Suzuki RG500 GAMMA

From: Nick Fordham 
Subject: MAG ARTICLE

Two Wheels - September 1987
 
Servicing Suzukis RG500 GAMMA - nothing like keeping the old razor honed
sharp, is there?
 
Suzuki waited 11 years before releasing the square four RG500, a brilliant 
half-litre sports two stroke, thus capitalising on an immense amount of 
development in the premier class of Grand Prix racing. The fact that the 
street version of the GAMMA is as potent as the 1976 world championship 
winning RG is quite astonishing but sadly these 153 kg weapons arrived
on our shores just as the government legislated them out of existence.
Stringent emission and noise standards allied to the introduction of unleaded 
petrol into Australia made 1985 the last year RG500 GAMMAS (and Yamahas RZ500)
scored compliance plates. The GSXR-750s kept the GAMMAS at bay on the
racetracks which, perhaps, gained them a greater marketing impetus but the 
RG is an extremely rapid and well balanced machine that a great number of 
experienced riders missed out on. And if you are lucky enough to own one 
they are not that difficult to service either.
So lets take a look into what exactly is involved in keeping the 70 kW 
powerplant on the boil! One major pain these days for mechanics is the lack of 
centrestands on bikes like the RG. A pair of car stands can be purchased and 
one under either side of the swing-arm supports the machine firmly - thus 
allowing all service operations such as chain lubrication and 
adjustment, raising the front end off the ground to check or adjust steering 
head bearings or to remove the wheel or forks. 
I recommend taking the bike for a ride prior to service in order to warm
up the gearbox oil and the chain. If the chain is dirty and somewhat neglected, its advisable to wash it with a brush and kero beforehand - dont use harsh 
solvents or degreasers that may deteriorate the Orings. Then set the bike up 
on the stands and make sure the rear wheel spins freely (ie. chain not 
contacting the stands.) Give the warm chain a good lube while either spinning 
the wheel by hand or let the motor do it for you at idle in first gear. Now 
you can get on with the rest of the work.  
Firstly theres the usual amount of undressing to attend to and I guess
that owners who are keen on 100 percent machine detailing will be familiar 
with the fairing removal procedures. It is simply a matter of removing the 
middle fairing panel for which a screwdriver is required to 
un clip the zues fasteners at the bottom edge and a 4 mm Allen key for the 
3 bolts along the top. Then use a Phillips screwdriver to remove the belly pan. 
There are three screws either side - one above the Suzuki logo and two on the 
steel frame mounted bracket. Next, remove the seat and side covers (3 mm Allen 
key for cover bolts) and you will confront the bare essentials.
The gearbox has two drain plugs underneath the crankcase. A 4 mm ring spanner 
or socket is required for the front one and 17 mm for the rear. The suggested 
change interval (20W40 oil is specified) is every 12,000 km but for the meagre 
700 ml of oil involved, enthusiasts will no doubt take my advice to half or 
quarter that interval in the interests of transmission gear longevity.
Fill the gearbox with 700 ml of oil (not friction modified of course)
and run the motor briefly. 
Wait a minute or so and remove the plug on the face of the clutch cover.
If no oil runs out you should add a little at a time until it begins to do so.
Next items to be dealt with are the fuel system and sparkplugs. The replacement 
interval on the latter is 6000 km. Fair enough, but gentle usage may 
necessitate more frequent replacement to maintain crisp performance. 
The standard plug is an NGK B 9 ES but if you are not subjecting your machine 
to continual hard work then the optional (one range hotter) B8ES would be more 
suitable.
Spark plug replacement and air filter service can actually be accomplished 
without actually removing the tank as there is provision to tilt it backwards 
and prop it in place after the fuel tap has been unbolted. I prefer to have 
the extra working space offered by removing the tank 
although the fuel lines are a bit of a hassle.
The air cleaner is found nestling in an impressive container formed by
the steer ing head casting. The element is made of washable foam that 
Suzuki recommends be oiled with two stroke oil every 3000 km although this 
sounds excessive if the machine is not campaigned in the dirt too often! 
I use petrol in a four litre icecream container to wash the filter (repeat 
with clean petrol if necessary) then dry it and apply the oil. After working
the oil through the foam squeeze out as much excess as is possible and when 
reassembling, ensure that the filter seals perfectly against the intake 
housing.
For once vacuum gauges wont be necessary to synchronise the four throttle 
slides! But before we go into that there is preliminary work to be attended 
to, like removing the plastic inlet tracts leading to the carburettors and 
draining all four carburettor float bowls to see if any gunk or water is 
lurking there. Now check that each outer cable has between 0.5 and 1.0 
mm of free-play at the point of entry on the carburettor top. Without
the specified play, engine speed could increase when turning the handlebars 
and it would also not be possible to lower the idle speed.
The slides should all be open an equal amount at idle for smooth tick over. Off 
idle response with the engine at operating temperature should be crisp and the 
engine should immediately 
settle down to an even idle after cracking open the throttle. The latter 
conditi on is largely controlled by the pilot air screw that enters a 
passage in the side of the carb bell mouth. The specification is for 
1 5/8 turns out but this one responded best to a setting of 1 1/2 turns. 
More turns out represents a leaner idle mixture but regardless of the 
setting, they should all be equal.
You can use a thin piece of wire or a drill bit as a gauge for synchronising 
the slides at idle (about 0.5 mm is a starting point but this doesnt mean 
that the idle speed will automatically be correct) and its simply a matter 
of turning each idle stop screw by an equal increment. 
Large stop screws designed to be grasped by human fingers (average sized
ones at any rate) feature on the two rear carbs but Suzuki apparently doesnt 
concede that an owner may be able to perform four incremental adjustments, so 
the front pair have semi hidde n screws (adjacent to the fuel inlet pipes) that 
require a screwdriver to turn.  In other words they only want you to turn the 
idle up or down on the rear cylinders which is not conducive to my brand 
of tuning!
 
