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Front End
- Forks and Wheel
- Steering Head Fittings (new VIN, Control Refurb)
- Steering Lock
- Speedometer Drive Unit
- Gauges
- Fuel Petcock
Forks and Wheel
I wanted to use under slung style brake callipers on the front end of this project bike, and although it doesn't look pretty (my personal opinion) I have seen several folks just take their GT750 forks, and reverse the right for the left, left for right and turn the lower fork legs so they face backwards. I'm told that the GT750 calliper units are not designed to be mounted 'upside down' in this fashion. To be honest, I'm not convinced it would be a problem although I do see two potentially tricky bits:
- If you do reverse mount the GT750 front brake callipers, then the oil drains for the fork tubes will be pointing up and to the front of the fork making fork oil servicing a bit awkward
- Bleeding each front brake calliper completely may be an issue unless the wheel is turned so the calliper to be bled is on the 'high' side which would position the brake bleed screw at the highest point.
Rather than take a chance, my current plan is to either use the GS750B forks to replace the GT750 ones and go with a single rotor front brake, or use the GS750EC or EN front forks to preserve the look of the GT750 dual front disc.
The GT750 uses a 35mm fork tube as do many other makes and models - when specifically looking at older Suzuki's, the 1977, 1978 and 1979 GS750B, C, EC, EN and N are simple fits. Generally speaking these are just a 'drop in' swap using the original GT750 triple tree: undo the pinch bolts, slide out the old tubes, update the triple tree bearing cups (more on this in a minute), slide in the new tubes with their lower fork legs, tighten everything up and away you go. As nearly as I can see, there are just a few things to pay attention to:
- If you want to re-use the wheels and front brake rotors from the GT750, then you need you to carefully check the donor bike models. According to the Zedder index, only the 1977 GS550B and GS750B have the same brake rotor part number (59210-37001). This part number was also used on the RE5, GT500, GT550 and GS550E. The GS750EC and EN which have the 'snow flake' cast wheels use a different brake rotor part number which is about 1/4 inch smaller in diameter than the GT750 front rotor. Bottom line - double check before buying, or buy the wheels with callipers and rotors together with the forks just to be certain it will all fit.
- The GS750B, C and N all have single front brake rotors and spoked wheels - if you want dual front rotors then you need to find GS750EC or GS750EN fork parts to get the lower right side fork leg that has the brake calliper mounts. According to Zedder, the GS750 B, C, N, EC and EN all use the same inner fork tube so the lower outer fork legs are interchangeable between these models (the same fork seal and dust boot are used on the GT550, GT750, RE5, GS750B, GS750C, GS750EC, GS750N and GS750EN) - but you then have to sort out the disc rotors.
- In 1979 a leading axle front end was introduced with the GS750L (it has a stepped seat 'low rider' configuration) so it isn't enough to know just the year of the bike you are looking at as a donor vehicle - the GS750B, C, N, EC and EN all used forks that had the axle bolted to the bottom of the lower fork leg.making more parts interchangeable with the GT750 (speedometer drive, spacers, axle etc.).
- Whenever you have a GT750 front end apart, even if just to repack grease etc., consider installing a tapered roller bearing upgrade kit as it does make a difference to the handling as well as just the ease of maintenance. These are readily available from many sources- All Balls Racing is one option.
- The lower bearing race is an interference fit with the bottom of the steering stem - I use a heat gun to warm the bearing race up to the point where it is too hot to hold, and then find it usually drops into place
- Frequently with older Suzuki's the fork dogs that limit the degree of turning radius are damaged - these are the steel tabs welded to the front of the fork neck, and they tend to get pushed into the middle over time especially if the bike has been dumped at some point. If you have access to an oxy-acetylene torch set, then its an easy fix - if they are bent and you chose to ignore it, then you risk denting your tank.
Steering Head Fittings
- The wiring leading into the headlamp rubs off the printing on the VIN (vehicle identification number) label used on North American bikes become illegible over time - and if you sand blast your frame for painting, or powder coat then of course it will be gone completely. Although the VIN number is stamped into the neck of the frame, it is still nice to have the sticker, and these were available for a very reasonable price from Tyler Technical Services in Australia. Unfortunately they no longer supply them so the hunt is on for an alternate.
- I have refurbished the left and right handlebar switch assemblies by painting them satin black, and then refreshing the lettering using a small bottle of orange enamel modelling paint from Testors, which is available from any model supply shop - I daub it on with a Q-tip and the wipe off the excess with my thumb.There are lots of little bits and pieces in the switch assemblies so it is fiddly work, but I think (and yes I am biased !) the end result was worth it per the photo below.
