The bike started as an R100RS model that I’m converting to an RT. So at this point, the parts and cable routing correspond to an R100RT.

I started by installing the RT handlebar in the brackets I previously mounted on the Toaster Tan top fork brace. You can read about how I installed the Toaster Tan brace here.

• 31 BMW 1983 R100RS/RT Install Toaster Tan Top Fork Brace

Parts

I replaced the right handlebar perch, front brake master cylinder, brake lever and throttle cam cover which are available as a single unit (part# 32 72 2 302 368). The master cylinder was badly corroded and I managed to break the perch where it mounts on the handlebar when I stepped on it in a careless moment. The new perch does not use the same throttle cam as the original perch: The new cam has a larger diameter hole (15 mm) instead of earlier 8 mm hole so I had to buy a new throttle cam as well (part#32 72 1 457 081).

The bike came with the front brake light switch attached to the front brake line manifold  mounted on the spine tube under the tank.

As that switch often traps an air bubble when you are bleeding the brakes making it hard to clear all the air, I opted to use the brake light switch that attaches to the right handlebar perch along with the RT length sub-harness that connects the switch to the main harness.

I replaced the upper throttle and choke cables, and the clutch cable with the longer RT length cables and replaced the left side clutch switch and choke lever cover which had faded quite a bit.

I have a set of heated handlebar grips that came on my 1977 RS project bike and decided to install them on this RT conversion.

Part #	Description	Qty
32 72 2 302 368	HANDLE UNIT, RIGHT – D=15MM (from 09/81)	1
32 73 1 242 594	CHOKE CABLE – L=764MM (from 09/80) [RT]	1
32 73 1 242 127	ACCELERATOR BOWDEN CABLE-L=675MM (from 09/80), Handlebar [RT]	1
32 73 2 324 956	CLUTCH CABLE – L=1520MM [RT]	1
32 72 1 451 975	CAP, Choke Lever Cover	1
32 72 1 457 081	CAM DISC – 42MM HUB 1ZÜGIG (from 09/80)	1
32 72 1 232 662	BUSH, Lever Pivot Pin	1
32 72 1 231 610	FELTRING,Cables	1
61 31 1 243 403	CLUTCH SWITCH	1
61 13 1 244 090	WIRING HARNESS, BRAKE LIGHT SWITCH, FR (from 09/80), Front	1

Install Right Side Perch Assembly

Here are the parts for the right side perch assembly.

I slide on the new perch with front brake master cylinder.

NOTE:
Older style perches, like the original one on this bike, use a serrated wedge that fits into a slot in the hole for the handlebar. But the newer style perch I bought does not use the wedge. See the later section about installing the left side perch to see what the wedge looks like and how to install it.

Install Right Heated Grip

I thread a piece of garden wire up the inside of the handlebar and pull it out of the hole in the center of the handlebar.  To make it easy to get to the hole I rotate the handlebar so the hole points up. I wrap the end of the wire around the heated grip wires and pull them through the handlebar and out the hole in the middle.

I wrap the end of the pull wire around the handlebar to keep the throttle tube on the handlebar until I got it engaged with the throttle cam and secured by the top cam cover.

Install Front Brake Light Switch On Perch

The right perch has a threaded hole for a small diameter front brake light switch.

The front brake light switch includes a thick washer that fits between the switch and the face of the perch so the plunger is the correct distance from the handlebar lever. I screw the switch with washer into the hole in the perch.

NOTE:
The pictures below show the washer installed on the switch. Your front brake switch may, or may not, need the washer, to operate correctly. On this bike, the washer pushed the plunger too far from the brake lever so the brake light was always on. I removed the washer, reinstalled the switch and the front switch worked correctly. 

This shows the switch configuration that worked on my bike without the washer.

I put a small dab of NO-OX-ID A Special grease on the spade terminals to prevent corrosion and then attach the spade terminals on the new front handlebar brake light switch sub-harness to the switch terminals. I push the rubber boot up over the switch body and apply a little smear of silicon seal where the wire entered the boot to keep water away from the switch terminals.

Install Throttle Cam

The throttle cam fits on the hub inside the the cam housing on the top of the right perch. The cam teeth point down. I grease the teeth with wheel bearing grease and put it on the hub.

Different Size Throttle Cam Holes

The earlier version of the perch that came on my bike has an 8 mm hub for the throttle cam. Therefore the perch, cam and throttle cam cover are different than the new version so I had to get the throttle cam with the 15 mm hole for the hub and could not reuse my existing throttle cam. 🙁

Install Throttle Tube and Throttle Cable

There are alignment marks on the top of the throttle cam and on a tooth of the throttle tube. The mark on the throttle tube should be across from the line on the top of the throttle cam.

When I they are aligned, I insert the small nipple on the end of the throttle cable into the slot on the end of the throttle cam and attach the throttle cam cover so the lip on the bottom of the cover engages in the groove on the throttle tube.

Install Right Handlebar Switch Assembly

The right side switch assembly attaches with a screw to the underside of the body of the perch.

Finally, I install the throttle lock screw and tighten the Allen pinch bolt to secure the perch to the handlebar.

Install Left Side Perch Assembly

Here are the parts for the left side perch assembly.

The perch, handlebar lever and choke lever need new paint.

Paint Left Perch Parts

I stripped them using my bead blasting cabinet and painted them using flat matte black brake caliper paint.

I put screws into the threaded holes in the perch to keep paint out of the threads when I paint the perch. After the paint dried for 24 hours, I baked the perch, and the clutch and choke levers in the oven for an hour at 200 F to harden the paint.

