I think I have a bad slip ring seal on 85 k100 and am tearing my bike apart so figured I would just replace it.  I am wondering if it is all original parts (I assume its original. Well maintained my ass) can I just replace the seal or do I need to replace anything else, as I have heard they changed the design of the pump a bit.

This service bulletin tells part of the story. There are substitutes for the special tool mentioned. Step-by-step instruction can be found under the Mechanical heading in the Portal's K100 Forum Tech page.

What you will likely find when you go in there is you will also need a new impeller and shaft. They did change the pump a bit and the impeller to shaft fixing is one and the later design is better.

The fact that it may be original is not necessarily an indication of poor maintenance. After such a timescale there are a few 'usual items' that occur and this is one of them. It's a credit so many have survived this long.

Shaft condition can vary wildly. I've seen shafts that look like new and I've also seen shafts that look like they were installed by Henry Ford.  (A LONG time ago.)

Gees I know Fords aren't much chop but henry having a K says a lot about his own product

I appreciate all the info.  I will order the new impeller and other parts.

We've experienced an unexpected run of warm weather so I decided to install the oil/coolant pump rebuild bits in my 1995 K1100LT.  'thou old in years, it has a mere 24 K miles on the clock and I'm fairly sure no one has ever been in there since it left the factory.  When I went to free the hose clamp to drain the coolant at the pump I noticed there was coolant on the end of the hose.  Upon closer inspection, I found that every point on the cover at the lower fasteners also had a drip of coolant.  I'm now wondering if the slip ring has actually failed or the pump cover is the point where the coolant is escaping.  I should add that the coolant leak is extremely slow - on the order of a few drops during a couple weeks of the bike resting.  I understand there is a small drain hole under the pump or cover where liquid exits when a seal fails, but I couldn't locate it.  When coolant or oil escapes due to a failed seal on the pump shaft, would it fall below the bike on the right or left side of the pump? Is it likely that the cover seal (silicon ?) has failed simply due to age?  I'm inclined to believe that is what has happened because there is evidence that the cam chain cover is weeping as well. 
Should I go proceed to install new pump seals as a matter of course or just re-seal the cover(s)?

The weep hole for coolant or oil leaking past failed seals is circled in the attached image. If it's clogged unclog it. Then wait for it to leak. Catch up on your reading. If it doesn't leak,  the cover or other joints could be leaking. It doesn't sound too serious yet.

Thanks for that photo - very helpful.     Another question: if there is a seal failing, it it likely to suddenly let go in a big way, or continue to worsen slowly over time?

@brickrider2 wrote:Thanks for that photo - very helpful.     Another question: if there is a seal failing, it it likely to suddenly let go in a big way, or continue to worsen slowly over time?

I've never had the pleasure of this particular seal failure, but it's in the nature of shaft seals to let you live in denial, for a while. Enjoy it.

What Laitch is saying is yes, they drip slowly until you get so fed up with seeing the puddle, you finally get round to doing something about it.

I fussed about a similar leak this past riding season.  Finally got to where I just didn't give a sh$t about it and instead turned my attention back to enjoying riding the beast.  I keep an eye on the oil level/consumption but that has been as steady as a rock.  Part of the old girl's charm for now 

If the weep hole is blocked the first you will know about a blown seal is coffee coloured oil. This happened to my silver K100 and ended up having to flush the motor and the coolant system. I’d replace the seals if it’s weeping. Better to do it at home in comfort than have it go fully 1000 miles away.

I decided that, having come this far, I'd be foolish not to go ahead and put in the new seals and be done with it. I will thereafter enjoy a dry underside of the engine for a good long while.  (Assuming I don't screw up that tricky water seal.)

I installed the MotoBins oil seal and the water pump slip ring according to instructions in the Clymer manual and the videos on YouTube.  I'm  stuck with a problem I can't sort out.  When I torque the bolt to fit the impeller, the shaft binds and will not turn. 
There are inconsistencies in the instructions as well.  The Clymer directions make no mention of the spacer in the schematic 124.  Is the spacer that comes with the MotoBin rebuild kit to be used only for drawing the shaft through the slip ring? When I put the MotoBins spacer on the shaft, the impeller sits so high that the cover cannot be installed. 
I'm working on a pump with the new style innards - pressed steel impeller and the shaft with the provision for a bolt in the impeller end.  
What am I missing here?

Firstly go and get a packet of thick washers that will fit on the shaft.
install the new rubber seal and then fit the new style ceramic seal.
Grease the bolt end of the shaft lightly and install the new gear shaft until it stops.
Fit enough washers on the shaft to leave a space so that when you insert the bolt in and tighten it will pull the shaft through the new seal. keep undoing the bolt, adding washers a repeat until the gear face on the shaft sits level with the case face of the pump. remove the bolt and washers , install the spacer and impellor and fit the bolt. i use a little blue loctite.

@brickrider2 wrote:. . . Is the spacer that comes with the MotoBin rebuild kit to be used only for drawing the shaft through the slip ring? . . . What am I missing here?

Are you working from these guidelines found on the K100-forum tech page? If you aren't, reviewing them might add clarity to the procedure and the use of the new spacer.

you dont need to use the new spacer to pull the shaft through. I found that it just confused stuff. Just work out how to pull the shaft through so its flush without deforming the ceramic seal. Using washers acheives this. Think about what you are trying to do before spannering.
The main aim is to only pull the shaft through until the gear face is level. Adding any more washers past this point compresses the spring in the seal and makes the shaft rotation tight.

Okay, let me try to explain the problem again.  First, let me say what it isn't.  The problem is not installing the oil seal or the slip ring.  The problem is not drawing the shaft through those parts.  I've done that.  The question I have is about assembling the bits on the water pump end of the shaft. The impeller sits WAY proud of the flange.  The cover will not even come remotely close to fitting over the impeller.  I seem to have an odd impeller that is unlike others I've seen in illustrations or in DIY videos.  It appears to have the spacer already incorporated into the (pressed steel) impeller, such that if I use the spacer that came with the rebuild kit, it locates the impeller way out beyond what can fit in the housing.

https://photos.google.com/share/AF1QipMwRyhu8r1cFXmtYiUiSJkHUgLYDjVPb9Dwb5LgzQRujOscK2vnRHITcJTQYj0S8A?key=eUN2TDRQbFV1bzNoTUVqYzMyQkZLbHI1dm92SGVB

I had another, closer look at the impeller.  I put the "spacer" part of the impeller in a vice and whacked the impeller with a mallet.  The part separated into two pieces.  The two pieces had been fused together with corrosion so tightly I thought it was a single piece.  The problem was that I had been trying to use two spacers between the slip ring and the impeller. I put the new spacer in place and the dimensions now seem as they should be. The pump is now back on the engine. Tomorrow the gasket goo should be ready for me to take up the fasteners to their proper torque values. I'm embarrassed that such a silly oversight could have confused me.

There remain some odd aspects of these rebuilds.  My pump had a washer with a rubber seal between the impeller and the slip ring that doesn't appear in any schematics I've seen. In addition, I found torquing the bolt on the shaft bound the shaft, preventing it from turning.  In the end, I just used less torque and a generous helping of blue thread locker. 

Thanks to all who offered ideas.

Ah! Nearly been caught by that one too. The only giveaway was that after cleaning it with a wire brush, there's no sign of a machining shoulder between the spacer and the shaft, so I figured that had to be two separate pieces. That and the new spacer in the kit.