Memories are made by emotions, good or bad these memories are usually accompanied by a smell, taste, song, place, or thing, and it will follow you for the rest of your life. This 1978 BMW R100S resto-mod is happening at a very special time in my life... she will feel many of my emotions during her resurrection.
Last year (2014) Joshua Buck of Partshaus, Long Beach rang me up and told me about a 1978 BMW R100S in his possession. It had been sitting in a independent BMW repair shop for a few years, tucked away in the corner because her owner couldn't fork up the money to get her fixed. She was tired, her cylinders needed boring and heads needed to be reworked. The frame had been spray-painted at one time in her life to cover up some minor bondo work on the the front frame tubes, most likely the previous owner at one time had cylinder guards on her. The "S" fairing was long gone and the seat was a Denfield /7 model with a secret compartment for a medical kit. The paint had deteriorated away by the California sun, the front axle was stuck, front rim was bent, and the valuable speedometer looked like an empty shell. Nothing was good about it, but I wanted this 1978.
To each his own, as of now, I believe if anyone is going to restore an airhead, it should be a R75/5, R90S or a R100S. These airheads in my opinion holds the most intrinsic value out of the 70's airheads, maybe when I mature more I'll get my hands on a RS later on. The idea for this R100S rest-mod is for her to accompany her sister bike, my 1976 BMW R90S. The R90S build stays more in line with era correct OEM components, while this R100S will borrow a few key OEM components from 1981-1984 airheads; forks, clutch, gearbox, and swingarm. Of course these mating preferences have been done countless times before my time, but it was the next step for me to pursue. Time to get the rolling chassis up.
Starting with the front-end and frame first. New BMW steering head bearings are installed on the triple-tree. I usually put the triple tree in the freezer first so the bearing will slide down easier on the stem. Using a pipe you can either press the bearing down or use a rubber mallet to perform the same task.
My past builds always had a BMW center-stand to prop the frame up, however for this build I may be using a custom center-stand. The bearings inner-races on top and bottom of the steering head are installed first. It's easiest when done on the floor. If you powder-coat the the frame and subframe, be careful during installation of the subframe. It's best to install the bottom of the subframe first, screw it in lightly and then attach the top, this way you will not damage the powder coat on the frame.
A 1984 BMW R100 swing-arm will be used for this build. Heavier and bulkier, it was recommended by a BMW builder when I was searching for a swing-arm brace.
A 30mm socket helps to press the bearings in.
Its a good idea to put the drive-shaft boot on the swing-arm first before installation.
A 33/11 final drive is being used here. Most 33/11 came standard on R90S' and 32/11 came standard on R100S'. However, I think there was an option from the factory to choose either one for your S-Model. If I can time travel I would go to a BMW dealer and make sure of this and get it in writing, because its only hearsay from BMW old-timers, and old-timers argue over these things. So I'm not going to get into it. I have heard that in Europe, R100S & R100RS came with 33/11 final drives.
This 33/11 final drive was a spare that I found during one of my BMW picks. I do not remember where I got it though. The crown gear teeth as you see here have been re-splined the correct way. (Contact me if interested in re-splining or rebuilding your final drive) The final drive is the most robust part of the twin-shock airheads, you almost never have to change the bearings unless you were very irresponsible. Both crown and pinion gear seals have been replaced.
Front-end is from a 1984 BMW R100. I wanted to go with dual Brembo calipers instead of the ATE calipers this R100S came with. At first I wanted to convert the wheels to spoke wheels, then realized the hassle and cost that followed. I had to justify my thinking, telling myself the R90S already had spoke wheels. Snowflakes aren't bad, I think it makes the bike look more aggressive... I'm justifying the situation again. Rubbers are Bridgestone BT45's, these treads don't follow the grooves on the freeway as much.
Work Performance Springs accompanies the front-end. (contact me if interested in Work Performance Springs)
Ohlins performance shocks are used in the rear. So far I am enjoying the golden-yellows on my R90S. (contact me if interested in Ohlins Performance Shocks)
Rotors are from EBC, fair price for the build, but I may try Spieglers rotor services next time. Both front and rear axles are stainless, even the axles spacer on the front wheel is stainless, these two components oxidize the fastest when using OEM plated versions.
In my opinion, during a restoration, it's best to purchase the master cylinders new instead of rebuilding, unless the master cylinder is in above average condition. The brake fluid really goes after the paint and by the time you clean, repaint, purchase rebuild parts, you might as well save some time and purchase it new. Sell the old one on ebay.
Tommaselli clip ons are used for this build.
To be continued.