46 BMW 1977 R100RS Check If Frame Is Bent

Evidence Frame May Be Bent

There is significant damage to the front top center panel that goes around the headlight shell and the top fairing bracket tab that is bolted to the steering stem is sheared off. That makes me wonder if the frame is bent.

Top Center Headlight Panel Damage

Top Center Headlight Panel Damage

Top Center Headlight Panel Damage

Top Center Headlight Panel Damage

Broken Top Fairing Bracket Plate

Broken Top Fairing Bracket Plate

Broken Top Fairing Bracket-Tabs Securing Plate Torn

Broken Top Fairing Bracket-Tabs Securing Plate Torn

There are ways to check if a frame is straight that do not require a jig. Here is a good reference.

I decided to call a friend of mine who retired after being a BMW mechanic for many years to find out how he checks a frame for being bent. He offered to let me borrow a frame jig that he has. Cool beans, access to special BMW tools. 🙂

Frame Jig

I picked up the frame jig which consists of four parts: a steel frame, a steering stem steel rod with a locking nut, and two locating pins with graduated markings that fit into the rear of the jig and align with the swing arm bushings.

Frame Jig Frame, Steering Stem Rod and Locking Nut

Frame Jig Frame, Steering Stem Rod and Locking Nut

Pins Locate At Swing Arm Bushing

Alignment Pins Point At Center of Swing Arm Bushing

Graduations on Swing Arm Bushing Locating Pins

Alignment Pin Graduations Used Keep Jig Legs Parallel to Steering Head

Font End Removal Before Installing Frame Jig

I need to remove the front end of the bike. I previously removed the body panels, wheels and fenders for repair and painting and you can read how I did that here.

With the body panels removed, I remove the brake calipers, the Telefix fork brace and fender bracket, the lower fork sliders, the control perches, the handlebar grips with their wiring for the heating elements, the handlebars and mounting brackets, the steering damper, the top clamp and finally, the steering stem. This work is similar to what I did on the R75/5 tear down and when I replaced the fork seals on the 1983 R100RS forks. You can see how I did this work here:

Here are some details of this work on the 1977 R100RS.

Remove Disk Brake Calipers

The front calipers on the 1977 R100RS are ATE units and are secured with an eccentric pin. I remove the rubber cap and the nut with enclosed spring to expose the eccentric pin. I use an 8 mm bolt and catch a couple threads inside the eccentric pin so I can pull on the pin while wiggling the caliper back and forth to free the pin.

Using 8 mm Bolt to Pull Caliper Eccentric Pin

Using 8 mm Bolt to Pull Caliper Eccentric Pin

Caliper Eccentric Pin with Puller Bolt

Caliper Eccentric Pin with Puller Bolt

Remove Fork Brace

The fork brace on the 1977 R100RS is a Telefix. It’s secured by several bolts. Then the stock fender brace is removed from the fork sliders which frees the lower brake line brackets from the lower fork sliders.

Telefix Fork Brace Parts

Telefix Fork Brace Parts

Telefix Fork Brace Close Up of Orientation

Telefix Fork Brace Close Up of Orientation

Telefix Fork Brace Cross Brace Bolts

Telefix Fork Brace Cross Brace Bolts

Stock Fender Brace

Stock Fender Brace

Fender Brace Brake Line Bracket Mount Details

Fender Brace Brake Line Bracket Mount Details

Remove Lower Fork Sliders

The lower fork sliders on the 1977 R100RS attach the same way as the R75/5 sliders. The damper rod secures the lower fork slider with a 10 mm nut on the end of the damper rod. I like to use my cordless impact driver to remove the nuts.

Cordless Impact Driver

Cordless Impact Driver

Using Cordless Impact Driver to Remove 10 mm Damper Rod Nut

Using Cordless Impact Driver to Remove 10 mm Damper Rod Nut

Lower Fork Sliders Removed

Lower Fork Sliders Removed

Remove Heated Grips

Another difference is in removing the handlebar grips since this 1977 R100RS has heated grips. My handlebar on/off switch was relocated to the lower left sub-frame mounting bolt and a splice was placed in the wiring to that switch. I had to cut the wires of the splice so I could remove the wires with the handlebar grips as the wires are routed inside the handlebar.

