1987 K75S restoration...this one's gonna be "fun".

[daveson]

Depending on the symptoms, it might be that the gear position switch is the problem, rather than the cluster.

[Romonobyl]

It's the display itself, the LCD segments are all blurred and barely readable. The bike spent a fair amount of time in direct sunlight when I was still riding it, not sure if that has anything to do with the problem.

[Laitch]

It's the display itself, the LCD segments are all blurred and barely readable.

To me that means that the numerals are still readable so if they are reflective of the correct gear positions, you might be interested in this account of treating the fragmentation problem. The links in it to specific products are dead but other products are likely to be available.

[frankenduck]

Many times the gear indicator being wonky is due to the switch failing. How to troubleshoot and replace the display if the LCD is decaying:
https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/gpi/gpi.htm

[Romonobyl]

Throughout this project I've held the attitude of spending as little as possible on this bike until I'm sure it will be salvageable, at least to the point of the engine running. Well now that I'm this far in I realized if I want it to actually work I'm going to have to take a crowbar to my wallet, in for a penny in for a pound as they say. I got inspired while perusing my wishlist on Euromotoelectrics and found the hall effect sensor was on sale. I'm suspecting that to be partly responsible for some of the starting issues even though I have a lot more troubleshooting to do, but it's the disintegrated electrical connector that was the real deal-maker. That's one circuit I'd rather not mess up with bodged wiring. I also added a few smaller parts to the order, including a new elbow for the air cleaner box as the old on was cracked in multiple places.

While waiting for the parts I decided to get proactive on other items needing attention, such as:


Mr Injector.jpg (81.42 kB . 768x576 - viewed 582 times)

These really put up a fight. I had to remove the fuel rail first then pry each injector out individually, it wasn't easy but I finally prevailed. They're on the way to Mr Injector, hopefully they'll be able to restore them.

I also removed the airbox to give the area a good cleaning and make sure the air flow sensor vane wasn't stuck, that's when I found the elbow duct was bad so that went on the list.


20241228_143717.jpg (71.89 kB . 768x576 - viewed 559 times)

I had already spliced in a fuel pressure gauge and when the pump would work it gave about 35psi of pressure and it held when shut off, so the regulator is still good but all the hoses were rock hard so they all came out. The vacuum hose will be easy but the two fuel hoses are preformed. I know of a technique using stiff wire and hot water to make custom formed hoses from bulk fuel line, I think I'll give that a shot. I also ordered a computer-safe test light which will be in tomorrow, that way I can do some proper troubleshooting instead of blindly attacking the poor bike with jumper wires and a multimeter. Hopefully my ham-fisting didn't cause any harm.

[frankenduck]

FYI: Typical failure symptom for HES is that they fail when they heat up so I doubt the HES is causing you starting issues.

[stokester]

There are times when a "computer safe" test light using an LED is required but there are times when an old school incandescent lamp will work better because it adds a draw to the circuit which can help identify a poor connection.
Mr. Injector is a good call.  I've had a couple of sets rebuilt by him for a very fair price.

I'm not familiar with a way to preform the fuel line hoses but although the OEM ones are overly expensive, they do last a long time and fit properly without any extra effort but then I also use the Oetiker clamps with the proper clamping wrench as well.

[Romonobyl]

I decided to give the custom-molded fuel hose technique I read about a try. I bought a 15" long piece of fuel injection hose from an auto parts store, which is the perfect length for the return line from the regulator to the tank. I straightened out some clothes hanger wire and threaded it through the hose and followed the bends of the brittle old line as close as I could.


Hose Molding.jpg (70.38 kB . 768x576 - viewed 544 times)

The next step was a big, flat pan of boiling water. Fortunately I have just the thing with an electric skillet that I almost never use, so I dusted it off and filled the pan with hot water and turned the heat to max. It finally just started to make small bubbles so I switched it off and dropped in my masterpiece.


Hose Molding 2.jpg (76.88 kB . 768x576 - viewed 577 times)

I gave it about 7 minutes then plunged into some ice water.


