K75/K100 handlebar clamp measurements...

[justabill]

Hey folks. I am using some K75 parts on a mod project for my R80 rebuild and am planning to use K75s handlebars and impact pad. I can see that these mount to the front of the handlebar clamps / risers normally.

I am curious if any of you knows or can measure the distance between the clamps or the distance between the mounting holes on the impact pad. It's 80mm on the R bikes, but I suspect it's more on K bikes.

Thanks for the help!

 

[51797]

Measured 90mm on my '85 K100RS. Suspect it would be the same on a K75.

Frank

 

[98lee]

I got 89mm on a K75S fork. The ears on the “crash pad” are pretty flexible and will tolerate as tight as 70mm.

The center to center of the bar clamps is 72mm. I use A&S barbacks and the ”crash pad” mount holes on the barbacks are 72mm apart and work fine with the original pad.

The triple clamp you pictured is not a K75 style which has cast in bar clamps. K100s have the pictured rubber mounted
bar clamps.

 

[justabill]

I got 89mm on a K75S fork. The ears on the “crash pad” are pretty flexible and will tolerate as tight as 70mm.

The center to center of the bar clamps is 72mm. I use A&S barbacks and the ”crash pad” mount holes on the barbacks are 72mm apart and work fine with the original pad.

The triple clamp you pictured is not a K75 style which has cast in bar clamps. K100s have the pictured rubber mounted
bar clamps.

Not sure I am following. Sounds like about the same distance as @51797, but you are using the barracks which have a narrower (17-18mm) mount point for the pad and it is all still good?

I ordered this style pad (BMW: 32711453157):


With these bars (BMW: 32712300384):


Mating it all to the top of a ToasterTan airhead top clamp, which has the bar clamps at 80mm OC. My plan is to have a custom bracket under each clamp to provide a mount point, but can also simply drill and tap the lower clamps if push comes to shove.

I've had a heck of a time finding good info on early K bikes. Especially when it comes to those heated grip optional bars.

Bill

 

[98lee]

Bill,

What do you need to know? I’ve got 6 K75Ss and tons of parts I can measure for you.

The only difference between heated grip bars and non heated grip bars is the hole in the bottom of the bars between the bar clamps for the wires to come out and two small threaded screw holes to hold the left grip on. These holes can easily be drilled to makea non heated grip bar into a heated grip bar.

 

[justabill]

Wow! Thanks.

My goal is to have it end up looking like something BMW might have done, even if they never did. Boxer2Valve did a very similar conversion to an airhead a few years ago and used these two parts on their project. It wound up looking solid in the photos of that bike and show a pretty clean result, but they breezed past too much of the details in their videos to really get it. They simply drilled and tapped the lower clamp for an M6x10 at 12mm above the bottom of the clamp. When I mock it up, that does not seem to work well and the pad and bars seem to want to fit asymmetrically. That's what got me wondering about the intended geometry of the bars and the pad on a K75. I also noted the flexibility in the pad.

As for the measurements, I did some rough CAD to illustrate. The red line is the centerline of the handlebar. Green surfaces are the machined top of the lower clamps forged into the whole part. Blue surfaces are the surfaces where the pad mount holes are placed.


What would be really good to know is:

• What distance between the pad mounting holes on the top clamp? This was the 89mm or 90mm from earlier posts, I think.
• How far below the clamping surface is the hole placed? The handlebar centerline would also work for the top end of the measurement here.

• How far rearward is the surface where the mounting holes are from the centerline of the bars?

Having this geometry from a K75S would let me know where the pad mount points need to be in relation to the lower clamps on the airhead, so I can get an accurate bracket designed and produced. I may end up needing to design new lower bar clamps instead, but that will depend on the needed geometry.

 

[51797]

Not sure I am following. Sounds like about the same distance as @51797, but you are using the barracks which have a narrower (17-18mm) mount point for the pad and it is all still good?

I ordered this style pad (BMW: 32711453157):
View attachment 96580

With these bars (BMW: 32712300384):
View attachment 96582

Mating it all to the top of a ToasterTan airhead top clamp, which has the bar clamps at 80mm OC. My plan is to have a custom bracket under each clamp to provide a mount point, but can also simply drill and tap the lower clamps if push comes to shove.

I've had a heck of a time finding good info on early K bikes. Especially when it comes to those heated grip optional bars.

Bill

That pad and handlebar looks exactly like what is on my '85 K100RS. Not sure if the K75S uses the same parts.

Frank

 

[justabill]

That pad and handlebar looks exactly like what is on my '85 K100RS. Not sure if the K75S uses the same parts.

Frank

According to the parts fiche, these parts were on the K75S and K100RS.

Each part had a change during production resulting in new part numbers also.
Bars
32712300384 older
32712308147 newer

Impact Pad
32711453157 older
32712308032 newer

There is some sloppiness in how these parts (especially the pad) are listed in various places, but I am pretty sure the newer version is this one:


That makes sense, because I think the newer version of the bars are a little wider also.

