Big bore for Bol d’or

Team Bike’s Honda RC30 has grown in capacity for the Classic Bol d’or

WHEN OUR HONDA RC30 broke a piston at Spa (Bike October) it wrecked the engine. Genuine RC30 crankcases aren’t in plentiful supply, so we’ve used the rebuild as an opportunity for a creative attempt to overcome our power deficit against the GSX-R1100S that are allowed at the Classic Bol. Standard bore on an RC30 is 70mm, and the liners (cast into the engine cases) are quite thin, so there’s no scope for overboring. But the RC24 VFR750 road bike has much thicker steel liners. A combination of RC24 cases, with 74mm 929 Fireblade pistons and an RC30 crank (and the rest of the RC30 internals) should give a capacity of 840cc. But it’s a lot of work. I took a set of cases down to Stephen A’lee at GT Motorcycles Engineering. There’s ten hours machining just in the rebore; it takes eight passes of the boring bar to increase each bore size by 4mm, and setting up on the V4 cases is fiddly. The head gaskets need to be modified too, which is a bit stressful because it involves sacrificing a genuine Honda RC30 gasket set and they’re hen’s teeth. To deliver the fuel mixture to the big engine we borrowed a set of trick magnesium flat-slide carburettors. We’ll run it on the dyno on Thursday. Which is a bit of a rush as we need to load the van for the Bol the following Monday. Don’t worry, we’ve got a spare 750 if the 840 doesn’t work as well as we hope.