SUZUKI TR750
Our Malcolm is moving on with the saucy Suzuki triple build – what could go wrong with a simple stroker?
Malc Shaw is finally on with the engine.
The build is progressing but there’s still a massive amount to do. Although it was going to be some time before I needed the engine, I had a lot of the parts lying about and I thought it was time to start assembling the bottom-end.
First thing was to send the top and bottom casings, barrels and head off to Steve Woolston at Kent Vapour Blasting.
Steve’s a bit of an entrepreneur and into bikes himself, starting the business around three years ago and just about to invest in a large bead-blasting cab so he can do frames: yep, another shed-dweller working from home now. He does a really nice job, well priced and is very meticulous.
All the parts returned looking much better than on departure and probably manufacture. Despite Steve having given them a good wash after blasting I used a power hose and air-line to go over everything a couple more times just to be sure. The thought of one of those little glass beads getting in a bearing is not good! I also used a variety of machine taps to go through every threaded hole, making sure they were clean and the threads were in good order.
Cleanliness with reassembly is key, so I found a ‘special’ place in my workshop as far away from foreign objects as possible
and on a clean surface. At any point the engine is left, it’s wrapped in towels to prevent any ingress of unwanted elements.
All the engine bolts were cleaned with a wire brush on the bench grinder (which lives elsewhere), then given a bit of a buff up on a polishing wheel; 40 years can leave some odd crud in the threads!
Now, I’m going to say I have always used a workshop manual, no matter how easy or simple I think an engine is to put back together. I believe it is good practice for most of us to have something to reference as we go along. Its surprisingly easy to leave a small part out or get something out of sequence, so a way of checking can save time and upset (or upsets) in the long run. Some of the manuals are a little bit lacking in diagrams, so use a parts book from the manufacturer as they generally show everything and can often be found online.
I just took my time, following the manual and pictures I’d taken on disassembly. Each part had been cleaned and checked before being put back in its rightful home. The first part to go back in is the water-pump breather pipe. Next the gear selector drum and forks can be positioned (photo 1), at that point making sure everything fits/rotates freely and moves as it should. Then the water-pump drive and impellor, checking the clearance between the impellor and bottom casing. Oil-pump drive, gear change shaft and kick start shaft followed.
Both gear shafts were positioned and checked for engagement and that the gears were being selected by rotating them and selecting different gears. The water-pump drive dropped in, making sure all locating dowels and bearing half-clips were present and correct.
All looking good until I noticed (why had I not seen it before?) the bearing next to the sprocket on the gear shaft was damaged (photo 2). It’s a bit odd, but I suspected previously this engine had suffered a chain snap at some point and it’s the only explanation I have. An email to Robinsons Foundry (thank you again for efficient service) had a new bearing supplied within a few days.
Removing the bearing was relatively straightforward. I’ve a reasonably cheap bench press, a very useful tool, even if it does leak a bit of oil! A couple of pieces of angle iron supported the bearing and carefully pressing down on the gear shaft with a block of aluminium (photo 3) had it off with little fuss. The new one was again carefully pressed on. A little later than planned and all was back together (photo 4).
The crank which had been rebuilt by BDK was then dropped in, making sure the bearings all located properly, ready for the top casing (photo 5).
I used Michel Gasket Cement supplied by Yambits to seal between the two casings, making extra sure of coverage around the crank, then all the casing bolts were tightened in sequence with a drop of Loctite on each, crank, gears, etc., checked again; only once its running will I know if I’ve got it right!
I’ve run through that part a bit quick. It’s a standard rebuild, and yes, I would like a Nova gear kit, but where do I stop? So, all new seals fitted and everything given a dose of oil. One deviation is those horrible countersunk cross-head screws Suzuki use which are absolute pigs to get out and seem always to deform even when using an impact driver to remove them
(photo 6). They have been replaced with A2 stainless countersunk socket head variants, each cut to the required length
(photo 7). A bag of these cost pence from the likes of Tool Station. If I do have to get them out in the future, hopefully it will make things much easier.
On to some modifications. I’m not going to use a starter motor for a couple of reasons. I can use a much smaller battery and the weight of the motor itself. Also, the tacho is going to be electronic so the drive is not needed. That leaves two holes that need to be blocked off! I turned up on the lathe a couple of aluminium bungs to the required dimensions, grooving them to accept an O-ring for oil retention and knurling the tops for a bit of decoration
(photo 8). The tacho drive is held in place with a small bolt so this was utilised to hold that bung in place, but the one for the starter motor required that I make a small bracket to help retain it in place. This was made from some stainless sheet by the usual process of making a card template first, then transferring it to the metal. It seems to go in okay and does the job. The other starter motor holes were blocked up with cap head stainless bolts, otherwise gearbox oil could leak out (photo 9).
I started to look at the left-front side of the engine where the starter clutch is fitted (photo 10, standard bike). I wondered if there was anything there that since I was not using a starter motor I could omit. Clearly there was a double idler gear which now did nothing, so it was binned (photo 11). Also, most of the starter clutch is now redundant, but it still drives the ignition system and water-pump.
Weight on the end of a crank in a lot of instances is not beneficial, potentially putting extra strain and imbalance on the crank, plus if you can reduce that mass it helps the engine spin up faster (also reduces engine braking, but there again it’s a two-stroke!).
The starter clutch weighed quite a bit, so I took it apart to see if there was anything I could do to reduce the mass (photo 12). Fairly quickly I could see that I could leave half of it out. A phone call to Matt at BDK helped to confirm my thoughts. I also thought that I could machine some of the excess material of one part. I’m not sure what it was made of but it was incredibly tough and very hard to machine on the lathe, but very slowly did the trick. The large plastic gear (note to self, not to use the one in the picture) which drives the water-pump has to stay as its driven from the crank, the drive pin for the ignition is still in the right place, but once all back together (photo 13) there’s a significant weight saving. Now where’s my bacon butty!
Thanks to: Kent Vapour Blasting – 07399 813647