BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

Oi, it's been fun making this work and especially with the caliper some of yous have given me some great help. So thanks for that! A few months ago I was on Ebay looking at random junk like I do, and was just looking for "17 inch mag wheels" for my chopper. My rear brakes have never been the best, and was considering a disc brake rear and ditching the front in true chopper tradition. I found the BMW K100 and fell in love with the pattern of the wheel. Only 20 smackaroos and even had free shipping. The splines for the driveshaft were fucked which is why the price was so cheap, but there are tons of these wheels with bad splines on ebay. The bike is normally single side swing arm, and shaft driven. "But will it work? It's probably too wide" was that first thought. So with a little internet research found out the specs were 17x2.75 and well hot shit I was already running a 2.75 rear tire on that 2.5 five star wheel. So naturally I bought the goober and devised a plan.

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(edited)

Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

My game plan was a simple one. have the hub milled out to press in a spacer that could hold my sprocket and a bearing. And have the other side where the ruined splines were, milled just enough to press fit another bearing, I chose 6301 (12x37x12) because the OD required the least amount of materiel to be removed from the spline area, and gave me a 12mm ID for a standard axle most mopeds would use. When I got the wheel I was ecstatic. My original plan did not include milling the open hub, just getting a spacer made to press in, so I cut out a good bit of the triangle gusset bits to make room, using a depth gauge on my micrometer to make it decently even, later on the machine shop ended up milling it out just a teeny bit anyway, to make sure it was 100% even the whole way around and the spacer would not try to sit crooked once pounded in.

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This was my work cutting away some of the gusset.

I found a machine shop in my town, NYE machine. I saw their specialty was "prototype production and one off work". SUPER pleasant guys and only 60 an hour. they enjoy being the one shop willing to help the local guy with a project out.

Here are the results after the milling of both sides.

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Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /
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Here is the press in spacer, drilled and tapped for a tomos sprocket, and milled for the 6301 bearing. Ready to chill and then smack into the heated hub and sit flush and flat thanks to them milling the wheel out a little giving it an even shelf to sit on. SHOULD THIS EVER SLIP: I'll drill and put a setscrew in to help pinch the spacer, but this was pressed in with green "slip fit" locktite. I think moped power won't ever be enough to break this loose but I at least have the back up plan. Now you can see in previous photos behind the spacer lie the 4 counter sunk holes that will hold my rotor adapter. It's a pain that when I need to change the rotor I'll have to knock the spacer out but it's not chintzy and should come out with some heat and a good pounding from the backside by placing a rod in through the bearing on the other side.

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I did indeed run into a slight road block. My wheel came with no rotor and a new one even used was upwards of 150-200 bucks. No thanks. I had a cr80 rotor laying around and they are significantly cheaper to replace. SO I had another spacer made to adapt the patter. In the last photo you can see how it all sits on the wheel.

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Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

ALL PUT TOGETHER. Bearings pressed in, and adapter bolted on with loctite. (I goofed and pressed the spacer in the first time without putting the rotor on first. The bolts are countersunk behind the spacer so they had to go in and tightened down first.) I also made a custom 12mm ID axle spacer for the inside.

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The caliper had a natural mounting position right in that nook of the swingarm and old shock mount. The axle is off of a.... Well I really have no clue but it fits and has a cool "t" handle on one end and an allen key spot.

Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

SPEAKING OF "OLD SHOCK MOUNTS" I converted it to a floating rear end. A long time ago that bushing was long gone and rotted. And so to avoid having my swingarm be able to move almost an entire inch side to side, I welded the fucker. I later realized this does not really let shocks work because nothing can flex. So why not reinforce whats there and take the shocks off? Some 1/8in wall tubing did the trick, and I added some gussets to areas I thought may have been weak or potential breaking points. (Shout out to my boy cj with the nice welding, and machine shop use later). Also a visual of where the caliper would sit.

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This is where it got fun. My buddy CJ works in a machine shop sort of area, he modifies large trucks for a living (extending frames, adding lift gates etc.) and his boss was awesome enough to let us use the machinery and space after hours to make the caliper bracket. At first I thought this was a simple task. " Just get it to sit where it needs to, then somehow bolt it to the swing arm or that old shock mount." Then someone on here pointed out to me "what if the chain would need adjustment....?" And to that I said, "fuck".

