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:
- 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 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 and
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., always install 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, but I
bought my last kit from Parts N More
- 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.
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Steering
Head Fittings
- The
wiring leading into the headlamp rubs off the printing on the VIN
(vehicle identification number) used on North American bikes as can be
seen
to
the left and as 
well,
if you sand blast your frame for painting, or
powder coat it then the sticker will be gone. Although the VIN is
stamped into the neck of the frame, it is still nice to have the
sticker, and these are available for a very reasonable price from a Tyler
Technical Services
in Australia. As you can see to the right, they are not exact replicas
as the frame date has a larger field than in the original to allow you
to enter the year which is pre-printed on the factory version to the
right. I bought a cheap set of machinists number stamps from Princess
Auto for less than $3, and added all my numbers to the foil decal - it
now looks quite nice !
- 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.
- 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 sometimes be bought pre-cut
on eBay - I have bought from here
in the past.
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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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Top
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,
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. |
 |
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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.
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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Updated
May 28th, 2011.
© Ian
R. Sandy