 

[51797]

I installed heated grips on my '85 and the handlebar is wider leaving a gap at the ends of the pad, just about what the updated pad would fill.

Frank

 

[98lee]

Wow! Thanks.

My goal is to have it end up looking like something BMW might have done, even if they never did. Boxer2Valve did a very similar conversion to an airhead a few years ago and used these two parts on their project. It wound up looking solid in the photos of that bike and show a pretty clean result, but they breezed past too much of the details in their videos to really get it. They simply drilled and tapped the lower clamp for an M6x10 at 12mm above the bottom of the clamp. When I mock it up, that does not seem to work well and the pad and bars seem to want to fit asymmetrically. That's what got me wondering about the intended geometry of the bars and the pad on a K75. I also noted the flexibility in the pad.

As for the measurements, I did some rough CAD to illustrate. The red line is the centerline of the handlebar. Green surfaces are the machined top of the lower clamps forged into the whole part. Blue surfaces are the surfaces where the pad mount holes are placed.
View attachment 96595

What would be really good to know is:

• What distance between the pad mounting holes on the top clamp? This was the 89mm or 90mm from earlier posts, I think.
• How far below the clamping surface is the hole placed? The handlebar centerline would also work for the top end of the measurement here.

View attachment 96596

• How far rearward is the surface where the mounting holes are from the centerline of the bars?

View attachment 96597
Having this geometry from a K75S would let me know where the pad mount points need to be in relation to the lower clamps on the airhead, so I can get an accurate bracket designed and produced. I may end up needing to design new lower bar clamps instead, but that will depend on the needed geometry.

Bill,

Sorry to take so long to get back with an answer.

Here is what a K75 top fork clamp looks like:


To answer your measurement questions:
Center to center of the pad mounting holes = 88.95mm
Centerline of pad mounting hole to top of lower bar mount = 7.70 mm
Face of pad mount to bar centerline = 31.75mm

Something you didn’t ask: center to center of handlebar mounting bolt holes = 72mm


This is what the barbacks look like:

The measurement between the barback pad mounting holes center to center = 71.52mm. Pad fits fine.

 

[98lee]

According to the parts fiche, these parts were on the K75S and K100RS.

Each part had a change during production resulting in new part numbers also.
Bars
32712300384 older
32712308147 newer

Impact Pad
32711453157 older
32712308032 newer

There is some sloppiness in how these parts (especially the pad) are listed in various places, but I am pretty sure the newer version is this one:
View attachment 96598

That makes sense, because I think the newer version of the bars are a little wider also.

Bill,

BMW changed the overall width of the S bars in 9/87. They widened them from approx 23” to approx 24”.
The parts fiche has a typo. Part #072 is the discontinued narrow bar. Part # 384 is the replacement wider bar. It SHOULD say: (FROM 9/87). Part# 159 is part #384 that has been drilled for heated grips.

Drilling for heated grips is pretty easy. Drill hole in bottom of bar center for wires (be SURE to deburr inside and outside edges of hole to protect wires). Drill and tap two small holes for mounting screws of left grip. Heated grips are mounted on a tube that need the screws to prevent spinning. Right side is mounted to the throttle tube which has the standard retention method.





The pad without the accordion looking sections on the ends (part # 157) is for the early narrower bars. The ends of the pad cover the bar from left switchgear to right switchgear. When they widened the bars by 1” in 9/87 there would have been a 1/2” gap between the end of the pad and the switchgear on each side, so they added the accordion looking sections to take up the gap. Which pad to use depends on which switchgear and lever perches you plan to use and how much gap you want.


Here is how the S bars fit the S top clamp. There is plenty or room to widen the bar clamp centerline if desired. Center to center of the bar mount bolt holes is 72mm




Here is how later bars fit with the later pad: (no gap to switchgear)

Here is how an early narrow pad fits with K100RS 4 valve bars:
Gives me some bar space to mount the GPS and the 4 valve bars are 1” wider than the later K75S bars.


Let me know if I can help with anything else.

 

[justabill]

This is excellent. Exactly what I need. Thank you so much!

I'll noodle around with this and if something else pops up, I'll let you know.

Side note, I am going to be in the Bay Area at the end of the month. (Born in San Jose, grew up in Lodi). If you PM your address, I would be happy to drop off a bottle of something nice while I am in the area. Really, this will save me at least two iterations of having something custom made for my build.

 

[justabill]

I am gong to end up with wide bars on the narrow pad. That will give me room for a mount like you're doing. Cool.

 

[justabill]

The custom parts arrived this week. Thanks again @98lee. These were $180 delivered from PCBWay and took a month to get, including a two week lag due to the Chinese New Year. I have some minor fiddling to get it all together the way I want, but it's going to work fine, I think.

Custom compared to original:


Dry Fit:

 

[98lee]

Bill,

Very nice!