A Little Progress

Each step with the Hedstrom motor has been a little challenging. The heart of the motor is the flywheel / crank assembly, so a lot of time was spent to get it right. A new crank and drive pin were sourced, but the pinion pin has a gear machined on the pin, which made it hard to find. So I elected to grind and plate the original back to stock dimension. The new rods were sourced from Carrillo, and odd length bearing rollers were custom ground to length. When I got happy with all my clearances, I began assembly. My first speed bump was the new rods were to wide.

The stock flywheels are forged steel on these motors, so I decided to mill some material from the inside of the wheels.

 

 

With the rod endplay set, I started the truing process. First, the drive and pinion pins were torqued to each wheel, going slow and keeping them straight.

 

 

 

Next, the crankpin (with rods) was installed and the process of truing these wheels began. The old tapers with new pins did not want to cooperate, and I wound up having to lap all 4 tapers to get the wheels true.

 

Changing to lighter weight rods and Aluminum pistons severely changed my balance factor.

 I had calculated the original factor at 58%, and with the new components, it was now slightly over 80%, so I decided to remove some weight from the counterbalance side of the wheels to get back to around 60%.

 

With the crank true and balanced, a trial fitment in the cases developed more issues. The rods were also to wide for the oil baffles, so back to the mill to remove some meat.

Secondly, with all the pin lapping I now had .035" crank endplay, which would bind the rods. All the bushing had been sized, and I really didn't want to redo them all, so I ground a hardened spacer .023" thick, pressed the bushing out, and installed the spacer behind the bushing.

Finally, all endplays, bearing clearance, shaft run out, etc.. were within specification, the bottom end was buttoned up!