OK right rear 850pxOK right front 850pxOK left rear 850px

Eng No. POH/O 59674/S

Extremely rare High-cam JAP engine based on 1935 works engines as fitted to TT Cottons, HRDs and OECs. The production versions were a last ditch effort by JAP to win custom from the smaller British manufacturers who were turning away from traditional outmoded JAP powerplants to Matchless.

So it was a modern engine with bolt-through cylinder, down daft carb and internal two-way oil pump. They reached the market in 1937 and were fitted to upmarket Cotton and OK Supremes machines as standard and other marques such as Montgomery and Coventry Eagle only by special order. To quote from JAP themselves. Valves, rocker gear and short push rods are fully enclosed, oil passing up from the rear off-side cylinder head stud which is drilled internally from the crankcase to a central standard in the rocker gear. From this point it is distributed to each rocker by a T pipe, the oil draining back to the crankcase through the single push rod tube that gives the appearance of the overhead camshaft design. The camshaft is chain-driven from the end of the mainshaft, a Weller tensioner keeping chain tension constant. The crankshaft is mounted on a roller main bearing on the drive side, and on the timing side a pressure-fed bronze bearing bush. The caged bigend bearing is fed under pressure from the dry sump lubrication system. Cylinder head and barrel is cast iron with single exhaust port and downdraft inlet port. In addition, the head is designed so there is a large air space between the valves and under the enclosed rocker gear. Reputedly reconditioned and external appearance suggests this could be so as nuts and bolts are in good nick which I consider to be a fairly accurate indicator of general condition. Crankcases in perfect condition. Chrome is great but some minor damage to the cast-in rockerbox (see pics) and very minor fin damage. The original Amal carburettor and float bowl which came with the engine are included. Magneto sprockets and chain are missing. These engines are extremely rare and desirable


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