JAP JOR 500cc Hi-cam TT Rep Race Engine 1936

Engine No. JOR/V 47488/S

In 1934, JAP developed the hi-cam race engine in a last ditch effort to remain competitive at the Isle of Man TT. JAP retained OK Supreme to provide the rolling chassis for their 350 and 500 machines. Three in each capacity were built. HRD (Vincent) was also provided with 3 engines for the 500 race. Unfortunately, all failed to finish.

The following year, HRD was provided with another 3 engines modified with twin carb, twin spark heads. 1935 was also the first year of HRD’s own engine which performed slightly better than the JAP engines.

From 1936 to 1938, Zenith offered a C5 Super with JAP Hi-cam TT Rep engine which was based on these ’34 engines. Few must have been sold and none survives intact. No other English manufacturer offered a model with these hi-cam JAP engines. Individuals could order these engines direct from the factory.

The only other engine I know of this type is fitted to an OEC racer that was in Australia. It hasn’t been seen in recent years.

There is some information about these rare engines in Jeff Clew’s excellent JAP: End of an Era, pages 158 – 168

This engine has a 1936 date stamp. It has an iron head and therefore could only for a 1936 Zenith C5 Super. In first appeared in the 1936 Zenith catalogue, listed as the C5 Super: the top-of-the-range 500. Below is an excerpt from the catalogue which states: “Engine: 80mm x 99mm, 498cc J.A.P TT REPLICA, steel flywheels, massive bearings, cylinder well spigotted into crankcase, ball journal camwheel bearings, Dural connecting rod, fully enclosed valves, automatic lubrication to pushrods, rocker gear and valves. Adjustable oil by-pass to cylinder”.

The engine appears in good general condition. The fasteners are all in very good order indicating it has not been butchered. I have lifted the cylinder head and as you can see, it has new valves and a new high compression piston (81mm bore) fitted. The inner timing cover has been cut and professionally repaired. With the magneto and outer cover fitted, the repair cannot be seen. The condition of the timing gears, cams and cam followers indicates very little use. It has also been rebuilt since it last ran. Although externally similar, these engines differ greatly from JAP’s hi-cam road engine which have a single pushrod tube, cast flywheels, timing side bush and much lower spec internals.

I know of 3 racing JAP engines sold in recent years. In May, a 250 with unknown internals sold for over $8,000. Two years previously an incomplete circa 1933 500 engine sold for over $11,000 and last year a 1931 350 in as excellent condition sold for a tad over $11,500.



This entry was posted in Parts. Bookmark the permalink.