Just picked up a K75 - need input on the plan of attack

[oneplustwo]

Looking for some input on my tank.  I think it’s in good enough shape. (Also, I don’t need the level since I’m getting rid of the lunchbox.)

[oneplustwo]

So I replaced the fork oil in my Showa forks with 410 cc of 10 at and it seems like one side only damps on rebound and the other doesn’t damp on either stroke. Would that be a clear indicator that I need to rebuild both of them?

[oneplustwo]

Sorry. I was referring to left and right. Left feels like zero damping on compression and rebound. Right only has damping on rebound.

[moto949]

Hi again.

Though I'm not an expert on K75 fork internals, I would like to help by repeating the advice I offered when your post started... "make sure you know which forks you have". Not likely, but if they are Showas (which I believe were put on all K75 models starting in 1992) then you have the proper amount of fork oil. If you have the earlier forks, you have wayyyy too much. Your bike is a 1990, yes?

I understand that an "S" stamped into the earlier non-Showa forks stands for "sport" (not Showa) which confuses people. Another point is that earlier forks only had rebound in one leg and only compression in the other. The forks worked together as a system so overall it mattered little to split up their jobs. My guess is you have the earlier forks on your 1990. BTW, back then, K75S forks had different specs to the other K75 models.

I'm not sure how you're gauging the rebound and compression characteristics unless you are riding the bike. Are you just sliding the fork tubes in your hands? Bouncing the bike? Are the fork caps even on when you're doing this? *Remember, if the fork caps are off, you are losing the springing effect as the air inside the fork compresses - that's important. More or less oil in the forks determines this amount of springing, felt during brake dive or hitting heavy dips. Even a tablespoon difference can be felt, so be precise. Now, oil thickness is more apparent to a rider in the mid-stroke of the forks as the oil flows through the circuits responding to stutter bumps, curves, etc.

Anyway, you'll need to do some research to make sure what you've got, first.

[oneplustwo]

I had thought I had the Showa forks based on the s stamped on top based on another thread I had read.  But apparently maybe not. The bottoms have BMW logo and I cant find a Showa indication anywhere. Is there a definitive way to tell one way or the other? 

In any case I was judging the damping given the one shock is clearly damped in rebound and the other is not at least relatively. I have both tubes separated from the clamps entirely (with the top caps screwed in) since I was tearing everything apart to relube the head bearings and such. So I was just compressing the shocks individually pushing against the floor. So maybe they’re fine and I should just reassemble?  The bike supposedly was working fine according to the PO and doesn’t have a ton of miles.  Open to suggestions!

[Inge K.]

So maybe they’re fine and I should just reassemble? 

Yes, with the correct amount of oil for the sport fork, which is 280 cc in each leg.

[oneplustwo]

Can you buy these anywhere? Both of mine are clearly cracked. Couldn’t find them on beemerboneyard or via google search.

[johnny]

greetings...

whats the part number of that cup... i may have a couple...

j o

[Laitch]

Can you buy these anywhere?  Couldn’t find them on beemerboneyard or via google search.

Yes, you can. What term did you use to search for them?

[rbm]

RealOEM lists that part as 31421451829.  Should still be available from BMW dealerships.

[oneplustwo]

Thanks!  I didn't try cup.  I tried cap and cover and seal.  This Real OEM site is amazing though!  I don't know how I haven't come across that site before!

Looks like they're $20 each which seems like a lot so maybe I can live with the crack. 

But Johnny, if you have a couple old ones lying around, I'd be happy to pay you for them assuming the price is reasonable.  Let me know what you think.

I went ahead and put 280cc in both and sealed them up.  I still need to repaint the lowers and then they can go back in the triple clamps.

Thanks all!

[Laitch]

Looks like they're $20 each which seems like a lot so maybe I can live with the crack. 

What's hard to live with is grit that gets in the fork seal and causes oil to leak out and has the potential to damage the forks, which also allow oil to leak out. Those cups are a method of wiping grit from the fork tubes and protecting the seals. A pair of fork gaiters is another method and there are other devices. You're in a good position to consider installing something right now.

[oneplustwo]

Agreed.  Hopefully Johnny has some he’d be willing to part with.

Or are there aftermarket or generic ones that would work vs OEM?

[rbm]

If you do consider gaiters, the Rancho RS1952 automotive shock boot will fit perfectly, are readily obtainable at automotive shops and cost you minimally.

[oneplustwo]

i found some eBay ones for $14.  It says they're for a K75C but I think they are also 41mm so I'll double check that.  But that should do the trick!   

https://www.ebay.com/itm/132595440871?ViewItem=&item=132595440871

[Laitch]

It says they're for a K75C but I think they are also 41mm so I'll double check that.

Maybe you should measure yours. 41.3mm is the pre-1991 Sport fork tube measurement shown at MAX BMW. Having vernier calipers and a micrometer is helpful when identifying parts for your bike.

[oneplustwo]

Just measured and mine are indeed 41.3.  Good call on checking mine to be sure.

[johnny]

greetings...

i do not have that part number...

j o

[oneplustwo]

I stripped and sanded the tank down with my random orbital sander in decreasing grits from 60 to 220 and then a scotch brite pad.  I kinda like the look and plan to keep it this way.

