2. Engine

Engine Issues
The Puller
August 6th Rethink
Threads
Water Pump Trick
Oil Pump Testing
Engine Installation
Blue Haze
Pipe CLeaning and Mini-Rollout

Engine Issues

After doing some soul searching, I've settled on a way forward. Basically as mentioned previously the engines that were included in the basket case are the wrong ones for the model year, and in any case are not in the best of shape - one has a holed piston, and the other has had some sort of catastrophic mechanical failure that has destroyed the cylinder barrel as seen in the photo to the left. I'm assuming there are still bits of a connecting rod under the leaves at the bottom of the barrel but given the general condition there doesn't seem to be much there worth saving other then the engine side covers and (perhaps) the water pump. The second engine is slightly better in that it isn't seized, and other than the holed piston there doesn't seem to a lot more wrong with it but of course till I tear it down I won't know.

As I was picking through the Kincardine Rubbermaid containers, Fred and Janice here in Calgary made me an offer which I couldn't refuse of another 1973 model year bike. This one has been sitting outside since Adam was a boy and is a very tired old soldier, but it does have the right engine for the model year and a few other good bits and pieces so it should work out, assuming that I can get the engine apart - getting the barrels off these older GT750's can be next to impossible. I've borrowed Fred's puller which should make it easier, but we'll see.

So the plan then is as follows:

Keep the Kincardine Rubbermaid Suzuki rolling frame seen below to the left as it is already nicely painted - the front end has a few problems, as does the centre stand, but I have some parts on hand left over from the GT/GS750 project bike I finished earlier this year so I don't expect too much trouble - plus it has paperwork which is a bonus !
Use the engine, instrument cluster, radiator and a few other bits from the donor bike from Fred and Janice seen in the middle photo - most of the rest of the bike is too far gone to salvage. The tank, while not really usable, does have the right pattern for the paint and so will be useful as a guide.
At some point later this year or next, I'll have something that will resemble the photo to the lower right !

The next step then is to strip the donor bike down, salvage what I can and also go through the Rubbermaid tubs that came with the Kincardine bike to see what should be kept from it. It should at least keep me out of trouble !
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The Puller

Getting the barrels off of the GT750 engine can sometimes be damn near impossible. What happens is the cylinder head studs corrode, especially the locator studs, and the barrels become firmly stuck. In the past I've pulled the cylinder head nuts and then filled the bolts holes with 3-in1 or PB Blaster penetrant from Canadian Tire, left them to soak for a few days or a week and then been able to eventually wrestle the barrels off.

Suzuki actually recognized that getting the barrels off was a problem quite early in the production of the GT750, and made a change to the cylinder head bolt washers (service bulletin GT-5 of May 1, 1975) to try and address the corrosion issues, and also made available a puller (service bulletin GT-25 of August 15, 1975). Both of these service bulletins, and all the others, are available here . The problem with the Suzuki puller bolts, is that if the barrels are REALLY stuck, then you risk stripping the threads you have to cut into the barrels per their procedure, and then you are totally stuffed !

An alternative is as per the photo to the right which was made by John in the local Calgary Water Buffalo group. Basically its a flat 1/4 inch think steel plate drilled out in the same pattern as the cylinder head. The plate is bolted to the top of the barrels and then 7/16th inch threaded rod is run through nuts welded to the plate, down into the cylinder bolt holes till they seat on the tops of the studs. Then, if all goes well, you just walk the barrels off by progressively tightening the threaded rod which pushes against the tops of the studs and lifts the barrels up and off.

This is a view showing the barrels pulled up part of the way; you can see the degree of corrosion on the studs which meant they really did not want to let go ! In a case such as this, a puller is almost mandatory.

I was just tearing this specific engine down for parts as it is one of two that was included in the 1973 Suzuki GT750 basket case that I picked up in Kincardine, Ontario. While the barrels, crank and pistons were all scrap (lots of severe damage, and signs of seizure), there was a brand new (or at least virtually unused) nylon water pump gear and as well, the side covers,gear clusters, and the actual crankcase halves were in good shape as well. As the pistons were first over size, it looks as if the engine had been rebuilt, and then blown up very soon after putting it back on the road. I'm sure I will be able to use a few of the engine components in other projects at some point.

August 6th Rethink

More problems - so making a few changes to the plan.

