1976 Honda RC500M

 


 

On May 2nd in Fermo Italy at the 500cc Italian Gran-prix, Honda unveiled this bike. The RC500A1E Type ll. It was Honda's first "designed from the ground up" Grand-prix motocross bike. News traveled fast through the pits that day that Honda had a new ultra trick bike. Pierre Karsmakers qualified fastest to World Champion Roger DeCoster during time trials. In the first moto Pierre was left standing on the starting line with a fouled plug. The second moto Pierre won wire to wire. The journalists that covered this race, talked more about the bike than the race itself. It definitely stole the show. No bike drew more attention since Yamaha came out with the monoshock in 1973. Honda had arrived.

When you look at this bike it is immediately apparent that there was a lot of thought in designing this bike. The attention to detail is amazing. A lot of innovations that are used to this day were started with this bike. I have tried to explain this in the text below. Other than paint (the original was too far gone) the bike is in 100% original condition including the tires since the day it was parked.

Karsmakers shows Honda power for the first time in Fermo Italy at the 1976 Italian Grand-Prix. Pierre went wire to wire for the win.The world would never be the same.


1976 Honda RC500M Photos


Pierre Karsmakers' comments:

We got this bike a few days before the Italian Grand-prix. During time trials, I had the fastest lap times, but the bike was pinging a little on top end. I told my mechanic to put in a larger main jet to cure this. Instead he put in a colder spark plug and the bike wouldn't start for the first moto. By the time we put the warmer plug in I was already a lap down. I still passed DeCoster and was in front by 29 seconds but a lap down. The second moto though, I got the holeshot and wheelied away from everyone! The bike was so fast and had a very smooth powerband too. The motor had a very good characteristic. The suspension was also fantastic. The bike was so superior at the time, everybody was just shaking when I was there (laughter). It was really a good feeling. It was the first bike made just for the long travel design. I had a special set of Koni shocks made just for this bike. The spring rate and the damping were just right the first time. Koni made all the right calculations when they built them. The front forks were fantastic also. The only problem I had was sometimes the fork gators would get caught between the external springs. That, sometimes was not a nice feeling. That was the only problem. The bike was very reliable, no problems at all whatsoever.

I was very instrumental in the design of this bike. It involved a lot of testing, meetings and travel all over the world. I was actually the guy responsible for getting the countershaft sprocket moved close to the swing-arm to keep the chain from coming off due to the long travel. It was the perfect bike. The bike was fantastic!


Detail Photos


Dave Arnold's comments:

When the crates with these bikes arrived, you knew something was up. The crates themselves were a work of art. They were made of a mahogany type wood, and when we opened them up.....WOW. You could just smell the horsepower. There was so much titanium and magnesium, everything was so trick. There was actually a smell that I can remember to this day. This was a works bike like no other. Prior to this we would get the bikes and parts and we were pretty much on our own for the season. This time we knew Honda was serious. When we took them out to break them in and set them up, we went to Saddleback. The motors were just so shriekingly fast! They were almost too fast. Honda's ability to stay on top of engine development at that time was second to none. They were definitely pushing the envelope with this bike. Each bike came with two front ends. One with external springs and one with internal springs. With the new chassis and laid down shocks, every thing came together.

 


Details


 

    • Up front the knurled fork tubes are held into very stout billet triple clamps. There is a steel X brace that ties the top and bottom clamps together. This was to reduce flex while turning the bike. The pinch bolts are hand machined steel. A very clever yet simple cable guide attached to the top clamp is made from aluminum. The entire front end is very rigid.

 

    • The RC500 motor is actually about 400cc. The cases are sand-cast magnesium coated with a special coating to prevent corrosion( Honda was the only company to do this). The little cover below the counter shaft sprocket contains all the shift linkage that is normally behind the clutch basket. You can actually adjust the shift throw from inside that cover. Several aluminum motor mounts were available to move the motor location up to 15mm to the front or back for different weight distribution. Bolts are titanium. The carb is magnesium with a brass bore insert for the slide. This allowed for a reliable use of an aluminum slide to reduce rider fatigue. Ignition timing is adjusted externally.

 

    • The clutch basket and large primary gear are one piece made from machined billet steel (see photo in works parts). This provided a very solid yet light weight clutch. The crank shaft is a very special unit that in 1976 dollars was around $10,000.00! (see photo in works parts). Kick start boss is titanium as are all the case screws. The gear lever still has the rubber safety wired to it from 1976.

 

    • The rear hub is a conical design sand-cast magnesium unit that is very light and very strong. The ring at the outer spoke end is a machined piece of steel to keep the spokes tight. All the wheel spacers are titanium. That is the original 4.50 Metzler rear tire from 1976. The rim is an extra wide works 2.50 D.I.D. to allow more tire surface on the track. This concept was just starting and has been carried through to this day.

 

    • The rear swingarm is a very rigid hand formed aluminum piece that for the day looks like an overkill. Notice the flap on the side panel to keep the rear brake cable from getting caught in the shock spring. Rear backing plate is sand-cast magnesium.

 

    • These are the very first cartridge front forks (production bikes did not see cartridge forks until 1981). They use very large external fork springs covered by the large fork boots. The idea was to have the springs on the outside so there would be less oil foaming inside the forks. This worked well, but the draw back was that the giant fork boots restricted air flow to the motor. This caused the motor to get too hot for mud races. The forks also featured a five way preload adjustment similar to those found on rear shocks (notice below the fork boots).

 

    • Even the chain roller is drilled. Foot peg bolts are billet steel. In 1976 Honda used steel fasteners at all stress points. Notice all the other bolts are titanium. Every part on this bike was made to be an RC500.

 

    • The silencer, which does little to keep the bike quiet has a gusset that also acts as a guard to keep the riders boot from hanging up.

 

    • A special intake duct hand formed from aluminum, fiberglass and rubber feeds the air box. Remote reservoirs were necessary to keep the shocks from overheating on the new long travel bike.

 

    • The rear shocks were custom made for this bike by Koni. The stock Showas did not provide the same quality suspension that the front forks did. Koni was commissioned right away and came up with these shocks that are adjustable and have remote reservoirs mounted in the air box. The rear suspension was greatly improved.

 

    • Inside the air-filter cage is a very special part. It is a venturi that was designed in Japan by bolting up an engine in a dyno room. Turning out the lights, using a strobe lights and a high speed movie camera, they would open the throttle and then chop the throttle. This would create a back vapor. Where the main part of the vapor ended, is where the length of the venturi was determined. This was to give the bike more throttle response at low RPM. During this test they also noticed that at full throttle the cylinder would ever so slightly actually separate from the cases!

Pierre Karsmakers on the Type II at a test session in early 1976.  The bike went from a blank sheet of paper to a state of the art GP bike in about 3 months.


Historical Photos


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