Motorcycle Repair: 520 or 530 final drive chain replacement

Question
Is it perfectly fine to switch out the old 520 chain along with both final drive and rear wheel sprockets on my CL72 Scrambler 250 ? Looking at the worn condition of these narrower sprockets 40T rear wheel and 15T drive. I would like to replace them both with Classic Hondas new 37T rear and 15T final drive and use a new 530 chain with 94 links that I had purchased previously. I found out later that the new chain roller spacing was way to wide for the narrow older sprockets. The engine # is CL72E1108XXX and frame # is CL721108XXX, they are only apart by five numbers so they are the original factory installed units. There also seems to be an abundance of the larger width sprockets readily available on the market. Now is there any problems that I could be creating here other than maybe a higher top speed?  Thank You for Listening Bob 5/10/2015.

Answer
Bob, you have to use the early style sprocket patterns for the 1964 CL72s with 520 chains. They came with 40t setups, to help get the 250cc version going with some energy. The "big brake" CL77s used a 37t rear sprocket, along with 15t front sprocket, but with 530 chain pitch links. The sprocket hole spacing and the center hole sizes are different between the two sprocket types. The later sprockets can be interchanged with CB77 rear sprockets, but they don't work on the early Type 1 rear hubs and sprocket carriers.

The CL77s have an extra couple of horsepower, so they got higher gearing, which they could pull. CL72s need the transmission ratios "X"d and that helps the 1-2 gear shift spread. Otherwise, they tend to bog down with the wider ratio gearing as produced and the bikes will struggle with higher final drive gearing due to lack of power.

In a practical consideration, you really don't want to get a CL72 moving at very high speeds on the highway, mostly due to the fact that the bikes have poor braking power and it is pretty much impossible to lock up the brakes in an emergency. The move to the "big brake" setup was to improve braking for the street. The front brake was sourced from the CB450K0 and the rear from the CB77. The DLS brakes have good braking power on the street going forward, but do not fare well in the dirt while trying to hold the bike on a hill or rolling backwards.

I have extensive restoration guide files available for Scramblers, if you need comprehensive repair/restorataion information on these bikes.

Bill Silver
www.vintagehonda.com