So with a suggestion from scooter trash and a little R&D and found the normal design for most bikes was to basically make the wheel spacer into the bracket, so it moves and stays with the wheel.

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This is the one I used for a reference. Very basic and a small slot like a drum brake hub to hold it in place. I did it a little backwards and drilled a hole in the bracket and welded a nut to the back Then made a slot in the old shock mount tab so it could be bolted into place easily. But we'll get to that in a bit.

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Here is the chunky spacer and washer (this combo put the wheel perfectly center when I pushed it all the way against that side). With some fun arts and crafts and I was able to make a rough, but pretty damn close rendition of what the bracket needed to look like and where the holes needed to go.

Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

Using a huge industrial sized metal brake, we chomped down some nice thick sheet. we got to use a large "hole punch thing" that apparently can make 1inch holes in 3/4inch plate steel. A little overkill to make the 1 inch hole for the spacer to be welded to, but that's neither here nor there. Then came the flapper wheel to give this lovely lady some curves

( ͡° ͜ʖ ͡°)

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a little belt sander to smooth over the edges, and we were ready to weld this thang up!

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Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

OOPS THE PLATE WAS WELDED ON THE WRONG SIDE OF THE SPACER TIME TO START OVER. ( was supposed to be on the far side, so now the curve is totally off)

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But hey, we're in a machine shop. So we made a new one from scratch.

I cut and ground down the plate while CJ used a big ol' lathe to make a new spacer.

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That should do it!

Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

This was a kind of weird process, we had to put a bolt through the plate to make sure it held the caliper at just the right spot so it "hovered" over the rotor at an acceptable height, as well as at the right angle. so what we did was put some thin wire around the OD of the rotor, then sat the caliper on top. It was now "hovering" above to rotor at a uniform height. With the spacer on, we pulled back the wheel as far as it could go, and got the red mock up dots over top the mounting holes the best we could. The actual mounting holes for the caliper were quite tricky because we could not go through the back for the bottom one due to the rotor pattern and wheel straight up blocking it. The old shock mount was right in the way for the front as well, So we ground it out, but it was a tight spot and we could not get good visualization on where the hole really needed to be. Even for the top bolt hole, the rotor blocked most of it from the back. We ended up eyeballing it from the front, figuring we had enough meat on the bracket to pivot and adjust the caliper to get the bottom just right and keep it even.

When we got it where we wanted we clamped it to what was left of the swing arm shock mount (oh yeah, I chopped all the material we did not need off the old shock mount so it looked a little nicer) then drilled through the old shock mount and the plate as far back as we felt comfortable. Then we placed the wire under the caliper again and drilled the top mounting bolt for the caliper, this was eyeballed but we got it right where we needed it. The red marker dot was a guess reference from when we were shaping the plate, but ended up being damn close.

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You can see in the previous photo of the mount and caliper together, that hole is already there because I forgot to take one of just the completed caliper mount. We used a plasma cutter (because why not) to make the hole in the shock mount into a slot so it could be adjusted forward for chain tension. (even though it cannot make much forward movement because of the tire size rubbing the front cross bar of the swing arm). Lastly we welded an M8 nut to the back of the plate.

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We mounted it all back together with the bracket bolted in place to the swing arm. With the top caliper bolt in snug but not super tight we once again placed the wire between the OD of the rotor and caliper. When we got it exactly where we wanted it, we cranked down the top bolt. and took it all back apart. Now the caliper was sitting on the bracket exactly how we wanted it, and was held in place tightly by the top bolt . We then used a punch to center the bottom mounting hole for the caliper from the rear.

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Re: BMW K100 Wheel swap. An in depth thread.

Anonymous User /
scootertrash

Awesome wheel!

Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

Now with all 3 bolt holes as perfect as we could get them came the moment of truth. Mount up and see how she looked. The lower bolt of the caliper still needs some metrical ground out to fully tighten down, but even tightening how it is as far as it could go..... She spun fantastically with no sound of grinding or rubbing.

I'll be grinding out where the lower caliper bolt goes this week and probably switching to M8 allen key bolts so I don't have to grind out as much. The one that mounts the swing arm to the caliper bracket also needs to be shorter as you can see in the one photo, it nips the big bolts coming from the rotor mount at the current length.

