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 in 1969 are what I call the "new" style cylinders. This applies
to all twins from 1955 through 69. I can't remember if it also applies to the
singles. Maybe someone can tell me and I will include the info here.
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 provide enough splash for the right side and
seizures, or collapsed pistons are common. In about 1960, someone help me here,
BMW added oil pressure lubrication to both cylinders. The problems caused
by lack of lubrication were solved.
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 isn't hard to do and is a
great upgrade.
The problem comes in when one tries to use an "old" style cylinder on an
"new" engine case with the hole for oil pressure. The shape of
the old cylinder base is such that the oil pressure hole won't be covered and it
may leak badly.
The gaskets for the two styles are also different. The original gaskets were
all 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 a two photos to show the differences.
New
old
New style cylinder photo supplied by Lonnie Walker, thanks.
The cylinder on the left is the new type and the one on the right is the old
style. 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 the new style. See the three holes? Only two
are used, but with three, it doesn't matter which way the gasket is installed,
it has no "front" or "back." The gasket on the right is the old style. See the
difference in shape of the coverage? One of the two outer holes in the new
gasket will have oil pressure. If the wrong gasket or cylinder is used, it
will leak badly.
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