Hose Molding 3.jpg (52.83 kB . 768x576 - viewed 545 times)

Well I was less than impressed with the results. The wire was too stiff to remove easily and when I finally got it out the hose had very little shape to it. I tried again this time with a piece of solid copper wire I scrounged up and exaggerated the bends considerably. Here's a banana for scale:


Banana Hose 4.jpg (31.72 kB . 768x576 - viewed 577 times)

This time I let the water get a bit hotter and left the hose in for about 15 minutes...better but still not great:


Hose Molding 5.jpg (65.97 kB . 768x576 - viewed 559 times)

Oh well, lets see if it works...


Kinked.jpg (47.99 kB . 768x576 - viewed 548 times)

Overall not too bad. That is the tightest bend and is a bit kinked, but so was the original hose and I blew air through it with little restriction. Actually that was the only bend that needed to be molded in, the rest of the hose reaches the regulator easily even without being "molded". I'll need to trim it down a bit but that will wait until I'm ready to reinstall the airbox.


New Hoses.jpg (59.93 kB . 768x576 - viewed 551 times)

Thanks for reading, more to come...

[Romonobyl]

FYI: Typical failure symptom for HES is that they fail when they heat up so I doubt the HES is causing you starting issues.

I don't doubt it. I would have held off on buying a new HES until testing it if it wasn't for the dissolved plug. I'd rather stick with the factory connectors at both ends of the harnesses for the more critical components.

[Chaos]

That's not the first time I've seen a banana used along with something being bent.

[Romonobyl]

While I'm waiting on the folks in Idaho to resurrect my old fuel injectors and for my other parts order to be delivered, I figured I should revisit that crusty "fuel level" sending unit. I drained the tank and removed the old unit.



Like I said...pretty crusty. I also just learned that these pictures should be taken in landscape to orient properly when uploaded, too late now but you get the idea.

The rheostat was packed full of crud that I should have cleaned out prior to the initial installation, better late than never. I went to town with a small brush, swabs and contact cleaner (I've read a lot about Deoxit here, is it really worth the price premium over standard contact cleaner?). I got it as clean as I could before hooking up the multimeter.

 
Resistance.jpg (92.78 kB . 768x576 - viewed 749 times)

The rheostat showed open for the entire sweep until it hit the bottom stop where it read about 122 ohms. If this was a real sending unit paired with an actual fuel level gauge then I'd be suspect, but this only operates a warning light so why there's even a rheostat is beyond me. I have no clue what the actual readout should be but it's not working like a proper potentiometer. In order to really clean this thing I'll have to take it apart, which involves bending four metal tabs that I hope don't break.




20241230_172226.jpg (30.27 kB . 768x576 - viewed 750 times)

Success, and not surprisingly I had a bit more cleaning to do.
Of course being a BMW it isn't wired like a typical rheostat either, this uses an unusual (to me) dual-wiper design that slides across both the wire coil and an adjacent metal plate, completing the circuit between the two and creating the variable resistance. The plate indicated open to both wires which isn't good, and the only way to get back there was to remove the phenolic plate with the wire coil. That's when I decided I can live without a low-fuel light for awhile, it's easy enough to get to this part as long as the tank is empty so this concern will get shelved for now.
What is of bigger concern is the fuel pump wires, upon a closer examination the insulation is in pretty bad shape and cracks easily.


Fuel Pump Wires.jpg (31.12 kB . 768x576 - viewed 729 times)

Of course this requires special wire meant to be submerged in fuel, so there's another part I'm waiting on. Par for the course on a project like this.

[daveson]

The reason for being able to measure the level is for when the optional extra fuel level gauge is chosen.

I don't like the kink in the hose, it's too much. Maybe it could be routed differently. It might get worse on a hot day. You can also get external coils to eliminate kinks.

[Romonobyl]

The reason for being able to measure the level is for when the optional extra fuel level gauge is chosen.

I don't like the kink in the hose, it's too much. Maybe it could be routed differently. It might get worse on a hot day. You can also get external coils to eliminate kinks.

Yeah, I'm going to work on that hose a bit more. A little restriction is no big deal because that's just the return line from the regulator so the flow rate and pressure aren't very high, and the factory setup didn't look all that different, but I think I can do better. I'm looking for something I can use as an internal mandrel and try a bit more heat and maybe that will work a little better, or go with an external support like a spring as you mentioned. I'll make it work one way or another.

