Triumph Frame Differences

[LarsL]

Hey Guys.
I have on hand a Triumph frame with TL prefix number. I think its a 38/39 250/350. With the typical bolt on hard tail.
Question is, are the front part of the frame similar to the early pre Unit frames?
Will my 6t engine fit in this frame?
Will it hold the extra power of a 650?
I have a bolt on hard tail for a 650 laying around also thats a bit streched and dropped that i was thinkin putting on this TL frame. That way i have the right gear box mounts also. To me the frame looks similar but i dont have it here to take messurements.

Thanks
Lars

[LarsL]

Heres the TL frame.

[TriNortchopz]

Bit of info to confirm the TL frame ('46-'48 3T) and something for the 3T model...

Frame prefixes were 'TL" for the 3T up to 1948.and TC for 1949.

http://www.triumph-moto-oldtimer.ch/Seriennummer.pdf

"1946 3T; First year for Triumph's new 350 Twin, intended as the 'little-sister' to the 500cc 5T Speed Twin. A solid performer for a 350."

https://www.classic-british-motorcycles.com/triumph-350-twins.html

[LarsL]

Yeah. The number starts with TL.
But need to know if a 6t engine will fit. Seems like its similar to my 50 thunderbird.

[TriNortchopz]

make it fit.

[Dougtheinternetannoyance123]

Okay, Ill wade in here. Assuming its actually a 350 frame.
" Triumph Engine Numbers

1937 to 1949
The year and model were used as a prefix to the engine number
From 1937 to 1939 the final digit ( 7, 8 or 9 ) was used.
From 1946 to 1949 the final two figures ( 46, 47, 48 or 49.)
The model numbers were T or 5T for the Speed Twin, T100 for Tiger 100, 3T for 350
twin & TR5 for Trophy.
Typical numbers were thus:

8-T-1234 ( 1938 Speed Twin )
47-5T-23456 ( 1947 Speed Twin )
9-T100-45678 ( 1939 Tiger 100 )

Pre-war frames ( 1937 / 39 ) used the prefix TH for the 500cc models ( 5T & T90 ) and
TF for the Tiger 100.

Engine numbers commenced at:
1946 - 72000
1947 - 79046
1948 - 88782
1949 – 100762
1950 to 1962 Pre-Unit 500 & 650cc
Engine numbers had a prefix indicating the model type along the lines above such as
3T, 5T, 6T, T100, T110, 3TA, 5TA etc. This was followed by a number from the list
below.
YEAR - Pre-Unit 500 & 650cc
1950 - From 100N
1951 - 101NA to 15808NA
1952 - 15809NA to 25000NA then 25000 to 32302
1953 - 32303 to 44134
1954 - 44135 to 56699
1955 - 56700 to 70929
1956 - 70930 to 82799 then 0100 to 0944
1957 - 0945 to 011115
1958 - 011116 to 020075
1959 - 020076 to 029363
1960 - 029364 to 030424 then D101 to D7726
1961 - D7727 to D15788
1962 - D15789 on

------------------------------------
So, based on your picture, your frame LOOKS like a 500 or 650 frame, although notable early rigid frame preunits TR5s had a unique frame totally different (Resembles a rigid BSA Single) So, to recap the obvious,, Triumph did not make a 650 PU until 1950 but a 650 will fit in a pre 50 frame. Prewar engines are similar but drastically different, but I believe the mounts are the same (Not 100% certain on the mounts but I believe so, check and compare parts books to be sure, if not I can make a phone call and ask several friends who have prewar bikes)

*long list of difference in the engines, primaries and even the trannies, thats a discussion in itself*

But to the point, I had an opportunity to buy a known 350 rigid preunit roller,, I looked into it at the time and was advised its possible to stick in a 500 or 650 PU engine/trans package in one but not without a lot of surgery and fab. Also, depends on full custom or period correct parts, In THAT case be advised that MOST 350 parts are all different. Oil tank, battery tray, fenders, primary inner/outer so a lot of fettling work (Fettling is a english phrase synonymous with Bodgery, not far from Buggery and sodomy. In other words, a lot of cursing, alterations and modifications to make it fit)

There is several FREE online sources to consult factory illustrated parts books and a comparison will show you what parts interchange by part number as well as visual clues. If you cant access the really early years, PM me off line and I can send you digital versions.

