SUZUKI TR750
Malc Shaw’s wallet takes a massive beating this month!
Last time the exhausts had been built and fitted and I felt the essence of the bike was coming together. There were a few niggles and areas that I was thinking needed to be addressed, both practical and aesthetic.
First the engine. To recap, previously I had spoken to BDK Race Engineering. The brief was not out and out bhp but a usable, tractable engine.
I’d had a number of conversations with James at BDK and in order to save a few quid had altered the inlet angle and welded stubs in to mount the 38mm Mikunis. The rest was then up to BDK.
One area of concern with GT750 engines under hard use is exploding clutches. It appears that once tuned and abused, the clutch can be marginal and a bit prone to slipping, the heat generated being the issue. BDK’S solution is to modify the clutch basket to take an extra plate; this apparently gets around the problem. To complicate matters further, there is also a band which runs round the clutch basket. Despite researching this and reading various threads on different forums, I did not get a clear sense of whether it stops the clutches breaking. Some say don’t remove at any cost, others seem to think it makes little difference. Of course, the solution is to fit BDK’S dry race clutch set up. Cost and loss of the kick-starter unfortunately for what I’m trying to achieve, will not allow for this.
The ‘Water Buffalo’ or ‘Kettle’ are names the GT750 lovingly acquired due to its propensity at times to overheat and blow head gaskets. BDK’S advice is once there’s any tuning of the engine this becomes a greater issue. Their solution is to do away with the head gasket and O-ring the block. (Photo 1) An advantage is also that if the head is removed the O-rings can be re-used.
With the head, I opted for the muchmodified centre plug option. The head is machined and domed caps fitted; these are removable, therefore in the event of problems on one cylinder that damages the combustion chamber, they can be replaced and the whole head is not scrap. To my mind the other benefits are each cylinder now is the same, plus I would think that with a centre plug and revised squish the flame path has got to be improved (Photo 2).
The block was going to be ported (photo 3 and 4), bored, new pistons, clutch modified, etc., and the crank fully rebuilt. It was a simple case of sending everything off, nailing the screaming wallet in an open position to the bench and waiting.
The turnaround time was quite reasonable and once everything was ready, I took a trip to BDK to pick up all the bits. I was very happy with the results; now I had ports one could fall down and James was helpful with information and a few other parts I required.
One area I wanted to address was the seat unit. I had a fibre-glass one that I’d modified to fit, plus cut a bit of depth out of the rear portion to slim it down slightly. I was not overly happy with the material and knew it was going to be hard to get the sort of painted finish I wanted on it. The alternative was to have one made in aluminium. One name that kept coming up was Simon Parker of Parker Fabrication in Bournemouth.
On the day I visited Simon was not at his workshop, but invited us to his home. I got to see a couple of his own private classic cars he was restoring. What was apparent was the skill he has in making very complex panels. Thanks go to his wife Denise for the cups of tea!
Simon was in the automotive restoration trade for around 10 years before starting his own company, Parker Fabrication. He’s time-served old school and it shows in his work. He’s been building alloy tanks and fabricating parts for bikes for at least the last 25 years. Check out his website for details. He was involved in the design, development and production of the Henry Cole Norton tank and seat. He also does work for a number of other manufacturers, Norton included.
The fibre-glass seat was handed over as a ‘buck’. Simon made a few recommendations and I left things with him (Photo 5). A couple of weeks later a parcel arrived with my new alloy seat, formed from 2mm aluminium. It’s the business, will look much better than the GRP seat and I should be able to get a good painted finish on it. (I know, Bertie wants me to polish it!)
Aluminium is soft and malleable. Simon had said it might need a bit of careful tweaking as he had not built it on the frame and a bit of reinforcement where my weight was seated may be needed, so as not to stress and distort it.
Quite a bit of time was spent finding the centre-line of the bike, the seat and carefully measuring. A further alloy plate of thicker material was cut and sat on the frame. The mounting hole centres were found by machining a point on to a screw thread (use a drill and a grinder if you don’t have a lathe, it works), then I screwed the thread into the mounts on the frame until the point was just proud, basically a transfer punch. (Photo 6) By putting a bit of weight on to the ally plate the four mounting holes were then marked out and could be drilled.
The exact position of the seat unit in relation to the alloy plate was figured out and the alloy plate was bonded to the base of the seat unit with epoxy resin and fibre-glass strands. It’s important to use epoxy as it’s a glue and will bond better than a styrene-based resin. Then for belt and braces I used some carbon-fibre weave cloth with epoxy resin on the underside to add further strength to the seat unit (photo 7). The holes from the alloy plate were then drilled right through the ‘sandwich’ and lined up well enough to mount the seat.
I obtained a cheap Chinese rear number plate/indicator mounting bracket. Quality quite good, how they make this stuff at those prices I don’t know. I stripped off the parts I did not want (photo 8) and machined up a further mounting bracket (photo 9).
I also made a thicker ally plate that was shaped to fit inside the seat unit which had threaded holes made in it. The idea here is to spread the load of the number plate bracket and to give a good fixing. Again, very carefully I lined everything up and drilled through the seat unit. The plate with the threaded holes was bonded inside the seat unit with JB Weld, an experiment, which has seemingly worked OK. I now have a fixing point for the rear lights and number plate.
One issue is the bike has no steering lock! The fault is mine because I have used inverted GSX-R forks, of 53mm diameter where they touch the lock. The bike is designed for classic racing and right-way-up forks which I think have a maximum limit on the diameter of 41mm. The lock stops are easily modified, but the forks ‘hit’ the top of the rad. With a lot of looking at, it occurred to me that the way the standard GT750 rad is built there is room to slim down the top tank without losing any core depth, and move the whole rad back a bit against the frame. I bought from India (ebay) an ally GT750 rad (photo 10), stupidly cheap for what it is. However, it’s a ‘copy’ and dimensionally it did not solve the problem. A bespoke rad was deemed the only solution.
At a show previously I’d spoken with West Mercia Radiators, more out of interest than need at that time. They appeared to be able to make almost any rad required. A phone call and a chat with Andrew regarding my requirements had me sending a standard rad to him covered in masking tape with various instructions on of what I needed. We agreed that he would not put mountings on it as I could make these and then get the rad fixed exactly where it was needed.
Andrew was off on holiday in a couple of weeks and had a full order book. However, he said he would get it made and sent to me before he went. He must have burnt the midnight oil, but did deliver on time: a great service.
The rad looks good, is slimmer by 25mm (photo 11), but has a more efficient core and fits as intended. I made the four brackets from cutting down some one-inch by two-inch 6082 aluminium box then machining them to size and shape (photo
12). That was quite a few hours in itself, so if you’re using a professional to make you parts, check first the price and don’t suck loudly through your teeth at the reply! A well-made bracket takes time. Oh, and the wallet has clamped itself shut and is recovering in intensive care!
Thanks to
• BDK Race Engineering: - 01508 481713 • Parker Fabrication: - 01202 434899, mob 07789423786 • West Mercia Radiators: - 0121 5564142, mob 07779716931