I think it's time to get to the frame next!  But I need a tail light first.  Any recommendations on an LED tail/brake/turn signal light?  I see a bunch on eBay and amazon but not sure if any of them are all that great.  This one is the leading contender at the moment: https://www.amazon.com/Partsam-Universal-Motorcycle-Flexible-Motorbikes/dp/B0140XMI1Q/ref=pd_cp_236_2?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=80460301815383741&pf_rd_r=1V4Y3PJ53PRJFKQKC309&pd_rd_wg=8LqRy&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&pd_rd_w=eAmw3&pf_rd_i=desktop-dp-sims&pd_rd_r=2af27424-74e7-11e8-b5a7-659282df66eb&pd_rd_i=B0140XMI1Q&psc=1&refRID=1V4Y3PJ53PRJFKQKC309

Figure it's tough to go wrong for $10.

[Laitch]

But I need a tail light first.  Any recommendations on an LED tail/brake/turn signal light?
Figure it's tough to go wrong for $10.

Do you understand that you'll need to modify the flasher relay to use the LED turn signals and do other modifications to use an LED brake/tail light successfully?

[oneplustwo]

I'm using the motogadget m.unit as well as the Motoscope Mini, Motosign Mini, and m-Button.  My understanding is that I can basically eliminate all the relays except the starter relay.  I haven't dug into the electrical plan too much yet though so I may be wrong here.  I'm considering just redoing most of the wiring though to clean it up.  As I mentioned, still need to dig into the details a bit.  But I think I have some of the basics down at least.  Not entirely clear on the speedo, some of the indicator lights, and the ignition stuff among other things but that is all on the list of things to probe into.

Separate question as I dig into the frame modification... I'm thinking about just getting this eBay seat: https://www.ebay.com/itm/26-inches-BMW-K75-K100-K1100-80s-90s-solo-cafe-racer-Brat-seat-CODE-S3191/112610955247?hash=item1a3822cfef:g:ru0AAOSwR29ZKnVd

Seems like a reasonable value and it's basically exactly the look I was looking for.  Also, it should bolt right up after the requisite frame modifications which is nice.  Any other suppliers out there that would offer something similar?  I also had the thought of bring the stock seat to a local upholsterer but I doubt it would be as affordable.

[oneplustwo]

I got my eBay dust fork seals and they fit will.  Looks like the old ones have a coat of white lithium grease or similar on the inside mating surface.  I've read that this kind of greasing just collects dirt and makes things worse and that the residual fork oil is good enough to seal things well.  And I also saw in my repair manual that Gleitmo 805 is specified as a "lubricating grease in bushing" which isn't entirely clear to me.  In any case, what's the prevailing wisdom on whether to grease these or not and with what?

In other parts news, I got my new spark plug wires and some other bits from beemerboneyard today.  I ordered the saddle from Texavina as well (the primary seller of the ones on eBay linked below).  Once I get that in I'll finalize the frame chop and then it's surgery time!

[DEcosse]

Hi Neighbour - where in Bay Area are you? I'm down in Pleasanton

I'm using the motogadget m.unit ...  My understanding is that I can basically eliminate all the relays except the starter relay. 

You will need to keep the FI Relay as well as starter relay
You'll also need to have some means of decoding the GPS signals for the Neutral Light (which I'm sure you would want)
And also might want to multiplex some of the alarm signals - you are only going to have one 'spare' warning light available on the Motosign and would think you want to alarm for low Oil Pressure and Overtemp at minimum
Some notes on that here - http://www.k100-forum.com/t13951-instrument-wiring-acewell-2853-verifications-and-observations
(I'm not sure if you have both - & + connections available for each lamp - if so, you can feed (-) directly to the red one, then no transistor is required)

You can find good schematic & notes on wiring the M-Unit on the K-100 forum by zach_ross if you search -
Here's his diagram -  http://www.k100-forum.com/t13951-instrument-wiring-acewell-2853-verifications-and-observations

[oneplustwo]

Howdy!  I'm in San Francisco near the Zoo.  Let me know if you're in the area.  Happy to buy beers and talk K-bikes!

Thanks for the tips.  I was reading the FI relay was going to be needed as well although I was wondering if I could get away with using the motogadget auxiliary output for that since that can handle 10 amps and I believe the fuel pump is fused for 7.5A.  Also, for the alarm signals, the m.unit has two auxiliary inputs as well so perhaps I could configure it to have two different signals to the same light for oil pressure and overtemp.  Obviously, still need to decode the capability of the m.unit as well.  There's a lot out there on the older versions but the newer version has some more bells and whistles that may help with some of this stuff.

Regardless, I still have a lot to figure out about the electrical stuff (and other systems!) so it will be a journey for sure. 

[DEcosse]

As I read some more on the newer one, you should be able to use Aux or 2 and control the output using the Yellow/Brown - that should work well with the same control as the OEM
If you can use either polarity on the Motosign, then couple of diodes are all you need and connect them directly - but again, you can use one of the aux as a driver if you need it be positive.
There's no documentation for the Motosign (that I could see) but imagine you will have separate +/- for each LED?