Elaine's 1950 BMW R51/2 Restoration Journal Page 2

Here is the new, rebuilt crank. Vech asked Ed Korn to install later model, R50 rods with 20mm wrist pin bushings so we can use R50 pistons for more compression, more power. During the first few seconds of starting a newly-built engine, there's no oil because it hasn't had time to distribute throughout the engine. Vech makes sure that expensive crank assembly is protected by forcing oil into the crank assembly before installing it into the engine case.

Vech heats the case to expand it and to install the crankshaft with rear main bearing on it. You should have seen Vech's eyes when he realized the flywheel wasn't marked. No matter how big his eyes got, he couldn't see a mark on the R51/2 flywheel. Nope, not one mark. He quickly figured out "OT" (top dead center) by playing with the rods. He found a spare R51/3 flywheel and compared it to the R51/2 flywheel. They are the same diameter. After matching the two "OT"s he was able to mark the R51/2 flywheel by copying the marks on the R51/3 flywheel for "S" (idle) and "F" (full advance).

Show you the money!? Here are my perfectly new 344-degree sport cams. They are a reproduction part available from Bench Mark Works and manufactured with the approval of BMW Mobile Traditions.

The original timing chain and sprockets are the old, pin-chain type. Pin chains have a nasty habit of sometimes seizing during operation. This wrecks the cam gears and can possibly even break the case. Vech arranged a mechanical improvement with machinest, Bob Davis of Mountain Home Machine Shop. Vech asked Bob to machine off the original sprocket teeth and replace the teeth with new roller chain sprocket teeth. Those are the old sprockets in the photo and the new teeth are installed. The new teeth allows the use of modern roller-type chain which is less expensive and which should give advantages, such as a quieter engine and less need to adjust the chain.

I ended up with five cylinders, but all of them had broken fins. Vech chose the two best cylinders. He chose the worst cylinder and used duck-bill vice grips to break two fins off the bad cylinder. We sent the good cylinders and two cylinder fin pieces to Bore Tech. Bore Tech will repair the broken fins, bore the cylinders and impregnate them silicone carbide. The pistons are original 69mm Kolbenschmidt AG Germany.

The R51/2 has a pre-war type oil pump. After Vech installed it, he tested the movement of the engine and the cam was jamming on something to do with the oil pump. It took quite awhile of examining various oil pump shafts until he spotted the problem inside the shaft hole. One of the screws that retains the front cam bearing in the block was too long. It protruded too far inside the oil pump shaft cavity near the cam. This caused the oil pump shaft to jam. It was a matter of installing a shorter screw and we were in business again.

The R51/2 has a very long and narrow oil pan. Vech always adds extra magnets to oil pans. The wear of the engine is metal (magnetic) and a lot of it sticks to the magnets rather than finding its way into the oil slingers. All pre-1970 BMW motorcycles have oil slingers in one form or another. They must be cleaned as part of their maintenance. For more information, read this article about Earles Fork motorcycle oil slingers. The principle is the same for all other pre-1970 BMW motorcycles.

The BMW R51/2 engine is twin-cam with chain. In the photo, you can see see the difference between the new sharp-pointed pin chain sprocket teeth installed in the engine vs the old, squared-off teeth on the sprocket in Vech's hand. We haven't tested the sprocket idea yet, but as soon has he heard the idea, our motorcycle racing friend, Norbert Nickel, ordered similar sprockets for his R51/2 racing machine.

We have a complete gasket kit from BMW Mobile Tradition, but a gasket was missing. Maybe R51/2 motorcycles never had a gasket on the oil pump, but Vech wanted one there. He took a ball peen hammer and quickly crafted a paper gasket. Not until I met Vech did I know what a ball peen hammer was for -- making gaskets! He taps the small ball part of the hammer into holes to cut the gasket perfectly. He taps the larger head of the hammer around the outside of the part to cut the gasket smoothly around large, outside edges. It's fun to make gaskets. Sometimes Vech and I quarrel over the hammer and about who gets to make the gasket. Maybe the truth is that I think it's fun and Vech thinks he does a better job.

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