It has been a good week ! I started the engine on the current project for the first time, and although there were no mosquitoes to be slain, there was enough smoke generated to have done the job if there had been any. 🙂
The engine sounds healthy and I’m hoping that the remaining small jobs can be completed quickly so I can get the bike in for an inspection and then on the road. That last part is a bit up in the air, as there is still a lot of snow about, and of course still quite a few weeks of potentially wintry weather still to be had, but there is at least a light at the end of the tunnel.
Just to recap, this is what the bike looked like when it first arrived (just click on the images to see larger versions):
And this is how the bike looks now:
The gauges will not be back from Allan Tucker till sometime later this summer, so for the moment I have temporarily mounted a spare set from a later model machine. I still have a few things to tidy up – the exhaust pipes refuse to seal properly for example, and I also need to finish the fuel tank installation – but I’m pleased with how it looks and sounds.
Now we just need for all the white stuff to be gone !
Time to get the switch gear sorted, and of course nothing is straight forward. The 1972 model GT750 used a one year only set of switches, and good working examples are difficult to locate. As well, internally the left side switch is quite different from later models as it has individual block switch modules for each function.
I actually just had one left switch for the GT750 and a second left switch that was from either a T500 or a T350 of the same year as it was unpainted aluminium. The GT750 switch gear was originally painted in gloss black. This unknown left switch also had the connector block cut off and so needed new wiring and black plastic sleeving, but otherwise looked complete. As can be seen in the lower part of the photo (just click to see a larger version) . it was also wired differently from the GT750 version seen toward the top of the photo, having different colour codes and termination points on the headlamp switch modules internally.
Disassembly of these switches is not for the faint of heart as there are a lot of really small components inside them: small springs, even smaller steel balls, little brass slider contacts and little tiny screws which seem to disappear as if by magic into the darkest deepest recesses of your work area, never to be seen again ! My first step then, was to clean the the switch blocks with electrical contact spray cleaner without attempting to disassemble the individual component parts, temporarily reconnect nine-pin connector blocks and then check with an ohm meter to see whether they worked at all. A couple of the switches did not work at all on the silver left switch and so then needed careful total disassembly to properly clean them. During reassembly I lubed the interior contacts with dielectric grease, and also did so for the modules I didn’t disassemble.
When wired up temporarily to the bike, and with the power on, they now all worked reliably with the exception of the horn button on the ‘real’ original GT750 switch. A closer examination showed that the circuit board was cracked, and so when pressing the horn button, the flexing of the board caused intermittent contact. This early switch was also a different design than later ones and is actually missing the lower metal clamp that provides support for the board to keep it from flexing. You can see the early switch (left) and a later one (right) in the photo to the left. I’m not sure when the change was made, but it would have been after frame 16153. The left switch was completely redesigned for 1973 and later models using a round housing similar in shape to that already used on the right side, and the headlamp on/off and high/low beam switch was simplified. The combination horn and turn signal module however used in the newer left switches was the same up until sometime in 1974. Luckily I had a later style scrap left switch and so was able to salvage a working horn/signal switch module.
The internals for the right switch gear are pretty much unchanged through the course of GT750 production.
With the switch modules sorted out, I then stripped the switch cases down for painting. When SWMBO’d was out shopping, I cured the painted cases in our counter top toaster oven for an hour. 🙂 Once they had cooled down, I added the orange paint (I use Testors Tangerine 1126TT) for the lettering using the ‘dab and wipe’ method and re-installed the internals, using new black sleeving and connector blocks that I buy from Vintage Connections in the USA.
The final result looks pretty good, and also works which is always a bonus ! On to the final finishing steps as I get closer to seeing whether the engine will fire up ! And If you are interested in all the different switch gear used during the GT750 production, they are covered in ‘The Field Guide to the GT750’ which you can find at this link.
Oil pumps, and more specifically Suzuki oil injector pumps, have been occupying a good deal of my attention recently. For an in depth understanding of what they are and how they work, I suggest you take a look at the excellent overview of Suzuki GT750 injector pumps written by a friend of mine, Richard Nowson, which can be read at this link. The design of these for the Suzuki GT750 is quite robust, but they are also 40+ years old now, and like all things mechanical (and otherwise I suppose !) are starting to show their age. I needed a working pump for my current project (which is documented here), and so I dug into my ‘box of bits’ to see what I could come up with.
