Author Topic: K75$ -- hammer pants  (Read 3238 times)

Offline thestza

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K75$ -- hammer pants
« on: February 09, 2018, 01:01:41 AM »
evening.


bought a K75S about 2 years ago. all stock from what i can tell so far (minus the corbin seat). love the bike but also wanna streamline it a bit... not sure the exact form it will take just yet. i have limited mechanical experience but am curious... and somewhat OK with diving in.


here is the bike around when i bought it (next to my homie's badass R100RS):



anyhow, i've been calling the bike Hammer Pants. hoping to chronicle the build here and looking forward to learning from everyone here on the forum.
  • gross angeles
  • 1988 k75$

Offline thestza

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Re: K75$ -- hammer pants
« Reply #1 on: February 09, 2018, 01:37:10 AM »
so. although i'm a bit unsure of the final touches. i know i wanna strip down the bike and modify the silhouette... here are some amazing examples built by people way more skilled than me:








obviously, there are some common features here. some of the work here is waaaaaaaaaaaaaaay outta my league. however, i do wanna re-work the stance like these examples: shorter / more compact fork / front end and a re-working of the lines in rear too... i don't have much mechanical experience but am very curious and love design. in truth, many of the modifications i'll be making will be based around aesthetics -- learning the skills needed to achieve the desired result.
  • gross angeles
  • 1988 k75$

Offline thestza

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Re: K75$ -- hammer pants
« Reply #2 on: February 09, 2018, 02:35:33 AM »
a few months back, i removed the front faring, rear assembly, front fender, and instrument cluster... for the faring, a user here posted a link to a very useful write-up that i used for reference (see attached .pdf or use this link -- hopefully, it will stay active: http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/k75sfairing/K75S.Fairing.Removal.pdf).


and here is the 'spread' of everything removed:


 
  • gross angeles
  • 1988 k75$

Offline thestza

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Re: K75$ -- hammer pants
« Reply #3 on: February 09, 2018, 02:46:14 AM »
so... the bike had been buried in the garage during a home renovation for about 6 months. last week, i went to try and start it again, and, of course, it didn't fire up. my friend suggested i test / check the battery first... hooked it up to a battery charger / 'maintainer' and it was dead. re-charged it, reinstalled it, and it fired right up!


i was super worried about letting it sit for so long but very relieved it was only the battery -- i've read that these engines are solid and am glad to see that it's true (so far...)[size=78%] [/size]
  • gross angeles
  • 1988 k75$

Offline thestza

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Re: K75$ -- hammer pants
« Reply #4 on: February 09, 2018, 02:55:06 AM »
another quick note or two... ever since i purchased the bike (especially if it has been a hot minute since i last started it), lots of foul smelling smoke comes out when i start it. when i rode the bike regularly, this problem wasn't nearly as noticeable. i always use the center stand when parking the bieke... in doing some research and reading around, i've seen that this may be due to faulty / leaky valve glide seals but would love some input from the forum here.


also, i forgot to mention in a previous post, the exhaust is aftermarket. it's got a supertrapp installed on the bike which was available once upon a time (although it seems like it's no longer available / supported). here's a link to some info about the model number if anybody is curious: http://forums.supertrapp.com/showthread.php?125-BMW-K75S-system
  • gross angeles
  • 1988 k75$

Offline thestza

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Re: K75$ -- hammer pants
« Reply #5 on: February 09, 2018, 03:37:30 AM »
glad the bike is running again. next order of bidness is to start to tackle the stance / front end. i've been searching motobrick.com and k100-forum.com, youtube-ing, and of course googling for potential solutions. i know that i want to lower the fork to achieve the aggressive stance that i'm after but was unsure of the methods to achieve this. i've also never rebuilt a fork...

there is lots of information out there, but from what i've gathered so far, there are a few options:
  • the cheapest and simplest is to 'slide' the fork tubes up in the triple trees... this is not possible with my current setup because the stock bars on the K75S are mounted directly above the fork tubes. i can maybe move them about .635 mm or 1/4" but that's it. there are a couple of work arounds to this however: installing some handlebar 'set backs' can give you the clearance you need to slide the tubes up further. you can remove the stock bars and install strap-ons... i might go the clip on route if i can't solve it another way...
  • the next option, although way more expensive, is to replace the entire front fork. cognito moto sells kits that will allow you swap in a gsxr front fork: https://cognitomoto.com/collections/fork-conversion-parts/products/complete-gsx-r-front-end-with-rim -- if i had the money, i would definitely just do this. it looks super badass, seems like a relatively simple install and you get a rad / high performance upside down fork on your ride. there is a user here that has used this method and his bike looks amazing: http://www.motobrick.com/index.php/topic,8807.0.html
  • it seems there are other fork replacement options but the gsxr was the one i investigated the most...
  • finally, the last option is to rebuild the fork / install shorter springs and maybe shorter spacers. this is the option i'm pursuing at present as it struck the right balance of cost / performance / aesthetics... i'd like to avoid strap-ons if possible (for purely aesthetic reasons), and i'm hoping that i can replace the springs and maybe shorten the spacers and get the look i'm after but not spend too much in the process
finding information about the fork surgery / using shorter springs has been a challenge. most people warn against lowering the front end too much as it alters the bike's geometry which can impact handling, braking, etc... although i understand and respect this viewpoint, it's not for me, personally. i want the look i want and am willing to take risks / hits to achieve what i'm after... i ride very slow... everywhere... SLOW