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I hope you enjoyed reading this way too long, novel of a post.

I sure had fun making it. -Nathan the Wizard(edited)

Re: BMW K100 Wheel swap. An in depth thread.

Well done. Always liked the amount of sketch that bike has. Lol

Re: BMW K100 Wheel swap. An in depth thread.

Dirty30 Dillon /

That's a sick conversion. Very impressed and happy to see something out of the box that is not half-baked.

Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

Haha I always love comments like these because I whole heartedly understand that while I always try to do my best work, and to do things the right way. Some of it is just... off.

“Oh nice! a rear disc! Now what?”

“Oh I’m ganna take off the front brake to make it look cleaner and more simple”

“Wait why would you do that?”

”Aesthetic”

Re: BMW K100 Wheel swap. An in depth thread.

Post a pic of the whole bike!

Re: BMW K100 Wheel swap. An in depth thread.

I would really like to see pictures of it from both sides.

Re: BMW K100 Wheel swap. An in depth thread.

Anonymous User /
scootertrash

Better is better!

Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

> Jeff Parr Wrote:

> -------------------------------------------------------

> I would really like to see pictures of it from both sides.

There are shots of both sides of the wheel in the thread, or do you mean both sides of it mounted up the the bike? My dished sprocket was delivered tonight. So if that’s what you mean I’ll take some tonight with the chain mounted up and such!

Re: BMW K100 Wheel swap. An in depth thread.

Yes the whole bike with rim mounted an both sides.

Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

Not much to see from the sprocket side (no sprocket currently, but can be spaced out to match the dished front. Want to play with my gearing a little) I hope you can see what you were looking for in these!

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Re: BMW K100 Wheel swap. An in depth thread.

Nicely done and very cool.

Re: BMW K100 Wheel swap. An in depth thread.

Is it just me or is that swing arm pretty skimpy ?

Seems like the first bump of most any size would have that thing in pretzel shape .

The brake looks good , but , what it's mounted on ???

Re: BMW K100 Wheel swap. An in depth thread.

Side profile... the whole bike... like this! Lol

I wanna get a feel for the flow! Your bike is making its way into my top 10 favorite of all time.

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Re: BMW K100 Wheel swap. An in depth thread.

hell yeah, that fucks.

Re: BMW K100 Wheel swap. An in depth thread.

With the shape of the swingarm end you could take some tubing and make some top stays that matched for that bmx looptail look.

Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

Let me finish up my new sissy bar and tail light, then I’ll post the whole thing ;^) my old sissy bar used to mount to the shock mounts I cut off , and it was aluminum round stock so it had a little flex to it and while I would put my weight on it sometimes I always kinda wanted to make a new one using square steel stock this time

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Also if you’ve seen the bike in the past it had dual rectangle headlights. They fried and I used a regular bullet light for a while. I found a new pot of those same rectangle fog lights on amazon and I’m putting them back on.... with a twist...

Re: BMW K100 Wheel swap. An in depth thread.

Anonymous User /
scootertrash

Nice and tight!

Re: BMW K100 Wheel swap. An in depth thread.

Wolf Wizard /

> P D Wrote:

> -------------------------------------------------------

> Is it just me or is that swing arm pretty skimpy ?

>

> Seems like the first bump of most any size would have that thing in

> n pretzel shape .

>

> The brake looks good , but , what it's mounted on ???

The swing arm has been reinforced in 4 spots so I’m hoping she holds well. Two lengths of 1/8in wall pipe as supports and two gusset plates added where it turns from tubing to the plate.

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Also, In green you can see the actual mounting bracket/ spacer. You can see it keeps the wheel center and also hugs the old shock mount for added support. It’s 1/8inch steel plate I think.

The red bolts are the two end bolt holes on the bracket they secure the caliper to the bracket, and lastly the blue bolt works as a stay, keeping the bracket in that same position and locking it on tight. There is a bit welded to the back of the bracket that the blue bolt tightens into.

Re: BMW K100 Wheel swap. An in depth thread.

awesome write-up, it was long but well written and detailed. the pics are great with action shots and all. keep it coming

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