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Engine
- Starting Point
- Metal Polishing
- Engine Rebuild Notes
- Before Starting
- Sources
- Miscellaneous
- Carburetters
- Engine Start !
Starting Point
I am not going to list a blow by blow account of how I did my engine rebuild - the best source of information is one of the repair manuals available via eBay or an on-line bookstore on the internet. The one I like to use is the now out of print Haynes Suzuki 750, 3 Cylinder Models, Owners Workshop Manual (ISBN 85696 302 X). If you can't find one of these, the Clymer manual Suzuki 380-750cc Triples, 1972-1977 (Manual # M368) (ISBN 0-89287-285-3) is still in print - it just isn't as good as the Haynes manual - and if you do shop for the Clymer, the older ones from the 1980's include an additional chapter (chapter 9) which is missing from the more recent reprints, and which covers performance improvements, etc.. What I will do is highlight a few things to consider as you do your own rebuild.
This is what I'm starting with - it is a fairly late, 1977 model year engine (see the list of frame and engine numbers in my 'Field Guide to the Suzuki GT750" located here) that I've been saving as the crankcase halves were in good shape and it turns over smoothly. Of course, until I open it up I won't really know what problems it has, but at least it isn't seized. I do have two other engines to use as donors should it be required.
Metal Polishing
All in all, a couple of hours well spent - all I have to do now are the rest of the covers ...........
November Notes from the Engine Rebuild
First of all, I'm not a mechanic and as a result, these notes represent my personal opinions which may very well be incorrect – you are welcome to use any of this information, but you do so wholly at your own risk !
I've divided this into three areas:
- common damage and things to look for before starting,
- parts supply and related issues and lastly
- the important dealer notices, with comments on the various manuals and a few'miscellaneous' items.
Things to check before starting
First of all, in many cases these 2 cycle engines will be seized solid as there is so much exposed cylinder wall due to the port openings, which provide lots of surface area for moisture to enter and corrode the internals. I have had had some success at freeing stuck engines with putting penetrating oil in through the spark plug holes over several weeks, but not as often as I'd like. If it is seized due a mechanical failure, then the crankshaft will almost certainly need to be rebuilt and that together with the rebore, new oversize pistons (if you can find them - dealers do not always have them anymore depending on which country you live in), rings, gudgeon pins etc., will easily cost $1000+ in USD - probably closer to $2000 . If you are in Canada and sourcing NOS parts, then expect to pay even more as Suzuki dealer prices in Canada are roughly double what owners pay in the USA. Of course you can order parts from places like Dillon Brothers in the USA, but then you have the exchange rate, shipping and import costs to deal with. Depending on where you are located, a seized engine just may not be worth repairing.
- Update: When I wrote this in 2008 parts availability was not great here in Canada, and while it hasn't improved a lot it is better. Internet parts supply of course is much improved. Those points, along with the fact that seven years later there are just so many fewer good usable spare engines to choose from, the situation now is that you just pretty much have to fix what you have. Interestingly, the cost of the parts to repair an engine hasn't changed much - you are still looking at something like $2000, if you can do most of the work yourself and just farm out crankshaft rebuilds and cylinder boring.
If the engine turns freely, then there are (at least) four areas worth examining as a part of the engine assessment:
- The exhaust bolt threads in the cylinder barrels are frequently damaged – these can be repaired with heli-coils, but specific to this engine, the previous owner had actually snapped off an Easy-Out in one of the bolt holes making it very difficult to do anything with it, and as well two other bolt holes had been badly stripped, so I ended up putting aside this set of cylinders for this project, and using another set of cylinders with pistons that I had on hand. As it happens, the second set of cylinder barrels were also off a late model engine so it has the same porting, although to be totally honest I just want the engine to run and so I personally don't really care whether the performance is as good as it could be. Removal of broken off Easy-outs is possible, so I may refurbish this set of cylinders in the future if I can find a local service here in Calgary similar to this one offered in the USA.