The oil injector pump on a two stroke is obviously a critical engine component and if the pump fails you risk having a solid block of scrap metal in fairly short order ! It is possible to run pre-mix, but due to the design of the crankshaft bearings, doing so is not recommended. Before trusting your engine to a pump with no known history, as a minimum it makes sense to bench test it and I wrote about one way to do that some years ago at this link. Since then, I have made a bench top tester from a scrap crankcase I had. The kickstart shaft on the Suzuki GT750 also drives the oil pump, so a friend of mine turned down the end of the shaft on his lathe so I could mount a pulley and then drive the assembly from a fractional horse electric motor. I’ve attached a video of it in operation below:
I really should fit a guard as the HS&E folks I used to work with would likely have a fit, but it does the job.
If you listen to the sound of the pump, you can hear the change in tone as the pump lever is pulled forward. Below is a photo (just ‘click’ to see a larger image) of the underside of the top cap showing the rod that is being rotated. The slot in the middle rides against a pin on the top of the rotating piston. As the shaft rotates, the slot allows the piston to increase its stroke and so pumps more oil. It is important to note that the pump always pumps at least some oil – backing off the pump arm adjustment will only decrease oil flow at higher throttle openings, so if your engine smokes a lot at idle then backing off the adjustment doesn’t actually do anything. Over time, what can happen is that the top of the rotating piston will wear, and/or the shaft will wear, and should this happen the pump stroke increases and more oil is pumped – a sort of built in fail safe design I suppose.
Note: when reassembling the cap, it is possible to reinstall the shaft 180 degrees out of phase so that the pump will run at full output volume at engine idle. Make sure that the slot in the shaft faces away from the bleed screw and toward the pin as shown in the photo. Also note that later style pumps do not have the pin.
Often when pulling the rotating piston out of the barrel, you forget to hold the pump upside down, and so all the springs and pins fall out of the rotating piston ! Early pumps have three pins/plungers and later ones have only two. Should this happen to you, don’t panic – the springs are all the same and the short plunger fits the bore having the draw hole nearest the driven end of the pump shaft, as shown in the photo to the left.
The third plunger in the early pumps actually is used to draw oil from the injector tank and was found to be unnecessary and removed. I don’t recommend mixing and matching pump parts as there are a number of design differences.
For example the rotating piston in the early type having the third plunger also has a restricted inlet at the top of the rotating piston. Richard goes into much more detail about the different pump designs in his write-up.
There is an oil seal in the underside of the pump body which is still available from Suzuki (part 09285-08002). The rest of the pump was not intended to be user repairable, but as is often the case necessity is the mother of invention. New top gaskets are available from several places – I buy mine from Reiner in Germany as the exchange rate for the Canadian dollar usually favours the Euro, but Ian Beardsley in the UK (check this link) also sells them and the quality is excellent. The same gasket is also used on pumps fitting the GT550 and the GT380.
One item that so far at least I have not been able to source is the small u-cup oil seal used on the actuator shaft. When this seal fails, injector oil starts to leak out the end of the shaft at the top of the oil pump. This seal is an odd size, and while I have managed to find some that are close, the fit isn’t ideal. I’d be happier if there was more contact area between the seal and the shaft bore. The replacements do seem to work, but I only have about 8 hours of run time on one and so am not yet confident of how long they will last. I’ve attached a photo here showing a replacement seal installed on the shaft – as you can see it is the correct ID and OD, but is really too narrow for the slot in the shaft, so I plan to keep looking for something closer to the right size.
The bottom line is that after a couple of days of sorting, testing, rebuilding I now have a couple of injector pumps I’m happy with ! I’ve put the test pump with the replacement oil seals to one side for the moment and will circle back to run it for a few more hours on the test rig before I actually try it on an engine.
The build is getting close to being complete – just fiddly things like the handlebar switch gear to be done, and then perhaps I can make some smoke in a week or two – maybe. 🙂
The chain guard (or chain case if you prefer) on the 1972 and 1973 model GT750 is plastic, and you often find that the mount points are damaged. Over time the two special ‘top hat’ washers typically go missing, and just using an ordinary flat washer compresses and then eventually fractures the plastic, making it a scrap item. As these original plastic guards are becoming hard to find, it makes sense to use the correct fittings, especially as they are still available from your friendly neighbourhood Suzuki dealer under part number 09169-06010. Locally here in Calgary, I deal with GW Cycle World which is a family owned business who have been very helpful to me over the years. Recommended.
