Between 1962 and 1965 Honda made four different 50cc twin cylinder Grand Prix racing motorcycles.Money seemed no object and all had differing engine castings and configurations….
All were air cooled 4 stroke twins with gear driven overhead camshafts.
The RC112 of 1962 was a 2 valve DOHC engine, 49.61cc, bore 33.0mm x stroke 29.0mm, listing over 10bhp at 17,500rpm, 0.45kg of torque at 15,000rpm, magneto ignition, wet sump, 9 speed gearbox, 62.5kg machine weight, drum brakes SLS front and rear, tyre sizes 2.00-18 front and 
2.25-18 rear, max. speed over 140kph(87mph).
The RC113 of 1963 changed to a 4 valve DOHC engine, 49.61cc, bore 33.0mm x 29.0mm stroke, listing over 10bhp at 19,000rpm, transistor ignition, 2 carbs,( piston valve), wet sump, 9 speed gearbox, 53kg machine weight, front brake a push bike calliper type, rear 2LS drum, 2.00-18 front and 2.25-18 rear tyres, max. speed over 
140kph (87mph).I
have no specification listing for the 1964 machine, but it was the RC114, a twin cyl. 4 valve DOHC engine..
The RC115 of 1965 again was a 4 valve DOHC engine, 49.75cc bore 34.00mm x 27.4mm, listed as over 13 bhp at 20,000rpm, transistor ignition, 2 carbs ( piston valve), wet sump, 9 speed gearbox, 50kg machine weight, front brake a push bike calliper type, rear 2LS drum, 2.00-18 
front and 2.25-18 rear tyres, max. speed 154kph (96mph).
Interestingly the machine weight fell from 62.5kg to 50kg over 4 years development with the max. engine rpm rising from 17,500rpm to 20,000rpm & engine power from 10bhp to 13bhp.
I recall there was a rumour at the time, never substantiated, that Honda had a 4 cylinder 50cc engine under development,,, amazing!
Looking at the pictures the crankshaft fits into a human hand!! The gear wheels in the 9 speed gearbox must have been really thin, almost like a slitting milling machine cutter.
For 1962 Honda produced a production racer in 50cc format for selected sale to the racing public. Called the CR110 Cub racer, it was an air cooled single cyl.4 stroke engine, DOHC with gear train drive, 49.99cc with 40.4mm bore x 39.0mm stroke, 8.5bhp at 13,500rpm, 0.46kg torque at 11,500rpm, magneto ignition, 8 speed gearbox.
As well Honda produced a sports model of the CR110 for the road! Same engine
details, but 7bhp at 12,700rpm, 5 speed gearbox, max. speed 100kph (62mph), 2.25-18 tyres front and rear, 75kg dry machine weight with a price then of 170,000 yen.
Then Honda retired from formal Grand Prix racing around 1968 and it all became history…..
Data and photographs for this blog are acknowledged from “Honda Collection 1”, Honda Collection 2” (published by Honda Motor Co.,Ltd, Honda Collection Hall Museum Project and printed in 1994 by Neko Publishing Co.,Ltd, Japan) and “Motorrad Classic” 5/2000 Sept./Oct., published by Motor Presse-Verlag, Stuttgart, Germany.
Left click on photos to enlarge.
front and 2.25-18 rear tyres, max. speed 154kph (96mph).Interestingly the machine weight fell from 62.5kg to 50kg over 4 years development with the max. engine rpm rising from 17,500rpm to 20,000rpm & engine power from 10bhp to 13bhp.
I recall there was a rumour at the time, never substantiated, that Honda had a 4 cylinder 50cc engine under development,,, amazing!
Looking at the pictures the crankshaft fits into a human hand!! The gear wheels in the 9 speed gearbox must have been really thin, almost like a slitting milling machine cutter.For 1962 Honda produced a production racer in 50cc format for selected sale to the racing public. Called the CR110 Cub racer, it was an air cooled single cyl.4 stroke engine, DOHC with gear train drive, 49.99cc with 40.4mm bore x 39.0mm stroke, 8.5bhp at 13,500rpm, 0.46kg torque at 11,500rpm, magneto ignition, 8 speed gearbox.
As well Honda produced a sports model of the CR110 for the road! Same engine
details, but 7bhp at 12,700rpm, 5 speed gearbox, max. speed 100kph (62mph), 2.25-18 tyres front and rear, 75kg dry machine weight with a price then of 170,000 yen.Then Honda retired from formal Grand Prix racing around 1968 and it all became history…..
Data and photographs for this blog are acknowledged from “Honda Collection 1”, Honda Collection 2” (published by Honda Motor Co.,Ltd, Honda Collection Hall Museum Project and printed in 1994 by Neko Publishing Co.,Ltd, Japan) and “Motorrad Classic” 5/2000 Sept./Oct., published by Motor Presse-Verlag, Stuttgart, Germany.
Left click on photos to enlarge.
3 comments:
These tiny Honda engines (and bikes) are a sight to behold, no-matter what your cycle bent! They are engineered with spiderweb detail and beautifully finished at all angles. Even today, Honda are still doing things with 'almost tiny' motors that are truly amazing, just look at the lastest CB250RR (and imagine yourself at 18 yrs old again!). I just bought my wife a 1992 Honda CB250F (grey import, not sent to Aust). It's DOHC, water cooled, 6 speed and just a great bike, plus it flies if you want it to. The tacho shows a redline starting at 16,500!!, gulp, for a leaners type road bike! You can't but love the Honda's.
In 1970 I bought my first motorcycle- a Honda CL100- and in the shop, on display, was one of these bikes. I'd never seen anything like it, and haven't since, and, at age 14 it changed everything I thought about motorcycles.
I've been searching for the last 10 years for some information on that bike- and finally found this post. Thank you SO much for the information! I wish I could say you've put a long story to rest, but I suspect you've sent me off on even a longer one... :)
Thanks a lot for these very nice and detailled photos,
and alos for precise comments!
A French rider who saw these bikes on European circuits!
Patrice from France.
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