- The water pump shaft should be checked – if the owners used the Suzuki or Clymer manuals, they may have tried to follow the directions and pull out the pump shaft using pliers as described and possibly causing damage similar to what is shown in the photo. I have only occasionally been successful removing a water pump by just pulling on the shaft, as the pump body is a very close fit in the lower crankcase half and it only takes a little bit of corrosion to really 'glue' it together. The safest method has been to remove the pump by spitting the crankcase and then gently tapping the pump shaft out from inside the transmission case as described in the Haynes manuals. There are other ways which can work - take a look at this page for a few suggestions.This shaft shown below was unusable due to extensive previous 'plier' damage seen on the right hand end, and had to be replaced.
- The original fitted chain was an endless link chain and many owners ran them till they just broke, This often caused extensive damage under the left side engine cover – in some cases breaking the cover – and invariably took out the gear indicator switch. As this may also have done considerable damage to the upper and lower crankcase halves, it is worth checking whether these are salvageable before going too far. In any case, the needle roller bearing (09263-16006 or 09263-16012 fitted to the A and B models) that holds the end of the shifting cam often is often found filled with road grit, as it was difficult to clean properly when previously changing the gear indicator switch following chain damage, and it will either need to be well cleaned or replaced once the crankcase halves have been split.
- Most bikes will have been dropped at some point in their lives, and if dropped on the left side will possibly have damaged the side covers, the points mounting plate and the threads on the end of the breaker cam shaft. This is the half shaft that is driven from the starter clutch directly off the left end of the crankshaft. If this half shaft is straight, then if you are lucky it can be cleaned up and rethreaded - otherwise it must be replaced. The other parts are available via eBay or possibly your dealer. As well, the tip of the side and centre stands are frequently bent or ground off as these drag easily on corners. The cover photo of the Clymer manual to the right actually shows the lean angle limit for these bikes quite well – in the photo, the left side of the centre stand can be seen to be just about to start dragging. This is the older version of the Clymer manual which includes Chapter 9 (as indicated by the orange cloud in the upper right of the cover) which is missing from later editions. As the ISBN numbers are the same for both versions (which is a bit of a cheat when you think about it) , the only real way to tell is by checking the table of contents or the page count - the older copies were 165 pages, and the newer ones only 151 pages.
Supplies and Refurbishment
Gaskets and seals are available from several places, but even a dealer will often offer after market gasket sets which usually are provided by Athena p.l.c. in Italy. While the quality is fine, the actual sets themselves are a bit disappointing:
- At the time of writing, the top end kit includes the required gaskets but does not include the three o-rings which are also needed for the base of the cylinders, to be fitted under the base gasket which they do include.
- The 'full' gasket set is for a J or K and does not include the o-rings needed for the drive shaft oil retainer plate on later models, or for the gear shift indicator switch. While it does include the small o-rings for the oil pump, it doesn't include any of the banjo bolt gaskets needed if you want to refurbish the connections on the oil distribution lines. As well, the o-ring supplied for the starter motor is thicker than the one fitted originally, making reassembly difficult. Also, it does not include the paper gasket for the front lower water hose pipe fitting.
- The oil seal kits available from dealers, and places like Parts n' More do not include the oil seal (09284-16002) that was fitted in the A and B models, and which goes on the the end of the shift cam shaft underneath the gear indicator switch, or the seal for the clutch rod.
Update January 2015: there are now several good suppliers of gasket sets available via eBay - I like the ones from CruzinImage. And of course there is also Suzuki as a source. Suzuki actually is the only source for the correct head gaskets as the later ones are thinner than the early ones which are also in the after market kits. Speciality suppliers like Cometic in the USA can also supply various gaskets to your specifications, including copper ones.
The water pump is supposedly not rebuildable, but most of the internal parts are available either as original Suzuki parts as they were used on the RE5, or in after market kits. I bought mine from Erik Potze, but he recently advised me he was no longer carrying them – you can still order water pump parts from GTReimer in Germany - just send him an email and ask about kit number 17010-31099-000-Z. If you live in the UK then Crooks Suzuki also sells kits, although they are not really set up to deal with overseas buyers. A photo of the disassembled GT750 water pump is shown below.
The water pump repair kits include, referring to the photo above from left to right, the bearing, the oil seal, the two large o-rings located on the holder set for the pump driven shaft, either a carbon faced seal or a Teflon seal (if it is an after market kit), the small o-ring, the drive pin, the large circlip and the small circlip. Also included,but not shown are the banjo bolt washers for the drain line that runs from the top of the water pump housing through to the area of the water pump cover inside the transmission case. If the bellows (fourth from left, lower row), the seal seat ( sixth from left, lower row) or other parts are damaged then, if GTReiner is out of stock (he sells the mechanical seal under his part number 17470-31010-000-Z), new water pumps are still available for purchase from your local friendly Suzuki dealer for about $160 USD if you live in the USA, and for much more than that if you live elsewhere.
