Technical Articles

a very sophisticated rigid Knucklehead—Part 1

REDGRAVE MOTORCYCLES was approached by a customer who wanted to build an up-to-date old-school custom bike, and although he wanted it built to a very high standard, he had no intention of entering it in the show bike circuit. The guys at Redgraves agreed to do the basic engineering work and supply all the components.

These days there’s a trend towards old school machines but with a little sophistication added, so what could be more appropriate than a rigid Knucklehead with a six-speed transmission, electric start and rear belt-drive. An engine capacity of 84 cubic inches was chosen as all out performance was not part of the brief; this combination will deliver a smooth running reliable engine with plenty of power to spare.

All the necessary parts were carefully selected from the inventory at Redgraves and thoroughly checked for their compatibility with each other. The basic components: a Knucklehead engine, a Spyke six-speed transmission, a Genuine Harley primary drive complete with outer chaincase and starter, 12 volt alternator electrics, and a super trick rear disc/brake and pulley assembly which will accommodate the rear belt-drive.

When the customer takes delivery of his bike, all the engineering and machining will have been completed; the owner will handle the painting and final assembly.

The concept. Bare bones mocked up with the four basic components: the frame, the engine, the transmission, and the rear brake assembly.

S&S Knucklehead crankcases as delivered from S&S with alternator left crankcase which will accept the very latest in 12 volt electrics. The card attached documents part #, serial #, bore sizes, deck height, pinion bearing diameter, and all the information a competent engine-builder needs to know. These crankcases are truly state-of-the-art, and although externally they are pure Knucklehead, inside is a different story with bulletproof construction and Evolution internals throughout.

These are the main bearings that S&S chose to use, the same bearings used by Harley for many years in their Big Twin engines. All the necessary hardware required to assemble the cases is included; any additional fasteners to complete the engine will be Colony.

A cherry set of Evolution conrods was rebuilt using an S&S crank-pin and a new set of Rowe wrist-pin bushes sized to suit the pre-Evolution wrist-pins supplied with the forged S&S 4.5” stroker pistons.

S&S forged stroker flywheels and all the bottom-end components prior to balancing, washing and assembly. All the moving parts were weighed up, calculations for a 60 percent balance factor were completed, and the special bob-weight was put together for the balancing of the new S&S flywheels. Balancing is all done on S&S balancing equipment.

Final figure for the balancing is divided in two and the wheels are balanced individually.

With balancing completed all components are thoroughly washed and assembled. After truing this crank is ready to install into the cases.

After establishing the correct end float, the left-hand main bearing and crankcase are installed.

Checking the diameter of the pinion shaft. Even though the inside diameter of the pinion shaft is recorded on the information tag wired to the new crankcases (1.7509” in this case), it is wise to double check. After confirming the size, a colour coded pinion bearing can be selected from the table in the H-D Evolution Service Manual to give the correct clearance in the pinion race.

Information tag that comes wired to the new crankcases.

It is now time to install and seal the right-hand crankcase. Assembly lube is applied to the main bearings and Threebond 1104 takes care of the sealing of the cases.


With crankcases sealed up for good we now have the makings of a very robust yet classic looking engine.

Next issue we will continue with the assembly of the engine, and at the same time, we will put an identical set of cases into the frame to see what is involved in marrying the Knucklehead engine with the six-speed transmission and rigid frame.

compiled by Richard Nicholls at Redgrave Motorcycles

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