After clearing the last of my stock in 2019, I continued to receive requests for the plastic GT750 J gauge shells from many owners from around the world. I have to admit, that I was hesitant about commissioning another order, as it took six long years just to recover my investment the first time ! While there are still quite a few of these machines on the road globally, it seems that outside of Europe (mainly France, Germany and the UK) the GT750 doesn’t have the same level of ‘collectability’ as a comparable Honda which impacts the value of the machines, and consequently the amount of money people are prepared to spend restoring them. And note that the cost of restoring these machines is beginning to escalate rapidly as it appears Suzuki has started to wind down their commitment to continuing to manufacture some of the critical parts, which in turn will drive higher costs for NOS and good used parts on the various auction sites, all of which just makes a bad situation worse. On the plus side, as I have fully recovered the cost of the injection moulds, the actual cost of a second run of gauge shells is less than what I had to pay for the the first run as now I am only having to deal with the actual production and materials costs. After some debate with SWMBO’d, I placed an order for a smaller second batch of shells in June of this year (2020).
As the order for this batch of shells was half the size of the first batch, once I had them on hand I prioritised sales to the many owners who had placed pre-orders, and who in some cases had been waiting for close to a year. My sincere thanks to all of you ! I now have about sixty sets left, and when they are gone, that really will be the last of them.
Prices are $120 CAD for a pair (speedometer and tachometer) or $65 each if you just want one, plus shipping of course. All the details about the replacement gauge shells are on my web site at this link.
Note: I do still have the reproduction reset knobs available for the GT750 J. Info for those is also on my web site.
I’ve been busy with ‘honey do’ items the past week, as in ‘honey do this and honey do that’ ! 😉 All things that needed nice weather, so it is all good. Here and there I have been able to slip away and spend a small amount of time in the shop, plus a few items have been arriving by post.
This Covid problem has really impacted deliveries, but things seem to slowly be returning to some semblance of normal which is nice to see. First up, a new GT750 J points cover arrived from Shaun in the UK. These are an item of absolute beauty and in very limited supply so if you are rebuilding a 1972 GT750 J, then you should not delay too long in trying to get one of these while he still has them. Look for them on FB at the “Suzuki GT750 parts UK” page.
Years ago, Keith in the UK wrote up a useful ‘how to’ for replacing the high tension leads on the Nippon Denso ignition coils used by Suzuki, which he graciously allowed me to link from my web site in the “User Tips” section. 7mm copper core ignition wire is available from many places (I buy mine from Walridge Motors in Ontario), but one thing I’ve had trouble tracking down is a sleeve of the correct size similar to what Suzuki installed on the ignition wires near to the coil. I have written an article for the CVMG newsletter which will appear in a future issue as well as in the ‘User Tips’ section of my main web site, but in short, on the triples there are 2 long sleeves on the left and right, and a shorter one on the centre. I buy mine from McMaster-Carr in the US, and while I’m sure there must be a Canadian supplier, I’ve just never been able to find one. McMaster-Carr also sells JIS machine screws which again I have never been able to find a Canadian supplier for. While you do get hosed on the US $ exchange rates, their service and delivery are first class.
And from Suzuki Canada, a surprise ! They actually had a GT380 timing gear in stock and managed to deliver it to my local dealer (Inglis Cycle here in London) in a week ! I nearly fell over in a state of shock, as the price was quite reasonable also, being less than $45 CAD. These gears have now (summer of 2020) been discontinued by Suzuki Japan and reproductions may possibly be made by a fellow in the UK. If that is confirmed, then I will post that information when it becomes available. Suzuki Canada has delisted a load of other vintage Suzuki part numbers this summer (including the GT750 nylon water pump gear), which was quite disappointing to learn. That specific GT380 gear is tough to do without so I suppose I should be thankful for small things.
