C72 from France

[sky.fred]

This is confirmed according to the article below: my 'inverted' gearbox was fitted to the 1959 models but models not intended for Americans or Europeans could be fitted with it beyond this date.

https://www.motorcycleclassics.com/clas ... 23mjzawar/

"Honda’s 1959 U.S. lineup also included the C92 Benly (later known as CB92), a spunky sport model powered by a perky 125cc twin-cylinder engine that touted the company’s racing ambitions, and that model was backed by the 250 and 300 Dreams. As noted, the original Dream engine relied on a dry sump with remote oil tank for lubrication. Its constant-mesh transmissions had a rotary-shift pattern (tap down for first through fourth gears, and down again to return to neutral), . The transmission for U.S.-bound Dreams featured the one-down/three-up return-shift pattern more familiar to American and European riders. "

That explains why I haven't been able to find a malfunction for weeks, because there wasn't one.

Honda Dream aficionados to eventually coin two phrases: “Early Dreams” and “Late Dreams,” the invisible line of demarcation helping owners (according to many Dream experts) distinguish between the model’s first run from 1960-’63, and subsequent models of 1963-’67 and mine is in the middle but surely an "early".

"In fact, according to Bill Silver’s book, Classic Honda Motorcycles, “after 901 of the 1962 bikes were built, the styling was changed to the type seen on all later [Dream] bikes.” Silver’s book points out that many other detail changes were made throughout the Dream’s production run, with variations sold in other countries and Japan often featuring sheet-metal-type handlebars, rotary gearboxes and turn signals similar to those on the C100."

[Michael Stoic]

Great research! And the puzzle is solved - or at least there is good guidance whether you decide to change the pattern or not.

--
Michael

[sky.fred]

I chose to go back up with a conventional gearbox and not the rotary. Driving the rotary can be surprising, if you don't count the gears and find yourself in neutral thinking you're in last gear. The same is true if you dream and forget that the gears are reversed, so you downshift instead of upshifting or vice versa.

I was thinking of fitting a 305 cylinder, but I've found that this means resizing the crankcase. It's not technically complicated, but I don't really want to modify this engine.
I think the ideal would also be a cylinder head, as the 250 with 305 pistons is likely to alter the compression ratio and, a priori, the crankshaft mass balance is not the same.
Does anyone have any feedback on fitting 305 cylinders to a 250?

For those who reassemble an engine, you can buy oil seal kits, but for half the price you'd be better off ordering them from industrial parts stores.
The list:
91205-259-000 8x21x6
91202-250-000 14x25x7 qty:2
91204-200-000 12x25x4.5
91205-200-000 22x26x29x8
91204-259-000 16x28x7
91206-259-000 20x30x5
91201-259-000 32x65x6.5
91203-259-000 30x62x8

[sky.fred]

The C72 now works perfectly with its new speed selection, which is smoother and more precise with this drum than before.

I installed a digital voltmeter to check the battery charge and the modification I made works. I'm running with a minimum of 12.8 V at idle and a maximum of 14.4 V at cruising speed, which means I can drive with the headlights on, as is now often compulsory in many countries.

I had done the timing statically, and when I checked it dynamically, using a strobe light, there were a few degrees of difference and the bike choked at high revs.
I don't have a comparison because I've never ridden another C72, but I think I can't do any better, but the 250 engine lacks a little power and especially torque.
I'm thinking of fitting a 305 engine next winter, as I've already cylinders.

[sky.fred]

End of the first chapter. I knew absolutely nothing about C72 and here's what I discovered during this restoration, so if it helps, I'll summarize.
First of all, there are "early" and "late" models, the line being 1963, but models exported to the USA/Europe and Asia were different whatever their date of manufacture
- Buy your oil seals in an industrial supply store, it will be much cheaper than the kits sold for motorcycles.
- You can replace the original rectifier with a modern rectifier-regulator. By bridging the alternator's pink and yellow wires, you can drive with the headlights on without discharging the battery.
- Early C72/77 models had round carburetor bowls. The gaskets supposedly sold for these round bowls are too thin and leak. It's best to make your own.
- Honda 125 cbs/sl floats are identical to C72 floats.
- Led headlight bulbs can be installed. The reference is Stanley A5676 12V.
- All M5 screws have a pitch of 0.90 (prior to 67 JIS), whereas the current standard is M5/0.80. These screws are hard to find.
- There are two types of contact breaker: Daiichi and Nippon Denson...... and they are not compatible.
- The timing chain is a 219 (DK or T both can be fitted but the diameters of the link pins are different) and 94 links. A riveted chain is preferable.

[Geoff Hastings]

Really nice work Fred, you worked methodically through the problems and not only solved the issues but kept us informed of the solutions. I did not know of the different type of gearbox selectors, that completely confused me. I had the the 305 and even with the extra capacity it was not very powerful but did make a nice cruising bike which is what it was designed as.