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Page 8                                      CHAPTER 8

                       MODIFICATION TO MOTORS = GREY

BLOCK = Choose an EJ or late EK block. These are best distinguished by a "B" for FB-EK or a "J" for EJ prefix. These blocks can be bored safely to 3-3/8 inches and some been bored to 3-1/4 inches or even 3-5/16 inches, the later giving a capacity of 163 c.i. The EJ block has the best oil flow in galleries, etc, and strongest main caps on grey motors most vulnerable point. Steel caps may be used but these require line boring. Main bearing strengtheners may be used but these are generally of little use. Unless you are going "Full House" the standard caps are OK.

FX-FC blocks are OK but can only be safely bored to 3-3/16 inches. Canadian blocks of early FXs were only good before the EJ block was made.


Use EK-EJ rods and crank as well in any modified block. If all rods are resized and checked and cranked trued and not ground to under .030 inches (thirty thou) no problems should occur.

Various cranks were adapted e.g. Dodge and Vauxhall but these required considerable machining as well as mods. To rods, etc.


If 3-3/16 inch bore is used for street use, flat tops are OK. If hi-domes are used the chamber height i.e. piston top to combustion chamber clearance must be checked. It is advisable, too, to cut a flame path across the top of the high dome piston so the crank can fire the mixture completely. Pistons are made in 3 inch and 3 and 4-ring configuration to 3-5/16 inch of 3 and 4 rings in all styles both flat top and high dome to suit all applications. If a cross flow head is used special pistons are made to suit the application.


Whether a modified, original or a cross flow is to be used is of crucial significance. A modified standard type head will give more than adequate results. Fitting larger valves e.g. Red motor valves, improve breathing immensely. Flow testing, port matching, machining, and polishing, shaving etc, to achieve proper flow. Compression ratio is raised by machining of the head surface - 30 thou to 120 thou, but the later requires high octane petrol.

Cross flow - whether Repco, Waggot or Dunstan were in standard form a vast improvement on the original. The Repco had hemi-combustion chambers, staggered rocker arms (same design as HRO Vincent Motor Bikes) needle like push rods, its own special exhaust and inlet, whether Webber, SU or injection Waggot was a chain driven double overhead cam engine. The head design was similar to a Repco X flow in combustion chambers, valves, etc. The head was used and developed for boats and speed cars, etc, and is seldom seen on streetcars. Waggot also produced a 7 bearing cradle for grey motors requiring a special crank.

The Dunstun Rotary valve head was a radical innovation in that is was a rotary valve head like motorbikes use. The valves never really successfully sealed so it never took off.

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