Spent a bit of time sorting out the oil injection system on the GT380 project today. I’ve written previously about using the Kawasaki oil injection valves to repair the Suzuki oil distribution loom so I won’t go over that again here. If you are curious, then just go to my web site and do a search for ‘oil injection’. The Kawasaki part number is 16128-009 and I normally buy them from the USA as the prices I’ve been quoted here in Canada make me wince. And I tend to not replace all the valves, but prefer to just do the ones that are actually leaking. I blame my thriftiness on my Scottish ancestry, and while it sometimes comes back to bite me, generally I have good luck ! 😉
The other issue area was the oil pump itself. I have pump data on my web site written by a friend of mine, who also has it on his own site (just do a search for the pinkpossum.com web site). Two pumps came with the project bike, but only one was complete. When dealing with something as critical to the operation of the engine as the oil pump, unless you know for certain it works, it is a good idea to give them a close look. I popped the top off the pump, and pulled the rotor, and at first I thought the pump might be scrap as there was some corrosion evident. Luckily it cleaned up and all the passageways were clear in the casting. After cleaning and reassembly with a new top gasket and new lower oil seal, I ran the pump on my test rig for an hour and it checked out fine, so I think I’m good to go.👍
The pumps used on the Suzuki triples all look much the same, but the pump arms differ, with the GT750 being stamped as any of a 310, 312 or 318, the GT550 stamped with 340, 341 or 348 and the GT380 stamped with 330 or 331. The pump bodies generally seem to be the same and only the pump arms and shafts seem to differ: different lifts will give different pumping rates. Early style pumps differ from later ones due to changes with the carburettors and had a third piston to pull oil from the oil tank. Later pumps rely on gravity oil feed to the pump. Obviously you don’t want a GT380 pump on a GT750, but the other way around would probably work fine and just be a bit smokier than usual. 🤣
The 1975 GT380 rebuild story continues. Looking at the old cylinder head gaskets, it was obvious the centre one had blown, and had been run that way for a while. I’ve included a photo to the left. The mating surface on the barrel was cut as could be seen using a machinist’s square. As I had to repair what looked like cold chisel gouges in the aluminium anyway, I also filled the cut marks and then lapped the head on a flat surface (I’ve included photos of the repair etc. below). I used JB Weld for the repair and have had good success with this in the past for similar repairs. 👍
The GT380 uses a one piece cylinder head, but has three separate barrels, and when I had the barrels fitted and torqued down I found that with the left and right cylinder head bolts in place, the centre cylinder had an 8 thou gap between the head and the barrel. I could torque the head down in the centre and reduce the gap but I wasn’t happy doing so as obviously this was flexing the head (which by the way was flat). This gap is most probably what caused the original damage and the blow out of the original head gasket and having just repaired the centre barrel I didn’t fancy ruining it a second time. So after thinking about it for a bit, I just cut the cylinder head into three pieces and my clearance problem was solved ! 👍
With the three cylinder head pieces fitted in place, and as the mounting points for the RAM AIR cylinder head shrouds are on the left and right heads, everything still fits, and looks no different than before. And while I suppose it is possible the harmonics may now be different (less cylinder head dampening) I know that at least a few other owners have also gone this route with seemingly no ill effects, so I’m not too concerned.
I’ve torn down the GT380 engine and split the case to take a closer look at the gear clusters and the crankshaft. This engine came to me loosely put together, and when I pulled the clutch cover there were indications of rust, so it seemed the prudent thing to do. I know most people first try to get an engine running before deciding whether to do any open heart surgery, but most of the bikes I work on haven’t run in decades so I normally skip that step and just start taking things apart.
In actual fact the engine was not as bad as I’d feared. I had a receipt in the box of bits that came with it for a set of new rings and this proved to be true. Sadly rather than honing the bores, they really should have been bored to the next over size as all three showed lots of scoring. While it should have run, the likelihood of the new rings ever seating properly was next to nil. I’ve ordered new first over pistons and rings and will get the cylinders bored locally here in London. The centre cylinder head was damaged, but not the two outside ones. What appear to be pry bar marks in several places come very close to the fire ring, but I should be able to fix these with J-B Weld.
There was corrosion on the clutch plates and likewise on the gear clusters, but no pitting. The very light surface rust cleaned up fine so other than changing a few of the bearings in the gear clusters they should be OK. Likewise the crankshaft seems fine. Unlike with the GT750’s, the crankshaft oil seals are quite small on these, and there is no play in any of them or the bearings, so I’m just going to change the outboard seals and one outboard bearing on the right hand drive end of the crank. If the seals do eventually fail, the engine is small enough that pulling it out again to have the crank redone will not be too big a deal.
