Chopper Tear Down Part 2: Knucklehead Primary

Kevin “Teach” Baas is set up on the left side of our vintage chopper build and is ready to remove the Knucklehead primary drive. The left side floorboard assembly will block removal of the outer primary cover. Kevin removes the floorboard and moves on to removing the small, fine thread screws that retain the outer primary cover to the inner primary cover.

You’ll notice that the inner and outer Knucklehead primary covers are not the typical cast aluminum cases that we have become accustomed to over the last 50 years. Rather, the inner and outer are thin, stamped, steel covers. With a belt driven primary drive, the only purpose of these covers is to shield the primary drive from elements and debris and to protect the rider. In fact, this Knucklehead primary drive and clutch can be fully functional without its inner and outer primary covers.

With the outer Knucklehead primary cover removed, Kevin can see that the primary drive has been converted to belt drive. Originally, it would have a double row chain. The clutch pressure plate and hub have also been slightly updated. Kevin removes the front sprocket and the belt. The motor’s crankshaft is tapered with a key. There is no compensator assembly.

Next, Kevin removes the clutch pressure plate. He uses a pick to remove the steel and fiber clutch plates. It is always a good idea and good mechanical practice to stack the clutch plates in the same order as they were previously installed. After a quick inspection, Kevin determines that these clutch plates have seen better days and will be replaced upon reassembly.

Kevin uses his half-inch impact to remove the clutch hub nut. As always, this nut (and shaft end) are left hand thread. No righty tighty, lefty loosey here.

The transmission mainshaft is also tapered and keyed. A clutch hub puller is used in order to release the hub from the shaft. The inner Knucklehead primary is also removed. Kevin disassembles and removes the bike’s shift linkage assembly, kickstand assembly and secondary chain.

Chugging right along…

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