BMW motorcycle cylinders
Old vs. New style /2 BMW motorcycle cylinders
This page is about the /2 BMW motorcycle models.
The cylinders used from 1951 up to about 1960 are the “old” style. From about 1960 to the end of 1969 are what I call the “new” style cylinders. This article applies to all twins from 1955 through 69.
The difference is in the lubrication of the pistons. BMW provided forced lubrication only to the left cylinder of the “old” style. It was expected for the crankshaft to “splash” enough oil onto the right cylinder to provide piston skirt oil. The crank does not give enough splash for the right side, and seizures or collapsed pistons are common. In about 1960, BMW added oil pressure lubrication to both cylinders. The problems caused by a lack of lubrication were solved.
It is possible and recommended to drill a hole in the case to allow lubrication to the right cylinder. A kit includes the template and a bit and instructions. You may borrow it if you are willing to pay the cost of shipping. Contact Richard Sheckler at firstname.lastname@example.org
The “new” style cylinders can be used on the older engines. They fit and seal perfectly. Still, no oil will be supplied to the right piston skirt. However, one can even drill a hole into the oil galley and get the lubrication to the right cylinder. This requires some knowledge, but it isn’t hard to do and is a great upgrade.
The problem arises when one tries to use an “old” style cylinder on a “new” engine case with a hole for oil pressure. The shape of the old cylinder base is such that the oil pressure hole won’t be covered and may leak oil badly.
The gaskets for the two-cylinder styles are also different. The original gaskets were paper. Later on, BMW went to the metal ones. I seem to remember that they also supplied metal ones for the “old” style cylinders. I think that the paper ones sealed better but were much harder to clean off after 15 years of use. I prefer the metal ones. I always use a very thin film of sealer on the gasket.
Here are two photos to show the differences.
New style cylinder photo supplied by Lonnie Walker, thanks.
The holes shown in the center of both are to return the oil from the valve cover area to the crankcase. Both types of cylinders have this hole. The crankcase is different, and the old-style won’t cover the holes in the case properly.
The metal gasket on the left is a new style gasket. See the three holes? Only two are used, but with three, it doesn’t matter which way the gasket is installed because it has no “front” or “back.” The gasket on the right is the old style. See the difference in the shape of the coverage? One of the two outer holes in the new gasket will have oil pressure. If the wrong gasket and cylinder combination is used, it will leak badly.
Updated 22 Oct 2019