Back in my luxury garage, er, living room, the full extent of my foolish behaviour was revealed. The front end came off easily enough, then the tank. Revealed were bent frame tubes around the headstock and indented exhaust tubes. Before I tore the engine out I tried to get it to turn over by rotating the back wheel. It was stuck in gear and no amount of force would make the back wheel turn. To cut a long horror story short, the reason the bike had crashed was because the engine had seized.
The frame, forks and wheel were dumped into a nearby specialist who in exchange for a £120 straightened everything out. Meanwhile, I was working on the engine. The cylinder head had two studs seized which snapped off rather than come undone. Just as well I had a helicoil kit! The head came off, the valve gear looking in good shape. The pistons were all there and apart from a bit of carbon build up looked as good as new. The cylinder was tyre-levered off and there were no signs of seizure.
Strange, but the crank would still not rotate. I had just dismantled a perfect top end for no good reason! I turned the engine over and split the crankcases. This time three bolts snapped off! Oh my god, look at the gearbox! One cog was stripped bare of teeth, which had stuck between the teeth of the other gears. I hate gearboxes and now I had to take this one apart. The cause of the break up was a shot gearbox sprocket bearing that had allowed the shafts to rotate out of line. The result of a too tight chain?
You don’t see very many KZs on the road, they never sold in vast quantities. You see even less in the breakers and finding one, despite phoning around all the breakers in MCN, proved impossible. When I enquired of my local Honda dealer of the cost of a new set of cogs, shafts and bearings he rubbed his hands together, gave me a wide grin and doubtless thought about booking a winter Holiday in the Algarve on the back of the profit he was going to make.
I looked at the box again and it seemed to me that I could get away with just one new cog and bearing. The bearing I got from a bearing factor at a third of Honda‘s quote and paid up for just a new cog, much to the dealer's disgust. A pattern gasket set was purchased by mail order and I was ready to waste another weekend reassembling the motor. When the box was back together there seemed a bit of a backlash between the gears and I told myself to take it easy on the changes. It all went together easily enough, my only real problem getting those four sets of piston rings back into the cylinder. Talk about needing four pairs of hands.
Reassembly of the motor coincided with delivery of my straightened chassis components. I decided to leave touching up the cosmetics and removing the dents from the petrol tank until I was sure that the motor would run. It proved possible to repair the instruments with Superglue and I replaced the cracked glass by cutting up an old visor to suit.
Much heaving and humping, swearing and cursing, saw the lump back together. I had to buy a new wheel spacer as that had disappeared. Much whirring of the motor ensued until it eventually coughed into life and settled down to a lumpish tickover. Out through the back door, down the garden and out into the lane. It felt bloody awful, The motor spitting back out of the exhaust, the bars shaking in my hands and the front brake refusing to work, the lever came all the way back to the bars.
Back home, I bled the brake lines, reassembled the exhaust system with some goo on the joints and inflated the front tyre from 15 to 30psi. Right, you bugger, now start behaving. And it sort of did, up to 50mph anyway. The engine ran cleanly, it steered as well as my Jawa 350 and now braked with enough force to fling the rider over the bars. However, there was a disturbing whine from the gearbox and it crunched rather than snicked into gear. Second and third were particularly noisy and the transmission felt very jerky at lower revs.
Beyond 50mph the engine misfired and I had to slip the clutch and rev the balls off it to get through the flat spot. Could the large dents in the downpipes be upsetting carburation? There was only one way to find out. The only way to fix the downpipes was to cut out the damaged area and re-weld some new tubing in place. It looked a right mess when I'd finished but carburation had indeed improved,
A new 4-1 was bought at the motorcycle show for £80. It was cheap because it was of the baffle-less type and, strictly speaking, illegal to sell. This went on with only a few hammer blows and I then spent a weekend trying to set the carbs up to suit. I failed and had to hand the bike over to a dealer. £75 poorer, the exhaust turned out not to be such a bargain.
Apart from the noise, performance was transformed. It would now rev straight up to 10000rpm without a moments hesitation and the acceleration threw one young lady right off the back. I howled around town giving aged citizens heart attacks and police officers a reason for their jobs. It sounded especially good on the overrun. More importantly, I could no longer hear the gearbox whine. Come to think of it, I probably wouldn't hear a Jumbo jet if it passed a foot above my head.
Encouraged, I finished off the cosmetics, including knocking out the worst of the tank’s bumps and then filled in the remaining ones. A complete respray in candy red improved the appearance no end. Polished up it looked the business. Pity it wasn’t that good to ride fast. It would get 130mph on the clock without too much of a contortion act but it weaved and wallowed, generally feeling as if it had flat tyres or a few loose bolts. I checked everything but could find nothing wrong. Either something was not straightened accurately or it does that from new.
A ride on my friend's immaculate CB750K1 convinced me that the older Honda fours were really bad handlers and I had to rush home for a new set of undies. I decided that my model wasn’t so bad after all. The engine got no attention and required none over the 15000 miles I did in the year I had it. The bike had 12500 miles on the clock when I bought it and a new set of Roadrunners that were still there when I sold it. The chains only lasted for 3000 miles - something seriously wrong with the transmission, obviously although I did not have to change the sprockets.
Once it was rebuilt I got some good use out of the Honda but my awareness of the frailty of the gearbox meant I did not trust it on long journeys, which, given its massive weight and girth, is what it would have been most suited for. Everyone thought it was rather strange than I used the CB around town and the Jawa to go on holiday!
I managed to make about a hundred notes on the bike when I sold it, as low mileage fours of this vintage were very rare - I had about 20 phone calls! That £100 profit is after every penny, save fuel, that I spent on the bike, so I had a year’s riding for nothing and a lot of fun into the bargain. I went and bought a CBR600 off another breaker but looked at that one very carefully before I parted with my money this time! I was more relieved than sad to get shot of the Honda - it looked fine, sounded great, had arm wrenching acceleration but there was no way I could ride it fast on anything other than a motorway. Not my idea of fun.
Terry Smithson