For Acacia - Honda 50cc GP Bikes

[dallara]

Acacia asked, in another thread, for some more detailed pics of some of Honda's amazing 50cc "tiddler" GP bikes, so I thought I would post a few here along with some info about 'em. Everybody seems to know about the Honda 250cc six-cylinder bike, but somehow the smaller displacement Honda's get lost in the shuffle... That's a shame, because in many ways Honda's 50cc and 125cc are far more intriguing and technically engaging.

Honda first attempted running in the 50cc World Championship in 1962 - the first year the class has been granted World Championship status. Honda decides to contest the class with a four-stroke, which would seem doomed to failure from the start as 50cc racing at the time was dominated by two-strokes. Honda's first 50cc contender was a single-cylinder known as the RC-110:



This bike had dual-overhead cams driven by gears on the right side of the engine. It had a bore and stroke of 40mm x 39mm and points for ignition. Compression is 10.5 to 1, and the engine produces 9.5 HP @ 14,000 RPM. It started the season with a five-speed gearbox, but later that was increased to six-speeds. The bore was also increased mid-season to 40.4mm, bringing the displacement to 49.9cc.

By the time the season rolls arround to the Isle of Man Honda has a new single - the RC-111:



It has new crankcases, a longer intake tract, and an eight-speed gearbox. By the time the series gets to Assen the bike has a ten-speed transmission, but the rider, Luigi Taveri, prefers the eight-speed and races with it, but in Finland he uses a nine-speed cluster.

For the last race of the season at Suzuka in Japan, Honda debuts a twin-cylinder 50cc bike - the RC-112:





It has a bore/stroke of 33 x 29 and two valves per cylinder, with a magneto ignition still with points. It is a wet sump engine with a nine-speed gearbox. Power is 10 HP @ 17,500 RPM. It is only raced this once, but it wins with Tommy Robb in the saddle.

In 1963 Honda temporarily dropped out of the 50cc class, running only the Japanese GP with an all new bike - the RC-113:





Bore & stroke is the same as the RC-112, but the engine finally gets a transistorized breakerless ignition. Still a wet-sump and nine-speed gear cluster, but now the engine revs to 19,000 RPM (with brief bursts to 20,000 allowed). Max power is 13 HP @ 18,500. This bike is the first of the 50's to use the bicycke-like caliper front brake clamping on the wheel rim. This is done to reduce weight and rotational inertia (so the bike steers quicker and lighter). The two sheet alloy discs are an attempt at streamlining at the front, but are not always used. The discs on the rear are used as heat-sinks for the rear drum brake. Later in the year this bike is replaced by the RC-114, which looks identical, but makes 14 HP @ 19,000 RPM, and is redlined at 20,500... yet can rev to 23,000!!! Top speed is over 110 MPH.

For 1965 Honda brings an all new bike - the RC-115:







This is where Honda started to get really serious! Bore & stroke is now 34 x 27.4 mm, giving the twin a displacement of 49.75 cc. In an attempt to keep flywheel effect to a minimum the cams are still gear-driven, but now off the clutch driven gear instead of the crankshaft. Still a none-speed gearbox and a wet-sump, but valve angle is flattened out to 56 degrees, with the intakes inclined 24 degrees form the bore axis and the exhausts at 32 degrees (previous engines had a 72 degree valve angle, with both intake and exhaust at 36 degrees). Both high and low exhaust systems are used during the year, but Honda finally settles on the high pipes for less frontal area, as they can tighten up the lower part of the fairing. Teh header pipes are made of steel, but the megaphones are made of aluminum to reduce weight. The bike now weighs a feathery 50 Kg (112.5 lbs)!!! Compare that to the RC-110's weight of 61 Kg (137.25 lbs)...

This engine produces 15 HP @ 20,000 RPM, and is safe to rev to 24,000 if necessary!!!

For 1966 Honda reaches the pinnacle of their 50cc development with the RC-116:





For this bike Honda shortens the stroke again, with a bore/stroke of 35.5 x 25.14 mm. Power is 16 HP @ 21,500 RPM, and redline is 22,500, with the engine safe to 25,000 RPM for brief periods!

Now think about this for a moment... That is a power output of 320 HP per liter... Not even today's F-1 cars, or MotoGP bikes can attain such power output. In fact, no normally-aspirated four-stroke engine has *EVER* eclipsed this output per liter.

Granted, the comparison is not all together fair, but it does show Honda's incredible four-stroke technology of 40 years ago!

Some interesting dimensions for engine internals... Intake valve size is just a tiny 13 mm, and the exhaust valve is 11.5 mm. Stem sizes are 3.5 mm, and an exhaust valve weighs only 6 GRAMS!

Truly fascinating machines, and the like of which we will probably never see again...

