The Cylinder Heads

The series V111 Jupiter was the first to have forged Y alloy cylinder heads with penthouse shaped combustion chambers. The heads were permanently screwed and shrunk on to the top of the cylinder barrels, which were machined from steel forgings, a copper jointing ring making the seal. The lowest cooling fin of the head is a steel band which is shrunk on after the joint has been made.


I decided to make the model cylinder heads removable, for serviceability. Four pointed grub screws would lock the head against rotation from under the steel fin which would be screwed on rather than shrunk. A compressible ‘use once’ copper ring would seal the joint.    


The valve seats are screwed into the roof of the combustion chamber, the originals being of aluminium nickel bronze. I opted for EN 1A as this had proved quite serviceable in the Bentley cylinder heads.

 The fins were cut with the heads screwed onto a fixture clamped centrally on the rotary table on the sine table. 

 As the cuts in each position were decided all nine heads were machined without moving the fixture, despite the fear that any error would be repeated throughout the whole batch.

 The exhaust and inlet ports were made by drilling from all directions and finishing with a diamond burr. Very laborious but safe.

 The sine table and small rotary table were used to achieve the 30º tilt and swivel required for repeatable positioning during the numerous operations on the underside of the cylinder heads.






 The 40TPI threads to receive the valve seats were screw-cut in the lathe as seen below.
 The two fixtures for the attachment of the valve rocker unit have triangular platforms which bolt to the cylinder head. 

 Here they have been bored, reamed and skimmed in situ to ensure perfect alignment of the rockers over the valves.

The 36 valves are stainless steel. They work in phosphor bronze guides which were pressed into the heads.


Each valve has three springs supported, for concentricity, by grooved washers top and bottom.





 The steel valve seats were screwed and gently peaned in position.

 The phosphor bronze valve guides installed.

 The special valve seat cutter I had made for the Bentley was used again, running in the guides, to cut the 45º chamfers of the valve seats.