So could-should you? (Try to stuff one in) Well that depends on a great many details. *** FIRST I am confused on your comments on the rear frame section. Do you have a unit hard tail, or a preunit hard tail thats modified or an aftermarket hardtail-rear section? I would have to check to see if the stock rear frame sections for a 350 interchange, if so, I AM in need of a factory rear frame rigid PU section and might have interesting trade materials or $$$$
But heres the rub. As you likely have figured out, a factory Triumph rigid preunit frame is hard to find and expensive if you do $$$$$$$ I could sell 2 dozen easily and I get inquiries about once a week. On FeeBay they tend to go for astronomical sums of beer slips.
So I can see the attraction.

Besides the fact they are spindly and prone to issues, you COULD do it and make it work. But just be prepared for a lot of work and not exactly the strongest-safest option. I was collecting this stuff when no one wanted the early rigid stuff but lots of people want them without fully understanding all the issues with early Triumphs. (Spindly 3 piece cranks, no rod bearings, crack prone heads, hard to find parts etc etc)

If you need measurements and photos I have several project bikes that range from 47 to 54. I think you will find the height of the motors the biggest problem.

[LarsL]

Sorry bout the confusion.
Here goes. I have a stock 50 thunderbird. And im going the 60s show bike bobber/chopper route. I have an extra aftermarked rear section also and therefore looking for a front frame section to go with that rear piece. Thats why i was lookin at this frame. Because the frames is so rare, i was thinkin i could spare the thunderbird one.

[TriNortchopz]

This info, from a different source, printed in Vintage Bike Magazine, also confirms TL frame designation as:

"Frame prefixes were ‘TL” for the 3T up to 1948 and TC for 1949...Thanks to Dave Gaylin and Lindsay Brooke for printing the above information in their book “Triumph in America”.

https://vintagebikemagazine.com/serial-numbers/

Triumph Pre Unit Twin, Tiger Cub and Ariel Motorcycle Frame Drawings
Here are some factory Frame drawings for Pre Unit Rigid and Swinging Arm Frame models, Tiger Cub models as well as Ariel Single, Twin and the Square Four.
Don't think these have ever been published in any manuals unlike the Unit models which can be found in the factory Workshop Manuals. Click on the images for a full size view.

1947-'53 Triumph 5T and T100
1950-'53 Triumph 6T

https://www.tonupclassics.com/2013/06/triumph-pre-unit-twin-tiger-cub-and.html

1950 6T Thunderbird...

https://www.classic-british-motorcycles.com/1950-triumph-thunderbird.html

[Dougtheinternetannoyance123]

Sorry bout the confusion.
Here goes. I have a stock 50 thunderbird. And im going the 60s show bike bobber/chopper route. I have an extra aftermarked rear section also and therefore looking for a front frame section to go with that rear piece. Thats why i was lookin at this frame. Because the frames is so rare, i was thinkin i could spare the thunderbird one.

Well, The stuff is getting so rare, I would NOT go butchering or modifying a factory matching numbers frame of any year up to 1970. People rationalize doing so, or parting them out but truth is, even today there is far more parts stashed that are orphans than there is factory correct-matching numbers bikes.
I am all for building a custom out of non matching orphan parts, but cutting up a classic is a crime.

(It seriously pisses me off to collect bits and pieces for a project over 10 years, or more and try to restore some raggedy ass crusty relic and then see some fuktard parting out a pristine one. A few times I have offered a trade and cash to save the nicer version, but usually get back some jack off bullshit of what a service to the community they are performing. A special place in hell for killers of cool bikes.) -Sorry, rant mode now off,

Anyrate, if you want to build a custom and preserve the nice stuff,, good for you.

What might help, is the basic measurement from the lower tube to the upper frame brace (Vertical) and one front to back (Horizontal) and that will establish a reasonable basis. I can snap a photo tomorrow of 2 frames, one with an engine in it. I could tonight but its late here, below freezing, and I dont feel like it. But happy to do tomorrow and will lay a tape measure in place for reference.