If anyone is interested I can dope out some data on the equally incredible 125 cc five-cylinder, which even had a weird split throw crank...

Cheers!

Dallara

[NoRRmad]

I'm interested!

[Kabusa]

Dallara,
Where the heck are you getting this impressive collection of pictures and information?! This stuff facinates me to no end. I love the quick evolution of the casting technology / application for the engine cases in 1962. 3 engines in one year in one class.
I would love to see the 125(s). I am sure I am not the only one!
Thanks. I am going to get another cup of coffee and have another look at those 50's.
Steve Kalafski (Kabusa)

[dallara]

Guys,

I'll be happy to do some pieces on Honda GP bikes. I just wasn't sure how many people would appreciate a bunch of info on Honda's on a BMW board.

As to where I get the info and pics...

Well, I was a true, dyed-in-the-wool Honda freak for decades... Almost wouldn't own or race anything else, and so I was a fan of all the factory's race efforts. Some of the info comes from memory, some from books I have collected over the years, other data from various places on the 'net, etc. I am always scrounging around for stuff on race machines of the era of almost any brand, but especially Honda. It doesn't hurt that I was a Honda dealer for 11 years, and that I worked in a couple of Honda shops as a mechanic, etc. before that. In my years as a dealer I actually got to meet some of the engineers who designed some of these bikes, like Shoichiro Irimajiri. He designed many of the Honda race engines of the 1960's - most notably the 250cc and 297cc GP sixes - and later basically scaled this up to 1047 cc's for the production CBX. He also went on to become president of Honda of America (Honda's production arm in Marysville, Ohio) before going back to Japan in 1989.

Irimajiri was responsible for the engine design of the RC-115 50cc bike above, and also did the RC-147 125cc Five and the RC-165 Six... Each one won the world championship in its class. Quite an impressive achievement for a young engineer just out of university in the 1960's.

Irimajiri was an interesting guy. He graduated from Tokyo University in 1963 with a degree in aeronautical engineering. He wanted to design airplanes but at the time Japan was still prohibited from producing aircraft due to the treaty from World War II. So he went ot work for Honda because he would get start out designing race engines.

Certainly he was a fascinating guy, and I was fortunate enough to meet him on two different ocassions, and each time he was extremely polite and answered each and every one of my numerous questions, taking quite a bit of time with me. But he wasn't the only one. I met quite a few of the engineers from the race department of the '60's. See, Honda liked ot take fresh, young engineers right out of school and put them to work first in the racing department. After stints there they would be moved into designing production vehicles, and then many would move into management. Mr. Honda himself is who started this program, saying that first and foremost Honda was an "engineering company", and it is the way Honda is run to this day. Maybe that's why the Japanese make such fine vehicles... Management comes from engineering departments, whereas here in the US management of vehicle companies comes from the bean-counter side.

Anyway, if you folks really don't mind a bunch of Honda stuff on a BMW board I will be happy to do a piece from time to time on many of the Honda GP machines... Even the ill-fated, but fascinating NR-500 oval-piston bike.

Just say the word!

Cheers!

Dallara

[dallara]

Here's a couple more pics of Irimajiri's RC-115 50cc championship winning twin...






Enjoy!

Dallara

[Capt. Blackadder]

This is brilliant, Dallara. More, more!

[dallara]

Okay, guys...

As long as nobody gets "bumpy" about me posting Honda lore on the Beemer board, I'm game.

So, what do you guys want to see next?

The 125cc five-cylinder?

250 and 297cc six-cylinder?

500cc four?

NR-500?

Any of the NSR two-strokes or endurance racers?

Got a fair amount of info on some of the Yamaha's ans Suzuki's of the era, too, and some on folks like Kriedler, MZ, etc. to boot.

Cheers!

Dallara

[collyers]

Fascinating stuff - are you writing these directly in the Forum, or are you doing this in Word/Excel & just pasting it into the forum after? Great photos & info. It might make sense to move it "off-topic", but if you do, post a notice at the end of this thread.

[Simon D]

I for one would be delighted to see more stuff of this quality, whatever the make concerned. How can anyone not love the jewel like precision of those little race bikes?
Years ago I read part of a paper from Honda to (I think) the SAE. It was pretty dry stuff even for a "geek" like me. The phrase that sticks in my mind was something like "we have completely matered the four stroke engine design apart from the low revolution area - below 14,000 rpm"
Other makers couldn't even get their engines to rev as high as the limit that Honda considered below worth bothering about!
As to the oval piston NR500, I saw that raced twice. It disgraced itself on the first occaision at Silverstone here in the UK.
The following year I went to Spa-Francochamps (Belgium) and watched from "LaSource" hairpin. As the pack sreamed through (4cyl 2strokes remember) there was a noise like thunder, literally like thunder, and all the racegoers, me included looked up to see a perfect blue sky. Mystified we watched the race but kept hearing thunder. About half race distance the penny dropped that it was Ron Haslam on the NR on the overun into the corner. Never heard anything like it to this day
Incidentally that race was the first GP victory for a young American rider who went on to dominate the scene much as young Rossi does now.
Who can tell me who it was?????
Si

[dallara]

Why, Freddie Spencer, of course!

