My research into the tappet covers (previous story) took me into early parts books which reminded me that Honda really struggled with crankshaft design issues in the early years. Considering that there were basically two types of engines: wet-sump and dry-sump with two versions each (for the balancing of either the 250 or 305 piston weights,) I have counted at least 64 different part numbers associated with the crankshafts used in these engines.
For the early dry-sump motors, Honda used a double row of rod bearing rollers which were 5x6.25mm. A total of 32 rollers per rod were used with a matching bearing cage and thrust washers to help keep everything in place. Honda’s own TSB info showed a change to 3x12.5 rollers in a single row of bearings, housed in a redesigned roller cage to match and the side thrust washers were eliminated. There were changes in the actual crankshaft material, going from cast iron to forged steel, bearing diameters were changed on the main bearings, and new oiling holes were added or altered. For a while, Honda used small breather passages in the outer crankshaft seals to relieve crankcase pressure and still keep the oil inside the engine. Good trick if you can do it! Honda tried seven different versions of the crankshaft breather seal. On the CE71 engines, there was an additional breather fitting machined into the camchain tensioner body.
Early dry-sump Dreams had the points cam attached to the end of the crankshaft attached to the rotor, similar to that of the 125-150 Benlys, then they changed the location to the cylinder head, using a distributor cap to route the sparks to each spark plug. After that, there was use of dual points and condensers firing two separate coils, one for each cylinder. Eventually, they discovered the dual fire coils, triggered by one set of points, firing each revolution with one side on the firing stroke and the opposite cylinder firing a wasted spark on the overlap/exhaust stroke.
For wet-sump models, the early crankshafts had ball bearings on the rotor side, replaced with roller bearings in 1962 to help support the weight of the magnetic rotor spinning merrily on the end of the crankshaft snout. Early connecting rods had slotted ends to lubricate the wrist pins. This was changed to a couple of drilled and chamfered holes in later editions. The right side main bearings were located with a stepped pin on the early designs; however there was a tendency to misalign the pin during crankshaft assembly into the cases, so the bearing and pin were changed to a larger type. Each of these changes required a new part number, of course. In 1966-67, the spline root depth was changed to a “shallow” style, so another part number applied to these editions.
As mentioned earlier, the crankshafts of the 250s and 305s are balanced differently due to the change in weight of the piston/rod assembly, so a CL72 has a 273 code crankshaft and the CL77s have a 278 code part number on theirs. Oh, there is one other variation for the Scramblers; a 274 code crankshaft for a Type 2 250 model, but those are mostly domestic versions, although a few did come to the US in 1962 and 1964.
For CBs, there are three types; 268 for a Type 1 engine, 269 for Type 2 engines used on CBM72s and CYP77 Police bikes, then the standard 305s which have a 275 code crankshaft.
Dreams used the base 259 code for the C72 and the big bore models received a 266 coded part for their Type 2 style crankshafts.
Here are the crankshaft product codes and a close approximation of the variations of each one:
10 x 250
2 x 251
10 x 253
3 x 254
1 x 258
6 x 259
6 x 260
3 x 261
1 x 265
4 x 266
4 x 268
2 x 269
2 x 273
4 x 275
3 x 278
3 x 275
This count assumes that the part numbers started with a -000 suffix part number in the initial design stages.
Many of the intermediate part numbers were superseded with improved designs which would interchange with the older parts, when used to update an engine. The early parts were scrapped and new parts replaced those of the previous design which proved problematical. Honda parts lists used to show all the variations and then the superseded part numbers, so you could track them to a certain degree. In the end, there was generally just one part number remaining to be ordered/used and all earlier versions were discarded and part numbers deleted from the system.
It often takes some concentrated effort to determine what actual part might work in your particular machine, even when you are armed with your serial numbers and an accurate parts list. In most cases, when a part was updated, the reference to the new part included the part numbers of other associated parts which were part of the upgrade.
When parts are at a premium or hard to source, sometimes you have to be creative in your choices. In the past year a CL72 came through the shop with a bad crankshaft. Finding a really good used 250 Scrambler crankshaft can be time-consuming and often disappointing, once received from a seller who isn’t fully aware of the issues that can be a part of the evaluation of the item. In the case of the CL72, there was a very nice, low-miles CL77 305 crankshaft available, so it was used in place of the 250 version. The customer was advised of the possibility of a different feel to the engine, because of some potential balancing mis-matches; however the bike was destined to be a garage queen rather than a daily driver, so with an already costly engine overhaul in progress the choice was agreed upon. Once running, the bike did exhibit some additional vibration that what I have remembered from other Scramblers I have ridden, but it wasn’t to the point of being a real annoyance factor.
If you find a NOS crankshaft these days, the cost will be somewhere in the $400-800+ range, all by itself. The question is; are you SURE that this crankshaft is right for your bike before you buy it? Although the crankshafts of the CB and CL range look identical, the extra oiling hole on the CBs negates use on the CLs and vice-versa. Using a CL crankshaft on a CB will result in a starter clutch hub that has no lubrication and will certainly fail sooner than later.
I hate to sound “cranky,” but those are the facts and there is no getting around them.
Bill “MrHonda” Silver