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Restoring my 1974 BMW R90S 900cc motorcycle

6th May 2021, 19:08 by Chirag Moro

I started to drive away and he bicycled after me and begged me to take the bike. Those days, they threw cars and motorcycles at you and the market was flooded.

BHPian Indian2003 recently shared this with other enthusiasts.

I bought the bike in 1984 at the height of the financial crisis. The guy was desperate to get rid of it. I offered him 1400 euros but he wanted 3000. I started to drive away and he bicycled after me and begged me to take the bike. Those days, they threw cars and motorcycles at you and the market was flooded. The bike became mine for 1400 euros.

This is the first run video.

The bike was run down but started easily and sounded nice. He told me that he had repaired the gearbox. He did not know what bike he was selling. This is the mother of all superbikes and the first production bike that passed the 200 km/hour mark. German Hans Muth sketched this bike on a piece of paper in a hotel room in Amsterdam. The same guy designed the Suzuki Katana.

The bike certainly raised eyebrows when it was released. From being an "old mans" bike, here was a potent tourer with twin Dellorto carburettors. These Dellortos have an acceleration pump built-in. When you open up, about 2 ml of fuel is sprayed directly into the cylinder head. Many of these bikes were used for racing.

After a few days of riding, I heard a worrying clicking noise from the gearbox and I parked it and it stayed that way for 19 years. I was going through a divorce and hid the bike in a backyard shed. I paid for the bike and did not fancy her getting half of it. In those years, the previous owner tried several times to buy it back, offering me twice the price but I declined.

In 2004, I decided to put the bike back on the road and started the stripdown in my living room and later moved it to a motorcycle club. The bike was sandblasted primed and resprayed in the original Silver Smoke.

All the work other than the sandblasting and conversion of the cylinder heads for lead-free fuel were done in house by me. I made up a paint room with an old kitchen ventilator and started by trial and error. I painted the tank 4 times.

There is no chain on the bike and it is shaft driven. I replaced the bearing and seal and adjusted with shims. This is a first-generation drive with no damping on the driveshaft.

The bike had contact breaker ignition. This was replaced with a Silent Hektik digital ignition. This was made for the VW engines used in small planes. The 260W alternator was replaced with a 400W stator and windings hand made by Jeff Lee in Taiwan.

The total cost of the project is difficult to say but when I started, I had about 6000 euros. Some of this money went on a trip to Germany and telephone calls and shipping. Parts came from several sources from Germany, UK, Switzerland, the US and Taiwan.

On my first trip to Germany with the bike, the club there figured that I could ask for about 15,000 euros. This is because it is the first generation R90S with a very low frame number of 350. The engine has the same number. The bike was produced in October 1973. All castings have this date.

These are the tools I started with. Bought over a period of 30 years:

Bike in the living room. The engine and gearbox are out. The rest of the bike was dismantled here and sent off for sandblasting. It was easier to start work as soon as I returned from work:

The instruments were all rotten. There were many people following me online and a German dealer contacted me and said I was welcome to drop by and check out his stock of old parts. I bought a new speedometer and rev counter from them. They even got me the original enameled BMW badges as the old ones were damaged by airgun pellets.

All ready for sandblasting but he was drunk and sprayed res Rustoleum and messed it all up. I had told him that I wanted them in bare metal but he tried to hide his shoddy work with paint. I refused to pay him and finally I agreed to give a 6-pack of beer for his troubles. I later found out that he is hooked on alcohol and drinks on the job:

I was boiling when I saw this. It was holiday season and all shops were closing. A guy who makes gravestones was kind enough to agree to do it for me. Otherwise, It would have delayed me for 2 months or 3:

The black parts are sprayed jet black. They were primed with a 2-component etching primer. All paints used were from Standox:

For the pinstriping, I sprayed on a base gold colour and taped it with 3 mm masking tape. After the base colour was laid on, I removed the masking tape before the clear coat:

The tank was the first part that was ready. I practised my spraying skills on the tank. This was my fourth attempt. I laid on 6 coats of clear coat. It was then wet sanded with a 2000 grade paper to remove the mosquitoes and then polished with 0000 grade steel wool before being cut and polished:

The heads were converted for lead free fuel and both valves replaced with exhaust valves replaced with the sodium filled Swiss Intervalve:

Here the cylinders are painted and the steel pushrod tubes replaced with stainless steel tubes:

The bike has a dry clutch and appears similar in size to the VW Beetle clutch plate:

This is how the previous owner repaired the gearbox. He just put in some sawdust to get rid of the noise. He had prepared the bike for sale that way. The box was full of a thick grey porridge. I called the previous owner and he denied it. I asked him to come over to see the birch leaf I found inside and he went silent. He had just opened the cover and added sawdust. This is a common scam to quieten gearboxes and final drives:

Here I have emptied the gearbox into a sink for some cleaning. The plastic selector wheel was replaced with a ball bearing and all bearings replaced. The input shaft spring was broken and a toothed gear had radial cracks on it. I bought a used gearbox for parts and all bearings were replaced:

I took the cover from a gearbox and machined it to make a tool to shim up the bearings. I made this at a trade school. I know the teacher and he lets me use what I want there:

These are the tools I made to extract the output shaft from the gearbox. One to hold the shaft and the other to loosen and tighten the bolt:

I made this tool in ABS first to get familiar with the lathe to practice for the gearbox tool. This tool is used to press in a big oil seal on the clutch side of the engine: