Author Topic: 1991 K75S - 30 year major service  (Read 1919 times)

Offline Laitch

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Re: 1991 K75S - 30 year major service
« Reply #50 on: October 06, 2020, 02:16:09 AM »
Here's Gryphon's take on the master cylinder change from the original post.
  • Along the Ridley in Vermont.
  • 1995 K75 80,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline kurtk75s

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  • Posts: 34
Splines - the good news
« Reply #51 on: October 07, 2020, 09:53:14 PM »
Pulled the gearbox.  Splines looked great, although a little dry.  The last time I lubed them was at just over 40k miles and I used Honda Moly 60, which was the hot shit at the time.  Now it doesn't even exist.  Shifting was fine before the bike went on the lift.

There was no evidence of leakage from either the main seal/ o-ring or from the trans input shaft seal.  I guess the drips that I saw migrated from somewhere else.  Most likely from the oil change that I did last year.  Bike hasn't been run since.

Also pulled the alternator to replace the monkey nutz.  The old ones were fine but this is easy preventive maintenance.

This bike is easy to work on but pulling the transmission does create a lot of clutter. 

Here is the messy workspace, the transmission splines and the clutch splines.  These are the best pics I could get with my phone.

  • Syracuse, NY
  • 1991 K75S

Offline kurtk75s

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Splines - the bad news
« Reply #52 on: October 07, 2020, 09:56:30 PM »
Here are photos showing the devastation of the drive shaft and pinion shaft splines.  Again, best I can do with my phone and some LED lights.

Edit:  These photos are after a little clean up.  When opened up, the splines were rusty and dry and there was a BUNCH of moly lube around the pinion shaft seal.  WTF.  Since the last lube (~7k miles ago),  I may have ridden in the rain for a day or two.  Most of my riding was in the desert.  What a crappy design for an, otherwise, stellar bike.
  • Syracuse, NY
  • 1991 K75S

Offline kurtk75s

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Tank Grommets
« Reply #53 on: October 07, 2020, 10:26:33 PM »
I have always hated those rubber tank grommets.  When lubed up, they work great, but if the bike is actually used, it is really hard to pull the 'studs' away from the rubber.  Mine cracked, then one disintegrated, then I took the remaining one and split it to have some cushion on the tank.  I remember being on the road and shoving cardboard under the tank to provide some cushion and keep it from rattling. 

I was just going to get some new ones from BMW but I happened to be in our local 'Runnings' store looking for other hardware for the bike (stainless bolts for the bag mounts) and saw that they had a rubber grommet tray.  They had ones that looked like they would fit the K bike, so I bought two ofthem at 3.29 each.  Turns out they are a little long:  the bottom lip obscures the groove for the retaining circlip.   So I cut that part off.  Now the grommets stay on the tank when you pull it but there is still a rubber 'sleeve' going through the hole.  When mounted with the circlips, it seems pretty solid and gives a nice cushion. 

Here is the bottom of the tank with the grommets installed.  Yes, that is a JBWeld fix for THE seam leak under the fuel pump.  Has lasted for 11 years.  I'll do something more permanent when it starts leaking again.

  • Syracuse, NY
  • 1991 K75S

Offline kurtk75s

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10/8 Update - Monkey Nutz
« Reply #54 on: October 08, 2020, 07:59:18 PM »
I replaced the monkey nutz on the alternator and reinstalled the alternator while the transmission was out.  Wow, did that make the process easy.  I read a lot of tips on how to do the install and most agreed that some sort of lube would make the process a little easier.  Now I see why:  the new rubber doesn't have a gap between the linked pairs like the old worn ones do.   So I looked around at what I had on hand and the easiest to get to was the squirt bottle of RuGLYDE that I used during the tire installation.  Should be safe on rubber, right?  Worked great.

When I closely inspected the old nutz, I could see cracks forming on the back side and rubber was definitely being shed into the alternator cup, based on the amount of cleaning I had to do.  So it is a good thing that I replaced them.  First glance told me they were OK.  This is definitely one of those things to do while you have the transmission out - if they haven't been replaced before. 

Here is a picture, I think you can see the cracking, especially on the right one. 
  • Syracuse, NY
  • 1991 K75S

Offline kurtk75s

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10/8 Update - brake bleed
« Reply #55 on: October 08, 2020, 08:12:41 PM »
This story is a little embarrassing.   Age is setting in.