I screw the clutch cable adjuster into the perch.

The left side perch uses a serrated wedge to keep it from twisting on the handlebar. It fits in a notch inside the hole for handlebar and is centered over the pinch bolt. The bottom of the wedge has “V” shaped notch that clears the shank of the pinch bolt and keeps the wedge in the slot in the perch.

I slide the perch with the wedge inside onto the handlebar and snug up the perch pinch bolt to keep the perch from sliding off the handlebar but loose enough that I can easily rotate the perch on the handlebar.

Install Left Heated Grip

I use a pull-wire to pull the heated grip wires through the handlebar and out the hole in the center of the handlebar as I did for the right side heated grip. The left side grip is secured to the handlebar with two small Allen bolts that fit into threaded holes in the ends of the handlebar spaced 180 degrees apart.

I roll back the end of the rubber grip to expose the holes in the grip.

After I screw in the two Allen bolts, I slide the perch down to meet the grip and roll the edge of the grip back into place so it covers the screws.

Install Clutch Switch

The clutch switch attaches to the left perch with a small screw. When the clutch lever is pulled in, the switch closes and allows the starter motor to spin the engine even if the transmission is in gear. There is a small ridge on the side of the switch housing that the circular lock ring on the clutch adjuster butts up against when the ring is tightened to lock the adjuster helping to secure the clutch switch in the perch.

NOTE:
Although I show installing the clutch switch with the perch mounted on the handlebar, it is much easier to install it with the perch off the handlebar. I recommend doing it that way as it is easy to cross-thread the small retaining screw that holds one side of the switch in the slot in the perch.

WARNING:
When I tested the electrical system I found that the clutch switch was not correctly seated in the slot in the perch because the case was too wide to allow the switch to seat fully. So the switch was closed all the time. This means the stater motor can be energized with the bike in gear and the engine running while the clutch lever is not pulled in. This is dangerous as accidentally hitting the starter button with the motor running can cause the starter motor Bendix gear to engage the flywheel teeth breaking the flywheel teeth and starter motor. 

I sanded the side of the switch using 150 grit paper until it slide all the way down into the slot in the left handlebar perch.

 

Install Choke Lever and Cable

Inside the choke lever housing is a semi-circular cut-out that holds a small plate with holes that catch the ball bearing in the bottom of the choke lever. The holes index the choke lever at two positions-fully closed and partly closed.

I put some wheel bearing grease on the bottom of the choke lever to lubricate it.

The choke cable slides through a slot in the side of the perch. The choke cable nipple fits into a hole in the bottom of the choke lever. I put some wheel bearing grease on the nipple to lubricate it and install the choke lever on the hub inside the choke housing.

A special washer with tabs and a large screw secure the choke lever to the hub. After I tighten the screw, I snap in the new choke lever cover into the hole in the lever.

Install Clutch Lever and Cable

The clutch lever is installed in the perch with a pivot bolt, wave washer and special lock nut. The hole in the lever for the bolt receives a nylon sleeve the bolt slides inside of. This keeps the bolt from wallowing out the hole in the lever and allows the lever to move freely when the pinch bolt is tightened. I install a new sleeve but it’s a very tight fit. I have to use a round file to remove a small amount of material from the hole in the nylon sleeve to get the pivot bolt to slide through it.

The clutch cable nipple fits into a barrel-shaped retainer that slides into a hole in the bottom of the clutch lever. The barrel rotates in the hole as the lever is pulled to avoid kinking the cable. I lubricate the barrel and the inside of the hole with powdered molybdenum disulfide. Since it’s a dry lubricant it doesn’t attract grit and dirt and it plates the surface of the barrel and hole lubricating them.

I install the felt on the inner clutch cable to keep grit and dirt from getting inside the housing. The felt is split so it can slip over the cable. It fits inside the clutch cable adjuster.

After I install the clutch cable in the clutch lever, I secure the clutch lever in the perch with the pivot bolt, wave washer and special locking nut.

Install Left Handlebar Switch Assembly

The left side handlebar switch assembly attaches to the underside of the perch with a screw. After I install the switch assembly I secure the left perch on the handlebar using the Allen pinch bolt.

Here is the left perch assembly installed on the handlebar with the clutch switch, choke cable and clutch cables installed in the perch.

Adjust Clutch Cable

I adjust the clutch cable with the handlebar adjuster. I want the length of the inner cable to be 201 mm between the rear of the transmission housing casting and the front of the barrel that fits into the clutch throw-out arm on the bottom of the transmission. I use a piece of coat hanger I cut to 201 mm to set the distance.

When the inner clutch cable distance is correct, I adjust the free play at the clutch handlebar lever. I tighten the locking ring on the handlebar adjuster until is snug against the tab on the side of the clutch switch in the perch. Then I loosen the locking nut on the rear of the transmission and tighten the bolt until there is no free play at the handlebar lever. I back the bolt out until I get 2-4 mm of free play and then tighten the locking nut on the rear of the transmission.

Handlebar Cables And Wires Routing Video

Here is a picture of the handlebar perches with the cables and wires installed on the handlebars.

This video shows how I routed the handlebar wires and cables.

VIDEO: 1983 R100RT Handlebar Cables And Wires Routing

Revisions

2020-07-27  Add note about front brake switch washer affect on switch operation.
2020-07-29  Add warning about ensuring clutch switch fits correctly in slot of left perch.