50cc tow & three cylinder 19 hp GP bike

[threewheels]

Here is some info on the 50cc GP bikes of the 50’s and through to the late 60’s
This one above is the Suzuki RK67. First raced in Europe 1965 by Hans george Anscheidt.

Now the good stuff. The RK67 was a twin cylinder 50cc rotary valve 18000 rpm screamer. 12 speed gear box kept this little weapon in its tiny power band. Hans is quoted as saying that a gear change every second was the only way to keep the bike on power. At 16000 rpm it was pulling, at 17500 a full 12hp was quoted. Then at 18300 it was time for another gear!

This engine was developed over the next three years and went from 12hp @ 17500 rpm through to a three cylinder model which the factory claimed 19Bhp!


Finally there was the RP68 which was a 14 speed three cylinder 20000 rpm 21 hp beast! Suzuki pulled out of 50cc GP in late 1968. At this time FIM introduced rulings of single cylinder 50cc GP bikes only. This killed off the class that had the best power to weight ratio in the world. 120mph race speeds and 16 speed boxes were to be used to use the RP68 powerband which was only 400 rpm wide! A pipe builders nightmare.


So is a BZM doing 16Hp @18000 RPM impressive for 2008? You may think not but the BZM can produce power over several thousands of RPM. The Suzuki was only a brief puff of power. Still if this class would have not been lost where would the BZM and Polini engines be today! Under the tank of the latest GP bikes.

I have been tuning two strokes and making tuned pipes for the past 15 years, With the development of the Zenoah engine for marine hobby use pushing 8+ hp at 17000 rpm my thoughts are towards a 52cc twin two stroke to run in a PB. After already making a 26cc engine that produced 12hp @ 21000 rpm I am keen to see if its possible to do the twin. Unfortunatley there is no 50cc GP road racing for seniors. With this in mind I think a single speed twin for a PB would be an interesting project.

Has anyone else had similar thoughts. All components except for the cases and crank center web would be OEM. Also we are looking for any 50cc race bikes from the 60’s. Honda, Suzuki, Kreidler etc so if you see any please let me know.
Regards
Dave

[Reaper1721]

sounds like an interesting project, i'd love to see a set of custom crank cases.
if you wanted to go build a water cooled twin without an overly large displacement, im sure you could use some blata rep pistons and cylinders, and a cag crank, to reduce capacity and compression, unless you milled down the bottom of the cylinder. im willing to bet that some of the youngens here would take one look at the cooling pipes for that kinda engine and say "WTF???"

seriously...im sure anything you build will be greatly admired by everone who sees it

[Squeeby]

I read that Honda had a 5 cyclinder 125cc that put out 36hp or so back in the 60s. I've also read they made 6 cylinder 50cc engines. Apparently reliability with those things were so bad back then that they'd bring a whole lot to the track and just keep swapping engines out until they found one that worked. Good luck with the project.

[Reaper1721]

Originally Posted by Squeeby

I read that Honda had a 5 cyclinder 125cc that put out 36hp or so back in the 60s. I've also read they made 6 cylinder 50cc engines. Apparently reliability with those things were so bad back then that they'd bring a whole lot to the track and just keep swapping engines out until they found one that worked. Good luck with the project.

bet that would have been fun

[Squeeby]

There's videos of Honda's 250cc 6 cylinder on Youtube, sounds like an F1 it's great