So now I wait till parts arrive, and for a machine shop to re-open post Covid-19 so I can get the bores done. Hopefully that will happen in the next couple of months. Fingers crossed anyway. 😉
And who out there is familiar with the GT380 neutral brake ? I have been doing some research and this clever (?) device was fitted to transmissions in the GT250, T350 and GT380 plus a few other models. I don’t know whether other manufacturers also fitted them, or indeed still fit them as I’ve never worked on anything newer than 1977 !
What it does is stop the rotation of the gears as you shift through neutral, to lessen gear noise when engaging from second or neutral to first. Suzuki used (possibly still uses ?) a rocking lever that has one end under the shift drum riding on the neutral détente pin, and the other end riding against a spring loaded pin which presses the rocking lever up against the underside of a a shoulder on the first driven gear.
On the GT380 I’m working on, the pin at one end was jammed in the bore, caused by aluminium shavings (see photo) that had been pared off the sides of the pin bore by the steel pin and leaving a step in the bore (see photo). With the pin jammed, the transmission didn’t shift properly due to a lot of drag (it was always partially in the ‘brake’ position). I was initially undecided about how to fix this so it doesn’t happen again. After spending some time swapping parts in and out and making a few modifications, it now seems to work just fine. 😎
The main problem was that the pin was catching in the bore and stopping the pin that rides on the underside of the brake arm from smoothly moving up and down. I had considered sleeving the bore, but the wall thickness is only 2mm which really isn’t a lot to play with. What I ended up doing was chucking the pin in the lathe and making a slight taper on the end. You can see the difference in the photo (somewhere near here) with a stock pin on the right and the modified one on the left (both pins are upside down in the photo – the dome end actually goes to the top). I’ve also polished the bore that the pin rides in.
I found that when I filled the pin bore with oil, it took some pressure to displace the oil up the flat on the side of the pin, so I also drilled a small oil hole in the side of the casting into the bore that the pin rides in. This will ensure that there is no chance of hydraulic lock. When the gearbox is filled with oil, the level should be above the top of the pin so I don’t see how this can hurt anything.
The last photo shows the neutral brake installed and you can also see the small oil hole I’ve added. The transmission now checks out fine, and shifts properly so next on the agenda is to take it all apart again and change some of the bearings on the two gear cluster shafts. Once that is done, I can button up the engine cases and spend a bit of time polishing the engine shrouds and engine side covers before I put the engine back into the frame.
I recently received another small batch of headstock or VIN labels from Jerry Ure in the USA (contact details are on my web site in the ‘Sources’ section and I believe he also sells on eBay – just do a search for ‘headtube tag’ or seller ‘jure’). I’ve ordered from him a couple of times previously and the quality is excellent and the cost is quite reasonable.
The headstock labels for Canada and the USA look the same, with the only ‘Canadian’ part being an additional Canada Transport ‘923’ label (later ones were stickers) that was usually attached below the VIN label. I’ve included a photo of the 923 label below. I have not had these 923 labels reproduced, but may do so in the future. The post 1971 Suzuki headstock labels in North America differ from most of the Suzuki VIN labels globally in not including the engine serial number, although they do include a month of manufacture. 1971 and earlier headstock labels (and they were not always on the headstock) look much the same as the ones used elsewhere around the globe and have both the frame and engine number.
Looking at the GT750 specifically, the 1972 headstock label lists lower weights than the 1973 and later versions (a GAWR of 847 lbs verses 884 lbs), possibly because of the addition of the twin front disc brake rotors, and the additional stiffening that was added in the rear of the frame by the swing arm and just behind the radiator. As well, the early labels were an anodised aluminium plate that was riveted to the headstock. These plates often do not survive, and in fact I am missing one completely, so I am considering making a small aluminium plate, attaching the new label Jerry has provided me to that, and then can rivet the new plate to the headstock. Finding the correct small brass push rivets is a bit of a pain and by the end of the 1972 model production these VIN labels were just aluminium foil labels anyway, so I may not bother. I like it to look correct, but I admit that I’m not obsessive. 😉
I have two consecutively numbered 1972 models, and so had Jerry make me a pair of new labels for them. He includes the serial numbers in the labels if you want that, so they are not stamped like the originals which is fine. You’ll also note the shape changed between the 1972/1973 labels and the later ones as they moved from being a ‘vertical’ style to a more horizontal format.