Steering Lock
- The steering lock quite often is seized up solid, and as I had a matched set of keyed alike locks and switches for this project, I wanted to get the steering lock working. I tried soaking it in penetrating oil, heating it, chilling it, shocking it etc., but it just was not in a mood to cooperate so I resorted to drastic measures. As I had several steering locks with no keys, and nothing else matching (ignition, seat latch etc.) I decided to make one of these a donor for the project bike. These locks are not designed to be easily re-keyed, and the body is a die cast metal which is easy to damage. The lock cylinder is held in the barrel by a metal tab just in front of the bolt, and the metal is pinched closed to hold the tab in place.
- On my seized one, I had to hacksaw the barrel down on either side of the lock pin to ensure I didn't risk damaging the lock cylinder, and then I cut through the retaining tab to free up the cylinder completely as shown in the photo to the lower left
- I dremelled the top off the key way of my donor latch, and then drew out the retaining tab, after which the lock cylinder just slides out of the barrel, and the lock pin can be pulled straight up. After cleaning up the barrel, lock cylinder and locking pin, I was ready to reassemble the lock as shown in the centre photo below (the retaining tab can be seen just above the lock cylinder, and the slot it goes into is seen in the barrel above it, just to the left of the lock pin bore). I'll save the donor lock cylinder as I can use the bits for re-keying other locks in the future. the assembled unit, with the retaining tab re-inserted and pinched shut again, is shown in the lower right. I'll either replace, or shine up the screws before re-installing it, but at the moment I now have a matched set of keyed alike functional locks and switches again for the project bike, which has saved me a few bucks on eBay !
- If you need a key - these can usually be bought pre-cut on eBay
Speedometer Drive Unit
In the process of putting together the front wheel, I noticed that the speedometer drive housing had a problem. Basically the output shaft to the speedometer cable would not turn when the wheel was spun. These drive units are not intended to be repaired, and no parts are available for order to repair them - they were available only as assemblies. The specific part for the GT750 (54600-34000 or 54600-34001) is no longer available from Suzuki and has been superseded by a new part number 54600-08C00 which can be bought new for about $84 USD in the USA from someone like Dillon Brothers or Alpha Sports (in Europe the cost is about 81 Euros from someone like CMS , and in Canada it costs about $136 CDN !). This speedometer drive assembly was used on about 25 different models of Suzuki motorcycle between 1973 through till 1982 so used speedometer drive assemblies should also be readily available on eBay. At any rate, I've had this problem before and I also had a few spare drives on hand, so I thought it worth the time to try to overhaul the drive assembly that I had, rather than try and find another one.
- The components of the drive assembly are shown to the left. Taking it apart is not difficult - remove the snap ring on the back, then the space washer and (if it is fitted) the thrust washer - and then what I do is just carefully pull the main gear through the seal. For the speedometer drive output shaft, the bush and seal unscrew and the output shaft then is free to be removed. Don't lose the small thrust washer on the output shaft ! There is a seal on the back of the drive housing facing the wheel, as well as a small one in the bush. As yet I have not had to look for a replacement for these.
- Referring to the photo - the main gear and output shaft are machined steel and as yet, I have not seen them fail (although I'm sure it could happen). On any of the units I've looked at, the problem area always seems to be the two small tabs on the inside of the driven gear which is really just a big mild steel washer with tabs on the outside to engage the wheel hub and on the inside to engage the machined main gear. As I've seen in the past, the problem with this unit was the inner tabs which I've marked in the photo above. The soft mild steel of the inner tabs is just worn away by the harder steel of the main gear, and eventually they do not engage at all. I was lucky to have a spare part, although I'm also sure a couple of small welds to build back up the metal, which would then need to be ground down and squared up, would work just as well.
- When reassembling, I repacked the drive housing with a bit of wheel bearing grease, taking care to ensure the bottom end of the output shaft is greased as it is a blind hole in the drive casing. As mentioned previously, some units have the thin thrust washer on the back between the drive gear and spacer washer, and some don't - basically if the snap ring seems loose such that the drive gear does not engage properly with the main gear, then it needs the additional shim.
Now that its all back together and installed, it seems to work fine - so on the the next item ......
Gauges
Next on the agenda is gauges - I'm starting with a box of bits which I've been collecting for years, and I'm hoping to get one good set of gauges out of the lot. There are several ways to rebuild these - the best write-up I've seen is by Paul Franchina who wrote an article published in 2004 for the VJMC member magazine and which also appeared in 2005 on what is now a dead speedometer repair web site. If you are a VJMC member, then you can find the VJMC version in the 2004 member archives, otherwise you can download a copy of the 2005 public web article from here.
