1974 R90S Project

November 1 2005 – I purchased a 1974 R90S as a winter project. Many years ago the bike suffered a hit to the rear. This damaged the rear sub frame and fender. This is why the bike is now sporting a fender from a Japanese motorcycle. Also the front fairing is an aftermarket version (Luftmeister). It looks like I will need a few parts to take the bike back to it original state. The following photos show the condition as the bike as I received it. The bike has 55k miles on the odometer. I think the engine may be seized as one sparkplug was out and the bike was outside. I can only assume some water has gotten into that cylinder. The serial number on the engine, ID plate and frame match (4071024). According to BMW archives this bike was built in November 1973 (they state this makes it a 1974 model). From a book I have, this is a European model (not U.S.) because of the serial number. The speedometer reads out in M.P.H., so I don’t really know the differences in the two models at this time.

The fairing is coming off – Anyone interested in it. It needs some love, I do have a windshield.

Both valve covers are damaged and need replacement. I think the front cover was painted black (not that way originally)

Here is the damaged instrument cluster

Note the wrong exhaust, rear fender, and seat.

This is the damaged sub frame. I will probably replace it.

Wrong handlebars

I have two side covers, both need work.

The clock and voltmeter are in the pods to the side of the main cluster. I don’t know if there is a place that reworks these, or if I will have to replace them.

November 5 2005 – Today I started to remove the non-original parts. The fairing, exhaust and rear fender came off (all now reside in the dump). I drained the engine oil. It was black, but no evidence of water (which is great).

November 13 2005 – Today I stripped most of the parts off of the engine to determine the cause of the binding in the engine. The transmission, flywheel, and all electrical components were removed. I can only move the crankshaft slightly side to side. Maybe there is some timing gear damage?

I still have not found the source of the binding, but I did find a lifter that was damaged.

November 14 2005 – I have discovered the source of the engine binding. The screws that secure the camshaft into the engine case had worked loose. They extended into the holes of the camshaft timing gear locking it in place. This also allowed the camshaft to float forwards which I believe is the cause of the broken lifter. The chain is loose and has worn away some metal on the crankshaft bearing holder. Also the timing gears are worn. This is evident from the nice shiny worn patterns on the teeth. The good news is that this area was nice and oiled. No rust and muddobber nests (which is what I was expecting).

December 4 2005 – I have gotten the engine torn down all the way. The loose screw above damaged the screw hole, so it was drilled out and helicoiled. I am in the process of cleaning up all of the engine parts. I have sent the heads and cylinders off to get them reworked. The photo below shows the new rear subframe, R90S seat, and rear fender fitted to the bike. The general plan at this time is to finish the engine before I start working on the other components. I will continue to accumulate the missing parts.

December 23 2005 – More body parts arriving. Here is a photo of the bike with its new seat cowl, grab handle and stop lamp. I have two sets of aluminum blinkers on the way. I also have gotten a new primered fairing. I am waiting on the brackets to mount it. But before I can do that the incorrect handlebars have to be removed as they interfere with the mounting. Body parts from different bikes are coming together to put another old BMW back on the road.

January 5 2006 – Here is a photo of the bead blasted engine. I am now ready to start reassembly of the engine. I just need to buy a few parts now. Notice to the right there are three of the four blinker housings polished up and ready to go.

April 5 2006 – I just got my clock, voltmeter, speedometer and tachometer back from North Hollywood Speedometer (818-761-5136). I had new bezels and glass put on the clock and voltmeter. The tachometer and speedometer were overhauled and a new correct tachometer face was installed. I was fortunate that the speedometer face was in good enough condition to be reused as no instrument service shop has the correct face. I have to say I am pleased with the way everything turned out. Having the instruments reworked was expensive. I shopped around a bit and found that North Hollywood had the best prices by far. I now have to focus on getting the housing ship shape. My housing is in bad shape with the tachometer glass broken. Apparently nobody can crimp on a new glass. A housing with the correct “O” text for neutral is not available, so I am going to have to decide what to do. I may order a later model replacement housing and see if I can get “NEUT” removed and “O” cast in its spot.

Ocotober 1 2006 – I have done quite a bit of work since my last update to the website. The engine is rebuilt, the carbs are rebuilt and I am getting ready to start the transmission. So here are the details of what has transpired. Here is a shot of the breather valve.

The parts on the right are the old breather valve parts. These tended to cause a turkey call emitting from the engine when worn out. The part on the left is a newer reed type breather valve from later model R bikes. This makes a nice upgrade.

The old breather valve is removed by chiseling out the body. I have also drilled a small oil drain hole down in the bottom of the breather chamber. You can see it in the upper right corner (in the breather chamber bottom). Oil tended to pool in this area and could blow out of the breather tube into the air filter area. This hole allows the oil to drain back into the engine housing.

Right above where the tip of my finger is where the drilled hole enters the main engine chamber.

Here is the new reed valve tapped into place. You have to watch the orientation of the valve when you install it. The cover that goes over it will only fit if the reed is in the right position.

Here is the crank, rods, new pistons and various other engine parts ready for reassembly.

This photo shows a couple of new holes drilled in the crank during the balancing process

Here is another photo showing the balancing holes.

This is a photo of the front of the engine assembled. New timing gears, new timing chain, as well as other parts.

Here is a photo showing the new oil pump gears. These are the later model that do not have a woodruff key, but have the flat spot. This required a new camshaft as well.

Here is a photo of the oil pump cover. I also used a later model cover that uses attaching bolts instead of the phillips head screws of the original. This made assembly and serviceability easier.

When I was getting ready to bolt on the heads I noticed the gasket holes did not fit over these locater bushings (I am pointing at one, there are two per cylinder). After a couple of phone calls I found out that BMW had issued a bulletin instructing dealers to remove these. They apparently made it almost impossible to remove the heads in some cases. BMW no longer sells the old style gaskets that fit around the bushings – so out they came.

This photo shows the assembled engine. I only have to get the starter, and electronics mounted. On top of the engine are the rebuilt carbs. I have also mounted the pickup from the Boyer electronic ignition on the front of the camshaft.

I got a piece of angle steel and mounted it to the front of my handy lift. I drilled the appropriate holes and mounted up the transmission in preparation for teardown.

 Here is a rear shot of the transmission.

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