Once I had the Calgary donor bike stripped down, I was able to put its frame along side the Kincardine frame and then noticed a few differences. Earlier GT750 frames in 1972 had a 2 bolt hole side stand and in late 1972 for the 1973 model year, this was changed to a 3 bolt side stand mount. For some reason, the Kincardine frame was the earlier 2 bolt hole style, and the side stand itself was not original and would need to be replaced. As well, on closer inspection the Kincardine frame had a broken engine mount. The engine and frame for the Calgary bike were original and so the serial numbers very nearly matched (Suzuki frame and engine serial numbers seldom match exactly, and can actually differ by a wide margin). As they were original and close, it seemed a shame to give that up. The frame was cracked in the rear fender stay - not really a key structural member and so could easily be welded. The centre and side stands were both in very good shape. The engine was another story entirely. The Kincardine frame of course had no engine, and so would have been a 'bitsa' bike anyway - given a choice then of building a 'bitsa' or doing a restoration, I decided to restore the Calgary frame and engine. Of course nothing is ever easy .....

Whenever the Calgary bike had been parked - sometime back in the 1980's - the oil was allowed to drain out and then it had sat outside in the snow and rain for the next 25 years or so. The barrels came off easily using the puller, but the sight that met my eyes once I cracked open the side cover wasn't pretty.

There was a lot of rust - my guess is that the engine probably had been in good condition when parked, but over the years had gradually become seized solid with corrosion. Basically other than the cases, barrels, cylinder head and side covers there wasn't much else I could really use - luckily I have several sets of transmission clusters, and crankshaft assembles so I can replace all the internals with parts from other engines. This does cause a bit of a potential problem though, as the number of teeth on some of the drive and intermediate gears changed over the model years, and I'm not sure which model year cluster sets I have on hand. As well, I will have to mix and ,match the gear sets a bit to minimise the lash in the drive train. Normally there are paint codes on the inside of the engine case, and sometimes on the gear clusters also to assist with lash adjustment, but for some reason this engine had no paint codes inside at all. The water pump, not surprisingly, is shot but I can either rebuild it or replace it. More work than I had expected, but all very doable.

Today I took in a GT750 crankshaft to Greg's Cycle here in Calgary to have new seals installed. Assuming that nothing much else is wrong with it, I expect It should be ready in about 2 to 3 weeks. I still need to check the barrels to see whether I need to use over-size pistons, or just re-use standard size ones, but that can wait till after the crankshaft is finished, and I have the gear clusters, crankshaft and all the other bits and pieces back in the cases.

The next few weeks then will be busy getting the above items sorted, plus I have another item I need to prepare for also. Our club is having a 'powder-coat' day here in Calgary in early September which I'd really like to take advantage of. This is made possible by a local supplier and basically you show up with your items prepped and ready to go, and take them home freshly powder coated for very reasonable rates. With a bit of luck I hope to have both a GT750 and GT500 frame ready to go, together with all the bits and pieces (battery box, side and centre stands, swing arm etc.).

Of course that means I'll need to strip down the 1977 GT500, which I haven't really even looked at yet.

Threads

A common problem with early 1970's Suzuki's is having the exhaust bolt thread strip that hold the exhaust flanges (and therefore the exhaust pipes) to the cylinder head. This is due to the soft aluminium alloy just wearing away over time with the repeated removal and installation of the exhaust pipes for cleaning or maintenance. An option to avoid this wear is to install studs to replace the bolts, and I know a few folks who have done that on their bikes, but I prefer the factory look. Being stripped is bad, but making it worse is that often what will happen once the original thread is gone, owners will open up the hole to the next bolt size (10x1.25mm) and just put in a larger bolt. Of course, once that one strips - and it's just a matter of time - then you are truly stuffed. In the past, your only real option at this point would have been to find someone who could TIG weld more metal back in, and then drill and tap a new threaded hole and to do this would generally require the engine be removed from the frame as the working space is quite limited.

For the 'first time' failure mode, installing a Heli-coil thread repair insert is generally what most shops will do - this is usually an easy, quick, long-lasting, relatively low-cost solution if you are lucky - the 'luck' part mostly has to do with whether you can access the thread to do the install without having to pull the engine - in some cases on a motorcycle it just isn't possible.

The inserts themselves are about $1 each (in the US), and are made of a hard stainless steel wire which has been coiled into a spring, and which you just thread into a retapped hole.

