ON OUR BENCH
1977 Kawasaki KH/H1F Hybrid
MG’S KH/H1F, Jim’s new YZF750 and Tyler’s YPVS
Invasive surgery required to remove old 250/400 mounts and line-up the 500 engine
The time has come to begin the real work and go beyond the point of no return: grinding off the KH engine mounts to fit the new H1 mounts. A lot of metal has to be ground away. The H1 plant is a tight fit. After a bout of “Are you absolutely sure?” “Yes.” “Really?” we set to with the angle grinder.
It’s vital not to accidentally gouge parts of the frame tubing with grinding wheel, which we almost avoided during the process of removing enough metal to get the engine sitting in the right spot (the fine finishing will be done with the frame shorn of front and back ends). For now it’s a case of rough removal of the front lower mounts and swingarm gussets so the engine can be offered up with the transmission output shaft and gearbox sprocket to determine chain line and barrel and cylinder head to frame clearance. We also had to grid away the top portions of the upper front gussets to clear the front extremity of the crankcases.
In goes the engine with the front mounts in position. The chain line is perfect, but the engine seems to be sitting 5mm to the right and the rear mounts do not line up. Odd. We wonder if there’s
supposed to be a little amount of offset. No. The centre cylinder should sit dead centre in the frame.
We knock out the rubber mounts and inspect them. The fronts are different: one has a spigot, one doesn’t. Neither should have spigots. The rubbers are moulded elliptically on the fronts too. All the others are concentric. It seems a previous owner has bodged a lower mount into becoming a front mount and the 5mm of spigot is pushing the engine 5mm to the right so the rear mounts don’t line up.
Temporarily fitting two non-spigoted front mounts reveals the engine will line up and the gearbox sprocket will need to be offset 5mm to the right. Not a problem. The problem, or rather the opportunity presenting itself, is now we need to make new engine rubbers.
The misplaced optimism of last month has
THE PROBLEM, OR RATHER THE OPPORTUNITY PRESENTING ITSELF, IS NOW WE NEED TO MAKE NEW ENGINE RUBBERS
now been replaced by the cold reality of just how knackered the H1’s rubber engine mounts are. They’re critical to getting the engine mounted and lined-up in the KH frame – and they’re not only beyond hope, but mismatched too – that’s what you get with unknown quantity engines.
The engine is otherwise in good shape so one curveball is not the end of the world. The trouble is the mounts (in decent nick, or new) are very hard to find. There’s a man in Germany (Volker Shulz) who makes batches of new ones – but typically he’s just sold out the latest lot and won’t be making any others until next year. The plan now is for us to make our own.
We have options: (1) hard mount the engine with ally plugs, (2) buy some 1-inch nitrile rubber and drill to fit the steel inserts, or (3) mould some polyurethane bushes around the inserts. The hard mounting option would give the best torsional stiffness but the niggly secondary vibrations from the triple might prove to be horrific to live with (although the original 1969 H1, not this 1975 H1F, had a hard-mounted engine).
Options two and three would both work, with two being perhaps the easier of them. We’re certainly not waiting until next year and the new batch of Volker’s items – good though they’re reported to be. We’ll also have to repurpose the incorrect front mount to its required spec (without spigot), which is easy enough. Then it’s a case of grinding off the old decayed rubber and fitting the new harder stuff, making sure the front mounts have the correct amount of off-centre.
We can only assume the front mounts are eccentric to position the most part of the rubber on the bottom to damp torque reaction that forces the front of the engine down under acceleration.
As ever, what looked like a straightforward fitting job turned out to be so much more. We stood around scratching heads and drinking tea quite a bit. What’s certain from this little episode is that the engine fit is critical to keeping the heads and barrels away from the front down tubes. The installation is cosy to say the very least. It’s also entirely worthwhile, and already the little KH looks excitingly dwarfed by the substantial H1 engine. And thanks to Andrew Walmsley of 3cyl.com for the excellent engine mount drawings which have proved to be absolutely spot-on.
Next month we will bring you all the fun and games of pouring polyurethane into moulds and messing about with more grinding and finishing. When the mounts are done, the cycle parts await. The prospect of an early summer finish though is looking more and more remote.
Output shaft installed with drive sprocket to determine chainline
This is the sort of unusable condition the rubbers were in
Rear gussets chopped back, will be replaced anyway
New front upper mounts all good, rubbers less so
Front lower mounts have to go – and they went
There’s no going back once the cutting disc is spinning
Original metal won’t give up easily. Not in its nature
It’s a tight squeeze, but it works
It’s wide in the frame too