When I installed the stainless lines on the front, I attempted to bleed the brakes afterward.  I use a vacuum bleeder because it makes the job SO easy - especially after draining the system.  So I went to the spot in the cabinet that I usually keep the bleeder and grabbed it - and it didn't work.  Complete crap.  I noticed it was a Harbor Freight jobby.  I disassembled it and saw that the internal pressure diaphragm (the thing that keeps the pressure building with each pump) had become brittle and had broken - the pump worked but it wouldn't maintain pressure.

So I added a task to the list to get a new Mityvac (I had the original for years and it worked great until the plastic handle broke - after 20 years or so!).  And the brakes sat un-bled.

Today I went to put away my 'transmission installation guide pins' (two long bolts with thread only on the end) and opened the wrong drawer in the cabinet.  Oops:  but what is this, a brand new Mityvac.  I do not remember buying it.  I must have had problems with the Harbor Freight one before and got mad and purchased this.  Why didn't I throw out the HF item?

I love this thing.  Front brakes bled in about 10 minutes. 





  • Syracuse, NY
  • 1991 K75S

Offline kurtk75s

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10/8 Update - clutch cable adjustment & right foot peg
« Reply #56 on: October 08, 2020, 08:26:12 PM »
I got the transmission back in and reinstalled the clutch cable.  I adjusted the cable to what I THINK are the right specs.  That is 75mm (+/- 1mm) of  bare cable and 5mm of play at the lever.  The new cable required the adjuster at the bar to be screwed out a lot (like a worn cable) and to get 5mm of play, the clutch rod adjustment bolt is also quite far out (see picture below).  It seems like the action of clutch release is 'normal' - but is it possible that the clutch pushrod isn't properly seated? 

Things are going to slow down a little now, I have to wait for some parts and do some cosmetic repairs before slapping things back together.  The worst is the right foot peg assembly that had been marinating in paint stripper (brake fluid).  I'm going to take everything off and sand blast the back side.  Damage shown in the second attachment.

  • Syracuse, NY
  • 1991 K75S

Offline Laitch

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Re: 10/8 Update - clutch cable adjustment & right foot peg
« Reply #57 on: October 09, 2020, 12:45:47 AM »
I got the transmission back in and reinstalled the clutch cable.  I adjusted the cable to what I THINK are the right specs.  That is 75mm (+/- 1mm) of  bare cable and 5mm of play at the lever.  The new cable required the adjuster at the bar to be screwed out a lot (like a worn cable) and to get 5mm of play, the clutch rod adjustment bolt is also quite far out (see picture below). . . .but is it possible that the clutch pushrod isn't properly seated?
It's possible that the rod is hanging up on the output shaft bushing, but it isn't likely considering the depth of your maintenance experience with this moto.

This is the way I perform an initial clutch setting. Your description doesn't seem to square with it. In the second panel, adjustment A is achieved using the clutch hand lever adjusting screw and its knurled locknut, not at the clutch actuating arm.





  • Along the Ridley in Vermont.
  • 1995 K75 80,000 miles
I wept because I had no radials until I met a man who had no splines.
https://tinyurl.com/RillRider

Offline kurtk75s

  • Motobrick Curious
  • Posts: 34
Re: 1991 K75S - 30 year major service
« Reply #58 on: October 09, 2020, 08:58:08 AM »
Thank you!  I did not understand the process. 

 

  • Syracuse, NY
  • 1991 K75S

Offline mw074

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Re: 10/8 Update - brake bleed
« Reply #59 on: October 10, 2020, 10:45:11 AM »

I love this thing.  Front brakes bled in about 10 minutes.

Let the brakes gravity bleed before using the Mityvac. Speeds up the process even more.
  • Michigan

Offline The Mighty Gryphon

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Re: 1991 K75S - 30 year major service
« Reply #60 on: October 10, 2020, 02:49:31 PM »
I'm just sticking the hose from the bleed nipple into a bottle of old brake fluid on the floor below the caliper.  Then I just work the brake lever with the bleeder open.  Release a little slower than when you squeeze the lever or pedal and the fluid won't reverse in the hose.  Only takes about 15-20 minutes start to finish to bleed all the brakes on a bike with ABS. 
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '91K100RS White/Blue, '89 K100RS Special edition White/Blue
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'91 K100RS "Moby Brick Too
'89 K100RS SE

Offline alabrew

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Re: 1991 K75S - 30 year major service
« Reply #61 on: October 10, 2020, 05:17:45 PM »
+1 TMG, I use a bleeder bag which makes this an easy job.
  • Birmingham, Alabama
  • 1985 K100, 1991 K100RS
Also:
2005 K1200LT
1979 R65
200,000 miles on BMW motorcycles

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