And Collyers, I writing all this directly into the forum. Why?

Cheers!

Dallara

[Acacia]

Wonderfull stuff!!!!

That is truely EYE CANDY!! Stuff of my youth!

In previous posts I have spoken about doing 3000 mile round trips on a Yamaha 100cc twin - 600 mile plus days, and 800 mile rides on a 50cc ( bored to 70cc) Mosquito engined Maserati. In the 60's. Friends said I would not get out of the city limits. They were quiet when I returned with an ear to ear grins that lasted and lasted.

This is a part of bike riding that few can even imagine. In a world of 1500cc plus cruisers and butt jewelry, with designs back to the 50's being cool, some of us quietly know better.

We ride BMW's, acknowledge there is space on the roads for all makes, and above all, are enthusiasts of the history of two wheels - at least some of us.

I could not get enough of this stuff. Keep it coming. I am not hearing any complaints.

Alan, thank you!

Acacia.

[Bones]

Here is my vote:
Bring it on!
Yes this is a BMW R1150R board, BUT........have you checked out virtually all other motorcycle boards? NONE, and I mean NONE have the quality of information shared with the depth and breadth of this board. Granted, much of the technical input comes from a few of the board members, but with so many topics that overlap between 1150R's and motorcycling in general, there is a pretty wide swath of information we all chew on , here.

We have beaten servos and ABS to a pulp. We have chewed on paralevers, telelevers, carbonized cylinders/pistons, spark plug engineering issues, etc. etc. You name it. The more you know about motorcycles, engineering in general, suspension issues in general, etc., the more you will understand about your R1150R.

Now, for those of us in the North, the bikes are getting put away for a winter's nap. There is time to read about all these other things.

And.........Dallara and I have had an "argument" over the past year or so. I have "argued" that he "needs" (or we all need him to ) write the definitive motorcyle book. It will be a multivolume text of sorts. Except, unlike virtually all of the other similar types of books, his will be INTERESTING to read. He argues that nobody would find it interesting. Hey, he is allowed to be wrong from time to time.

Dallara has been kind enough to share some of his knowledge about some very specific topics that were best handled by direct email and some phone calls. You have NO IDEA how much he has to share. "THE BOOK" as I keep referring to it as, must be written!

I say we vote to have him share his rough drafts of the chapters on these bikes with us on the board. We can act as "editors."

AND if you don't like it because it clutters the BMW nature of the board, you can use this new invention: the mouse.....just click off that topic. It is that easy.

I say VOTE YES!!!

Bring it on.

Bones

[darthrider]

Learning to ride on a small-engined bike is a big advantage. My first was a 50CC Puch Moped from the Sears catalog.
I think learning is best done on a bike that is better than we are, but only a bit better. Master that and look for a greater challenge.
Learning how to do all the 'motorcycle stuff' without enough power to do it is a good experience. Like learning to corner fast with no horsepower, only momentum derived high cornering speed, that sort of thing.
And learning all the things that let the slowest bike run all day up front!
I feel sorry for kids that start off on a Jap 600 sport bike.

[dallara]

Acacia, Bones...

You guys are way too kind. Nothing magic here. I just lived around it and tried to pick up as much as I could along the way.

And Darth...

I couldn't agree with you more. Learning to ride on smaller bikes teaches so, sooooooooooooooooo much about optimizing apex and conserving momentum. Bones and I exchanged some correspondence on that very subject once when he was shoppig track bikes...

Big bikes (and yes, folks... a 600 sportbike is actually a *BIG* bike) make you lazy when it comes to riding technique.

Guys, you want to learn to road race? And I mean *REALLY* road race...

Try a 125 two-stroke or a 250 GP-class bike. You'll learn more in one weekend on a 250 GP-class two-stroke than you will in an entire season on a 600 sportbike.

Of course, that's just my humble opinion...

Cheers!

Dallara

[Biff's R]

Guys,
I was at one of the local multibrand dealers earlier today, and I saw a 2005 Honda 50cc that looked like the above GP bikes. It had disc brakes, and the mandatory warning labels. At first I was confused, and asked if the bike was a used bike that had been retrofitted with brakes, and the warning label. BUT I learned that it was a new bike that had been built by Honda Racing. It looked like it would be fun to ride, but not today in the snow and ice.

I will try to get a picture sometime this week.