So I’m all set and just have to get down to the shop so I can get them installed ! The actual frame number of course is stamped into the frame, so all I have to worry about is sticking the right label on the right bike ! I also ordered a new label for the 1975 GT380 I’m refurbishing so that is now good to go also and can be seen in the top of the photo above.
I find lacing (of the wheel variety) to be quite relaxing ever since I stopped using a dial gauge while constantly fretting about the run out, and started just using an old spoke clamped to the wheel building stand. If it rubs – that spot is wrong, and if it rubs all the way around then you are good. I actually use old two spokes – one to measure the side to side, and one for overall roundness. If it is a new rim, then I protect it from being scratched with a bit of tape. On the Takasago rims there is usually such a large bump where the two ends were butted together at the factory and were welded up, that you never can get the wheel perfectly round anyway and I have been told that the factory tolerance was an 1/8 of an inch in the two axes. which seems like a lot. I don’t know if that is true, but you can get much closer than that just with a old spoke clamped to the side of the stand as an indicator, and when the tire is mounted it all seems to be good.
I’ve also been asked about the torque setting that I use, and to be honest, I’ve never seen one listed by Suzuki for these bikes or anything else from the early 1960’s and 1970’s. I aim for the same ‘ping’ sound when the spokes are tapped with the spoke wrench and have never had an issue.
I do a static balance once the tire (or tyre if you prefer) is mounted, and leave the wheels off the bike over night just in case I’ve pinched a tube and have a slow leak. In truth, since I picked up a Mojolever (just do a search for it with your favourite search tool) and a set of his nylon blocks for my tire change stand, I’ve had much better success with not pinching tubes. The next morning I temporarily fitted the newly re-spoked/re-shod wheels into the frame just so I could more easily move it around. It was a nice day, so I also fitted the tank and frame covers, rolled it outside and took a few photos.
The bike came with the tank and covers freshly painted, and they are similar to a 1974 colour that was offered. The bike is what we call here a ‘Heinz 57’ or a ‘bitsa’: the frame is a 1975, the date coding on the wheel rims would indicate they are from a 1976, the engine is from a 1977, and the headlamp is from a late 1970’s GS400, so using what looks like 1974 colour sort of fits with the theme. 😉
The wiring checks out, although I do have to rebuild the switchgear, as well as make a couple of small sub-harnesses. I have got the horn working again, and I now think I have enough bits to complete putting the gauges together.
Next on the agenda is to do something with the engine. 😎
I’m frequently reminded of just how small the world has become since the arrival of the internet. Yesterday Ian Beardsley from the UK dropped in for a short visit, a long chat, a few cups of tea and a sandwich. Ian is one of many people that I’ve known and chatted with via various internet boards, web sites and email over the years and who, like me, shares an interest in old Suzuki motorbikes. Ian maintains the UK based ‘Kettle Clinic’ board which is a great resource for Suzuki 2 stroke support. He is also one of two UK based suppliers of excellent quality stainless steel bits and pieces (see this link) for the Suzuki GT750 (and other lesser bikes 😉) , that I list on the ‘Sources‘ page on my web site.
Until yesterday I had no idea what he looked like as we had never met in person, although I have bought a few of his high quality stainless steel bits for the GT750 over the years. As we chatted, it was surprising just how many people we both ‘knew’ from the global Suzuki GT750 community: people like Alan T. in Barbados, Reiner S. and others in Germany, Erik P. in NL, Barry W., Alan H., and many, many others in the UK, along with people like Richard N. in the USA. And we also shared good memories about GT750 owners now passed, like Gary Cobbs, also from the UK. Of course we also talked about motorbikes, parts and pieces for motorbikes, some ‘how to’ techniques on finishing parts for motorbikes, and on and on until it became dark, and it was time for him to leave. All in all it was quite a pleasant way to spend an afternoon !