But what about the case where the hole has already been opened up to a larger size and has now been stripped again ? Or for that matter is a stripped Heli-coil ? I suspect you have a better chance of winning the lottery, but I seem to be blessed with bad luck when it comes to exhaust bolts so I've included this as a possibility. For this issue TIG has been pretty much the only option - till the folks at Time-Sert came up with their Big-Sert product line. These are oversize thread inserts - plugs actually - and are really clever, but also more expensive than Heli-coils. Of course, if your other only option is to pay for someone to do some speciality aluminium welding, then it starts to look like a bargain !

In preparation for having my 1973 GT750 cylinders re-bored and bead blasted, I decided to first tidy up the exhaust ports which had a couple of stripped threads - one was suitable for a Heli-coil repair as it was just a damaged 8x1.25 mm thread and so fairly small. The second one was a small crater of a hole that you could almost drop a 10mm bolt through without it touching, so I decided to try the Big-Sert and see how well it worked. Ten minutes later, as can be seen in the lower right of the photo, I had a brand new, very nice looking 8x1.25 mm threaded hole and was very pleased with the result ! The inserts are available in various lengths - for this size of bolt between 8 and 20 mm in-depth. I had the 'stock' length ones of 11.7 mm, as well as some longer ones at 16.2 mm, and opted to install the longer ones just to give more contact area on the bolt given it was after all an exhaust port being used to secure the exhaust pipe, and so subject to extremes of temperature and vibration.

As with Heli-coils, you typically buy a kit for each size of thread you are repairing. The Big-Sert kits contain all the bits and pieces you need to do the installation: drill bit, tap, reamer, install tool and inserts (of course you have to supply your own electric drill and tap handles). Unlike Heli-coils, Big-Serts are threaded plugs with a cam-lock built-in to stop the insert from moving once in place. It's a nice design and ideal for this sort of repair - but they are about twice the price of Heli-coils (if you shop around). I bought mine from ToolsQwik in the US - very helpful and easy to deal with, good prices and fast delivery. After including the postage cost, and currency exchange (there is no duty charged to bring these into Canada - just GST which you'd have to pay anyway), I still saved about 30% over what I was quoted for the same items here in Calgary, so as always it does pay to shop around.

I will be dropping the cylinders off at a shop south of Calgary in De Winton called RPM Services next week after Christmas, to be bored to first over size. I already have the pistons, rings, gudgeon pins etc., so it now looks like I will be starting to re-assemble the engine sometime in January. In the meantime, I still have to finish the wiring and sort out the fuel tank and a few other odds and ends on the GT500 I'm also working on, so I'm not short of things to do !

Water Pump Trick

One thing I wanted to do was modify the upper engine case to include a small change to make future water pump cartridge removal easier, if it should be required. This modification was first proposed by Allan Tucker on the Sundial GT750 board with input and tweaking from several board members. The original thread is located here. What happens is that over time, the GT750 water pump cartridge gets seized into its enclosure, and if you then need to replace a seal or o-ring, you have to remove the engine from the frame and split the cases to get at the top of the water pump shaft so you can tap it out of the case. With this simple modification, all that's required is to remove a small grub screw (which needs to be short - perhaps 5mm) and then you can insert a punch and tap the cartridge out of the case with the engine in the frame.

In the photo to the upper right, the screw driver points to the location of the 6mm x .1.0 grub screw (in the US they are known as a "set screw"). You need something that will sit flush with the upper surface of the engine case otherwise the starter motor has clearance issues and don't forget the Loctite !

A copy of Allan's instructions are available for download here (just right-click and select "Save Link As"). Of course, in my instance, as I had the engine apart, all I had to do was flip the case over and drill a hole up through the end where the upper water pump shaft bearing rides. I've included a photo of what this looks like to the left (again, at the end of the screw driver).

Hopefully I'll never need to use this, but it is a handy trick to have up your sleeve !

The engine cases are pretty much ready to go now; cleaned up and painted. As well, I've also changed out a few of the engine studs, and naturally the first one just twisted off flush with the upper engine case. This caused me an additional half day's effort to drill out the broken bit of stud, and re-tap the bolt hole to just clean up the threads. Quite annoying ! The only reason I even touched them was that the barrel locator shoulders on the two outboard studs had either completely corroded away, or had never been there in the first place looking at the photo to the right the shoulder on a new stud is clearly visible on the stud to the right of the photo. The one I removed and which I think may have originally had a locator shoulder is on the left, but really its just a guess. There was no sign at all on any of the studs of a shoulder, and as well per Joe, the owner of RPM Services, and who bored the barrels to first over for me, the barrels were worn slightly crookedly which makes me wonder if the locator shoulders were ever there at all. No way to know now of course, but following the re-bore the cylinder bores are now square to the bottom gasket surface, so presumably all will be well in the future now that the locator studs have been replaced.