  • gross angeles
  • 1988 k75$

Offline MEZ

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Re: K75$ -- hammer pants
« Reply #6 on: February 09, 2018, 03:39:43 AM »
another quick note or two... ever since i purchased the bike (especially if it has been a hot minute since i last started it), lots of foul smelling smoke comes out when i start it. when i rode the bike regularly, this problem wasn't nearly as noticeable. i always use the center stand when parking the bieke... in doing some research and reading around, i've seen that this may be due to faulty / leaky valve glide seals but would love some input from the forum here.


also, i forgot to mention in a previous post, the exhaust is aftermarket. it's got a supertrapp installed on the bike which was available once upon a time (although it seems like it's no longer available / supported). here's a link to some info about the model number if anybody is curious: http://forums.supertrapp.com/showthread.php?125-BMW-K75S-system
Hi there, glad to see your so enthusiastic about your ‘K’ bike, I’m relatively new myself, building a K75 Adventure travel bike elsewhere on here. One thing I did to mine which I think judging by what you have expressed so far is extend the swing arm/ shaft assembly by 50mm using a CNC machined block and extended shaft. I have 4 such CNC blocks available for sale if you need one ok. Keep posting and use the wealth of good knowledge these guys have, there a good bunch..!!!

Mez/ UK


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  • Angel of the North
  • GS12adv '06, K75 GSadv, CRF500L 'special'

Offline thestza

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Re: K75$ -- hammer pants
« Reply #7 on: February 09, 2018, 04:11:40 AM »
anyhow, i decided to dive in and get going... some kind soul on this forum posted the official BMW repair manual and i used that as reference (download .pdf from the following link: http://www.motobrick.com/index.php/topic,2252.0.html). the manual was helpful-ish although there were steps that weren't super clear to me... i made a FUGGIN MESS of my garage -- disassembled a few bits in the wrong order on got oil EVERYWHERE... oh well, i learned a thing or two at least. here are some pics of where i'm at and how the bike looks currently:





so... this is where i'm at... i wasn't able to fully disassemble the front fork so i need to do some more research... willl post again when i have an update
  • gross angeles
  • 1988 k75$

Online Chaos

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Re: K75$ -- hammer pants
« Reply #8 on: February 09, 2018, 10:29:27 AM »
Wow!  Didn't know they still made PBR  :eek:
  • sw ohio
1987 K75S    VIN 0231
Original owner, Original litter
200,000 miles (plus or minus) and 5 paint jobs
2012 Ural 2WD sidecar (BMW's bastard step child)

Offline Laitch

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Re: K75$ -- hammer pants
« Reply #9 on: February 09, 2018, 10:36:32 AM »
i wasn't able to fully disassemble the front fork so i need to do some more research... willl post again when i have an update
You'll find directions in this pdf starting on page 161.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline thestza

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Re: K75$ -- hammer pants
« Reply #10 on: February 09, 2018, 02:59:50 PM »
thanks Laitch. i put that link in my original post as well -- it's definitely the one i used for reference when trying to take apart the fork tubes. however, it seems something happened with the formatting and my text is microscopic... is there no way to edit posts (i'd like to correct the font / sizing issue to maybe help others in the future). i looked on the support page and found this article which talks about how to edit and / or delete posts: https://wiki.simplemachines.org/smf/Posting but i don't seem to have access to either... do i need to request edit access from a moderator?
  • gross angeles
  • 1988 k75$

Offline thestza

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Re: K75$ -- hammer pants
« Reply #11 on: February 09, 2018, 03:00:54 PM »

Wow!  Didn't know they still made PBR  :eek:


they do! and it's just as delicious as it's always been!
  • gross angeles
  • 1988 k75$

Offline Laitch

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Re: K75$ -- hammer pants
« Reply #12 on: February 09, 2018, 03:02:29 PM »
they do! and it's just as delicious as it's always been!
Undoubtedly. It's great slug bait, too.
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline billday

