Tuesday 9 July 2019

Suzuki GT380


The bike was on its centrestand outside the vendor's house. It looked surprisingly good for a fifteen year old machine. The result of a mere two owners since the GT380 was sold in 1975 and no more strenuous use than summer commuting. It started after four kicks, bit of a smokescreen but that was expected on an old stroker with 29000 miles on the clock. The 3 into 4 exhaust was rusty but intact and the paint was a bit faded but no rust.

The first spin usually reveals a lot about a motorcycle. In this case that there was hardly any power, lots of weight and an excess of wallowing. The owner looked a bit concerned; to check the engine out I'd screamed it up the street with full throttle in second. By the time I returned the cloud of pollutants was just starting to clear.

The owner wanted £500 but after I muttered something about the motor needing new crankshaft seals and a rebore, £325 was all it took to get my greedy mitts on the stroker. The ride home revealed the three cylinder engine as being a gutless heap, refusing to push the wallowing machine to more than 90mph. Despite critical weight redistribution, as in getting my head down between the clocks, the suspension revealed its age and the frame as being made of a substance nearer jelly than steel by the way the handlebars shook wildly in my hands the moment the speedo hit 91mph.

Grabbing the front brake lever until it came back to the bars and stamping on the foot pedal, soon had the speedo down to 60mph and my heart rate back to something like normal. Back home I could find nothing that was actually loose but suspected that the minimal swinging arm mounts were to blame for the hinged in the middle feel of the frame.

It was pretty obvious that the bike's forte was as a cheap and cheerful commuter, so it was slung into the ten mile trawl to work every day, with the winter coming on I could keep my other bikes warm and safe in the garage. The GT380's pleasant to ride at low speeds, keeps ahead of the cagers and proved generally reliable.

Except when it rained. Rain got into the wiring, causing one or even two cylinders to cut out. There didn't seem all that much difference in performance as a twin but when it went down to being a single and the power suddenly came back in on the wet road it would throw the back tyre off in an arc. This was more or less controllable as I was always poised in readiness. It made the GT a more interesting bike to ride.

The same couldn't be said for the front disc brake in the wet. Quite powerful in the dry, water caused it to work only as an on-off switch which even after a couple of years I couldn't adapt to. Engine braking wasn't much cop, so it was down to planning ahead and using the rear drum brake. I suppose if I fitted some decent rubber rather than the half worn breaker's specials, the front wheel skids might've been controllable enough to let me use the brake in the wet!

Every 500 to 600 miles the engine would start to run rough, needing the points and ignition timing set with a strobe. All kind of engine nastiness results if this is neglected. Oil consumption was reasonable at 300mpp and the smokescreen cleared up if the bike was given its head a couple of times during the commute.

I was impressed with tyre wear, 2 millimetres of tread would last about 5000 miles, which was all anew chain would do - ridiculous given the low power output. Fuel was also poor, but no surprise for a big stroker - 30 to 40mpg, usually nearer the former than the latter. Still, it proved reasonably cheap during the winter commuting session (October to March).

During the better weather the GT was neglected as I enjoyed my other bikes. Poor thing sat at the back of the garage sulking. I did buy a spare engine for fifty quid, the owner reckoned it ran perfectly but I hadn't heard it going. Come October when I started the GT the clouds of smoke refused to clear up. The crankshaft seals had dried up of oil and worn rapidly when the engine whirred into life. The spare engine was in an identical state.
 

I couldn't justify an exchange crankshaft but found a bottom end in good nick for £40. The engine was treated to the best cylinders and a new set of pistons and rings - spares are still available from Suzuki but they take weeks, sometimes months to arrive... it was December before the GT was back on the road.

I ran the bike in over 200 miles, keen to see if any new power was available. It wasn't, but the handling was becoming even worse with lots of wallowing and wobbles at a mere 70mph.

The shuffling was added to by the seat base corroding away under me. I was taking bets as to whether a silencer or the seat would fall off. Losing a baffle ruined the carburation with flat spots in the 3000 to 6000 rev range. A lot of GTs still have the original exhaust because the two stroke lubrication process deposits lots of oil on their insides. By the time the baffles start falling out silencers are not far off from being paper thin.
 

A new set of exhausts cost more than the bike was worth. I decided that the answer was to convert the 3-4 into a 3-4-2 exhaust and slip two GP100 silencers on (they were available cheaply in the breakers). I was pleasantly surprised at the quiet, efficient running until I tried to go above 5000 revs and found it wouldn't. I decided that this was excuse enough not to renew the swinging arm bearings as it wasn't fast enough to worry a CG125.

The lack of revs became more worrying when fifth and sixth gears refused to engage. Imagine my chagrin when the small ends starting ringing out in protest. They had looked a bit dubious when I did the rebuild, but I thought they might've had 5 to 10000 miles life left in 'em.

My neighbour two doors away crashed his Suzuki GT250 and broke both legs. Whilst he was still semi-comatose I convinced him to give me the wreckage for fifty quid. The only thing I could salvage was the two cylinder motor, but that was all I wanted. This went into the GT380's chassis without much hassle; they were of the same era and it wouldn't have surprised me if their frames were basically similar.

The 250 engine seemed to weigh half as much and put out twice the power. This was partly illusion, it had a pulse of power at 6500 revs that after the sleepy GT380 brought a grin to my face until, with 80mph on the clock, the chassis felt like it was falling apart under me.

Soon after that I finally put in some new swinging arm bearings, half a dozen washers in the front forks and a less knackered set of shocks out back. It was much better but nowhere near as nice as something relatively mundane like a GS400. Top speed proved identical to the 380, but it was a lot more fun getting there and fuel worked out at nearer 45 than 40mpg.

I was quite happy with this machine until the seat finally fell off, surprising me sufficiently to roll the bike down the road at about 50mph. The GT's alternator took the brunt of the crash, writing off the crank and engine cases in the process.

The chassis survived, save for a few dents and bent ancillaries, so I had no choice but to use my rebuilt GT380 engine. This consisted of the best bits from my huge pile of worn parts, about the only thing I'd really sorted was the gearbox, by replacing the bent selectors. A 3-3 exhaust topped by a set of RD expansion chambers made the GT sound much meaner but produced several severe flat spots below 5000rpm. Still, it looks like the plot will get me through another winter. 


MLK