the crankshaft had much smaller journals and slimmer conrods towards its ends (roller bearing of course)
the 5 cyl 125 cc machine had a 2cyl crank (from the 50cc twin) coupled to a 3 cyl type crank
with 5 seperate exhaust pipes there was no great need for equal firing intervals
you just have to love that Lucas pre-engaged starter motor(on the BRM) all Mini ,Triumph and MG owners have learned to love over the years ....keep your fingers crossed it will start once more....on a wing and a prayer..never knew this was Formula 1 technology....
Basically a power plant mounted inside of a few train cars plus and extra for the fuel. There are only two remaining one is near my house. They were turbine powered Locomotive engines burning bunker oil.