________________________________
1991 BMW K100rs (16v)
    

Two Wheels Better

Two Wheels Better
Moderator
Moderator
I asked the Google Gods, by incanting 'Brembo brake master cylinder lens' into the hallowed search engine vessel, and got dozens of various sized sight glasses, some with o-ring and clip, including for Brembo.

The sight glass, lens or window on my 20mm spare R11/K11 MC measures 20mm. The hunt is on.


__________________________________________________

1970 R60/5, '77 R75/7-R100, '85 K100'87 K75C, '87 K100RS, '93 K11-K12 Big Block, '93 K1100RS, '95 R100-Mystic, '96 K1100RS, '98 K1200RS, '00 K1200RS, '02 K1200RS, '03 K1200GT, '04 R1150R'04 R1150RT, '05 K1200S, #1 '06 K1200R, #2 '06 K1200R, '07 K1200R, '09 K1300GT, '13 R1200RT-P & 2022 S1000XR

"Do you ever read any of the books you burn?" "That's against the law!" "Oh, of course."
~Ray Bradbury, science-fiction writer (22 August 1920 - 2012)
    

parky

parky
active member
active member
Cheers me old china, I'll have another hunt. I'd love to see what it actually looks like - the profile et al. Once the piece is out, it's not going back in, and this this my daily ride. Thanks again for your troubles, much appreciated.


__________________________________________________
1991 BMW K100rs (16v)
    

duck

duck
Life time member
Life time member
You really should try the epoxy thing I mentioned above.  It DOES work and is not irreversible in the event that you find a suitable sight glass in the future.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

parky

parky
active member
active member
Alright, alright Duck, I will give it a whirl. And the beauty is that I be able to have a good look at the form factor of the old window. Thanks.


__________________________________________________
1991 BMW K100rs (16v)
    

stanthomas

stanthomas
Silver member
Silver member
Sight glass on my '91 K100RS 16V is leaking too. Magura 20mm m/cyl. Window's not damaged so assumed to be corrosion around the edge, which would be consistent with the general state of neglect.

Has anyone been able to source a replacement window? Seems to be a larger diameter than more recent bikes.

In the absence of a new part, my thoughts are to press out the sight glass from the inside, clean up the housing, replace the o-ring and put it back together. Anyone done that?


Failing that, are any of the master cylinders on later BMWs, e.g. R1150, K1200, compatible with the K100 switch gear? Has anyone managed to fit a modern radial m/cyl, GSXR say, without changing the switch gear?

    

Rick G

Rick G
admin
admin
The first time I recall this problem was about 6 years ago and no sight glass was available then and AFAIK that is still the case. A few years ago I ended up making a small aluminium replacement and pressing it in but then there was no sight glass but it didn't leak.
If you find a better solution please share it.
I know that Rossco had the same problem and used some black sealant of some sort, a search may pay off for that. Not all the silicone sealants are brake fluid proof but he found one that worked.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 2004 K1200GT 1998 K1100 LT, 1986 K75 GS.
    

Laitch

Laitch
Life time member
Life time member
RicK G wrote:I know that Rossco had the same problem and used some black sealant of some sort, a search may pay off for that. Not all the silicone sealants are brake fluid proof but he found one that worked.
Rossco seemed to sum up his repair in four posts.
Post 1.
Post 2.
Post 3.
Post 4.


__________________________________________________
1995 K75 81,000 miles
Master (front) Cylinder Sight Glass Window (20mm 16V) Usa-lo10
    

stanthomas

stanthomas
Silver member
Silver member
Following on from #12, above...

I took the master cylinder off the bike, drained the fluid, put it in a bucket of water and blew some air into the outlet union. Sure enough, a steady stream of bubbles from the top left of the sight glass.

Popped the sight glass out with a bit more air. Although under water, the sight glass came out rather violently and sustained some damage in the process. Might have been cracked before but definitely cracked now. On reflection it might have been better to 'jack' it out with a non-compressible fluid (water). The damage is to the outer flange:

Master (front) Cylinder Sight Glass Window (20mm 16V) Y4mOSAUSQKUnkRznGmyHZBUxtaqnmdqknZ0HL2pghSSj4XzoUQmXzkC5OqPA51rAY848qBnQ-aUOyevuUnS7q92cjUx4GklOwPFOfEVjTUONvPgR3VLq-yu0OIgZIb_IzweqOSt-htEI7eCxFTiYese_38j8Ah22mOX9XMU94rWav4Cwj036bac7xtvmPjmvBZ8PCEFqZ2jYDycK_jb1-KTgg?width=1120&height=617&cropmode=none

As anticipated, the master cylinder body was quite corroded and the seat for the sight glass o-ring was noticeably pitted. The body was stripped and left to soak in Coke (mild phosphoric acid) for a few days. Then cleaned using Scotchbrite and a shaped aluminium 'scraper'. The objective being to flatten the pitting as much as possible, removing all oxide but no metal. Even so, the o-ring groove was still pitted and not the finish you want for an effective seal.

