MOTO-ARCHAEOLOGY:

CARBON-DATING THE '60s HONDA 250-305 TWINS

by Bill Silver

Often, when you discover a vintage Honda 250 or 305cc twin available for sale, it is lacking the title or other necessary documentation. Depending upon the state or country's requirements, you will find it necessary to "create" some paperwork for registration purposes. The first step in this process is to determine the correct year of production.

On the early-'60s Honda twins, this can be pinpointed accurately, using the frame/engine serial numbers, found at various locations on the bike. First, you will notice that Honda's serial numbers carry a letter (or two), followed by a number (i.e. C or CA77, CB72, CL77, etc.). The "70-72" designation (like CB72) denotes 250cc models, while the "75-78" designation signifies 305cc models (like CL77). All 250-305cc (C70-71 & C75- 76) twin engines, built before 1961, were "dry-sump" design (separate oil tank). After 1960, the C/CB/CL 72/77-series engines were all of conventional "wet-sump" design (all oil carried within the engine).

Honda's chassis were classified as either: C "Dream" (touring-style); CA or CE (US-only versions of "Dream" touring models); CB, "Super Sport" road models; CL "Scrambler" (dual-purpose); CR (production roadracing models); and CS, the "Dream Sport" (usually featuring high-mounted side pipes). The C (or CA, CE or CS)-series "Dream" models have stamped, sheet-metal frames and swing arms, riding on 16" wheels (except some CE71s) and equipped with "leading-link" front suspensions. All other models will have tubular-type frames and swing arms, fitted with 18" (CB) or 19" (CL) wheels and conventional, "telescopic" front forks.

The "CR" four-stroke production racing models, from 1962-64 all have DOHC, 4-valve heads, 5 or 8-speed(CR110) transmissions, twin DLS magnesium front brakes (except 50cc CR110s), open megaphone exhaust pipes and 18" wheels, featuring alloy rims. There were a few rare "street-bike" versions of the CR110 (50cc) and CR93 (125cc) models, with full lighting systems and muffled exhausts. Probably less than 50 of these were ever produced. CR72 and CR77 models were built in very small quantities and few exist in the US. Only one bike is known to be actively Vintage-raced in the US, at present.

For 250-305cc bikes, built before 1965, the identifying process is relatively easy. In the late '50s and early '60s, the year was often coded within the serial number (i.e. C71 59 12345); the center numbers denoting the year ( in this case 1959). Later, the first digit of the 5-digit frame (and 6-digit engine) number was used as the year code (i.e. CB72-11123), a 1961 250cc Sports model. Here's an overview of the most popular models:

CB models: The CB72/77-series were numbered as follows: '61-63, first digit in frame (five digits in '61-62; and six digits in '63) and engine serial number (all six digits) was year of manufacture (i.e. CB72- 1XXXX; CB72-2XXXX or CB77-3XXXXX). In '64, frames and engines both started with 100001 (both six digits); 1965 models started with 1000001 (seven digit frame and engine numbers) and continued in that fashion. Generally, the frame and engine numbers are within 150 numbers of each other or less (often within 15 numbers), if they are the original factory pairing. One possible reason for the mismatch is that Honda would pull engines from the assembly line and dyno-test them for durability, performance and any design/manufacturing flaws. Interestingly enough, I once owned a '64 CA77 which did carry matching 108106 frame and engine numbers; a very rare occurrence in my experience!

Getting back to the CB's, there are several variations, other than the "regular" Hawk/Super Hawk versions. Apparently, some (but not all) '64 models with 4XXXXX serial numbers may be found with Type 2 (360 degree crank) engines OR they may have been models destined for the German market (modified to meet special noise restrictions). The rest of the 100001-on ('64) series bikes all seem to be normal Type 1(180 degree crank) engine versions, however.

Then, you may also find the odd CP77 frame, which may or may not be a "Police version," (which is usually a CYP), as well as a CBM72, which has high bars, turn signals and a Type 2 (360 degree) crankshaft. There are also "domestic" versions of CB77s with Type 2 engines. (I owned an original '62 model carrying CB77E-260474 and CB77-62-60453). Deviations from the "normal" numbering sequence usually denotes models for specific countries or special applications.

From 1965-on, there is no definitive break between years 1965, 1966 nd 1967, that I have been able to discover. Although the chrome-fendered CB models, with the "oval" tail light, were introduced from frame number 1056084 and onwards, which was at the end of the production run in 1967. The TYPE 2 aluminum fork, which appeared at CB72-1005228 & CB77-1030130, seems to be found on all '66 and later model year US bikes, according to their wiring harness tags. However, the "domestic" CP77 models featured this fork design in '65, a year before the US models received theirs. Total production for this period ('65-'67) was 56,432 (frames), so you can roughly divide that figure by three, yielding about 18-19,000 per year.

Early models of the '61-series CB engines (and C/CA models) used a "rear breather" crankcase design and the first 280 bikes had a single- leading shoe front brake. There are three different crankshafts, three transmissions, two series of pistons, three series of camshafts, four different MPH speedometers (running in two different directions!), early steel and late alloy fork assemblies, three different fork crowns, etc. etc. for the CB-series bikes. Always check your engine and frame numbers before ordering parts!