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Re: K75$ -- hammer pants
« Reply #13 on: February 10, 2018, 09:30:02 AM »
so. although i'm a bit unsure of the final touches. i know i wanna strip down the bike and modify the silhouette... here are some amazing examples built by people way more skilled than me:

Sorry, I don't see how any of these is an improvement on the original. But have fun with your project.
  • New York State, USA 10977
  • 1985 K100

Offline thestza

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Re: K75$ -- hammer pants
« Reply #14 on: February 10, 2018, 01:56:15 PM »

Sorry, I don't see how any of these is an improvement on the original. But have fun with your project.

totally. the originals are super beautiful bikes. it's really just personal preference -- tailoring the bike to match my specific needs and design sensibility... i love the engine block and asymmetrical nature of the bike in general. it all feels very futuristic and brutal (the good kind of brutal). 
  • gross angeles
  • 1988 k75$

Offline thestza

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Re: K75$ -- hammer pants
« Reply #15 on: March 06, 2018, 01:45:08 AM »
made some slow progress these past couple weeks...

FORK / FRONT END
as mentioned previously, i'm wanting to lower my front end. after considering options, i've decided that rebuilding / replacing the springs in the fork is probably the most economical. however, i'm not totally sure how much i want to lower it / what my ideal stance is... so, it seemed like finding a way to experiment with different ride heights before purchasing / committing to a set of springs might be a good idea.

unfortunately, the stock handle bar configuration doesn't really allow for the fork tubes to be positioned higher in the triple tree. however, i remembered that when i purchased the bike, it had some handle bar clamp risers / extensions that might allow some additional clearance. i dug them out and attached them to the triple tree and threw in some bars temporarily. this should give me the clearance i need to experiment with different setups and find the exact amount to shorten the fork:






SPORT / S FORK CONFIRM
when reading through the manual while tearing apart the fork, i noticed that the different K75's came with different forks. i don't know much about the history of my bike and so i wanted to confirm that i'm dealing with the correct equipment as i move forward. for fellow K-first timers, the K75S is supposed to come with brembo 'sport' forks -- which are labeled / imprinted with a graphic 'S'. i took a photo in case it might be helpful for others:







PITTED FORK / DAMAGED AXEL
also, when removing the front wheel, getting the axel out was very difficult... i read in some other posts that the axel should slide out super easy, so i took a closer look at it and noticed that there are some rough spots (which might have contributed to it being so tough to remove). the images below shows the raised areas along the axel and the pitted area in the fork where the axel is received. anyhow, i ordered a used one off ebay that will hopefully be in better shape








REAR END
last thing for now is that i chopped his butt off. i marked the frame with tape to serve as a guide to help cut and then hacked through it. this next set shows his pre-chopped butt, then his butt post-operation, and a quick 'mock up' of where i'd like the new seat line to lie. it's my hope that i can relocate the factory frame loop with some some further chopping and welding









so anyway, that's where i'm at -- at the moment. more to come soon-ish i hope.
  • gross angeles
  • 1988 k75$

Offline Laitch

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Re: K75$ -- hammer pants
« Reply #16 on: March 06, 2018, 05:19:37 AM »
unfortunately, the stock handle bar configuration doesn't really allow for the fork tubes to be positioned higher in the triple tree. however, i remembered that when i purchased the bike, it had some handle bar clamp risers / extensions that might allow some additional clearance.
Usually, those who want to lower the bike on its fork tubes for an aggressive look use strap-ons bars to help achieve that. Why did you not consider using those?
  • Along the Ridley in Vermont.
  • 1995 K75T 68,000 miles
I wept because I had no radials until I met a man who had no splines.
http://www.motobrick.com/index.php/topic,296.msg53303.html#msg53303

Offline The Mighty Gryphon

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Re: K75$ -- hammer pants
« Reply #17 on: March 06, 2018, 09:04:30 AM »
If you want to replace that whack front axle, I have a good K75/K100 axle you can have for $23 which is $10 + $13 shipping.  It will include the end cap, screw and spacers.
  • In my garage in Marilla, NY
  • '94 K75RT Mystic Red, '92K100RS White, '94 K75S Dakar Yellow
Current:
'94 K75RT "Ilsa, She Wolf of the SS"
'94 K75S "Cheetos"
'91 K100RS "Moby Brick Too

Offline thestza

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Re: K75$ -- hammer pants
« Reply #18 on: March 06, 2018, 11:04:19 PM »
Usually, those who want to lower the bike on its fork tubes for an aggressive look use strap-ons bars to help achieve that. Why did you not consider using those?


hi Laitch. that's definitely an option i'm considering. my hope is that i i can dial in / find the desired right height / stance with the parts i have available, then purchase any additional parts to get a clean and rad looking end result. 
  • gross angeles
  • 1988 k75$

Offline thestza

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Re: K75$ -- hammer pants
« Reply #19 on: March 06, 2018, 11:41:15 PM »
another quickie... last weekend, while everything was apart, i put on some new tires and painted the wheels and triple trees. here are some pics of that along with the spray paint i used. it's hard to tell from these pics, but everything came out pretty ok.  i'm super happy with how the tires look (will post pics of the wheels + tires once everything comes back together).










