Suzuki GS550E — Quarter Turn Throttle Conversion.

 Converting your throttle tube to a 1/4 turn.

I'm pleased to say the GS550/673 is going really well — the engine has been faultless so far. One thing that is annoying me though is how bumpy the front end is, and it's really obvious since sorting the Bandit. The 1200 front end is now feeling incredibly refined and plush after a fork oil change, so I wanted to change the springs in the front of the GS to try and help her out.

As luck would have it, a pair of new Progressive springs came up on eBay for $110 delivered. Result! Although the general consensus now is to fit straight-rate (linear) springs, this was a bit of a bargain. However, they got stolen on the day they were delivered by some scrote who told the postie that they lived at my house. And that was the smaller of three parcels! Luckily I got my money back via Paypal, but that's besides the point. I was not impressed.

Metzeler Tyre Test — Suzuki GS550E

First, a bit of history... hey, life isn't all just fun you know!

When the old GS came to me, that fateful morning in 2012, I knew it was going to change my life. It sat there for a long time, mournfully looking to be put back out there, to race around on the mountain roads, to show what it was really capable of.

But I had a GSXR1000 and a DRZ400 supermoto for the fun stuff. This one would wait. However, it kept looking... and I kept ignoring. 

Until, one day, it was reassembled enough to run under its own steam. The excitement was building. The little GS felt proud, there was potential and we could both see it. She was ready to go out and try the roads for the first time in years. The front tyre, however, was looking a bit lame. So I bought a secondhand Dunlop on eBay that was originally fitted to a Harley, the little GS wasn't happy about that, but it meant we got to ride. The rear Barracuda (the what?) had plenty of tread left so she was good to go. And for years she rode around on those old tyres, the front now being seventeen years old 😱.

Suzuki GS673 Conversion — The Road Test.

 What'll it do mister?

There are no certainties in this life. All we can do is work with the best we've got, and to the best of our ability. When you work with old vehicles, you are left with a hell of a lot of choices. Replace everything for fear of something breaking down the track, or use experience to decide what will keep going, and maybe rely on a little bit of luck. It's probably fair to say we use all of these methods without a second thought.

It would be nice to change every bearing, gear, thrust washer, bolt, moving part etc., but that generally isn't viable. Instead we check, measure and work out what we can get away with. Lots of parts aren't even available anyway so sometimes we are stuck with far greater tolerances. When there is wear in vehicles, we immediately feel it when we ride or drive them but, as human beings, we automatically adjust to cope with the discrepancies. Some better than others.

Sure it's nice to be on a brand new bike, where everything is perfect, but they also leave me feeling somewhat robbed (not just with the cost of them either:). They let you get away with things, incredible brakes, plush suspension, tyres with more grip than you know what to do with. You may even think you're better than you actually are (oof, perish the thought!). 

But with old stuff you feel everything that is happening, hold the bars too hard through the bends and the weaving starts, fight it and things get worse. But relax and let it work everything out for itself and they usually settle down quite nicely. You feel that you're achieving something, that a living being is out for a blast with you, stirs the soul don't they say? (It does get tiring though...)

So ladies and gentlemen, just once, get on an old bike and be amazed at what they will do if you're just prepared to put in the effort...

Suzuki GS550E — GS673 Conversion Progress.

 Finally getting there...

Once painting of the cases was done, I put the crank and gear clusters back in the crankcase. Turning everything over, something I hadn't noticed originally was pitting in the teeth of one of the gears. It turned out I needed sixth drive gear (obviously unavailable from Suzuki now), but a search on eBay came up with a NOS one in Cyprus. With a delay on postage due to COVID-19, all I could do was wait. 

The pitting is visible in this pic. The largest gear in the top cluster.

One NOS gear from Cyprus. Whoop!

GS673 Conversion — Cleaning The Crankcases and Painting Engine.

The 673 kit.

The next step for the GS550 is to relieve the crankcases slightly so that the bigger diameter liners will fit inside. I'd just ordered a new Dremel as my old Draper version was getting a bit tired. That thing has been amazing and I've had it almost twenty years — it's done lots of porting and polishing. Anyway, i was in the process of grinding out some of the casing when the Draper tool finally gave up and spat chunks of plastic out the side. The Dremel came just in time!

If you're wondering about the quality of the deburring tools, sandpaper barrels etc., the Dremel ones are superb! I've always bought the cheaper versions and they wear out in seconds, The Dremel ones are worth the extra cost. 

But on with the job. 

I found it easier to slip the cylinders over the studs, turn the case upside down and mark where the liners were touching. Then remove the cylinders and start grinding. Bit by bit, they went lower and lower.

Suzuki GS550E 673 — Stripping the Engine, Decking the Barrels.

And skim the head!

The next thing on the list was the broken fin on the barrels. I cut out a similar shape from some old aluminium that was lying around, then filed it somewhere near. I wanted the barrels to be hot before welding to avoid cracks etc., so a trip to the oven was in order. Half an hour at 150 Celsius was perfect and the liners slid straight out. This was even better because No.4 sat slightly proud before I started.

Roughly shaped, let's take a look.

Suzuki GS550E — 673 Conversion.

Slight Misfire Halts Play!

It finally happened, I knew the engine was on borrowed time, but it's been happily running me around for the past couple of years, relatively drama free. Now, still running reasonably well considering, it's misfiring on one cylinder and after a quick compression test, no.4 was found to be sadly lacking. You could also hear the familiar chuff-chuff out of the righthand pipe from a burnt exhaust valve.

The reason, you may well ask, why this engine was on borrowed time was because there is wear in the camshaft journals, so not ideal to do a top-end rebuild with the original head. And finding another head for one of these seems to be impossible in Australia. Plenty in the UK and America, but postage wouldn't be worthwhile.