Heated Grip Wiring Goes Inside Handlebars

Heated Grip Wiring Goes Inside Handlebars

Heated Grip Wiring Splice to Relocate On/Off Switch

Heated Grip Wiring Splice to Relocate On/Off Switch

Heated Grips Have Wires Inside Handlebars

Heated Grips Have Wires Inside Handlebars

Heated Grip On/Off Switch Harness with Part of Splice

Heated Grip On/Off Switch Harness with Part of Splice

Remove Handlebars

As shown in the R75 write-up, I remove the handlebar mounts, the instrument bracket and the handlebars.

Instrument Cluster Bracket Location on Bottom of Top Plate

Instrument Cluster Bracket Location on Bottom of Top Plate

Instrument Cluster Bracket with Rubber Bushings

Instrument Cluster Bracket with Rubber Bushings

This exposes the top steering stem nut. I remove it and the top plate.

Remove Steering Damper and Steering Stem

The R100RS has a hydraulic steering damper. The damper is attached to two pins–one on a bracket mounted to the frame and the other on a plate mounted to the bottom of the lower triple clamp–with a wire clip to secure each end of the damper to a pin. Once I remove the wire clips I pull the damper off the pins. I remove the two Allan head screws that secure the damper adjustment housing on the bottom of the bottom triple clamp and remove the cover with the internal rack gear, locating pins and springs. Be careful as the springs can sprong quite a distance if the pins come out of the bracket.

Inside the Fork Damper Box on Bottom of Lower Triple Clamp

Inside the Fork Damper Box on Bottom of Lower Triple Clamp

I use a plastic hammer to drive the steering stem down and out of the steering head. I support the lower triple clamp so it doesn’t crash to the floor when the steering stem comes loose.

Steering Stem with Lower Triple Clamp and Bearings

Steering Stem with Lower Triple Clamp and Bearings

Install Frame Jig & Measure Straightness

After I remove the steering stem, I remove the carburetors so the legs of the frame jig can fit next to the swing arm pivots.

Now I can install the front end of the jig in the steering head.

Frame Jig Orientation & Steering Stem Bar With Round Nut at Bottom

Frame Jig Orientation & Steering Stem Bar With Round Nut at Bottom

Steering Stem Bar Installed

Steering Stem Bar Installed in Steering Head

Frame Jig Installed In Steering Stem

Frame Jig Installed In Steering Head

I secure the jig to the steering head by tightening the round nut on the bottom of the rod to snug the jig tightly to the steering head. I check that the jig is solidly mounted in the steering head and does not move when I push on the jig.

I insert the two swing arm locating pins into the holes at the rear of the jig next to the swing arm bushings.

Pin Inserted In Rear Hole of Frame Jig

Right Pin Inserted In Rear Hole of Frame Jig Aligned with Swing Arm Bushing

I orient the right pin so it fits inside the swing arm bushing and is centered.

Right Pin In Swing Arm Bushing

Right Pin Centered In Swing Arm Bushing

Then I adjust the right and left pins so that the distance on the graduations on the pins is equal distance from the inside of the jig leg.

Left Pin Offset

Right Pin Offset

Right Pin Offset

Left Pin Offset

When I am sure the two pins are at the same distance from the inside of the jig frame, I look at the left pin to see if it is exactly in the center of the left swing arm bushing. It’s about 2-4 mm off center toward the rear.

Right Pin In Swing Arm Bushing-Off Center 2-4 mm

Left Pin In Swing Arm Bushing-Off Center 2-4 mm

This is a minor deviation and does not indicate that the steering stem nor frame spine tube are bent. GOOD NEWS!!! 🙂

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