Honda 6 cylinder 250cc bike from 1966

I remember reading an article about that engine.

Valve adjustment:

a) disassemble engine b) put plastiguage on top of pistons. c) assemble engine d) crank engine over once e) disassemble engine f) measure plastiguage g) grind end of valve stem to suit f) h) assemble engine

(No rockers, cam drove the valve stems directly.)

You can't get any less valve train mass than that. It must of had a very high rev limit before the valves started to float.

The RPM's were probably high for that era, but have you ever checked the red line on a '06 Yamaha R6? Max HP is at 14,500 RPM! Red line is 17,500 RPM. This out of a production bike, with a warranty! Greg

16,500 rpm

Tom

I seem to recall that Honda had a watercooled 4-valve 50cc triple in development that revved to _well_ over 20K. This was to replace the 22.5K rpm twin that made 320 bhp/litre. See:

for some nice pics, including a completely disassembled 250 six motor, all neatly laid out.

Sounds like a 2 stroke to me, especially with the revs to keep it alive. Needs a bit of tuning. I'd have to see a phote of a head to believe it's a 4 stroke.

Bart D. Hull snipped-for-privacy@inficad.com Tempe, Arizona

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tomcas wrote:

Oh, they were 4 strokes, and built much like a bike that I have now. I don't think that the HP per liter of these engines has been surpassed to this day, by 2 or 4 strokes. correct me if I am wrong.

If you're referring to the Honda six, it was definately a four stroke. Tuned to run at pretty much unheard of revs for it's time, it did not idle so well, apparently. That and the fact that it was running six megaphone exhaust pipes, effectively tuned to help produce high rpm power.

I had a back issue of the Brit bike mag, Classic Bike, in which they had a teardown and some test reports on that one. It was right about the era of these bikes, IIRC what I read, that the FIM set in place a bunch of rules limiting the numbers of cylinders for given displacements (or perhaps it was limiting the numbers of gear sets in the transmission), effectivly ending that particular evolutionary (revolutionary?:-) )path.

Has a couple shots of one of these Hondas that has been put back on the track by an outfit called Team Obsolete. They have some cool toys!

Cheers Trevor Jones

Here you go, Bart. Find the valvetrain.

Interesting, Even looks like 4 valve heads. Too bad you can't really see how the valve train was put together. (Shim over bucket, shim under bucket or shim on valve stem.)

Still no reason for it to run so poorly down low. Lots of race bikes are "race tuned" (pun intended) so they barely run, but they sound cool. When they run properly they really put out hp and torque. My parents used to run a motorcycle shop since 1976 to about 7 years ago, so I've seen my share of the aforementioned "race bikes".

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Ted Bennett wrote:

Perhaps you need to send your resumé to Honda? Perhaps they are in need of your "expertise" in the field of

250cc 6 cylinder factory racers?

Tom

It's just about the most famous racing motorbike ever made (and most famous rider). Kids who were my age could draw the engine from memory. Don't you just _know_ how the valvetrain on this bike worked? Many of my generation did when they were about 8 years old.

Yet _you_ think "it sounds like a two stroke"

Cam on valve stem, no shim.

The lack of any significant flywheel mass might explain the poor idle (:

As would carburetor technology in the '60s.

Peter

Really? Have another look.

Hmm, could be memory and/or eyesight playing tricks.

I do specifically remember reading the bit about grinding the end of the stem to adjust clearances, but those twelve bits above and below the valve springs do look like they could have a pair of "buckets" - is that the technical term...

(some googling ensues)

- no answer, but nice pics

- put it on the yellow, Mike.

I wasn't born yet in '66.

I was riding motorcycles when I was 4 or 5, but that was in

1973. If you haven't worked in a motorcycle shop you just wouldn't understand the irony of most "race bikes."

My current bike is a 1995 Triumph Speed Triple that was a Speed Triple Challenge race bike. Then it went to a local Triumph Dealer and "race tuned" to 65 HP for the owners personal use. (Dynojet dyno tested after I purchased it and before I fixed it up.) This bike stock is about 87 HP.

With minor tweaks it now puts out 110 hp at the rear wheel. (Another dyno run.)

Just one example of many that I saw. I truly admire the professional motorcycle race teams, but despise the B.S. of the wanna be racers.

It is a shame that most of motorcycle history is not well documented. I'm sure most of you that "knew how the valve train worked" were around to witness it in person or see it in a then current motorcycle magazine. Now some of the truly odd bikes get written up now and again. (I'm thinking of the Moto Guzzi V-8 road racer that was a small displacement motor as well.) Anybody here ever see one of those in person?

Time for a ride on the Triple, it's 78 degrees and clear here in Sunny Arizona.

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Andy D> >

You could be partly correct. It is very possible that it had bucket style cam followers without any method of shimming the valve clearance. Greg