Now look at the slide and youll notice a dot in the centre. The next
step is to somehow wedge open the throttle grip (I use a strip of rubber) so 
that the top of the dot aligns exactly with the top of the carburettor bore. 
Simply, if the slide heights are found to differ its a matter of determining 
the one that is opening the least, lining it up with the bore and lowering 
the others by giving the cables extra free-play. Snap the throttle open
and closed a few times, re-employ the ingenious device you have come up with 
for locking the twist grip and re- check the adjustment. Hopefully, at the 
finish, the cable play wont exceed 1.0 mm because too much play will prevent 
the slides from opening fully. A bad value situation for against the stop 
types!
Now that the dots are aligned perfectly, leave the throttle in that position 
(for chrissakes close it before attempting to fire the thing up!) and proceed 
to check the oil pump al ignment marks. 
The pump resides above the countershaft sprocket. If the mark (a line)
on the control lever doesnt exactly align with the fixed index mark then 
adjust the pump control cab le to suit by loosening the lock-nut  and 
adjusting the outer cable length by turning the threaded body. 
Dont forget to tighten the lock nut.  Thats about it for the fuel and oil 
systems, but the automatic exhaust control (AEC) cables can be checked while 
delving in the vicinity. (A few drops of oil for all the cables - clutch, 
throttle and AEC - is recommended every now and again too.)  The specifications 
require each of the four cables to have a slight free-play of 0.5 mm but they
probably wont need attention.  The control unit is electronically activated 
so that between 7500 and 7800 rpm the actuator pulley instantly rotates the 
valves (via the cables) which closes off the exhaust sub chambers thus 
effectively decreasing the exhaust header volume. From that point on 
shes on the pipe so to speak by virtue of the fact that the reverse sine
pressure waves arrive at the port sooner causing a more efficient induction 
of fresh mixture. The whole setup is basically maintenance free and you would 
be made well aware if a problem did occur.
 
Final servicing tasks may include clutch lever free-play (2-3 mm), chain
tension (20-25 mm play), tyre pressures, general electrical check (bulbs etc), 
and charge rate (13 .5 V -15.5V @ 5,000 rpm). The coolant is supposed to be 
replaced every two years and dont forget that no grease nipples are provided 
for the swing-arm and suspension linkages (nothing new) so you may feel 
inclined to spend a wet Saturday arvo dismantling the whole show to 
introduce some fresh grease.
Before closing, a word on the 6,000 km recommended interval for
de-coking the ex hausts and cylinder heads - youd have to be keen! Firstly, 
its completely unnecessary and secondly, theres a considerable amount of work 
involved. I can envisage the performance benefiting from an exhaust de-coke at 
around 20,000 km but modern lubricants wont really cause detrimental carbon 
deposits on the piston crown and in the combustion chamber. So leave the 
heads in place until there is a real need to remove them such as new piston 
rings or a rebore. 
Sorry, I cant really estimate how far down the track that will be.
 
Service Data and Specifications
Cylinder numbering      1-LF, 2-RF, 3-LR, 4-RR
Displacement            498 cm3
Bore and stroke         56 x 50.6 mm
Compression ratio       7.0 : 1
Oil pump discharge      3.2 - 4.0 ml per minute @ 2000 rpm (fully open)
Pilot screw             1 5/8 turns out
Idle                    1350 - 1560 rpm
Fuel level              5.5 mm +/- 0.5 mm
Float height            17 mm +/- 1mm
Ignition timing (CDI)   14 BTDC below 1700 rpm, 26 degrees 2700 -
6000,11 above 
9500
Sparkplug / gap NGKB9ES 0.6 mm - 0.8mm
Charging voltage        13.5 - 15.5 V @ 5000 rpm
Steering geometry       rake 25.5 trail 110 mm
Fork Oil                15 W
Fork Oil level          97 mm
Fork Oil capacity       441 ml
Fork air                standard setting zero
Drive chain slack       20 - 25 mm
Oil capacity            Gearbox 700 - 800 ml, Tank 1.5 litres
Coolant capacity        2 litre, 250ml catch bottle 50 : 50 mix anti freeze water
Fuel type               85 - 95 octane (or higher) UNLEADED
 
 
Service Intervals (As per service manual recommendation
P/N99500-14000-01E)
 
3000 km         Air filter
6000 km         Battery, replace plugs
12,000 km       Transmission oil
2 years         replace coolant and brake fluid

Rob Koopman ( Rob.Koopman@inter.NL.net ) ^{RG500 Index}