Jack Moore P6A engine


Hopwood | 500cc | Bracebridge Street | Burman | Twin cylinder | 16H/ES2 | 64mm x 77.4mm




Hello Sump People

Just read the interesting article about the Jack Moore Bike that was published ahead of the Salon Privé event in September [2020].

I can tell you from first-hand observation that when both engines were dismantled, prior to restoration, an amount of wear was noted in each which would equate roughly to 20 to 30 thousand miles of running.

The shaft-drive motor was the most complete of the two engines and appears to have started life as the basis for the in-line 350cc shaft-drive twin. This project does not appear to have got very far before a significant change to the plans for it resulted in a cross frame twin cylinder engine with a Burman gearbox bolted directly to the back of the crankcases as seen in post-war BSA motors. This gearbox having a bevel gear adapter converting it to longitudinal shaft-drive.
At the same time that this conversion took place the engine was bored and stroked (64mm x 77.4mm) to enlarge it to a capacity of 500cc.


The crankshaft of this shaft-drive engine is quite unusual in having steel con rods using crowded roller big-ends along with ball bearing mains. The factory records indicate a 16H frame was allocated to the shaft-drive engine but whether this actually was constructed as a roadworthy machine is not clear.

 It then appears to have been used by Bracebridge built into a small tractor chassis for pulling trailer containing castings around the site. Finally it was then was sent off to Trusty Tractors for consideration as an alternative power source in one of their farm vehicles.




Meanwhile a second Jack Moore engine was constructed, this time in the form of a conventional twin cylinder 500cc.

This second engine was very different internally, using a crankshaft similar in construction to that of the later Model 7 engine along with equally similar alloy con-rods. The stroke had been reduced to 73.5mm while the bore was increased to 65.5mm. Both of these numbers once again are very close to Model 7 engine dimensions.

It seems reasonable to assume that the second Jack Moore engine was used to test major components later used in the Hopwood Model 7 design. Likewise, the basic design of the Moore engine, using twin camshafts and gear timing wheels was later in the design of the lightweight twins a decade later. The Norton Navigator using identical pistons.

Both of the Moore engines have similar frame mounting points on their respective crankcases and these line-up with those on a Norton 16H/ES2 frame. The plans for the second engine was also inform (sic) that this was destined for an ES2 frame. However, as was found out the hard way, getting engine to clutch to rear wheel chain alignments was almost a 'road too far' requiring numerous modified fittings to achieve this.

The other major problem that probably condemned this engine as a non-starter is the number of oil seals required in the barrels and cylinder head. There are individual sets of three for each valve plus two external pushrod tubes all fighting to keep the motor oil-tight—the combination of steel, iron and aluminium plus heat making this near impossible. No wonder Hopwood went for integral pushrod tubes and a cylinder head with minimal joints.
Photographs show major chunks from both engines.

Phil Hannam
Norton Owners Club


Click here for the original Jack Moore story on Sump





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