Introduction to VF750 / RS750 / HRC RS850

VF750 race kit

The first VF750 engines built by BGC were standard VF750F (chain drive cams) fitted with HRC race kit components including: camshafts, followers, cylinder heads, valves, pistons, con rods, sump extension & various gear box components.

Heavy duty Tsubaki cam chains were fitted along with modified cam chain tensioners, with modifications to the camshaft oil feed these engines proved to be completely reliable in 24 hour endurance racing. Considerable time was spent in the dyno room and on the flow bench, but power output was ultimately limited by the cam chain induced rev limit. Nonetheless, a well prepared race kitted VF750 was competetive with all but the exotic works bike of the day.

HRC RS850

Though firmly in the factory exotica catagory the RS850 engine was in theory available in component form from HRC. Assuming one had both suitable credentials and a very healthy budget, an engine could be built from new parts, it is however more likely that these engines were only built by HRC in very small numbers, and supplied to factory supported teams. The crank cases and cylinder heads were standard VF750 castings, heavily modified by HRC, and the crank cases welded and machined to accept the gear drives for the camshafts, as well as the semi wet liners necessary to accomodate the 75.00mm pistons. Con rods and valves were titanium, manufactured by Jet Corporation and Megacycle respectively. The cylinder heads were (I seem to remember) finish ported by Jerry Branch, so there was a considerable USA contribution to these early HRC engines.

Several HRC RS850 engines were rebuilt by BGC and raced in international events where capacity classes accomodated them. The rev limit was a comfortable 11,500rpm due to a tendency towards head gasket leakage and failure, should they be regularly pushed too hard. Torque and power delivery was superb to the point that several riders fortunate enough to race an RS850 commented that they were almost boring to ride whilst at the same time recording lap times full seconds faster than they had achieved on other machines.

RS750 or VF750R

Much of the above applies to these gear driven cam 750 engines, though the existence of full parts & price lists suggested that some engines were assembled from new parts other than by HRC. They differ from the RS850 in that the standard VF750 cast-in cylinder liners were retained, and head gaskets were therefore not problematic, allowing a rev limit of 13,000rpm.

A number of these engines were built by BGC & raced extensively in world championship events. VF750 crank cases were modified in the same manner employed by HRC, by welding & machining to accept the cam shaft gear drives. VF750 cylinder heads were machined for the gear drive upper supports, and ports modified according to our own flow bench development. Crankshafts, gear drives, and most other components were from now redundant RS850 engines, with either titanium con rods, race kit steel rods, or Carrillo's.