To be honest, you would be far better off with a custom built aftermarket frame of known materials, Not to mention avoiding 70 years of metal fatigue and the dreaded DPO issues (Dreaded Previous Owner). However a factory frame might be a necessity? Your profile states you are in Europe? If so, I know some of the issues. I have several German friends who visit and they have the TUUV issues (Missing umlauts)

I have another frame I am doing a build with. Its a 1960 or 61 Duplex and someone modified it and added a hard tail. Too far gone to restore But a really WELL done modification. Im building it with a mix of hot rod parts and factory parts to resemble a 1952 Blackbird but with some serious performance stuff hidden inside. (Morgo 750, later unit type rods, later crank, hot cams, Belt drive primary etc etc.) The idea is LOOK basically stock but some subtle mods. No harm-no foul to a stock bike. I have 2 other duplex preunits I am restoring. Ones a really early 1960 Bonnie,, only a few numbers off the first bike made.

One of my others is a dilemma. Way too rare to modify or customize but too hard to find all the correct factory race parts. Its a 1953 T100C. I have a local guy who restored one and I know all the special parts they use. So I am compromising. Building it as a period race bike. Ill eventually sell it so if someone with more time on their hands and unlimited bank account wants to source the rare alloy Un-Ob-Tain-ium race kit parts, its still viable.

[farmall]

Well, The stuff is getting so rare, I would NOT go butchering or modifying a factory matching numbers frame of any year up to 1970. People rationalize doing so, or parting them out but truth is, even today there is far more parts stashed that are orphans than there is factory correct-matching numbers bikes.
I am all for building a custom out of non matching orphan parts, but cutting up a classic is a crime.

I've a '59 Thunderbird I'm going to do for a Sunday ride (no chopped nor bobbed) but zero stock pre-unit parts will be harmed and if I accumulate the rest of it I'll restore or if I don't get the bathtub I'll do the period "Trophybird" (even dealers removed the bathtubs which is why they are a hassle to find) minus the bathtub (I've not quite inventoried my needs yet as other bikes are ahead of it.)

Breaking a restorable stock machine would be brain damaged because the entire chopper scene always had one goal, be as much like a chopped rigid Harley as possible! Since those old Britbikes are barely viable in the modern world (ghastly brakes, no horsepower unless built strung out and delicate drivetrains) if I only had the T-bird and wanted a chop I'd sell it to a collector fast enough to leave shock waves and get a Harley for the far more durable engine, greater displacement and torque, much more HP potential, plentiful engine parts, and abundant used stock, vintage custom and custom parts. Even an Ironhead is a much better piece.

I could certainly see building one with a new frame because there are lots of takeout drivetrains, fixing an existing titled chopper etc since they are already too far gone for someone to restore, but a pre-unit isn't a very good MOTORCYCLE and chopping it just makes a slow delicate niche art object that will NEVER be the Harley (or to be pedantic, include the few flathead Indians) it was chopped to ape.

Your bike, your call but consider exactly why you even want a chopped elderly Triumph over a Harley when you own a machine that could sell for enough to give you a choice. The reason the US has cheaper Triumphs than Europe is they didn't survive US usage unless the owner was a skilled mechanic so they died young then went into barns. They didn't grow powerful or robust with time. Your ride, your call, think it through and have fun whatever you choose!

[Dougtheinternetannoyance123]

All right, Sorry it took so long, But recovering from Surgery and had to wait till the Ol' lady was asleep to sneak out of the house to go to storage. If you want better pix they will have to wait. I have multiple frames I could measure, But all require moving stuff and Im on light duty @ the moment.

So, I have several years of frames to sample from, 1948 and up, This one is a late 1952 I think but can take pix of others if it helps. So, im in too much pain and tired to do the conversion to metric but its an English bike built with a confusing array of British Empire measurements so INCHES it is.

