website statistics

Shell Bearings Renewal


Many RM engines have been converted to take shell big end bearings and this may have been done by a previous owner. The current owner may need to renew these bearings and in some cases a crank shaft regrind will be necessary.  To assist in this the critical bearing data are given below however if you want to convert to shell bearings from white metal ones you will need the information contained in our Maintenance Notes CD.


1½ litre engines

The usual choice of shells for the 1½ engine are the ones fitted into the BMC “B” series engine of 1622 cc capacity which are sold under the Part Number B4357 which contains the full set of 8 shells. The shells are 0.995" to 1.005" wide so they cover the full width of the journal and the bearing material is white metal. In common with many shells fitted to BMC “B” series engines, the housing diameter will be bored to 2.0200" to 2.0205".


Assuming that the B4357 shells are being used, the correct size of shell must be selected to match the crank shaft. The “B” series big end journal has a standard diameter of 1.8759" to 1.8764" compared to the 1½’s standard size of 1.875". Thus the Riley standard size is approximately 0.001" smaller than the standard “B” series size. It is very unlikely that shell bearings will have been fitted without regrinding the journals so there is no problem in using the relevant “B” series journal diameter. To determine which oversize of shell to use for a direct replacement, measure the existing diameter of the crankshaft journal and select the corresponding shell size.


“B” Series Size (in.) Shell Oversize

             1.8759 to 1.8764     Standard

             1.8659 to 1.8664           + 10 thou.

             1.8559 to 1.8564           + 20 thou.

             1.8459 to 1.8464           + 30 thou.

             1.8359 to 1.8364           + 40 thou.

             1.8259 to 1.8264           + 50 thou.

             1.8159 to 1.8164           + 60 thou.


If the crank shaft needs to be reground it should be done to one of the above sizes and the appropriate shells used.


2½ litre engines

The shells most commonly used are those from the Bedford 200 cu. in. engine which are sold under the set Part Number B4424SA. The connecting rod will have been bored out to give a housing diameter of 2.5200" to 2.5205".


The standard Bedford journal diameter is 2.374" compared to the Riley’s 2.362". Thus the first oversize shell which can be used is +20 thou. The full range of sizes is,


Bedford Size (in.)          Shell Oversize

             2.364                   + 10 thou.

             2.354                   + 20 thou.

             2.344                   + 30 thou.

             2.334                   + 40 thou.

             2.324                   + 50 thou.

             2.314                   + 60 thou.


If the crank shaft needs to be reground it should be done to one of the above sizes and the appropriate shells used.


Bedford only list shells up to 40 thou. oversize although the larger sizes can be obtained with a little perseverance.


An alternative to the Bedford shell is the York Diesel shells as used in some Ford Transit vans and these are sold under the Part Number B6465SA. If these bearings are used the manufacturer’s recommendations for the journal size should be carefully checked.