Update: after some additional checking, I'm now convinced that on my engine the cylinder studs did not originally have a shoulder as these were introduced at engine number 38060. Over the next few days I'll get the engine rebuilt and then perhaps think about putting it back into the frame. I do still have some repair work to finish on the tank and fork ears before sending them out for paint so there are still lots of things to be done.

Oil Pump Testing

Recall from above that when I cracked open the cases, I found a bit of a mess as it appears the oil had leaked out and been replaced with water over the years, and things inside were rusted solid. Other than the cases, I was unable to salvage much of anything in the engine case at all - even the upper oil splash plate had rusted away and had to be replaced and the starter motor was a solid lump of oxide. I was lucky in that I basically had must of what I needed to replace all of the internals, but I did not have a good gear shift selector shaft and so had to do a bit of searching around to get one. The gear selector shaft on the GT750 was changed sometime in 1974 to have a longer rod on the left engine side. At the same time, the gear shift selector arm design was also changed, and the new ones had much less angle to them than the ones used in 1972, 1973 and much of 1974. Although I had the correct, old style gear selector lever, the gear selector shafts I had available to me had either corrosion or wear right where the oil seal would ride and so were not usable. After a bit of head scratching, I was very lucky (and thankful !) to have one offered to me for the cost of the postage by Barry, who is a fellow member on the Sundial Moto Sports Board, which is a great resource if you are dealing with these old 2 strokes.

I previously highlighted a few of the other updates I made during the engine rebuild here and at last I had got to the point where I was ready to button up the cases, as can be seen to the left. I had four GT750 injector oil pumps available to me - one was definitely suspect as on the bike I'd pulled it from, the oil injector tank was bone dry and missing its cap, which likely meant that water had been able to get into the pump itself. Although it turned, I didn't really trust it, and on the three other pumps I didn't have any history. A really good write-up on the Suzuki injector oil pumps is available on Richard's site here.

Having a working oil injector pump is a must - unlike other 2 strokes, the crankshaft design used on the GT750 Suzuki means you will likely burn out your main bearings if you try to run solely on pre-mix with out having the crankshaft re-designed. This sort of conversion is possible - Bill Bune's shop will do this for folks who need to run pre-mix for vintage racing applications for example, and I'm sure there are others. In my case though, it was going to be injector oil so I had to confirm I had a working injector oil pump !

To do this, I took a piece of flat steel stock, and drilled and taps mounting holes so I could bolt on the oil distribution loom and oil pump in a similar way to how it was mounted on the engine. The pump driven shaft protrudes though the bottom. I had a scrap oil pump drive shaft from one of my parts engines, and I drilled and tapped a hole in the bottom of it to take an 8mm bolt that I could drive with a 1/4 inch variable speed drill. The reason for doing this is that as the oil pump shaft is turned, it actually travels up and down about 4mm which meant I couldn't just connect the drill chuck directly onto the shaft - using the original drive shaft allows the pump shaft to both be turned and also allows it to move up and down. After testing the four pumps I had available, I was able to confirm that two worked fine, and that two were scrap so it was time well spent now rather than later after I'd seized up the new engine due to lack of oil ! In the photos below, you can see test rig mounted on the bench and the drive shaft on the bench beside one of the oil pumps. With the engine in the frame I can finally move onto other things !!

Engine Installation

I had the engine fully assembled on the bench and so now was the time to think about who to call to help lift it into the frame these things are damned heavy, awkward to manage and I'm not getting any younger. Come to think of it, neither are any of my friends ! We (worldwide GT750 folks) recently had a thread on this topic which can be here. The normal method is to left the engine into the frame from the right hand side and then somehow support it while attempting to slide in a couple of the engine mounting bolts. This can be a harrowing, possibly dangerous adventure when doing it by yourself as the risk of injury is high, and a male bonding experience if a friend helps you, as you get to learn new, colourful and highly descriptive words that extend and add versatility to your vocabulary ! It seemed like a good opportunity to try another option.