The horn on these is the early louvred style, having a chrome plated cover which is held in place by five aluminium rivets. As is often the case, the horn I wanted to use was not actually working, but luckily they are fairly easy to repair. I’ll post more detail on my web site at this link, but basically so long as the coil is good you can usually bring these back to life by cleaning the contacts, and then by adjusting both the points gap and the distance that the solenoid (hammer) is pulled into the coil before it hits the anvil . The anvil is threaded in from the back of the horn, and moving this in or out will change the pitch of the horn, although admittedly the sweet spot is quite small. What you do not want is for the solenoid/hammer to be set so it can’t move to open the contacts, as that risks burning out the coil. The adjustment is the small cross head screw on the back, and I use an ohm meter to ensure I am starting with an open circuit before applying power and trying to make adjustments. On this one, I had the louvred cover re-chromed, reattached the cover using stainless steel screws, re-sleeved the wires and it is good to go !
Suzuki changed over to having an AMP connector block to join the front and rear main wire harness together sometime after the 1975 model year I think. This was a great improvement on the earlier style of connectors which had a tendency to overheat and melt the connector jacket, and then potentially short out under your fuel tank. Not an ideal situation ! The harness I planned to refurbish for this project was the later type, and as part of that process I had to get the AMP connector apart. The AMP connector is a bit fiddly in that to release the pins or sockets from the plastic holders for cleaning etc., you need to compress in the two retainer tangs located on each side of the pin or socket that lock it into the plastic holder. You can see one of these tangs in the photo to the right. A similar pin extractor as used on the 3.5 mm flat blade crimp fittings will work which can either be bought or made.
The build continues – just steadily working through sub-components and checking and refurbishing as required.
The bearings on the points cover were shot, and so needed to be replaced. There are two, one of which (09262-30020) is no longer available from Suzuki so I buy both at a local bearing and seal supply place as they are standard sizes (SKF16006 and SKF 6302). The smaller bearing is held in place with a snap ring, but both are a tight fit. I heat the cover in our gas barbecue till they drop out, and then while everything is still hot I drop in the new ones.
The crankshaft I’m using is a later style from a 1976 or 1977 model engine, so it has the floating big end on the connecting rods. It has been fully reconditioned by Joe at RPM Services just south of Calgary. As a matter of interest, the new style crankshafts are 0.4 kg (0.89 lb) lighter than the older style due to the reduced width of the crank wheels. I’m also using the later style of starter clutch as I had several spare ones. The original design was changed in April 1972 beginning at engine 26030 and this is all described in service bulletin GT-4 which you can find at this link. I’m also using a later style points breaker cam. In the photo (just ‘click’ to see a larger image) you can see the older style on the left and the later style on the right. The newer style is 30 grams lighter as there is a notch in the wheel and the wheel itself is thinner.
The water pump drive gear was cracked as per usual – these are readily available from Suzuki in just about every country except the USA for some reason. Here in Canada they cost about $55 CAD so I just replace them. As well, I rebuilt the water pump and will be using the later style of clutch basket bearing having the needle roller along with new clutch plates and springs.
The transmission was ‘like new’ and needed no changes, so once I was sure it would shift through all the gears, I was ready to button up the cases. You can see some blue dye on the top case in the photo where I was checking for high spots and found some. This is the first time I’ve actually checked this fit using dye and there is a lesson there I’m sure. Normally I worry more about the cylinder and cylinder head fit because of the water jackets. I suppose I could have it skimmed at a machine shop, but I am hoping the base gasket will be enough to make the seal as I’ve never had a problem previously. I’m sure we will find out soon enough !
It is an annual event, and this year was perhaps a bit larger than usual. In addition to the ongoing changes and small additions I do as a part of normal house-keeping, I also do rebuilds on sections of the site on an annual, or sometimes semi-annual basis. New contributions from owners sometimes piles up as I go through the process of validating new material offered to me. And some parts of the site start to look a bit dated after a period of time, and just need a refresh.
