6. Front End

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Forks and Wheel


I wanted to use the under slung brake callipers on the front end of this project bike, and although it doesn't look pretty 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 caliper 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:

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 and tighten everything up and away you go. As nearly as I can see, there are just a few  things to pay attention to:
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Steering Head Fittings

Controls
old lock steering lock parts steering lock assembled


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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 The specific part for the GT750 (54600-34000 or 54600-34001) is no longer available from Suzuki and has been superseded by a new part number 54600-08C00 which can be bought new for about $84 USD in the USA from someone like Dillon Brothers or Alpha Sports (in Europe the cost is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 right.

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 ......

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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. 
Box of bits

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, rather than trying to prise it off as described in Paul's article. To reinstall the cut ring, the suggested method is to use a similar clamp/jig setup 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 guage rebuild service, and a set of gauges he has rebuilt will be used on my 1973 GT750 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.
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.   gauges

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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 carburetter 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 Cycles in the USA for about $50 USD, and new petcocks can be bought from your friendly neighbourhood Suzuki dealer for about $80 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.

Petcock

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 ).

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Dedicated to Ken Solar
  1. Home
  2. The Design Assumptions
  3. Disc Conversion
  4. Tank, seat and rear fender
  5. Engine
  6. Front End
  7. Ignition
  8. End Game
  9. Miscellaneous
  10. References
  11. Credits
 

Updated May 28th, 2011.
 Ian R. Sandy