As mentioned in the last article, the GT750 tank filler cover lock as used on the 1976 and 1977 GT750 is a different animal. Unlike the other locks used by Suzuki, this one has a crimped bezel which retains the lock tumbler, making it a real pain to deal with. For this reason, a number of people (including myself) will suggest that you try to find a tank cover lock complete with key because it is then easier to make everything else match it, rather than the other way around.
Referring to the photo below (just click for a large image), notice that the lock tumbler itself actually only has one leaf. This means a range of different keys will open it, as many keys will have the same lift at that position on the key. I have three locks in my spares box, and one can be opened with a 140 and a 150 key, and another will open with the 207 or 150 key. In theory, if a person had enough different keys then you should be able to find several that will fit any given lock. I suppose at one time, there would have been markings on the barrels which would allow you to work out which range of key numbers fit which locks, however only one of mine has anything interesting stamped on the barrel and the others are blank. There are what appear to be different casting numbers on the end of the barrels, but these numbers do not appear to relate to which key to use. So if you are in the unfortunate position of having a tank cover lock, but no key then you are in a bit of a pickle.
The good news is that Suzuki still sells these locks under part number 44280-37010 for about $34 in USD in the USA or € 35 in most of Europe. For some reason they are seriously silly money at the one place I checked in the UK (£62 !!! ). As a matter of interest, the same lock is used on several models of 1977 through 1979 GS750, GS550, GS400, GS425 as well as the 1976 RE5. Given that the new lock comes with two new keys, a new retaining clip, new gasket and also given how easy it is to re-key the other three locks on a 1976 or 1977 GT750, this then really is the logical path to take if you want a matching set of keyed-alike locks for your restoration.
Of course, if you are a purist, then go ahead and re-key the one you have ! The only hard part is first removing and then re-fitting the bezel without damaging it. You can make your life simpler when re-installing the bezel and either saw tooth the inside edge of the bezel so that you have many small triangular tabs to fold over (the same trick also works on the instrument stainless steel retainer rings by the way) or cut excess material away with a Dremel to leave four tabs (as seen in the photo) which will make it much easier to re-crimp into place. The bezel, the tumbler cover and the trap door are made of stainless steel and so will clean up nicely with a bit of care.
I’m still waiting for the exhaust to be re-chromed on my 1972 GT750 project, and so rather than just stand around, I’ve decided to do a but more fiddling with the next project, which is a 1975 GT380.
One of the (many) little jobs to be done is to assemble a working set of locks and latches and for them to all be keyed alike. For the GT380 I have collected together a set of latches to be worked on as seen in the photo to the left (just click on the image for a larger version). Re-keying these locks is not difficult if you have a spare one or two to provide you with a decent selection of tumbler parts to choose from. Over the years, I have at various times described lock re-keying elsewhere on this web site, but I thought it time to gather all the information into one place for ease of reference. Note that normally, on the 1974 through 1977 models at least having the flip up fuel cap, you do not have to re-key fuel cap locks as any Suzuki key from that era should open them. The 1976/1977 GT750 is a different case and I may cover that later, but right now the focus is on the GT380.
The Suzuki locks of this era having the double sided key blanks, used a 4 different leaves (possibly 5 but 4 for certain) for their key combinations in the tumbler that the key is inserted into. These leaves are set into channels and in their normal state, are lifted into the ‘lock’ position by a tiny little spring under the ear of the leaf which is very easy to loose if you are not very careful. The act of inserting the key, just pulls the leaves down into a position that allows the tumbler that the leaves are fitted into to turn in the barrel. So to re-key a lock, all that is needed is to alter the leaves so that which ever key you wish to use will, when inserted, allow all the leaves to sit flush with the tumbler. The first thing though is to get the tumbler out, without damaging the mechanism.