A method I've used previously for removing an engine has been to lay the frame on its right side, unbolt everything, and then lift the frame off the bike. Many people have also done the reverse to re-install the engine, so I thought I'd give it a try, and I'm pleased to say that it worked like a charm ! With the engine blocked up securely so that it wouldn't fall over and damage my lovely oil stained concrete floor, I just lifted my frame over the top and into position, slipped in a couple of bolts to secure it and then gently lowered it back so it sat upright on the motorcycle lift : job done ! The whole process took about 20 minutes start to finish with no back ache, no mashed fingers, no colourful language and there isn't a scratch on the paint that I can see. To the right is a photo of the freshly re-united engine and frame. Doing all this work on the lift, had the advantage of being able to adjust the working height so it was comfortable, and so much easier on the back. Recommended.

From there is was a simple step to re-install the front forks, and then get the frame back up onto the centre stand so I could remount the swing arm etc.

Blue Haze

Over the past several days, Calgary has been blanketed by smoke from forest fires burning in British Columbia. The haze in the air from all this smoke has been quite dense, limiting visibility to just a few kilometres at times - but that isn't actually what I'm writing about today. The blue haze in our small area of town was from the successful start-up of my rebuilt 1973 GT750 ! Needless to say, I was pretty pleased about the whole thing, and while it showed up a few niggling issues still to be sorted out, for the most part it was a complete success. Best of all I suppose, was that it started on the first push of the starter-motor button and when I double checked the ignition timing on all three sets of points, they were spot on. After some minor carburettor adjustment, the engine sounded strong and was idling smoothly.

I will have to take apart and try again to fix the fuel petcock, as I still do not have a good shut-off on the vacuum operated valve assembly, but that is minor. New ones are still available if all else fails, so it is currently more of an annoyance at this stage and will not slow down further testing and engine run-in, although it will need to be working properly before I try to have the bike certified for the road.

Next on the agenda is the finish off the front brakes, tidy up the the control cable routing, finish the seat and attend to a small oil leak on the right side. The right side engine cover was not in great shape on the gasket surface, but it was the original one so I really wanted to reuse it. While I had lapped the faces as best I could, there were still a couple of damaged spots that it now appears the gasket could not properly seal. I will probably just use a small a bit of JB Weld to fill in these nicks on the joint faces and that should do the trick.

The seat will be visiting Calgary Seat Cover on Monday. I have a reproduction seat cover, and I was going to re-cover the seat myself as it isn't really a difficult job. However when I did a dry fit, I found that with age, the seat foam had shrunk and hardened enough that the shape was not correct, plus of course it would not be very comfortable to sit on ! The folks at Calgary Seat Cover will re-skin the seat with a thin layer of fresh, high density foam to restore the original shape, and also install the cover for a very reasonable price so it makes good sense to just let them do it for me. I will install the stainless steel seat trim myself and it should be good to go !

Pipe CLeaning and Mini-Rollout

With the engine running well, the carburettors (mainly) sorted and the seat recovered, it was time to mount the exhaust system properly. I had planned to have the pipes 'tanked' at a local radiator shop, and while that is still on the agenda, I elected to just clean them out for now and get them mounted so the bike can be run in properly. After anything that shows up during the initial shakedown is sorted, then perhaps I'll pull them back off and get them re-chromed next year.

Two stroke exhausts can accumulate a lot of carbon build up, but I admit I was surprised at just how much there was in these. I made a scraper with a hooked end on it out of some flat bar I had (which is visible in the photo to the upper right), and then went around the inside of the pipe between each baffle till I had quite the pile of accumulated coke and carbon sitting on my work table. And this was only from the two larger pipes ! I also managed to clean out a slightly smaller pile from the two smaller centre pipes !!

Of course now I just have to be careful to not have anything white behind the bike the next time I start it up, as I've no doubt that there are all sorts of small oily bits of carbon loose inside the pipes which will expel all over anything behind me - might be fun actually .....

Suzuki used to sell a special sealing compound for the connector tubes between the three main exhaust pipes - of course this is no longer available. I used high temperature RTV orange silicon on the GT550 rebuild which seemed to work well, and so did the same thing with the 1973 GT750. Everything bolted up nicely and so it was time to roll it out and take a couple of photos.

I still need to put the warning labels and decals on, add the seat trim, and I do not doubt that I will have to play with the carburettors a bit more, but it is quite close to being completed now. Of course I'm biased, but I think its looking pretty good !