I have decided to repost my RS500 build, as it was not finished and PhotoFu*kit decided to stop sharing photos on 3rd party sites and a build is pretty much useless without photos – so to recap
This is the start of my new project an RS500
A couple of years ago I purchased a Suzuki RG500, a bike I have always wanted. The plan was to try and drag it into the 21st Century by updating and modernising where I could, this is the bike as I purchased it.
A Japanese import RG500, totally standard apart from the seat hump and pushing out about 74bhp. The engine underwent a full engine rebuild, gas flowed and ported, tripod filters, bored 31.5mm diameter carbs, bespoke expansion chambers and Zeeltronic programmable ignition. Plus new body work, wheels, suspension, dash etc. This was the end result.
I was pleased with the results, a modern looking bike that handles and now making 112.5bhp. One thing that always bugged me were the two rocket launchers (sorry expansion chambers) on display under the seat. As I wanted to keep the frame intact this was the only option I had, if I had cut the rear sub-frame and raised it several inches I could of hidden the under seat exhaust, err under the seat!
So it was always on my mind, what could I have achieved if I did not have any restrictions or barriers, so the idea of the RS500 was born. An Aprilia RS 250 frame married with a RG500 engine, tuned and modern suspension, wheels etc.
The Engine as purchased is a RG400 that was imported from Japan by Suzuki Race based in Ashbourne. Alan goes out to Japan for 2 or 3 months a year and buys up bikes, engines and parts – fills a container then ships them back to the UK and sells them as complete bikes and engines or strips them and sells parts. This particular engine was low mileage, approx. 7,500km (and when stripped the internal condition confirmed this).
Luckily enough when I had finished the Walter Wolf modernisation, I managed to pick up a second-hand set of RG500 barrels and cylinder heads – which were very low mileage and in very good condition, these are very difficult to find and very expensive! I actually purchased them from Darren Lane, who is an RG500 bike builder of some repute.
Before anything could happen to the engine it was initially used to match up to the Aprilia RS 250, to allow the necessary modifications, new engine mounting brackets and bespoke engine cradle, plus frame spar clearance for carburettors, but this will be covered later. The engine RG400 was stripped completely and all external parts and the RG500 barrels and cylinder heads were sent for vapour blasting at Projex Motorcycle Engineers.
The rebuild and engine tuning was entrusted to Mark Dent of Performance Fabrications, who is the guru on these engines. The full engine specification. All new bearings and seals, genuine Suzuki full gasket set, crank strip and rebuild, full engine tune, engine gas flow, crank web ignition pick up slot widened to allow greater static advance, modified carbon rotary valves, billet disc valve covers, complete Nova transmission and straight cut primary gears, TTW cougar red clutch, offset carburettor bore to 31.5mm and carb splitters plus a new generator and Performance Fabrication billet clutch cover
Initially you need to remove the original engine mountings from the frame, then you can dress and clean the areas back and remove the anodising, locally to where the new engine mount brackets will need to be welded. Once this has been completed the RG engine can be offered up to the frame, the clutch cover needs to be first removed as this will clash with the RS frame. I tried to position the engine as far back as possible and as high in the frame as I could, whilst fitting the engine centrally within the frame.
Another main area to consider is chain run, so basically the position of engine output sprocket in relation to the swing arm pivot and rear wheel spindle – during its suspension travel. This took a fair amount of time to find the best position for the engine in relation to the frame, this is always going to be something of a compromise. Then once the exact position is known new upper and lower engine mounting brackets can be fabricated and welded in position. One of the engine mounting bolts will need to be inserted and removed through a frame spar due to limited access, so an aluminium boss was turned and welded into the frame.
The next area to look at is the inside of the frame in relation to the clutch cover, I purchased a 3-piece billet cover from Performance Fabrications which is narrower than the standard cover, and will allow clutch removal with the engine in situ. The inside of the RS frame can be marked in relation to the clutch cover, the engine removed and then the inside ‘skin’ of the frame cut away to give clearance and then the inside can be strengthened by an aluminium fabricated section being manufactured and welded in place. Also, a cast hole in either side of the RS frame was ‘filled’ with an aluminium plug welded into position and dressed back.
The RG engine has its carburettors mounted on the side of the engine, the rear carburettors will hit the RS frame spars, so the frame requires modification to allow the carburettors to mount and also give clearance for the throttle cable exit. Again, the frame was marked in the correct areas, the frame spars were cut and modified then aluminium sheet cut and formed and welded in position to close and strengthen the frame spars.
The last item to be made was a bespoke engine cradle. The RG engine is mounted at the rear of the engine in 2 positions, the front engine mount is via rubber vibration mounts and a bespoke engine cradle – similar to how the engine is mounted in the original RG frame. Other schools of thought are not to use an engine cradle and instead to have a bracket from the frame mounting to the cylinder head bolts via rubber vibration mounts. I preferred the engine cradle which will give the main frame some additional strength, especially as the main frame has been cut and shut in a few areas (carb cut outs and clutch cut outs). Also, the engine cradle is in two halves, and either side can be removed independently, it also gives an area to locate brackets for radiator mounting.
If you look carefully at the bracket below the head-stock , the front hole mounts via a rubber vibration damper to one of the cylinder head bolts, on both sides of the engine to support the engine. I did not like the idea of this method, hence why I went for an engine cradle.
Now the frame has been prepped to accept the RG500 engine, the next stage was to send the engine away for tuning, gas flowing and rebuild. I decided to keep the engine self-colour as vapour blasted and to treat with ACF50 to help prevent corrosion. The engine went off to Mark Dent and came back fully rebuilt and tuned along with bored carburettors.
This is how the engine looked when I took it.
This is how the engine looked when I collected it.
Then starts the difficult task of connecting cables and pipe work, never easy on these engines. 4 carb cables, 2 choke cables, 4 power valve cables, 1 oil pump cable, plus all the pipe work for the carbs and oil pump. I knew this would be tricky as the RS frame is more restrictive than the original RG frame – I was expecting some fun and games when I eventually mated the frame and engine. Please ignore the blue tubing on the carbs – this has since been changed. I have fitted in-line 2T oil check valves (the small white cylinder by the carb in the following photo), RG500/400’s are notorious for leaking oil in to the crankcases, there are sprung ball check valves built in to the carbs, but the spring loses it’s tension over time.
Since the photo's were taken I have made all new cabling (bought the kit from Venhill), replaced the steel powervalve cover and fitted new tubing.
Now it was time to fit the engine into the frame, and try and route the cabling and pipework into the best positions/runs. A crazy thing with this engine is that the fuel pipes run between the two rear exiting expansion chambers - not ideal !
It is now time for some careful planning, most of the cables need to head over the top of the engine and either around or through the headstock. Other items that will have to be put in that location are. Battery, Power Valve Actuator, Coils, some pipe work for the radiator – which I would also like an electric fan, the two rear exiting expansion chambers, fuel lines, wiring loom (which I will be making from scratch), ideally the 2 stroke oil tank (this could possibly go under the rear seat unit). Also, the electrical ancillaries (CDI, Power Valve control unit, fan controller, regulator/rectifier).
A Tyga rear sub-frame was fitted, the bottom support arms were removed as the under-seat exhausts would clash. Mark Dent manufactured a new aluminium support, which locates on a new square tube section welded into the sub-frame and mounts on the top shock mount, a lovely piece of kit.
You can also see the Tyga rear sets which I decided to go with, at some point in the future I would like to convert to folding foot pegs if possible.