The Oily Purple

You will recall from an earlier post (see this link) , that the first of the three 1972 GT750’s I am restoring was to be in ‘oily rag’ condition, so no new paint, no new fresh chrome but rebuilt/refurbished mechanicals . I made a deliberate choice to use the early style of engine having the bolt on carburettors, and the early style of frame which lacked the added cross-bar between the two down tubes holding the radiator. So the starting point was a bare frame and a set of engine cases, together with some boxes of parts (as always – just ‘click’ on any photo to see a larger version) :

I had several original style crank shafts available, and also had a couple of the newer style ones. The two main differences between the early and late types are the lack of an oiling slot in the small end of the connecting rod, and the width of the fly wheels at the big end due to the change in fixed vs. floating big ends.

This photo shows the two small end designs – new on the left and old on the right. It is interesting to note that several of the engines I’ve opened up have shown bluing on the small ends indicating lubrication issues, and so using the newer style of connecting rod made sense to me. As well, the later style of crankshaft with the full floating big end was to me at least, also preferred. The older crankshafts being heavier may have contributed to the torque many owners attribute to the early engines, but I was less interested in that and very interested in engine longevity. In the end, I used a freshly rebuilt new style crank shaft and did the cylinder block conversion using shouldered cylinder bolts as were introduced with the late 1974 GT750 models and outlined in Service Bulletin GT-6 which you can read at this link. I also updated the starter clutch bearing and clutch main bearing to the later design, again with a view to engine longevity. I had several suitable transmissions to choose from, and I fully rebuilt the water pump using new parts sourced from Reiner in Germany.

The one thing I could not easily fix was the infamous water bypass line join face which was a source of leakage from day one on these engines, and which required a full engine strip to repair. In the photo lower left you can see the original design, and to the right the design that replaced it at engine number 36198.

The only solution to the water bypass problem is to be very careful about using the correct Three Bond sealant, and also to be sure to use some Bar’s Leaks or some other sort of radiator stop leak in the coolant.

I had several sets of wheels and brake drums to choose from, and laced up a couple of wheels using new spokes. Something to be sure to check is that if re-using old brake shoes, be sure that the linings are still actually securely bonded to the metal carrier. I have now seen several instances of the lining separating away from the metal carrier, which could seriously ruin your day if the lining came away completely while riding. New brake shoes are a better idea, and it is worth noting that any of the on-line parts listings I’ve seen for the 1972 GT750 front brakes still show you as needing quantity 4 of the front brake shoes. In actual fact Suzuki updated the packaging at some point, and now include two shoes per card, so rather than having to order 4, you actually only need to order 2 of part number 54401-07840.

The other thing I noticed was that the wheel bearings are quite small on the front drums, and in one instance showed signs of the bearing having spun in the carrier housing. To avoid this happening  again I secured the bearings with some Loctite 609 retaining compound which is specifically designed for this exact application.

The rest of the build was fairly straight forward, although I did end up spending quite a bit of time repairing the wiring harness. I’ve also installed a solid state voltage regulator sourced from Oregon Motorcycle Parts , and as well I’ve  installed an electronic ignition system from  Accent Electronics in Germany as I really like their design and have had no problems with it at all.  I also spent quite a bit of time on the clocks, using a pair of my reproduction shells and one of my reproduction trip reset knobs also.  I sell the shells on eBay and also directly on request, and as of last week have sold just over 200 of them to owners and restorers of the 1972 GT750 J all over the globe. For details, you are welcome to check this link.

I managed to put together a decent set of original paint ‘Candy Lavender’ tin, a serviceable exhaust set complete with the end cones and I recovered the seat using a Pit Replica cover from Thailand on a rebuilt seat pan using new foam. The end result is one I’m happy with. The bike looks time-worn and used, but handles and runs like new ! Now that the engine is broken in, I’m getting between 45 and 50 miles per Imperial gallon which isn’t bad for this model.

As always, additional detail on the build is elsewhere on my web site – you are welcome to check this link for the Oily Purple story specifically, and this link for the ongoing story on the next two 1972 GT750’s I’ll be restoring over the next couple of years.