Sometimes, the original engines have been swapped with other CB or sometimes CL engines. I have even seen CA engines in some CB chassis! CL engines are not equipped with electric starters, but can be retro- fitted with CB or CA starter motors and starter clutches, for CB installations. Or the CB engines can be relieved of their starter motors and then installed in a CL chassis! CHECK THOSE SERIAL NUMBERS CAREFULLY!

CL-72 models: CL72's were made from 1962-66, with CL77's being produced from 1965 through 1967. Bikes built through 1962 had 5 digit serial numbers (frame) and 6-digit engine numbers. Again, the first digit in the 5-digit series (6-digit in '63) is the year of manufacture. Thus, a CL72-21977 (example) is a 1962 model. It got confusing in '64, with an early bike series starting with CL72-1100001 thru 1109459 numbers, followed by CL72-4000001-4003437 (Type 2 engine or German-market bikes, perhaps?). CL72-1000001 and-up numbers (all seven digit) were '65-66 models. CL 72 models made after CL72-1008851 bikes had alloy Type 2 forks, big brakes and steel fenders and were made in late-1965, probably when the late-'65 (or probably '66) CL 77 models received their alloy forks and big 8" DLS brakes. CL72-4001597-4003196 and CL72-1000001- later models had rear brake cable anchored to the frame, instead of the cable receiver on the end of the swing arm bolt, which was seen on all earlier versions.

All 250 Scramblers, through CL72-1107409, have "double-eye" shocks and a matching swing arm. Shocks with clevis ends on the bottom were used, thereafter, on the CL72's and all CL77 models. The slip-on exhaust silencer seems to have been introduced with '64 models. Later versions were welded-on to the upper pipe. There are at least three sets of exhaust pipes/mufflers for the CL-series machines. The CL77s: CL77-1000001 to 1014495 were built as '65 models and were equipped with CL72-style steel forks and the "small" SLS brakes. The chrome fender bikes with the "oval" taillight started production from CL77-1043098 (generally '67 models). The "CB450" headlight, with bulb screw adjuster, began with CL77-1042143. From CL77-1033482, the rear shocks used an improved rear shock cover with a larger collar design. Longer exhaust heat shields were used from CL77-1046212 onwards. The rubber-mounted seat and cushioned front footpegs were introduced from number CL77-1033482, along with an appropriate frame change to accommodate the redesigned forward seat mount. Front fenders and stays were changed, with the introduction of the Type 2 (aluminum) forks at CL77-1014496. A modified crankshaft with larger splines was begun at CL77E-1043132. C/CA "Dreams": I haven't researched all the information on C/CA-72/77's, but the pattern seems to be much the same as the CB-series. Of course, ALL C/CA engines are Type 2 (360-degree crank) engines. While "Dream" frames often seem to have no serial numbers, they are normally found in a location on the left side of the frame, behind the engine, below the swingarm pivot, and next to (sometimes under) the footpeg mounting bracket. It is an obscured area, often covered with grease and dirt. Many U.S. CA77's are stamped CA78, but the engines are all marked CA77. '61 and early-'62 models had different styling on the tank and chrome side panels, as well as a myriad of other smaller details concerning the handlebars, cables, fenders, seats, plastic side covers, etc. All Dreams, through 1965, used a tall, thin, wide 12v battery (6v on dry-sump models), which was then superseded to the CB-type battery. The frame's battery tray, tool tray, and side cover were all modified to accommodate this design change. Seven-digit serial numbers commenced in 1965 on Dreams, too.

Almost all models, sold outside of the U.S., had turn signals (winkers) factory-installed. There are several different versions of "winkers," which correspond to the legal requirements of different countries. Sometimes, you will find 250-305 models registered as '68-69 models, but remember that they ceased production in '67, to make way for the CB/CL 250-350 models introduced in 1968!

The final way to date most complete, original bikes (that haven't had a wiring harness fire, modification or some similar misfortune) is to check the harness between the steering head and the battery connectors (usually somewhere under the fuel tank) for a small white tag, attached to the outside of the harness wrapping. It will usually show both the part number of the harness, often including the model and THE DATE! It is the date of manufacture of the harness, but almost always corresponds to the date of the bike, too.

Well, so much for a "brief" history of dating Honda "big twin" motorcycles, produced in the early-mid '60s. Starting with the 1970 models, U.S. regulations required manufacturers to show the month/year of manufacture of all motorcycles. This ID tag, which includes the frame serial number is usually found on the right side of the frame's steering head. Since 1981, the 17 digit VIN codes have been standard on all motorcycles. They can be decoded too, but that is another story
Bill Silver, VJMW

P.S. Due to the confusion by Honda's many running modifications, I wrote a "Restoration Reference Guide" for the CB72/77 models in 1992. I have recently completed a 250-305 Engine Repair Guide, as a companion piece. The latest editions of the CB book now incorporate a CL section, too.