[Ingo]

The kink (if sufficiently tight) will lead to increased fuel pressure at the injectors,  resulting in over-rich fueling.  The tank level sender has the resistor for the fuel gage only. The plate in behind is for the low level light exclusively. That has nothing to do with the resistor and without the gauge the resistor board has no function,  might as well not be there. The second wiper and contact plate behind it grounds the circuit and set the low level light .

[Laitch]

The kink (if sufficiently tight) will lead to increased fuel pressure at the injectors,  resulting in over-rich fueling.

That will be easy enough to determine tapping into the delivery line to the fuel rail with a pressure gauge during idling and revving—a test with which the OP is already acquainted.

[Romonobyl]

Well, after some minor introspection I've decided to no longer make a new post for every little step in this process. I've done similar threads on other forums before, but they weren't nearly as well informed and moderated as this place with no where near the participation. My last entry about the crap-tastic fuel level sender is a perfect example that drove my decision, there are already plenty of posts on this topic by folks far better informed on the specifics than me. So from now on I'll do more research on the site to see if what I have to offer will serve any purpose rather than posting tired and possibly inaccurate information.

Therefore here's a brief update:

The fuel pump wires are here but I don't like the generic ring terminals that I have, so I ordered some higher-end parts along with a meter of PTFE heat shrink. This is not an area to go cheap on. While I'm waiting on those parts (that seems to be a theme here) I thought it would be a good time to see what shape the front brakes are in. Much to my pleasant surprise they came apart with little fuss and other than the perished rubber everything looked like new. Even the pads still had some decent meat left on them, unlike the rear caliper that was paper thin.


Front Calipers.jpg (84.62 kB . 768x576 - viewed 482 times)

After a thorough stripping and cleaning I slapped the halves back together and bagged/tagged the hardware. Three rebuild kits are next on the order list. What I'm not certain of is the rear master cylinder. I managed to finally break the mount bolts loose so I could remove it from the foot peg bracket (it took a little heat). I scrounged up an old M7 bolt from the hoard pile, hacked off the head and sawed a groove about an inch down the length. Stuff in a piece of Scotch-Brite and I've got a reasonably good master cylinder cleaner-upper. I know others have done this with a wooden dowel but this seemed a bit more durable.


Hone.jpg (71.01 kB . 768x576 - viewed 459 times)

Hone 2.jpg (64.65 kB . 768x576 - viewed 484 times)

Polished MC.jpg (52.11 kB . 768x576 - viewed 532 times)

It's hard to tell from the picture but the cylinder cleaned up better than I expected. There is a slight amount of pitting at the very bottom of the bore but that's not where the seal rides. I'm debating on risking a rebuild or going with the adapting of a generic master cylinder route that has quite the following here. I'd really like to stick with as many original parts as possible but I'm not too keen on blowing $80 on a rebuild kit only to have it bleed all over my garage floor. I'm interested in any advice the pros here might have as to which way to go considering the condition of my part.

The engine is on hold until I get my injectors back, they should be in Idaho sometime tomorrow so it'll be awhile. Until then I have a new and improved 4-pin plug to replace the problematic one for the fuel pump, that and the brake bits should keep me occupied while Mr. Injector does his thing. I can't wait to hear this motor run again, just hearing it turn over with the starter brings back fond memories.

As always, thanks in advance for any input.

[natalena]

You're getting a lot accomplished for a "fun" project,  kudos to you. Did a rebuild on the front MC, which looked much worse than your rear MC, and it's fine after 7ish years. I'm with you on keeping original parts when possible. Slack time seems to get filled with checking wheel bearings and shaft/spline/drive gear stuff...time murderer's.  Cheers
* not original, but Spiegler ss brake lines would be nice and good ROI.

[Romonobyl]

You're getting a lot accomplished for a "fun" project,  kudos to you. Did a rebuild on the front MC, which looked much worse than your rear MC, and it's fine after 7ish years. I'm with you on keeping original parts when possible. Slack time seems to get filled with checking wheel bearings and shaft/spline/drive gear stuff...time murderer's.  Cheers
* not original, but Spiegler ss brake lines would be nice and good ROI.

Actually my front master cylinder seems to be in pretty decent shape. I haven't taken it apart yet but the lever moves freely and other than a leak under the reservoir (very common, already have a new O-ring) it looks much cleaner than the decrepit rear cylinder.
I'm definitely going with new hoses everywhere. I've seen the mod where the two front calipers are plumbed together with a hard line over the fender and a single hose runs from the MC to the right brake, I like that idea. There's a place near me that does custom hoses, just bring your old stuff or tell them what you want and they'll hook you up. Not sure how much that costs but it's also a possibility.

