The Last Five Digits
By Bill Smith
How many times have we looked at the steering head tube on a CMF (Chrome Moly Frame) Penton motorcycle and wondered what do all these numbers mean? First let's address the two types of frame numbers. The first type consists of 8 digits. This type pertains mainly to the Sachs powered models though I have found KTM powered models using this as well. As stated in several past newsletter articles and the website Production Year Guide, the first digit represents the year (i.e. 2 = 1972) and the next two digits represent the month (i.e. 05 = May). For example, if the frame number were 20555144, this would be a model built in May 1972, with the remaining digits being the actual serial number.
The second type consists of the same 8 digits but also has an extra 7-, 51-, or 54- ahead of the original 8 digits. These extra digits could be called production codes for the lack of anything else to call them. These digits were only found on the KTM powered models. If the 7- appears, you are looking at an all-new Jackpiner model starting with June 1972 through June 1973. The 51- and 54- seem to start where the 7- number ends which is June 1973 through September 1976. This period was the time when the rear conical hub first appeared and numerous design changes started. To find the year, month, and serial number, you simply disregard the 7-, 51- or 54- and look solely at the last 8 digits. For example, 7-20655454 would be a model built in June 1972, with the remaining digits again being the actual serial number. In some cases, frames have been found with no frame numbers stamped in them at all. It is believed this type of frame was most likely a replacement frame.
With the production code, year and month being addressed, what is left? The last five digits. In the past, I would always look at a set of frame numbers and say to others, or myself the 7-, 51- or 54- didn't mean too much. The next 3 digits are year and month, and the last five digits are "just the serial number." I never realized how important the last five digits were until a few months ago. The last five digits are the whole key to total production to all Penton/KTM models. Not only is it the key to total production but the year and month production as well when using the year and month part of the frame number. And it's even the key to who has the earliest or latest CMF 100cc, 125cc, 175cc, 250cc and 400cc models. Remember the talk about the steel tanker models and V-001 being the very first Penton every produced and how everyone was trying to find steel tankers with the lowest "V" serial number possible? Now that holds true with the CMF models as well. How do I know this? After compiling over 200 frame numbers, I put them in ascending order by using just the last 5 digits of the serial number, and to my surprise, the year and month part of the frame number automatically ascended in perfect order as well. What was so interesting about this was that the serial numbers never quit climbing from June 1971 to September 1976. Another interesting note was that in one or two cases the year or month seemed out of order and did not follow the expected pattern. In these cases, it showed that the frame number given to me was an error, whether it was the year, month or the 5-digit serial number. And in every instance, an error was found and corrected.
What this list has shown me to date is that the earliest frame number I have recorded is 10650190. So we know now that CMF production started in June 1971. If the 5-digit serial number started with 50000, this would be the 190th unit ever produced. If the 5 digit serial number sequence started with 00000, this would be the 50,190 unit produced, and that sounds almost impossible. So guessing, I would say that the base serial number was 50000. The highest number I have recorded is a 54-60993213. So if you subtract 50,190 from 93,213, this puts total production from June 1971 to September 1976 at 43,023.
In 1976 a new frame number appeared on the all-new MC5, 125cc through 400cc models. These numbers started with 550xxxxx and seemed to stay with these first three digits for the next two years, 1976-77. Once again, I put the last five digits in ascending order and it appeared the serial numbers originally started with 00000. The earliest 550 frame number I have recorded is 55000865 which tends to make me believe that this was the 865th MC5 ever produced since 1976.
In 1977 another new frame number appeared on the all-new GS6 125cc - 400cc models. These numbers started with 701xxxxx. The earliest GS6 frame number I have recorded is 70100047. Once again, I tend to believe that this is the 47th GS6 model made from the start of production if starting with the 00000 again. Note: I have come across a 70201375 and a 70301662 frame number but have no other data on these numbers. Nor do I know when the first 3 numbers might have changed to a 702 to a 703.
After working with these frame numbers, I thought it might be fun to do some research into KTM engine numbers. With some 75 engine numbers to work with, I separated them into 3 categories: Type 52 which is the 175cc, Type 54 which is the 250cc and Type 55 which is the 400cc. However, I did not have any Type 51 125cc numbers available. What I learned was that putting each type in ascending serial number order showed that each size engine serial number started back at 00000 and went forward, unlike the frame numbers and all its models that ran consecutively year after year. And again, the year part of the engine number automatically ascended in perfect order as well. The lowest Type 52 number that I recorded was 2-5200566 (manufactured in 1972). The lowest Type 54 that I recorded was 3-5400341 (manufactured in 1973). And the lowest Type 55 was 4-5500164 (manufactured in 1974). This makes it seem very logical that you could actually have 2 different size engines with the same serial number.
In conclusion, the above information could be a very powerful tool to uncover the true history of production during the Penton/KTM timeline. I'm sure production didn't stay even year after year with models changing or swings in the economy. With the ability to find yearly and monthly production or who has the earliest or latest of any given model, the only thing we need is your input. If you even have a junk frame or two, like so many of us do, this could be the key to something down the road. It would also be great if we could receive European KTM frame numbers as well as any Penton frame number sold as KTM's on the west coast from 1975 on. I believe these models will have the same ongoing numbering system as that of the Penton and help shed even more light on the subject.
Below you will find hyperlinks to a Frame Number List and a Engine Number List. These lists are comprised of numbers that I found on the old Bike Registry, those given to me by friends and some found on the POG message board. In any case, I hope this allows you to enjoy our passion with even more interest and enthusiasm than ever before. If you do have numbers and would like them to be included on this list (your name will be kept confidential and not appear on the list), please email the information to Penton Owners Group. Be sure to include the full frame number and engine size if known. If you want to send your engine information, be sure to include the full engine number.