During this year’s update process so far (it isn’t finished yet) I have added about 400 new images – many of them new scans of service bulletins from Suzuki Canada, but as well I was passed a set of US Suzuki bulletins by Paul H. in the UK which were in colour. While they were duplicates of many I already had on the site, it seemed like a nice update and so I decided to roll them into the work list. Other areas that have been updated include:
sections of the GT750 Field Guide: new gauge photos, new prototype photos, additional JDM sales material (thank you Mike W.).
sections of the Resource pages: the service bulletin material already mentioned, additional indexes in some pages, updated photos.
and sections of my Projects pages – mainly in the 1972 GT750 project area as it was getting too big and needed to be sub-divided to make it a bit easier to navigate.
I also am in the process of adding an SSL certificate to the site. This will allow encrypted communications between your browser and the site. The only real difference most people will notice (assuming I don’t break it completely !) will be that you will see an HTTPS: cue in the address line of your browser address bar. The main reason is to stop having the site flagged as ‘insecure’ by most of the newer browsers, which started in large part this month. I’m not really doing any e-commerce which would require encryption, but it is a ‘good practice’ to follow in this day and age unfortunately.
And finally – I wrote a series of articles about my last build (The Oily Purple) which were accepted for publication by RealClassic magazine in the UK. This is a magazine I have subscribed to for some years now, as I like the style of writing and the self depreciating humour of the various contributors. It tends to not have the breathless ‘was this the best xxxxx machine ever’ sort of article which are all too common elsewhere on the news stand, and which I generally find annoying. RealClassic tends to feature articles about owning, maintaining and using old (and some not so old) motorcycles. If that sounds like something that would interest you, then you should pick up a copy, and you should especially buy the January, February and March 2017 issues as my articles are in them ! Information about the January 2017 Real Classic issue may be found at this link.
I continue to slowly bolt together my current 1972 GT750 project. With a bit of luck I should have the wiring finished this weekend, and then I plan to start building the engine this coming week. You can follow my progress (or lack thereof) at this link !
I realise that ‘anchour’ is an archaic form of ‘anchor’ , but as it could be said that a drum brake is archaic when compared to a disc, I’m going to go with it ! This article then is about the drum brakes on the 1972 GT750 – and more specifically the front one.
The front drum brake as used on the 1972 GT750 is a twin leading shoe (2ls) drum brake having two brake drums, one on either side of the hub, and four brake shoes in total with each one separately actuated. The idea is that the servo effect of having the 2ls will increase stopping capability – in one direction. Note that when backing a bike off a trailer for example, the brake doesn’t work very well at all in reverse and can lead to unpleasant surprises !
Recall that I had put a front drum aside to be dealt with later as it was badly corroded (photo above on the right – just click for a larger image) . I had both the front and rear drums cleaned at Top Gun Coatings here in Calgary who used a vibro-polishing process. This is perhaps not quite as good as vapour blasting, but it does give a very nice finish which is close to the factory original. On inspection, it was clear that while the front drum would be usable, it did have a few cosmetic issues. The gouges in the spoke flange on the left side were deep enough that I didn’t want to try to polish them out as it may have weakened the flange, but the ding in the edge of the drum (which can be seen in the photo above and to the left) needed to be addressed. Art, who is a friend of mine here in Calgary and who teaches welding at SAIT, managed to do a small repair on the edge that makes it look a lot better as can be seen in the photo on the right.
The brake shoe cams are handed, having a slight rounded trailing edge on the edge that lifts the end of the shoe when the arm is actuated. Consequently, you do need to install them on the correct sides. The rear brake cam (which is a conventional drum brake) and mounted on the right side of the drum, is the same part number (54440-11002) as is used on the left hand side on the early, pre-frame number 18325 bikes. The right hand cam (54430-31000) for the front is specific to the 2ls brake as used on the GT550 and the GT750.
At frame 18325 the cam design changed, with the new part numbers being 54430-31001 for the right hand cams, and 54440-33000 left hand ones. The difference between the new and the old cams is the thickness of the pivot block which was increased from about 7mm to be about 10mm. The difference is clearly visible in the photo to the left, with the original style on the left and the updated version on the right. Note the rear drum stayed with 54440-11002 which changed to 54440-11003 and was used on many models (T20 rear wheel, T305 rear, all years of T500 front drum brake, and all years of GT750 rear drum brake, plus others).
