Suzuki Component Manufacturing Date Codes
The methodology that this article is based on was originally developed and posted on line by John Brookes in the UK who operates a Kawasaki Z2 site at http://www.freewebs.com/750rs/. A copy of John's original article may also be viewed at this link.
John has very kindly agreed to allow me to use some of his material and I have extended his work to cover Suzuki in the 1968 through 1977 time frame. While John's material was originally developed specific to Kawasaki, I have so far been able to confirm that the same or similar dating methods were used by Suzuki in at least some cases. While this information may only be of interest to 'rivet counters' or (to use the UK term) 'anoraks', with each restoration or even each needed repair the original factory markings continue to disappear. This then leaves us with fewer and fewer benchmark examples of what the machines actually looked like, which parts actually were installed and also, what it is you actually are buying when paying top dollar/pound/euro or yen for a supposedly 'original'machine.
To quote John:
"Anyone who has looked closely at Japanese motorcycles from the Seventies may have noticed various numbers/letters stamped or marked on some of its components. In some cases, these are date codes and it should be pointed out that while these date codes relate to the date of manufacture of the part and not the motorcycle, in general it is normal to see a date of between 0 to 2 months before the manufacture date of the bike.
Before reading further, it is necessary to understand a little bit about Japanese dating practices. Since 1868, when Japan switched rulers from a Shogun to an Emperor, there have been four reigning Emperors: Meiji, Taisho, Hirohito (Showa), and Akihito (Heisei). Japan's traditional era is based on the emperor's reign and machines manufactured during the seventies were manufactured during the Showa reign. Hirohito (Showa) came to reign in 1926 and therefore a Gregorian date of 1973 would be the 48th year of Showa."
For the Suzuki years under discussion, you then have the following Showa equivalents: 43=1968, 44=1969, 45=1970, 46=1971, 47=1972, 48=1973, 49=1974, 50-1975, 51=1976 and 52=1977.
To further complicate matters, Japanese parts can be dated by either the Showa code or Gregorian code, and abbreviations are sometimes used also ('3' rather than '73' to signify Gregorian 1973 for example, and '8' for Showa '48' being Gregorian 1973).
I have looked at several frames and frame components that I have access to, and have yet to see stamping similar to what John describes as used by Kawasaki on items like the swing arm, torque arm, or elsewhere. I plan to keep looking, but as yet have not found anything.
Again, unlike Kawasaki, I have not been able to confirm that Suzuki or its suppliers explicitly date stamped the carburettors. They are however marked with the internal Suzuki model code/part number which mat actually be more useful, and I have found ink-stamped data on un-molested L/M/A/B carburettors which could contain date related data. I suspect that surviving examples of these are very rare, only as the ink stamping is easily removed using a cleaner or if the carburettor body has been vapour or soda blasted.
Early GT750 model carburettors were punch stamped. The internal Suzuki model number for the 1972 GT750 J was 310 which was also used for the 1973 K. The part numbers changed - 13201-31012 for the 'J' and 13201-31013 for the earlier 'K'.
This is a 'J' carburettor, showing model 310 and suffix '12R', with the '12' being the 1972 'J' and the 'R' being for right side carburettor. The middle and left carburettor bodies were similarly stamped.
A GT750 'K' carburettor, again showing model 310 but with the suffix stamping below of '13M' with the '13' being for the 1973 'K' and the 'M' being for the middle carburettor. Note that the '12' for the 'J' model has been struck out indicating it was originally a 'J' carburettor and updated at the factory for installation on a 'K' machine.
And then another 'K' carburettor, again showing model 310 but now with just the suffix stamping of '13L', and so is an 'actual' 'K' model carburettor with the 'L' being for the left carburettor.
Late production 'K' carburettors, as well as replacement (NOS) carburettors would have been stamped 31014 and 31015.
Below are a set of 1968 MK1 T500 Cobra carburettors - the one on the left stamped 15010 is the early style having the brass floats, and on the right you can see another that it has been re-stamped to show 15011 which had the plastic floats.
My 1977 GT500 has the stamping on the left side of the bell on the engine side of the carburettor and is stamped 15313 which matches the parts manual for the GT500 A and B. Earlier versions start at 15602 for the T500 MK2 through T500J, then 15604 and 15606 for later models up to the T500M.
These are a set of carburettors from a 1974 GT750 L, which was a one year only model code of 312 and suffix '10'. All three carburettors are ink stamped the same, confirming they all are for an 'L' model machine. Late production 'L' machines would have been marked as '31211'. The 'M3Z2' mark shows it as the middle carburettor and the '3Z2' could be a date code of some sort (3 might correspond to 1973) but I am unable to confirm that without additional examples.