Looking at the frame from the side 1st is while the engine is not formerly bolted in place its just sitting there for reference. But looking at the side where the centerline of the main bearing is where I took the vertical measurement. Might or not be right based on engine mounts. Going from mid tube on the lower horizontal frame tubes (Tube center line) to mid tube of the upper frames lower frame brace tube. V #1 = 20.5" inches. V #2= 19.5" inches. #2 is further aft to the rear and mid lower tube to the rear tank mount cast lug face. (Where the flat bracket bolts on)

Front to back going from front down tube 2/3rds down is a large cast lug, directly across is a smaller cast lug from the mid point-seat post downtube. So mid hole to mid holes is 12 & 5/8ths " inches



I can measure engines and other frames if you like. I have some with cast iron top ends (Both 4 & 5 fin heads, internal & external oil drains) as well as the all alloy close pitch fin heads and cyls. (T100 )
also later 8 bolt and 10 bolt heads. *** FYI, it is possible to swap enough parts off a 1973 and later short rod 750 (different stroke and bore) onto a preunit case. Ive done it on preunits and units. The Morgo & Routt 750 big bore kits are designed for long rod 650s and while do convert to a 750, they have the same deck height as a long rod 650. Some are "Cheater barrells" and run the same taper and fins as the 650 but there is also some with a more blocky style fins that are 30% larger and visually tell-tale. But to spot a clever short rod stroker swap, count the cyl fins. The short rod 750s run 1 less fin shorter height.

*** Cast iron Pre unit heads. There is several types and part/cast numbers. Lowbrow ran a tech page on ID of PU heads courtesy of a guy named Shaggy who wrote a spotters guide to heads. The height of them is I *BELIEVE* the same from Combustion chamber face to the Rocker box machined surface on all variants but I would have to measure to be sure. But they have several variations of fins. 4 vs 5 fins and then look at the top end oil drains. Most have the cast bung bases but not tapped. This is for external oil drain hard lines. Others drain internally. Then there is several variants of alloy heads. I have a sample of each and can post pix.

[datadavid]

I've a '59 Thunderbird I'm going to do for a Sunday ride (no chopped nor bobbed) but zero stock pre-unit parts will be harmed and if I accumulate the rest of it I'll restore or if I don't get the bathtub I'll do the period "Trophybird" (even dealers removed the bathtubs which is why they are a hassle to find) minus the bathtub (I've not quite inventoried my needs yet as other bikes are ahead of it.)

Breaking a restorable stock machine would be brain damaged because the entire chopper scene always had one goal, be as much like a chopped rigid Harley as possible! Since those old Britbikes are barely viable in the modern world (ghastly brakes, no horsepower unless built strung out and delicate drivetrains) if I only had the T-bird and wanted a chop I'd sell it to a collector fast enough to leave shock waves and get a Harley for the far more durable engine, greater displacement and torque, much more HP potential, plentiful engine parts, and abundant used stock, vintage custom and custom parts. Even an Ironhead is a much better piece.

I could certainly see building one with a new frame because there are lots of takeout drivetrains, fixing an existing titled chopper etc since they are already too far gone for someone to restore, but a pre-unit isn't a very good MOTORCYCLE and chopping it just makes a slow delicate niche art object that will NEVER be the Harley (or to be pedantic, include the few flathead Indians) it was chopped to ape.

Your bike, your call but consider exactly why you even want a chopped elderly Triumph over a Harley when you own a machine that could sell for enough to give you a choice. The reason the US has cheaper Triumphs than Europe is they didn't survive US usage unless the owner was a skilled mechanic so they died young then went into barns. They didn't grow powerful or robust with time. Your ride, your call, think it through and have fun whatever you choose!

All those harley chop guys around here fart around going 50-70km/h on their super expensive chops when going on group rides or going to parties. And they always have a big ass breakdown van following them😅 I never ride with them, its way below idle in 4th on my 500. Cams dont get enough lube at that speed😂

[farmall]

All those harley chop guys around here fart around going 50-70km/h on their super expensive chops when going on group rides or going to parties

Pussies and posers. It ain't the machines, it's the owners. Clearly they're such little bitches they have to ride dead slow (70 klicks is absurd) because they're scared of normal speeds. I won't own anything I'm afraid to flog and if it breaks I'll fix it. Posers like that are hilariously puketastic.

[datadavid]

Pussies and posers. It ain't the machines, it's the owners. Clearly they're such little bitches they have to ride dead slow (70 klicks is absurd) because they're scared of normal speeds. I won't own anything I'm afraid to flog and if it breaks I'll fix it. Posers like that are hilariously puketastic.

Yea i agree.. wont ever dispute that harleys are built beefier either, and they go quite well with dual amals and separate intakes