Sunday, 2 April 2017
I'd owned my 1981 Kawasaki Z250 for four years. I'd ridden it and ridden it with hardly a hint of a problem. Now and again the engine would become noisy and I'd change the oil and it became quiet again. With 45200 miles on the clock it began making some strange new noises. The more that I revved it, the noisier they became. There was a rattle, a knock (or two) and a sort of tingling. Blue smoke had started coming out of the silencers when I went above 70mph and the bike could no longer hold 80mph against a hill or strong wind.
It still averaged 70mpg and still seemed to accelerate alright. Friends said the mains were on the way out. They suggested scrapping the bike. But I couldn't afford to do that.
I decided to check the tappets. This was just a matter of removing four covers and sticking in some feeler gauges when the rockers felt loose. Close observation of the left hand pot revealed that the valves were depressed by a lot less than the other side when the engine was rotated. Removal of the engine from the frame and cylinder head cover from the engine (it's a lot quicker to write than it is to do) further revealed that two of the cams were worn away and the left hand end of the camshaft was sitting loose in its bearing - which consists of the head material. Reconciled to repairing the head, I quickly removed its bolts and split the camchain.
The camchain looked a little stretched and the tensioner blade was full of deep scores. The exhaust valves were pitted around their edges and one of them had a hairline crack running through it.
Everything was very black with carbon, and there were lumps of it on the piston tops. The bores were scratched, but not deeply. It took an afternoon to remove the barrel because of the tight fit with the crankcase. This revealed pistons with oil rings stuck in their groves and another hairline crack - this time in the bottom of the piston.
Full of fear, I checked the small and big ends but I could not feel any movement. So I could get away with a rebore and a new head. All my friends said I should scrap it or buy an engine from the breakers, but I had faith in the engine and had grown to love the bike.
A rebore and a set of oversize pattern pistons cost £45. This was the easy bit. I phoned around about twenty breakers until I found one with a low mileage engine which had apparently blown its big-ends. The head hardly looked used and I managed to bargain them down from £80 to £65. As this was complete all I had to do was bolt the engine back together. While it was out of the frame I cleaned off the grime and touched up the black engine paint. It looked quite reasonable by the time I finished.
I also cleaned the frame and repainted it using black enamel. My brush work wasn't very professional but by the time I'd cut it down with T-Cut it looked as good as new. The exhausts were pitted with rust and the (original) silencers were devoid of baffles, full of holes and sort of rust coloured. When I removed them they disintegrated. A pair of universal pattern silencers and a repaint job on the exhausts brought them back into civilisation. The paintwork was still OK and the alloy wheels cleaned up after a lot of elbow grease.
It was with much excitement that I threw the bike back toether. I pressed the starter and kept pressing until the battery ran out of power. Wired up to a car battery, it began spluttering and then leapt into life at about three million revs. Then it cut out, but ticked over nicely at the next press. Strange.
I spent the rest of the day pottering around on the bike, listening for engine noises and praying that everything would hold together. It did and the engine was very quiet, with just a gentle rustle of the valves. I carefully ran the thing in for 500 miles and decided I'd better do some regular maintenance — it's all very straightforward — and change the oil every 1000 miles.
I'd always found the Z250 easy to handle, it only weighs 330lbs and is very neutral in curves. You can back off the throttle or change direction without causing the bike to lose its head - this on very old shocks and forks with heavier oil. There's a weave at speeds beyond 80mph but it's never frightening enough to make me back off - the wind force and the vibes are more of a deterrent.
The pistons move up and down alternately, giving little vibes up to about six grand and just gets worse and worse as revs increase. It's mostly through the footrests and doesn't really harm the rider.
With the rebuilt engine run in, I find I can cruise at anything up to 80mph, but don't expect a Z250 to accelerate rapidly above 70mph in top gear. The engine is able to thrum along at low revs (down to 25mph) in top gear but subsequent acceleration is very poor. The engine really thrives on revs and riding on the edge of the redline makes the bike shift really well.
I have friends with RD250s and I have to ride the 2250 on the extremes of its handling ability and performance to keep them in sight. I usually catch up with them when they run out of petrol. I found the original bike very frugal — anything from 70 to 55mpg depending on how I ride. With the new head, it's not so good, I've actually been down to only 65mpg and the best has been 78mpg. Maybe it's the non-standard silencers, but it's still good, especially when compared with the 30mpg some of my mates achieve on their RDs.
The wheels and disc brakes are from a later bike, following a minor accident in which I buckled the front wheel - l was offered the pair at a bargain price, so it was cheaper than just replacing the front end. The brakes are OK, not as good as an RD, but they work in the wet and discs last nearly ten thousand miles.
I haven't had any problems with any of the electrics, it's even still on the stock battery. The front light's dim for fast riding on unlit roads but it's better than the old Hondas I used to ride and it's not so bad that I've been inspired to uprate it. Even the indicators still flash in a regular manner. So full marks to Kawasaki.
I put another 5000 miles on the Kawasaki with no problems, then another new noise, a loud knock, appeared one day when I was cruising down a motorway at 85mph - it was loud enough to hear at that kind of speed. I slowed down to 30mph (ever tried that on the motorway?) and it kept getting louder and the vibration was trying to shake the bars out of my hands.
Luckily, it was only ten miles to my house. You should have heard the bike by the time I got there - people turned round looking for the war and just found this little Japanese motorcycle.
Well, I knew my way round the engine by now and had the engine out and stripped down to the crankcase in a few hours. Just as I thought, the big-ends and the mains had finally given up at 50756 miles. Not bad going for a mostly neglected and thrashed high revving 250 twin.
I had a wonderful head and barrel but a wrecked.bottom end. I couldn't find any engines in breakers that were in good condition for less than two hundred quid, which was more than I could pick up a good runner for on the private market.
I took the crank out, but it was too far gone to repair. Then I heard about a GPz305 that had been crashed by one of the local lads. It was totally mangled but the engine looked intact and there was only 4500 miles on the clock. It only cost £300... all I have to do now is fit it.