I had most of the steel fasteners and speciality parts re-zinced by Wespen here in Calgary. On the GT750 J (and K and L) there are quite a number of chromed parts which on later models were left in zinc. In some cases the parts cleaned up like new just by having a good soak in Evapo-rust so that is an obvious first thing to try before sending items out to be re-chromed. The air vents (parts 36 and 37) are in two parts with a under grill which I left in zinc, and a top louvred grill which I had re-chromed. The actuator levers cleaned up well enough to re-use as is. There are a lot of parts in these brakes – I’ve included a parts diagram to the right. The lock tabs (part 42) I ordered from Ian Beardsley in the UK who supplies them in stainless steel. You can find them at this link.
As previously mentioned, I had Suzuki Canada reactivate the part number for the front brake shoes. I still smile whenever I look at the packaging as I’m not sure why they think they can charge the full price for used shoes (it says they are all factory tested ) but no matter. They work and based on the experience with the Oily Purple I built last year, I have to say they do work better than I had expected.
I am still in the process of final assembly. One thing I will need to source are the rubber air vent caps for the side plates. There are five of these (54676-31000) and many of mine have perished from sun and weather damage. I see that Eric of the Knalnaarpotz shop in The Netherlands has these available for about a Euro each. I have bought from him previously and recommend him, but first I will take a look through a couple of local hardware stores to see if they have anything close.
Once I have the wheels mounted and a rolling chassis, the next item on the agenda is the engine !
Some time ago I wrote a post about repairing the oil injector lines used on the GT750, and indeed the sort of oil injector line used on most of the late 1960 through 1970’s Suzuki two stroke models. You can find that article here. Assuming that the nylon oil lines themselves were sound, the key obstacle in repairing these lines has been the lack of a replacement option for the check valves located at the end of each line. These are obviously now old, they are easily damaged whether as a result of ham-fisted cleaning attempts by previous owners, or due to corrosion, and like any mechanical device they inevitably wear out. When these valves start to pass, injector oil drains through the injector pump into the crankshaft area and can potentially cause serious damage to the piston and connecting rods due to the risk of hydraulic lock. As well, leaking valves also will cause excessive smoking when the engine is first started. While all of these old two strokes smoke to some degree, from a ‘good neighbour’ perspective ideally it should be minimised if at all possible. A photo of what they look like disassembled is to the right. Just ‘click’ on the photo to see a larger version.
Recently, new manufactured injector valve ends have been offered for sale by David Foxall in the UK who sells them on eBay (see this link or this link) and I did seriously consider buying some from him but so far at least have held off for two main reasons:
I had a few questions and he was not very responsive to my queries, but most importantly,
the experiences of others who had bought them seemed mixed.
The two together gave me reason to pause, and so more time passed while I continued to splice and or swap good used valve ends for bad ones as per my original article. Then a Sundial member using the name ‘Vintageman’ mentioned in a post that he had used a Kawasaki OEM part 16128-009 which seemed to work for him. Needless to say, I bought a few to try out and am pleased to confirm that indeed they appear to be the same as the original Suzuki part in every respect that matters. While I was not able to accurately measure the crack pressure (the pressure at which the ball lifts from the seat), dimensionally the Kawasaki valves are the same as the Suzuki ones. When fitted into the nylon line, with the metal collar reinstalled they are oil tight and so far at least, they do not seem to leak.
The instructions supplied by David Foxall for the installation of his replacement valves, and which he very generously provides for download on his website, work well whether you buy from him or opt for the Kawasaki version. I also have them available for downloading at this link. While as yet I haven’t bought any of David’s valves, I may do so at some point just to compare them. Given his are from the UK, due to exchange rates with the Canadian dollar David’s are a bit on the expensive side, but with a bit of luck the value of the British pound may drop further due to Brexit, making them more affordable for overseas buyers like myself ! In the meantime, I have generally bought mine from Kawasaki in the US where they seem to be readily available and are a reasonable price even after converting from USD to CDN$. Kawasaki here in Canada seem to never have stock on hand, which is annoying, but as with Suzuki here in Canada is all too common.