Getting the chrome ring off and then re-installed is the hardest part, and rather than prising it off as Paul describes, a second method some folks use and which can be simpler to do is to use a small cut-off wheel (on a Dremel for example) and just cut the ring. To reinstall the cut ring, the suggested method is to use a similar clamp/jig set-up as Paul uses, but then use epoxy glue to fasten the ring which is held in place and positioned using gear clamps. If done well, the cut is not easily visible, and as the ring is not deformed in any way, the 'fit and finish' is a bit cleaner. Of course should you ever have to take the gauge apart again, you will have a bit of a problem because of the glue, but it can work quite well. The best option of course would be to replace the ring with a new one, but a special tool would be required to reset a new ring on the gauge housing. I have been talking to Wolfgang Haerter who does this using a lathe and tool he made for this purpose when restoring Laverda gauges, but it isn't an option for most shade tree mechanics. The ring size he uses appears to be about the same size as is used on the Suzuki gauges so I will likely have him give this a try in 2009, but of course he doesn't have anything to fit the water temperature gauge, so I'll have to sort that out myself.
Gauge sets are available fairly often on eBay, but generally suffer as they are obviously 30 to 36 years old, may have been sitting outside in the weather etc. and the speedometer usually is missing the trip meter reset knob as this is easily broken off or lost. Generally these old gauges will start at about $50 USD for a single gauge through to whatever level people get carried away with during the bidding. NOS and professionally rebuilt GT750 gauges are available from GTReimer in Germany, and sometimes from folks like Paul Miller in the US. Alan Tucker also has recently started offering a gauge rebuild service, and a set of gauges he has rebuilt will be used on my 1973 GT750 restoration which I'm preparing for the spring of 2010. These new or professionally rebuilt gauges will range in cost between about $200 USD to $400 USD depending on exactly what you are looking for - the plastic housed gauges on the early models usually cost more than the metal housed gauge sets used from late 1973 onwards.
Update January 2012 - I have had the plastic 'J' style gauge housings for the speedometer and tachometer reproduced. Information on ordering is available at this link.
Here is where I got to - you will note that the water temperature gauge is brown. The brown faced gauges appeared on the GT750 in late 1976 through 1977 and so in keeping with my theme, would likely have been used also in 1978 had a GT750 continued to be made. I have a brown faced tachometer which I will be rebuilding at some point in 2009, and am keeping my eye's open for a brown faced speedometer, but for the moment will make do with the most common blue-green coloured ones as I had enough parts to put one set together.
Fuel Petcock
The last (I lie - there is never a 'last' with something like this) thing I had to sort was installing the fuel tank, and for this I needed to first rebuild, and then install the fuel petcock. These are vacuum actuated - in an ideal world if the engine is turning over, then the fuel petcock automatically opens and fuel flows to the carburettor float bowls. If you check around on the web, you will hear any number of suggestions about changing the original petcock for a simpler on/off valve, supposedly to prevent fuel starvation, but to be honest this is not a problem I've ever had. The main problem I've run into has been too much fuel in the form of leakage - especially from the two mounting bolts, but also from the cup on the underside of the valve assembly as well as from around the fuel on/off/prime lever.
I bought a rebuild kit from Erik Potze in The Netherlands when I was living there - they are also available from GTReiner in Germany. Rebuilt petcocks are available from KnK Cycle in the USA for about $50 USD, and new petcocks can be bought from your friendly neighbourhood Suzuki dealer for about $105 USD in the USA. The parts included in the rebuild kit are numbered as items 1 through 5 in the photo below and include 1) shut off seal, 2) spacer block seals, 3) bolt seals, 4) cup gasket and 5) vacuum diaphragm o-ring. Also included, but not shown is a larger o-ring for later model petcocks.
Update January 2015: A new supplier offering replacement diaphragms and kits for the vacuum operated petcocks, as well as rebuilt units is Volker Schulz located at this link - excellent quality. The site is in German, but any modern browser worth having has a translate function available which makes life easy.
The two bolt seals (item 3) are quite important as the mounting bolts extend all the way into the tank, and consequently fuel will seep through past the threads, and drip below the valve, although it may appear that the leakage is from either the cup gasket (item 4), or perhaps the shut off seal (item 1). The original seals are a fibre or cork material and just perish with age - I have seen in several cases, where these have just been replaced with common flat washers and then over tightened to try and stop the inevitable leakage - it doesn't work. If you have a leak here, then get the correct seal washers (part number 09168-06010 or 09168-06023).