Rolls-Royce 20/25 - fit block



fit block - n/s


At long last!  The new cylinder block attached to the crankcase.  The tappet retaining bridges have been installed and bolted down.  Until the head is replaced the block is only held in place by these 6 studs.

fit block - o/s


The standard gasket between crankcase and block is made from 0.006" gasket paper.  This joint is notorious for leaking, which is not surprising given the materials, sizes and the length of the studs.  A replacement gasket was cut from 0.030" gasket paper and installed using Wellseal.

Despite the apparent leap forward in reconstruction, the installation of the block took two people about 30 seconds.

oil pump drive bearing


Left: new - right: old.  The bottom bearing for the oil pump / distributor drive shaft.  The old item looks far more attractive but was worn well beyond its useable life.

governor pinion


At the top of the drive shaft is the drive pinion  and connecting spline for the distributor drive.  As can be seen on the right, the old item was very badly worn, having significant wear to the middle of the teeth as well as dishing on the outer edges.

The shaft, which sits in upper and lower phosphor-bronze bushes, should have upper and lower shims.  There should be no end float in the shaft although it should still be free to rotate.  The shims also act to adjust the backlash between the pinion and its drive gear from the water pump drive shaft.

The original shims were so inaccurate as to give about 0.050" backlash instead of the prescribed 0.002-0.003".

measuring up


Setting up a Dial Test Indicator on the top of the oil pump drive shaft t measure the end float.  The top pinion must be fitted and fully tightened before measurement.

lost motion


The bottom shim was fitted prior to measurement.  The remaining end float was 0.031".

Total slack was 0.138".  The shims were stoned down to get an exact fit and accurate backlash.

shaft fitted


New pinion in place and locked onto the drive shaft.

During set-up the whole assembly, including the water pump drive shaft, must be installed and removed several times.  Accurate measurement and meshing adjustment is the only way to ensure minimal wear and quiet running.