Britbike forum Forums British Motorcycle specific Brands Triumph bulletin board Engine number query

Hi all,
I have identified my Thunderbird as a 1955 but with a rigid frame. On the same spot as the engine number there is another number that the Triumph club couldn't identify. Please look at the attached photo & give me your thoughts.

Could be a Police fleet number. Does it also appear on the frame headstock?

No, the engine number is exactly the same on the frame but not the bottom number. Someone mentioned they thought that the 'C' denotes a sidecar configuration from the factory which could match up with it being a rigid frame in '55

Also: WHY is there a letter "R" at the end of the serial number?
I have a lot of photos of 6T serial numbers, but none of them have that "R" at the end of them.

The "R" means "competition" ("Race") at the end of G.P and T100 numbers, but 6T bikes were lower performance transportation bikes.
Any answers?

The R will be for rigid, normal production’55 would be swinging arm.

What's the difference in the ENGINES that would require a letter "R"? The same crank cases fit in either frame.
And WHY is this the ONLY 6T serial number I have ever seen with that "R" at the end of it?

AFAIK, any spec changes were only recorded on the engine, eg “C” for combination. The factory spec for ‘55 was swinging arm, so a ‘55 rigid would have to be identified somehow!

Have you seen proof of this in factory literature, or are you just speculating?

A lot is speculation, as officially the ‘55 was swinging arm, but on another forum, the OP has confirmed that the basic numbers are correct. The Triumph club should be able to confirm the shipping recipient, the suspicion is that this was one of a special batch made for an organisation such as police or army.

Gentlemen, I APOLOGIZE.

An Australian friend has explained this matter to me, and I now understand that the numbers in question ARE authentic, and are from an ex-police bike that was equipped with a sidecar.

Photos he sent to me show the "R" is on both the engine case AND the frame, signifying "sidecar use," and the number below the engine serial number is the police department's inventory number for that bike.

On this site I learn something new every day.

Irish Swede,
That is very interesting as I have not heard that explanation before. My Dad bought the bike in 1960, I have the receipt but he bought it from another private person. It has always had the sidecar attached but when I enquired at the Triumph club in England they were just as confused as I am. This bike has always been painted a dark blue not like any other Triumph I have seen so could explained by being a Police bike!!!

That's great, but who stamped the R? Was it the factory, the distributor, or the Police Department?

Not to labour the point, but Triumph did not, as standard, make rigid frame motorcycles in 1955. It had to be a special build, so how else would the factory identify them?

Actually, Triumph built 130 rigid framed machines for the US flat track racing market in late '54 and early '55 for the '55 model year. They used the '53 T100/T100C rigid frame with the air filter tube provision in the downtube between the engine and gearbox. There were a few specific alterations around the steering head and side stand lug but were the same frame with rearset mounts. They were all in sequence in the 59XXX range and included an "R" stamp after the frame and engine numbers. The frame and engine stamp was different and did not match the one on the OP's machine.

Definitely a special build with some special parts built just for this model. Here's a couple, the dual air filter, Dunlop racing seat, and bracket for remote float mount.


Bill B...

Hi all,
I know it has been a few months since I last added to this post. I have pulled the whole bike down for stripping & painting. When I had a closer look at the frame I noticed a number on the opposite side of the frame stock to the frame number. It matches the extra number on the engine as mentioned in the original post. So it read 1747 but without the C at the beginning. It gets curiouser & curiouser..
AussieDerek

Here is a photo of the frame after it came back from the blasters.

Could be a fleet number as i mentioned above

Irish Swede,
I would like to correspond with your Aussie friend who seems to have some knowledge that I am missing. Could you contact him for me?