We will start with the steering lock first. Each tumbler regardless of whether it is for the seat latch, ignition switch or steering lock is held in the barrel with a locking blade at the rear of the tumbler. In the case of the steering lock, this locking blade is in a recess that Suzuki pinched shut as seen in the photo. To release the locking blade, you need to open up the slot, either by using a Dremel, or some means of prying the slot open. Having done so the locking blade may be lifted out and the tumbler will drop out of the barrel. There is a photo showing the disassembled steering lock near by. I use a bit of white grease on the locking bolt when putting the cleaned assembly back together and a bit of light oil on the tumbler. After testing to be certain the lock works properly, I reseal the locking blade either by pinching the slot closed again, or using a small dab of sealant just to hold it in place. Once installed in the steering head, it can’t fall out, so something like epoxy is not required.
For the seat latch, you need to first disassemble the rear of the latch housing by removing the two screws securing the backing plate. Having done so, the spring loaded latch arm may be lifted off its post. Under the latch arm you will see a pawl the slides the helmet strap retaining bar back and forth, There is a small brass spring blade recessed into a slot on this bar, so when pulling the bar out of its slot be sure to not loose this. Take a look at the photo nearby to see the spring preparing to escape. With the pawl out of the way, the spring loaded locking tab can be seen in its recess, and it just needs to be depressed using the blade of a small screw driver such that the lock tumbler can then be slid out of the front of the lock barrel. A photo of the whole assembly in pieces is somewhere near here. I know a fellow in the UK who makes some excellent quality stainless steel components for these seat latches, plus a few other items. If you wish to add some bling to your latch, then his contact information is located here.
For the ignition switch, there is a hole at the rear of the lock barrel (indicated in the photo) into which you insert a pin to depress the locking blade, and then the tumbler will fall out of the front of the lock. Corrosion and the passage of time may make it reluctant to leave, so just work slowly and don’t force anything. Note that this release only works if the switch is in the ‘Off’ position. Give everything a good clean, lightly oil the tumbler and put it back together again once you are happy with the key operation. While you are at it, it may not be a bad idea to open the rear of the ignition switch to give the contacts a good cleaning and some dielectric grease. It could also be a very bad idea. Just be aware that there is a load of spring loaded contact plates and ball bearings all waiting to make a dash for freedom under that contact plate, so if you do decide to do this, be very careful.
For the re-keying, I usually do these one lock at a time and with the tumbler removed, I just insert the key I want to use and see which leaves are not being retracted into the tumbler. These I then pull out (or in some cases push out from the under side) and substitute a different leaf having either more or less lift as required, such that all the leaves sit flush with the top and bottom of the tumbler when the key is inserted.I then give it all a good cleaning, lube with some light oil and put each assembly back together.
When doing these leaf swaps, there are just a three things to be aware of:
There are two styles of leaves. The older style has ‘pips’ on the side that lock the leaf into the tumbler, and the newer style of leaves do not have these. You can mix and match the different types of leaves, and if you have leaves with pips and are modifying a newer assembly, then just file off the pips. The leaves with pips normally have to be pushed out of their slots from the bottom of the tumbler.
Note that the newer style of tumbler that uses leaves without the pips has the annoying tendency to have all the leaves escape the tumbler if you turn it upside down which can result in loosing the tiny little springs. You have been warned !
The most important thing is to not loose the springs. If in doubt, do the disassembly inside a clear plastic bag so that if something does escape you at least have a reasonable chance of finding it. Disassembling the rear of the ignition switch inside a plastic bag is also not a bad idea, for the reasons noted earlier.
The last thing to note is that if you re-key the lock, then the key number stamped into the stainless steel cap on the face of the tumbler (later locks are not stamped – earlier ones are) won’t match the key that you are using. Because of this, where possible, I try to buy a key (there are several sources on eBay) that matches an available ignition switch, as that is really the only one that can easily be seen. The other locks (steering and seat), I just polish up and don’t worry about the number mismatch.
If all of this seems like a more work than you wish to take on, then there is a fellow I know in the UK who does offer this as a service (and no – I do not get a commission). You can do an internet search for Mike Yeadon to find him, or check the Kettle Clinic board in the UK (which is the second best source for free information after this web site 🙂 ), or contact me directly via email and I will forward your contact information to him.