I now have over 2000 miles on a rebuilt set of oil injector lines using the Kawasaki valves which are installed on my 1972 J (called the ‘Oily Purple’ which you can read about here). I am pleased enough with how they have worked that I am now in the process of repairing a few more sets to be used as replacements on other projects I am working on – the next one being another 1972 J model which you can read about at this link.
As mentioned previously, the frame had some damage that needed repair, and Jonathan and Derek at Trillion Industries did a great job. The area around the brake pivot post has been completely rebuilt, reinforced and I suppose should now outlast the rest of the frame ! Just ‘click’ on any image to see a larger version. As well the rear shock hanger threads were repaired so all I did then was clean up a few areas in preparation for having the frame and associated bits powder coated.
The powder coat was done at Top Gun Coatings in the north east of Calgary and it all came back looking better than new. They bake off all the oil and old paint on the parts in an oven before doing some touch-up sand blasting prior to the actual powder coat and I have to say that the finish they have achieved is excellent. Recommended !
I have the frame on the bench and have started bolting bits back on, checking for fit and seeing what is still missing, what can be repaired or will need to be replaced. I print out copies of the parts manual and go through each sub-component so it isn’t the fastest process, but focusing on the sub assemblies makes the whole project much easier to deal with.
The engine had seen some hard usage. At some point in its life, someone had managed to take it apart, and in the process had very nearly destroyed the barrels. The upper crankcase above the alternator had been broken and then repaired with what looked to be JBWeld, The front upper engine mount carrier had been broken and the shard of aluminium casting stuck back on with silicon and there was lots of damage elsewhere, including one of the water jackets being compromised. Quite sad to see really – I described the engine elsewhere as looking pretty good apart from the bits that were terrible ! The repair work was done by Trillion Industries , and like the frame repairs is excellent – recommended !
The next step for the engine is to have the engine cases and covers vapour blasted (also called liquid honing) by a company in Medicine Hat. This process is pretty common elsewhere, but not in Canada and I’ve only been able to positively identify three companies in Canada that will do the work. It is a glass bead process using high pressure water as the carrier rather than air, and so gives a softer, cleaner finish than can be obtained using just conventional glass bead and air. It will be interesting to see how they look !
Elsewhere, I have some parts back from plating and more to send out, both zinc and chrome, and I have to build some wheels. At least I am unlikely to be bored !
With “Oily Purple” on the road and running well, it was time to start work on one of the two sequentially numbered bikes. These are about 3000 frame numbers younger than the purple bike, but share the same early style frame design having the tubing welded into large cast lugs for the engine mounts, the two bolt side stand, no centre cross brace behind the radiator, the welded tubes for mounting the rear signal lights, and the poorly designed combination rear brake pivot/foot peg perch.
The xx153 frame seemed to be in better shape, so I decided to start with xx152. This had been poorly repaired in the area of the brake pivot/foot peg mount at some point with blow throughs and loads of weld splatter. The end of the post was badly damaged such that a foot peg would not even fit, but after an hour of careful filing, I did manage to clean it up. Just ‘click’ on any of the photos to see a larger image. As well, the upper rear shock mount threads were stripped and so those would have to be repaired. It is good to know your limitations, and both of these repairs exceeded my skill/comfort level, so after stripping the frame I will cart it off to Trillion Industries here in town where Derek can work his magic.
An examination of the rest of what was there yielded a lot of scrap, however the forks, wheels, headstock and a handful of other components looked to be salvageable. In my stash of stock piled bits I had a couple of fuel tanks to choose from, a seat, both front and rear fenders, good side covers. a radiator, the cooling fan, a complete and correct airbox, headlamp with the horseshoe chrome rim, plus several wire harnesses and assorted electrical bits sufficient to get the project done. I assembled a bit of this together as a ‘test’ build and the result does resemble a motorcycle.
The next step then was to take it all apart again, remove the engine and do an assessment of what it will need and start to farm out bits for powder coating, chrome and paint. And as well of course , get the frame over to Derek for repair. The other thing I still need to so is to sort through the bolts and fittings I have and see what else needs to be plated. I normally take a couple of coffee cans full of bits in for bright zinc plating, but for this build will also be having some cadmium plating of the spokes done, as well as some nickel or chrome plating of a few of the correct fasteners, as they are difficult to find. I have considered using stainless copies of the originals, but as with all things, cost does start to become an issue.