This is a GT750 carburettor from a 1977 'B' and is clearly marked with a 316, which is the model number for the M, A and B GT750's and the suffix of '23' which is specific to the 'B'. The 'R' indicates it is the right side carburettor. While I could make the assumption that the '761' is for a Gregorian January 1976 build date, I'd want to see more examples to be sure.
The full ink marking on the GT750 'M' carburettors would have been '31621', changing to '31622' which was also used on the 'A' and early 'B' machines, changing finally to the '31623'.
Like the carburettors, the fuel cocks were also part model stamped. While it is easy to pick out the GT750 J/K fuel cocks from the later ones, the 'J' fuel cocks were stamped with '31050' and the late production 'K' stamped with '31051', as are the NOS ones currently still available from Suzuki.
For the later models, the GT750 'L' was stamped 33150, the GT380 was stamped 33151. The GT750 'M' and early 'A' models were 33152. GT380 and GT550 'M' models were 33153. Most GT750 'A' models were '33154. For 1977 the spacer block was dropped on the GT750, and the body painted black - the number changed to '33600'.
The other stamping that is visible appears to be a date stamp - for the 'B' all the ones I've seen, including the NOS ones are stamped '77' - whether that is just the year, or a year and month I am not sure due to the small sample size. One earlier GT550 one that I have looked at (33153) is stamped '59' which could be for September 1975 - it is shown on the left below along side one off a 1977 GT750 B. The photo on the right shows an A fuel cock on a GT750, and is stamped 33152, which per the parts manual is correct and seems to have a date stamp of January 1975. Again, more examples of known provenance would be useful.
Sadly, I have not found any dating information stamped in any of the Suzuki switch gear I have examined. The best estimate I have been able to assemble so far is as per the chart shown below for the left switch gear specifically.
Kawasaki hubs were often ink stamped on completion with the full date of manufacture in Showa code. It is possible Suzuki hubs were also ink-stamped, but none of the ones I have access to show any sign of this. What markings and stampings are visible do seem to follow a pattern.
As with Kawasaki, several Suzuki cast parts do appear to have been ink stamped on manufacture. The best examples I have seen so far include the clutch basket assembly for a 1977 GT500, which while largely illegible does appear to be a Showa date, possibly November 1976 (Showa 5111).
And this is a brake plate from a 1977 GT500, which I think shows May 1977.
I have gone through my gauges for the T500, GT550 and GT750 and so far have found only one instrument that has a date stamp. Reference the photo below, this gauge is off a brown face, KPH 1977 GT750 and the date clearly supports this as it is a June 8th, 1976 date of manufacture. The others I have often have what appear to be quality control/inspection stamps, but no dates. If anyone else has examples I'd appreciate you contacting me.
Takasago Wheel Rims
For these, the Suzuki rims and the Kawasaki rims are dated in the same way. Again, quoting John: "Up until 1976, these parts use a Numeric/Alpha code based on Gregorian date. The number relates to year (with the first number dropped). For example 4 = 1974. The letter relates to the month running from "A" for January, 'B' for Feb through to 'L' for December."
Example: TAKASAGO 185 X19 4K 103
"The first stamp is the manufacturer Takasago, then the rim size, then a number, then a letter, then 3 numbers. The number after the rim size is the year the rim was made. 2, 3, 4, 5 etc....197(2) 7(3) etc. The letter denotes the month of manufacture.....A-L. Jan- Dec. The last 3 numbers tell you the model the rim fits."
The Suzuki GT750 front rim is 101 and the rear is 103 for 1973 and onwards. In 1972 and early 1973 the GT750 rear rim was a 101. For the GT550 they are the same as fitted to the GT750, at least for 1973 through 1977.
This is specifically a 1972 drum braked GT750 rear rim, type 101 made in January of 1972:
And this GT750/GT550 rear rim is from November of 1976.
For the T500 rims I have here they do not seem to have a model number. This front rim dates from February 1968, however the rear 18 inch rim while also from 1968 has a month code that breaks the pattern ('O'). It is either a different code, or perhaps was stamped incorrectly.
This November 1976 rear rim was installed on a 1977 GT500.
And just purely for interest's sake - my 1966 Yamaha also has similar coding, so this dating method is applicable to a wide range of mid-1960 through late 1970 Japanese machines using Takasago rims. The rear is a December 1965, and the front is February 1966.
Again a very big thank you to John Brookes for sharing his decoding work.