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  • On 3rd April 2015

The primary shaft is called “primary” for a reason.  Without it, your motorcycle will not move.  And neither will it start when you push the START button.  If you are rebuilding your engine from the bottom up, you will, of course, have to remove everything including the primary shaft.  Since it is press-fitted, a special tool is required to remove it.

Where is the primary shaft

 This special tool consists of two parts, which can be described essentially as a long bolt and a very heavy washer.  See below.

Pulling the primary shaft HONDA manual

The HONDA part numbers (for the CB550 engine) are 07936-3740100 for the primary shaft puller and 07945-3000500 for the weight hammer.  They are no longer available.

The way this special tool works is like this.  You screw the “primary shaft puller” into the primary shaft.  Then you slide the “weight hammer” as close to the primary shaft as possible and, with one quick motion, throw it towards the primary shaft puller’s head.  When the weight hammer hits the puller bolt’s head it creates a pulling force. Repeat that several times and the primary shaft comes out. Here is a photo of it:

Primary shaft

What do you do if you cannot get this special tool?   Well, you have to make your own.  It is very easy.  I used a big screw I had lying around.  It was about 8” long and about 5/8” in diameter.  I ground the end to reduce the diameter and then, using a 12 mm X 1.25 die, cut a ¾” long thread. (NOTE: The lower rear engine mounting bolt could also be used for that purpose.)  I used a thick galvanized washer weighing approximately a pound as a “weight hammer”.  It worked perfectly. Here is what it looks like:

primary shaft puller

What’s the primary shaft for?  Why is it there?  How does it work?

The primary shaft is there to help transfer the motion of the crankshaft to the rear wheel.  The primary shaft is connected to the crankshaft with a chain.  As the crankshaft rotates, so does the primary shaft.  You press the clutch, push the gear lever, the transmission is engaged to the primary shaft and the rotation of the primary shaft is transferred to the drive sprocket via a complex arrangement of gears.  The drive sprocket moves the chain, which rotates the rear wheel and off you go.