Unfortunately, replacement sight glasses do not seem to be available and ones for oriental bikes don't fit. So it was repaired with cyanoacrylate adhesive (super glue). Don't know whether cyanoacrylate is resistant to brake fluid but it shouldn't matter since the repair was to the outer flange of the 'glass with serves only to retain the o-ring which, if it's sealing properly, should not allow brake fluid to reach the glued area. The repair is less visible in reality than it appears in these pictures.

Master (front) Cylinder Sight Glass Window (20mm 16V) Y4mmubE5GNvRY45td6VdZnIDzuKlbNsaUvxuIbxEaI1MXTFLbrg3VD3jPK-dc_Je2QOgHHr0Ivl-9Y2GMhvCQ-5xR78qxP0h80FwgcE_E9jVpmQdE3KjD3C46rMY2JFn50gbXIuII3EBFHKg1bnKc3kuoiJz-UAXWg3TzYDNrZUPOsqoTujdkrxNfktXUmDN85ToZWWEcItG-TXt9gIQgnlkw?width=1024&height=715&cropmode=none

The o-ring was well greased using the Magura supplied lube in the master cylinder repair kit and the sight glass pressed back in with a new 2x16mm o-ring (EPDM, note). The sight glass is retained by the o-ring which sits in grooves in both master cylinder and sight glass. The master cylinder was placed in hot water for a few hours to soften the o-ring in the hope that it would conform to the pitted surface. No air bubbles evident when lightly pressurised.

Master (front) Cylinder Sight Glass Window (20mm 16V) Y4msOLhLRlAa1_XPgmlVGABuDv-nqD_iuP16j6FTEFotDobVLSYh16vvMr_8veGPFPSbxX0f5075c3BySi2446TZ7O40JiS8TEaPiBTV8Cf6Qz-0UQ5HHC2TowzKwYoi1cJBItn5Ni6NT_BIHeEs34g4687mEVwk_LtZ55jbrMH2w1N0N8uNQS61Sj2xtM3AqZ8fDBKuaI6OvqlmBs40JeuHw?width=1024&height=737&cropmode=none

It is possible that the assembly grease is providing the seal, only time will tell, but three weeks later and so far so good.


While it was apart, I cleaned the master cylinder up and sprayed it with black EHT; while it looks good on an exhaust, it's not the best match for the brake original. It will do for now.

Master (front) Cylinder Sight Glass Window (20mm 16V) Y4mrW8aGSQbNyxtztiZJMebsHIa6p8xOmK4MkH7wU-Jd03qEqZsAUWEVRN8mGgpgukYXI2EafcsxZbOH6BCGQKF7DxNMqe-FZT0pEN-LYY2T-1OHXzRmR-23vkqBUcL7zrD-rMtR1_eNWlqzBIJ29Llfz2NFdpjM3EYYP8HLwAG5MM_7hXUQO75KKbx-ZPiwKf8L34dsQz-O34nzPhjCNhngw?width=1024&height=707&cropmode=none



Last edited by stanthomas on Sun Oct 11, 2020 6:24 pm; edited 2 times in total

    

Suzi Q

Suzi Q
Life time member
Life time member
Would it be possible to turn a replacement glass up from perspex rod? Happy to have a crack at this, I must have a spare master cylinder somewhere that I can knock the window out of to copy.

BTW you're in Wrecsam - you're on lockdown and not allowed on forums!


__________________________________________________
Sometimes I'm not really Suzi Quatro.
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Tool marks in the perspex will be hard to remove and won't let you see the level.

This may be a case where casting some acrylic in a mold might be the best solution. I've seen articles describing the molding of taillight and turn signal lenses. Clarity might be enough to make a functional window.

Make the pattern on a lathe. Or maybe 3D printing.


__________________________________________________
Present:
1994 K75RT
1991 K100RS


Past:
1988 K100RS SE
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

stanthomas

stanthomas
Silver member
Silver member
chris846 wrote:Would it be possible to turn a replacement glass up from perspex rod? Happy to have a crack at this, I must have a spare master cylinder somewhere that I can knock the window out of to copy.

BTW you're in Wrecsam - you're on lockdown and not allowed on forums!
It's spelt Wrexham.

I did look up brake fluid resistant materials and acrylic seems to be suitable. Only direct reference I found was a rather expensive engineering grade acrylic from Germany.

    

MartinW

MartinW
Life time member
Life time member
Tool marks can be removed by polishing. I made a sight glass for my radiator overflow tank using a drill press with a cross slide vice and wood routing tools. Marks were  buffed out using cotton mops and plastic polishing compound.
Regards Martin.
Master (front) Cylinder Sight Glass Window (20mm 16V) Sight_11


__________________________________________________
K75s Hybrid
    

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