Home arrow VMCA Newsletters arrow Volume 2, Number 2 - April 1, 2005 arrow R24 through R25/3 Cylinder Modification
R24 through R25/3 Cylinder Modification PDF Print E-mail
Written by BMWVMCA NEWS   
Tuesday, 29 July 2008

R24 through R25/3 cylinder modification: Lubrication           

Some time back, Mark Huggett described a procedure for modifying pre-R26 cylinders and cases to later  factory specs.            

It is probably common knowledge by now that the early singles were prone to over heating and piston seizure. BMW partially remedied this problem in the later R26 and R27 models by adding an oil passage via a small groove cut in the outside flange below the cylinder base. They also drilled two 1.6 millimeter holes on each side of the flange 180 degrees apart at the groove in order to allow oil to be fed directly to the piston skirt. To feed the groove, they drilled a three millimeter hole in the crankcase bore between where the groove would meet the case, and into the oil passage that feeds the upper oil gallery.           

Some of the oil is thereby fed to the piston skirt. By keeping the holes to a minimum, some oil is still forced up to the rockers and valves.           

The very early R24 and R25 models used an oil pump with 9 millimeter deep gears. Sometime between the R25 and R25/2, they changed the gears to 10 millimeter, which would cause the pump to increase the flow of oil. If you are in doubt about which gears you have, take the pump apart and measure them. This is a good idea, because you will also be able to measure the lash between the gears. It should be about .001” for a brand new pump, .002-.003” for a good pump within spec.           

Out of six pumps I have sitting on a shelf, all of them measure between .008-.013”. The gears all seem to be in fine condition, while the pump bores are worn out. I think they can be repaired by sleeving them. 


Last Updated ( Tuesday, 29 July 2008 )
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