2. Engine

Engine Issues
Neutral Brake

Engine Issues

As previously mentioned I bought this bike as a 'stalled' project a few years ago and it came with a load of bits and pieces, so the first thing to do was spend a bit of time seeing what was there and also what was missing. For the most part, it seemed fairly complete, which was the good news. It was missing a few things (turn signals for example) but other than that at first glance it looked not too bad cosmetically. The bad news was that the engine had obviously just been stuffed into the frame to make it easier to move around, as none of the bolts were tightened. More bad news was that there was no oil in the gearbox, so I definitely had to open things up and check for corrosion.

Some receipts came with the bike indicating that the engine had new rings and that the seals on the crankcase had been replaced. Unfortunately, new Suzuki crankshaft seals and bearings were safely stowed in a bag in one of the boxes, and so the crankshaft had not been rebuilt when the other engine work was done. Pity.

In actual fact the engine was not as bad as I'd feared, although still not great. It did have new rings however rather than honing the bores, they really should have been bored to the next over size as all three showed lots of scoring. While the engine should have run, the likelihood of the new rings ever seating properly was next to nil. I ordered new first over pistons and rings and got the cylinders bored locally here in London. The centre cylinder head was damaged, but not the two outside ones. What appear to be pry bar marks in several places come very close to the fire ring, but I should be able to fix these with J-B Weld.

I did find some swarf in a few of the oil passageways which was a bit worrisome. After flushing everthing our well I'm hoping everything should be OK.

The crankshaft actually seemed fine. Unlike with the GT750's, the crankshaft oil seals are quite small on these, and there was no play in any of them or in any of the bearings, so I just changed the outboard seals. The one outboard bearing on the right hand drive end of the crank was not quite a smooth as the others, so I did change that one. If the seals do eventually fail, the engine is small enough that pulling it out again to have the crank redone will not be too big a deal.

Neutral Brake

There was corrosion on the clutch plates and likewise on a few of the gear clusters, but no pitting on any of the gears. The very light surface rust visible in the photo further down the page below cleaned up fine. The dogs and shift forks were also all in good shape. However it didn't shift properly. All the gears seemed tight with a lot of drag, and on closer examination I found that the neutral brake seemed to be 'on' all the time. This is the first engine I've seen that has one of these brakes, and so I've included a description of how it works and what it is supposed to do.

Closer examination showed that the spring loaded pin riding on the underside of the brake lever was jammed in the bore, and when I pulled it out I found that it was packed with aluminium shavings. Even with these cleared out, and lots of lubrcating oil in the bore, whenever I tried to cycle through the gear changes, the pin would bind. Some head scratching ensued. I considered sleeving the bore but there is only about 2mm of wall thickness which doesn't allow for much error. In the end I chucked the pin in the lathe and cut a chamfer on the lower edge, and also polished the bore. This allowed the pin to slide freely without binding. In a photo below, you can see the modified base on the pin to the left of the photo, and a stock pin to the right of it.

The pin itself has a flat on one side to allow oil to escape but I noticed that this was a slow process and it was possible to have a lot of back pressure from the pin with the bore full of oil. To minimise hydraulic lock, I drilled a hole in the side of the casting which allows oil more easily to escape (last photo below). As this area is fully submerged in oil in normal operation, it should be fine.

After making these changes, the gear selection testing was fine, so while I did change a few of the needle roller bearings in the gear clusters I left everything else as found. I put the engine back together and moved on to the frame and running gear.

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