500cc DomiRacer

Hello,

I am planning to build a 500cc Domi Racer engine to compete in classic races in Japan.
I plan to use parts from JS Jim for the pistons, connecting rods, valves, and cams.

After careful consideration, and taking into account the compatibility of the ignition system and various other parts, I concluded that using the crankcase from a Commando 750 would offer the most benefits.
I will use 500cc parts for the crankshaft, connecting rods, cylinder, and piston to create a 500cc engine.

So, I have a question for everyone: has anyone ever built a 500cc engine using a 750cc crankcase?
As shown in the photo, I did a test assembly, and it seems to be working fine.

In Japanese classic racing regulations, as long as the displacement meets the requirements, other factors aren’t usually an issue.

I cannot answer your question, but I’m very interested in your build! Please do a ‘build thread’ …

An excellent project but it would be better to use later 88ss/650 crankcases because the 88 barrels bolt straight on. The 750 cases require work to line up the barrel flange to crankcase stud holes. You can fit the early points in timing cover parts to the Domi crankcases with a little work (I did it on mine).

If unlimited funds are available go with late 750 Commando cases, alloy 750 barrel, a one piece 59mm stroke crankshaft, special lightweight cam followers, carbon fibre push rods, lightweight rockers and valves etc. Tune for up to 10,000 rpm. (That is probably just me dreaming!)