Note that the carbon seat (seen fifth from left on the lower row) is quite fragile and can be broken easily. The Teflon replacement I had was lacking the two small locator grooves required for it to sit properly on the bellows when the pump is assembled and the large circlip is installed. I used a small file to make the modification. Also note that the Teflon replacement seal take a while to 'bed' in and so small leaks may be apparent for a few tanks of fuel. If they persist, then a new pump is the probable cure.
- The oil seal seen second from the left is just a standard 10 x 22 x 8 ARS oil seal, and the bearing is Suzuki part number 08113-62000 and is still occasionally available from Suzuki dealers for about $6 USD in the USA - this is a NACHI 6200 series bearing, and there is a good reference chart available here which shows various bearings available from third parties, as well as cross references to different bearing manufacturers.
- The white nylon water pump driven gear will almost certainly be cracked through the centre bush as seen in the photo to the right.
This gear is still available from Suzuki in just about every country other than the USA for some reason and costs about $55.
- One option some folks have tried is to repair these gears. While I do not recommend this as the consequence of failure will be really expensive (!!), Lane Pipkin wrote up a set of instructions on how he did it. You can download that here, and just do a search of the internet for other options people have tried.
- I probably should not have been surprised at how much the clutch springs had set - they were all under the lower allowable wear limit, and were actually almost a full 8 mm (roughly a 1/4 inch) shorter than new ones. As well, about half the clutch friction plates themselves were close to the lower wear limit and so were replaced with other used plates that still had a lot of life in them. The point here is that the use of a good digital vernier calliper is a must when doing this kind of work.
- The clutch basket itself as seen in the photo to the left was also badly worn and showed signs of chatter damage. While I could possibly have cleaned it up, I had a spare one that was in like new condition and so I replaced it.
Additions, Changes and Miscellaneous
- Crankcase colour codes - if you are having to mix and match gears in the transmission or have had to change out a crankcase due to damage, then you need to be aware of the colour coding used by Suzuki to manage backlash in the gear train. The 1st and 2nd driven gears and the kick start drive gear are matched to the paint codes found under the clutch plate basket on the lower crankcase half on the right side. This information is also covered in detail in the service bulletin number GT-29 issued May 1, 1975 and
revised December 19, 1975.
- Note: the crankcase halves are a matched set as the crankshaft journals are line bored for proper fit and alignment. If you check in the area under the drive gear cover plate, you will normally find a stamp/chisel mark across the join. While it is possible to mix and match crankcase halves, it isn't recommended.
- Cylinder locator bolts - corrosion will generally 'weld' the cylinder barrels to the upper crankcase half. So far, I've been lucky and found that several weeks of soaking in good quality penetrating oil has been enough to eventually soften things up enough that the barrels can be worked loose, but that will not always be the case. John and Fred - our local GT experts - made a pull plate that is attached in place of the cylinder head, and which allows you to slowly pull the barrels up off the studs, after which you would probably need to replace the studs. If anyone is interested in more detail or photos, then take a look elsewhere on this site on this page, or also on this page. You can also take a look at Suzuki's solution given in Suzuki service bulletin GT-25 issued August 15, 1975 which describes their 'puller kit' (part number 99104-03100)- as I doubt this is still available from anywhere, you can create you own kit fairly easily - just read through the service note in the US Service Bulletin section for the details. In any case, when reassembling, I coat the studs with grease or something equivalent to hopefully slow down the rate of future corrosion.
- The Clymer manual as well as the Suzuki service manual talk about using emery paper to clean up the pistons and other areas (page 38), and the Haynes manual expressly says not to, which I'd agree with. The aluminium alloy is soft enough that particles from the emery paper could embed themselves in the surface of the piston which would not be good. I use a 3M Scotch pad soaked in a light solvent on the basis that if any particles should remain they will burn off.
