Mounting excitement triples
The 500 engine mounts are ready to be welded onto the 400 frame. It’s all happening
You can’t rush a good resto. Nor can you hurry love, as The Supremes so tunefully advised us. The KH/H1 project has been slowly smouldering away as we accumulate both knowledge and parts – in that order. It’s now at the stage when the whole thing is ready to coalesce into the smoking, snarling wonder-cycle we conceived as far back as Autumn 2017.
The Gary Clarke rebuilt crankshaft sits waiting to be installed along with a gearbox currently having all the dogs on all the pinions undercut. Even under enthusiastic street riding the stock ’box can jump out of gear. This is because under heavy load, the engaged dogs are pulled away from each other. They are very slightly undercut from the factory, by 2-degrees, but require a steeper cut (5-degree) for hard riding. Bent selector forks can mimic the same problem, and ours showed signs of hard use, but were not bent; the second to third gear fork was well-knackered, the other two worn but still OK for future service. We bought a very neatly remanufactured fork from Z1parts.net.
Miguel at BSD is undercutting the dogs and superfinishing the entire cog-set. Superfinishing (vibrating the pinions in a big box of glass beads) reduces contact friction, allows the ’box to run cooler and makes it last longer. For out-and-out racing some builders machine three engagement dogs off to make it a three-dog ’box, this gives slightly faster shifting, but the payback is a little more lash in the transmission, making the driveline a bit sloppier. We’ve stuck with six dogs.
The engine mounts were fabricated by Mick Reed at Radical Precision. The sections were laser-cut, the front lower mounts then formfolded and the bosses will be tack-welded before
being trued-up when we offer the engine into the frame with the output shaft and drive sprocket fitted into the cases to achieve a dead-true chain line. This will be the next stage before we build the bottom end of the engine.
That will then be farmed-out to ace two-stroke man Bob Farnham for the porting and combustion chamber reworking. He will also blend the spacers for the new 34mm Mikunis (up from 28mm) and the inlet rubbers for maximum flow. Then, when he’s nailed the top-end to the bottom, we’ll be bolting in a Zeeltronic ignition to fire the sparks at the new Wössner pistons.
The H1F engine is rubber-mounted, not in a complex manner, in the simplest fashion possible – big rubber slugs where the mounts are. When the rubbers get worn (like ours) the engine shifts in the frame which is far from ideal for besthandling practice, so our plan is to mould some new polyurethane bushes when we attack the rest of the chassis.
Meantime EBC have come through with a set of fresh fibre plates and a heavy-duty clutch spring set to handle the new levels of power this engine will produce. The first 1968 H1 produced a claimed 60bhp, the B, C, D, E, F gradually less, and the final 500, the KH500 of 1976 made 52bhp. We’re looking for a rear wheel 60bhp, maybe a little more, but a good useable spread of power with a fat midrange. We see no reason why this isn’t possible with Bob’s magic and a good set of expansion chambers.
So, it’ll be chassis next, while the engine goes together. This chassis will be as stock as possible. When we see just how much power we’ve got, we may have to think again. But for now, it’s get it all together and go from there. We aim to be on the road by early summer. And we cannot wait.
WE’LL OFFER UP THE ENGINE WITH THE DRIVE SPROCKET FITTED FOR A TRUE CHAIN LINE
Cases in the frame, and sad cases in the frame
Laser-cut lower rear mount
The H1F 500cc crankcases sitting on top of the KH mounts that will be replaced
Rear top mounts ready to bolt on for the dry build
Front lower engine mounts are substantial items