  • gross angeles
  • 1988 k75$

Offline Martin

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Re: K75$ -- hammer pants
« Reply #20 on: March 07, 2018, 01:51:40 AM »
Be aware lowering the stance of the bike will decrease your cornering clearance. This will reduce the speed that you can take a corner at. The original aim of the coffee racer was to improve the bikes point to point times. This involved enhancing performance and improving the handling.
Regards Martin.
  • North Lakes Queensland Australia
  • 1992 K75s Hybrid, Lefaux, Vespa V twin.

Offline thestza

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Re: K75$ -- hammer pants
« Reply #21 on: March 09, 2018, 01:12:48 PM »
Be aware lowering the stance of the bike will decrease your cornering clearance. This will reduce the speed that you can take a corner at. The original aim of the coffee racer was to improve the bikes point to point times. This involved enhancing performance and improving the handling.
Regards Martin.


hi Martin,


thanks for the heads up and definitely something to keep in mind. the bike is mostly going to be used for occasional commutes and farting around town on the weekends. i'm hopeful that the lowered stance won't present many problems in practice as i don't really do canyons, racing, or any aggressive riding, really. 
  • gross angeles
  • 1988 k75$

Offline stokester

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Re: K75$ -- hammer pants
« Reply #22 on: March 12, 2018, 05:05:38 PM »
Sorry, I don't see how any of these is an improvement on the original. But have fun with your project.
Good project to follow but I agree.  My K75S is dialed-in to my riding, good handling and high-mileage comfort.
  • Yorktown, Virginia
  • '94 K75S - '93 K75S - '91 R100RT - '78 R100S

Offline thestza

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Re: K75$ -- hammer pants
« Reply #23 on: July 19, 2018, 05:59:15 PM »
Hello again…

so lots of slow progress:

FORKS / FRONT END LOWERING
After considering all my options, i ended up electing to have the stock Brembo forks professionally rebuilt / shortened. I used a company called race-tech in soCal and am super happy with the results. They were able to shorten them by 2” which allowed me to get a bit closer to the look i want while still leaving a bit of travel.

Here’s the new / lower stance after put the front end back together...



MARKUP
From here, I used the image above to put together a markup / concept sketch for where i want to take the bike next. Roughly, this is what i’m hoping the bike will look like when i reattach the rear loop. I’ve been tossing around the idea of using a skateboard as a seat pan… overall, i like the new silhouette, but there’s a bit too much negative space between the engine block and the front wheel -- i’ll need to find something to do there… the k100’s look better in this regard as this area is much tighter and looks cooler (in my opinion). anyhow, here’s that…




NEW HANDLE BARS + CONTROLS
Next, i wanted to replace the handle bars. Which was slightly more complicated than i had anticipated. I had an extra set of renthals kicking around from a previous build and figured i’d use those… the stock bars are 22mm and the renthals are ⅞” (22.225mm). i figured the difference of .225 mm wouldn’t mean much in practice but that was definitely not the case. None of the stock controls would fit over the bars!

From here, i either needed to find some 22mm bars that i liked or come up with another solution… After digging around on multiple forums, i decided to sand the renthals down. This was a super scientific process that involved precise machinery and complex tools as you can see below
 



In any case, it worked! I slipped the controls and moved forward…


BRAKE LINES AND NEW FUEL HOSE
Because of the shorter forks, the front brake lines were a bit too long and bowed out too much. I figured this was as good a time as any to get new lines, so I purchased some (no pics of this at the moment). Soon after, when i went to fire up the engine, I smelled gasoline and saw that the fuel line running from the tank down to the injector rail was leaking slightly… so i replaced this too (super glad i caught this)




So yeah, that’s where i’m at currently. Hoping to weld the rear end on this weekend.
  • gross angeles
  • 1988 k75$

Offline thestza

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Re: K75$ -- hammer pants
« Reply #24 on: July 27, 2018, 03:05:52 AM »
Quick update: Re-welded the rear loop, bled both brakes and replaced the rear master cylinder. Hammer pants rides again! I had forgotten how much fuggin fun these bikes are!

  • gross angeles
  • 1988 k75$

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