- While large sections of the Clymer manual are lifted almost verbatim from the Suzuki shop manual (presumably they had an agreement of some sort allowing them to use the material) they sometimes fail to include information that would be useful - an example would be the reassembly instructions for the clutch assembly on page 46 and diagram 76 where they don't give information on which way the chamfer needs to go on the two large thrust washers. Due to the way the crankcase is machined, the inside washer has the chamfer facing inwards, and the second washer has the chamfer facing outwards as described on page 57 of the Haynes manual. This is mentioned in the Suzuki service manual also, but unfortunately without any real detail, other than to say its important ! They do provide a diagram in which you can just make out the correct positioning as shown below.
- The Suzuki and Clymer manuals list the NGK B7ES plugs as standard, however this was only true for the early models (J, K and L) - for later models the standard plug was actually the NGK B8ES which was one heat range cooler
Carburetters
- With the engine in the frame, and the electronic ignition fitted, it was time to dig into my box of bits to see what I could do in the carburettor department. The local Water Buffalo folks have been suggesting I use the Amal style VM 32 carbs as used on the early GT's, as these do provide better throttle response and also supposedly flow better than the Mikuni constant velocity(CV) BS40 carbs used on later models. In the interests of simplicity, I plan to start with the later style CV carbs as they are (I think) easier to set up and will require minimum modification to my current configuration and also are what Suzuki would have used in 1978 had they continued building the GT750. If I were to use the VM carbs, then I would have to find a three-into-one throttle cable, as well as the handle bar mounted choke lever and its cable assembly, fiddle with the air inlet boots on the engine as they are a different size, modify the air outlet from the air box as that is also different (or switch over to carb mounted air filters) and switch to a cable actuated oil injector setup rather than use the CV style pull rod.
Frankly - I just don't have the energy to start making this number of changes for this project, and since I have access to additional CV units via the local CVMG club to supplement the box of parts I'm starting with if required, then CV it will be. One change I will be making is to rejet the main jet on the centre carb to match the two outside ones as I will be using a three into three exhaust pipe setup, rather than the stock setup in which the centre cylinder exhaust was split into two pipes. For a main jet, I'm starting with a 115 rather than the stock 110 and we'll see how that works. The other thing I'd like to do, but will probably pass on for the moment is to install the 'anti-surge' fix that was detailed in Service Bulletin GT-36, March 11, 1977 and which can be found here in the US Service Bulletin area. As I will not be using a stock exhaust system I thought I'd wait and see whether it will actually be required.
I used the Keyster KS-0029 kits to rebuild the carbs - everything they supplied fit just fine, but I was slightly disappointed that the small o-ring (part number 13295-31210) for the needle jet was not included, nor was the fuel filter (13376-65010). Both of these are still available from Suzuki, but it would be nice of Keyster to add them to the rebuild kit just to make it fully complete. These kits are available all over the place and can be picked up on eBay for between $15 USD to $30 plus shipping. Luckily the kits do include new starter plungers which are not available from Suzuki, as these were all noticeably worn at the shoulder where the actuator engages it. The photo to the left is slightly out of focus, but gives the general idea of the amount of wear that happens on the neck at the right hand end of the old plunger, which is shown below a new one.
- Update January 2015: There is still a lot of debate in the owner community about the worth of using the Keyster kits. My own experience generally has been positive, and the new kits coming on the market from Keyster are now using ethanol tested components (fuel needle valve, gaskets etc.). Take a look at the results of soaking in a 25% ethanol gasoline mix at this link. It is in Japanese, but most decent browsers have an automatic translate option you can use. As well, the new kits include a range of jets and jet needles in their new 'fuel adjustment' kits for ease of tuning. Take a look (again in Japanese) at this link.
The other problem I had (other than the usual corrosion and cleaning items) was that the oil pump arm lever was missing the small plastic ball, or olive, used to connect the carbs to the oil injector pump rod. Each of the available carbs I had all showed the same problem as the metal bush that the ball mounted into was so badly worn that it wouldn't stay. Fortunately, our local GT750 guru Fred had a spare carburettor set I could use for parts, and so I swapped out the shaft as can be seen in the photo to the the right. My younger son Derek handled the metal polishing of the carburettor caps, and he did a nice job of making them look almost new again !
So - now I finally have a set of carburettors ready to go, and the next step will be to see if I can get the engine started !
December 29 update
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