I'm crossing my fingers on the injectors being repairable. I wanna hear that baby purr!!!

[Martin]

Packing silicone grease under the master cylinder boot will greatly extend the life of the cylinder. It will stop road spray/crap getting into the cylinder, re-grease every few years depending on riding conditions. Due to the silicone grease my OEM original cylinder with one rebuild kit is still fine however it now resides on a mates bike. I've been  running a Aliexpress cylinder since mid 2017.
Regards Martin.

[Romonobyl]

Well this sucks...


Dammit.jpg (38.15 kB . 768x576 - viewed 501 times)

Not the best picture, but that was the terminal on the fuel level sender where the positive wire for the fuel pump is supposed to attach. I was trying to solder on the new wire when it snapped off with just the slightest touch from my soldering iron. I guess it's a good thing, glass half full and all, that it broke now and not inside of a full tank of gas sometime down the road (literally). I've been researching the many posts here with clever alternatives to this notorious bit of kit, which certainly have my interest considering replacement options. EME has the only aftermarket offering, and at $270 each they obviously know it. Worse comes to worst I'll pry my wallet open, but only as a last resort. I normally wouldn't mind not having a functional fuel warning light, but unfortunately the knob for the trip odometer broke off at some point and not being able to reset the miles between fill-ups is problematic.

Oh well, fortunately I'll have some distractions soon. The seals for the brake calipers will be here tomorrow along with a new air filter. I already reinstalled the airbox with a new elbow, refitting the airflow sensor into the upper half of the airbox was a bit tricky but it's all back together and hopefully for good. I was able to re-route my custom "preformed" fuel return line so the kink at the tank is mostly gone, and best of all the fuel injectors are on the way back from Idaho (thanks Mr. Injector!) and will be here in 4 days. Once all that's back together the engine should be ready to run for the first time in 30 years...if only I had some fuel pressure.
I'm still doing a deep dive on my options, I'm impressed by the creativity many of you have on alternatives to this troublesome issue. I wish I had waited on messing with those wires until after I had the engine up and running but too late now. If anyone has any additional advice on this I'd greatly appreciate it.

Thanks as always.

[Laitch]

I normally wouldn't mind not having a functional fuel warning light, but unfortunately the knob for the trip odometer broke off at some point and not being able to reset the miles between fill-ups is problematic.

Here's a trip odometer knob but it's misidentified by the vendor. It looks like an trip meter knob to me—62111459244. If it was just the knob that broke off but not the stem onto which it's mounted, this might work.

[frankenduck]

Here's a trip odometer knob but it's misidentified by the vendor. It looks like an trip meter knob to me—62111459244. If it was just the knob that broke off but not the stem onto which it's mounted, this might work.

It LOOKS LIKE a K trip odo knob but look closer at the pictures. The Ebay one has a hole for a semi-circular shaft while the K bike trip odo knob has a slit in the middle.

[Laitch]

It LOOKS LIKE a K trip odo knob but look closer at the pictures. The Ebay one has a hole for a semi-circular shaft while the K bike trip odo knob has a slit in the middle.

Clearly, it is not what is labeled on the package. If all Motometer tripmeter knobs have the slot-over-spade knob as you have indicated, then what does this knob fit and can it be adapted to fit? It has certain similarities. Is it a radio knob?
eBay

Parts fiche

[Romonobyl]

It LOOKS LIKE a K trip odo knob but look closer at the pictures. The Ebay one has a hole for a semi-circular shaft while the K bike trip odo knob has a slit in the middle.

I thought the same thing until I zoomed in tighter on the picture. What looks like a "D" shape is actually a slotted hole, so it might be the right thing. I'll likely have to take my module apart to verify what it should look like.
The part number I found online for the knob I need (which is different from the Ebay offering) is discontinued pretty much everywhere. I did find a dealer in Italy that supposedly has one, but I think I'll keep searching.

Thanks to all for the replies.

[frankenduck]

There are actually two versions of the K bike trip odometer knob. There's an early one where the core part of it was made of plastic and another later one with a metal end as shown in your second pic. Here what the core part looks like for the early one: