Who Moved My Cheese... Racing Honda 4-Strokes in the 1970's
I purchased a brand new just released Honda SL125 back in the early 70's and immediately stripped the bike down to individual bits and pieces. First up was a light sand blast of all the paint and a new re-paint with the frame in canary yellow and the fuel tank a brighter deep yellow. The yellow colour scheme was for the Wynn's oils sponsorship who's main colour was yellow.
The rear shocks were replaced with British Girling shocks and the front fork springs were replaced with springs from a Bultaco set of forks, the actual model I can't now recall, as was the oil viscosity too.
Of course all the accessories and extraneous items were tossed and plastic mud guards were added. The wet battery was replaced with a quite smaller battery and had to be re-charged quite regularly as it was slowly discharging during racing.
The sheet steel plating under the seat was removed and crude 3-ply strips were fitted in placed of the steel to save weight.
All the lighting wiring was removed and the airbox filter was changed to a larger oil/foam type. The brand and design of the tyres were an ongoing test to which I was never really happy with. The gear lever had a spring load 90 degree hinge on the protruding shifter bar added and the right foot brake lever was re-designed to allow for better ground clearance and less lightly lever for damage when laying it down on that side. Handlebars, throttle, hand grips and levers were also upmarket trick brands and we had a single red warning light for oil pressure lost.
Now to the engine. As the SL100 and SL125 engine heads had a plain bearing overhead cam driven by a cam chain which was not easy to know just how tight to adjust the cam chain tensioner. We (the racing team) had already cooked a couple of cam plain bearings in the earlier SL100 engines due to over tightening the cam chain which in turn placed too-much pressure on the cams chain side of the cylinder head plain bearing.
The bloke who was the chief mechanic/engineer of the Honda shop indicated he could solve the problem by fitting a roller bearing in-place of the cylinder heads plain bearings. After some testing, etc he perfected the head with a roller bearing bearings. What an improvement, we never cooked another head and the engine appeared to run freer. I can't recalled the engineers name but damm he was good.
The bore was taken to the max blueprint size and the piston had its skirt all but removed and what skirting of the piston was left was drilled full of holes to further lighten the piston. Rings where replaced every month.
The head was also ported and polished and a new carburettor from a Honda SL350 was re-jetted and the main slide modified and fitted. If I recall correctly I believe the head or cylinder was shaved and the compression ratio raised considerably.
Oh yes, the valve springs were replaced after we noticed that we were getting the odd valve to piston contact markings on the piston. However I never had a dropped valve though one of my racing colleges did suffer dropped valves.
The exhaust was made out of lightweight steel and specially bent and shaped to travel back up and close to the frame up high as a straight pipe. I had two exhaust, both tuned to different lengths to give the engine the best torque according to the type of circuit I was to race on.
This was done after consulting with a exhaust specialist in Brisbane. His shop was in either Dutton Park or Fairfield I believe. Knew his job very well.
The tuning was done by doing speed and timed runs on a straight bitumen road and at measured distances and cutting the pipe shorter or a bit added on the archive benchmark timings. The same testing with the carby and spark plug was done later also. No dyno's back then. That was a slow, long and somewhat boring job doing these speed runs but it did appear to improve the bikes power on given circuits.
The primary and main chain sprockets were changed again according to the circuit and chains were replaced monthly too. The main sprocket was drilled for lightning to the point were we had a couple of failures due to too much lightning.
After all this the engine as taken up to Brisbane to a specialist engine shop and balanced and fine tuned. Not sure of the shop nowadays but I think it was just off main Moorooka Magic Mile area in South Brisbane.
The engine oil was Castrol but with a large amount of Wynn's oil additive's added. I spent a lot of time over a couple of months testing, adjusting and getting both the handling and engine running to its best. I'm not sure of what the maximum rpm was but I did see a electronic tacho on a lesser tuned Honda SL100 from the Sydney Honda team which was topping around 11000 rpm! How true the tacho reading was I don't known.
Our Honda/Wynn's team competed at (amongst other events) the Oran Park International Scrambles meet (motocross?) back around the early 70's I think when the British Scrambles champion, Jeff Smith came down to OZ with his BSA Victor 441. It was a big meet with an artificial scrambles circuit laid down on the inside area of the Oran Park motor racing circuit near the entry to the main road racing straight with the usual man made jumps, etc. a pretty flat and average circuit overall.
Upon our arrival in Sydney from Northern NSW's for the International race event us country youkles were billeted at one of the Honda reps house and somehow ended up at the St George's Rugby League club to have dinner.
Boy, were we 'set-up' by the Honda rep and unknown to us, yes we were all wearing our sponsors dress shirts with subtle logos and various sponsor names of the shirts - the dance floor band and compere for the nights entertainment out-of-the-blue stops the show... and announces to the 'world' that the club is very privileged to have with-in the guests tonight the Honda 'Works Racing Team' and came over to our table and bailed us up for some real-time interviewing live on microphone... (The Honda rep had pre-briefed the compere).
Jeez, did that take the rug out from under our feet! Here we are all from the country and thrown into the big smoke lions den! We sputtered and ad-libed and well, basically bullshitted our way through the comperes interview, for all the patrons and other guests knew we could all have been riding factory GP works road racing bikes in the world championships, as the compere blew it up out of all proportions - we even had a standing ovation and drinks were then on-the-house...
After this fanfare died down we crawled back under our table, moved tables to avoid attention and unfortunately broke-under-the-pressure (drinks-on-the-house) and we 'poured' ourselves out of the club around 2 am in the morning accusing others of treading on our fingers as we walked out of the club (hic!).
What an embarrassing setup that was and we were racing the next day, oh what you do when your young and innocent and lead by others in a big city.
Like all good plans, the racing Plan A failed... :-) Never mind the unholy hangovers and side effects, and they were big. Once racing got going my bikes bloody battery retaining strap failed after going higher over jumps then I had ever gone in earlier testing, etc back home and the landings whilst very firm were quite OK from my point of view though must have been harder on the bike as the battery parted company with the battery box area and was flying around the outside of the bikes side. I became aware something was amiss as there was something banging away a my left leg and really annoying me. Looking down I saw the small wet cell battery flying all over the place hanging on only by the two battery leads trying to depart from the bike in ever increasing spirals, rats! That was a disappointment as I was making up time (read hangover blurred world) and making up big-time by hitting the jumps flat out and sailing through the air quite a distance passing many a rider. Everyone seemed to be racing up to the jump/s, braking early and 'hopping' over the jump and then powering back on? Why not just scream over the jump, hang on for all life and land err upright and continue powering on. If the frame broke, so be it. :-)
As I said Plan A should never be used as my team mate on a Honda/Wynn's SL100 tried to outdo me in another race when on a particular lap I noticed he was getting everyone's attention (including mine) by doing high speed 'do-nuts' on the edge of the circuit with his bike cranked right over and him with his leg out fighting the bike in every increasing do-nutting speeds???
What had happened was the carburettor main slide retaining cap had unscrewed and had the carby set to maximum throttle and jammed open. He had then got himself in a do-nut increasing speed situation and was hanging on for dear-life trying to hit the kill switch which he said later was very difficult to get hold off due to just trying to handle the bike and not spear off into the fellow racers. Arrr the fun of racing. I think Jeff Smith used me at one stage as a launching pad for one of the main jumps when he was passing me, nice to be useful eh! :-)
The Honda SL100 and SL125 'worked bikes' were about as good as one could develop and build as 4-strokes go in those days, with a of of assistance and help from Honda with parts, workshop use, etc but the bloody screeching screaming smokey 2-strokes were far more powerful much to my frustration as I was then a 4-stroke man and still am. Over time riding the Honda/Wynn's SL125 I could only give the 2-strokes a hard time by learning to just about not use brakes coming up to corners and making up for the lost ground on the straights and also either stuffing the bike under the 2-stroke rider in the corner or flying around to outside of a corner if there was a good berm.
Enjoyed the racing of 4-strokes and for a long time refused to ride a 2-stroke. No offence to all you guys who love racing 2-strokes, just I'm a 4-stroke bloke. The sound of the exhaust, the engine braking, the steady pull with torque and the odd sound of a valve tapping the piston... Pure heaven. (As painful as it was back then) :-)
To be continued...
Rodger
