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Trumph 1940 Speed Twin


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  • Trumph 1940 Speed Twin

    Well as the title says I have just managed to bag this barn fresh 1940 speed twin, some of the bike may still be 1940 vintage....

    Its been used as a race bike a reportedly won the UK - VMCC championship in 1976, its been stood for a while so the first point of business it a spanner check and change all the fluids. I want to ride it for what's left of the UK summer before I get a proper chance to go through the whole bike.

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  • #2
    Great find! Be interesting to see what is inside.
    Here is an original ad for the 1940 Speed twin:
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    Last edited by TriNortchopz; 09-21-2019, 8:09 PM.


    • #3
      It looks more like a post war motor. Notice the Mag/Dyno in the TNC ads,, totally different motor. The bike here has a regular mag so clearly postwar.
      If its been sitting,, its a grenade. They have a sludge trap inside the crank main oil journals. The English term is "Swarf" which means a paste of sludge and metal and abrasives. Biggest noob mistake is firing up an old bike and trying to ride them. Its like a Asthamatic John Candy trying to run a marathon. Its not *IF* there will be heart failure but WHEN.

      So it needs a good cleaning and fresh seals and gaskets,, if good, you are only out time and a few consumables.

      2nd issue. Early 3 piece crank and spindly rods,, plus they dont use bearings. The rods run on babbitt coating so tolerances are likely knackered. Be a nice bike to restore but its not a daily rider and would take a lot of work to make it into one.
      But its very cool. I have a friend who is owner #3 of a 1940 T100 and nearly the last civilian model made and was shipped to BC Canada and sold thru the Trev Deeley dealership.


      • #4
        Interesting stuff^^.

        A bit more here to help identify:
        Triumph Speed Twin YEAR-BY-YEAR
        TRIUMPH SPEED TWIN CHANGES THE WORLD! From their earliest inception through the 1930s, most classic British motorcycles were single-cylinder designs with a few V-twins thrown in for sidecar duty. But the problem with both these configurations is vibration and a lot of it. As bikes grew in displacement and power output and the engine speed (RPM) began to climb, the vibes turned wicked, impacting engine life and rider comfort. Many things were tried but nothing could quell the forces of […]

        Triumph Dating Information:

        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


        • #5
          Hi thanks for all the comments, I will check out frame numbers but I already knew that the engine was not the original - if it had have been it would no doubt have been more expensive....

          Been going through the bike today, changed out gearbox and engine oil, the oil tanks had a proper clean as it runs on R, lots of little jobs ticked off, more updates to follow.


          • #6
            I like it. Please don't paint, polish and pimp it.
            What do you mean ride it? At the track or are you gonna put lights on it for road?


            • #7
              Since it has been modified for racing (note the tachometer drive welding on timing cover), makes it a bit more tricky to identify the year - I think it is pre-war; some things to note:

              Note: Attempts at dating should be based upon frame numbers as engines were fitted at random during assembly, whereas frames were numbered in sequence on production line.
              A Lucas MN2 magdyno supplied H.T. ignition and charging.
              The dynamo was a Lucas E3HM 6 volt regulated by a Lucas MCR14 voltage control box.

              1939 (Nov. 1938 to Oct. 1939):
              The cylinder barrel to crankcase fixing was modified from a six stud to eight studs. [I think I see 8 of 'em]
              The oil feed to the rockers was modified by fitting of an adjustable restrictor in the form of a coarse thread screw at the timing cover take off point. [there is a‘T’ fitting in return line on your machine]

              Only a small quantity of 5T / T100 produced before the factory was destroyed in November [start of 1940 production year].
              The oil pressure release valve was redesigned to a piston type replacing the previous ball valve.
              The steering head angle was revised to increase the trail aimed to give better stability at high speed.
              FORKS: The [girder] main central spring was weakened and supplementary tension springs added to each side aimed to give a more responsive action around the static load position.

              May 1945 to Oct 1946

              Redesigned crankcase to accommodate the front mounted dynamo and rear mounted magneto. [not the engine in your photos]

              The rocker box external drainpipes were deleted replaced by internal drillings through the cylinder barrel and head for oil draining. [I see the external oil drainpipe wrapping around under the intake manifold in your photos number two and three]
              The rocker feed was modified deleting the take off from the timing cover in favor of a "T" junction in the oil return pipe (Integral on the oil tank return pipe stub). [I can see the ‘T’ in the return line, but does not look integral to the oil tank stub].
              The engine breather was redesigned with a rotary valve driven off the inlet camshaft replacing the disc type clack valve situated above the left hand main bearing.
              A 6 volt negative earth Lucas E3H‐RD dynamo with a Lucas MR‐1‐4 voltage control unit clamped to the frame tube under the saddle.
              By a BTH K2C or Lucas K2F fitted with an automatic centrifugal ignition advance and retard.

              Front Forks: Triumph designed telescopic hydraulically dampened forks with internal springs.
              Oil tanks for all models featured the oil feed to the rockers welded to the return pipe stub.

              See more here:
              Triumph Int. Owners Club, 1938 - 1962 Triumph:

              Last edited by TriNortchopz; 09-23-2019, 12:31 AM.


              • #8
                Wow that's lots of info thanks for taking the time


                • #9
                  Zooming in on your pictures, (not great details of the motor) It appears I might have been wrong,, It does look like you have a Mag/dyno but missing the Dyno (Generator) and is a prewar set of cases. Better pix would tell for sure.

                  But as TNC posted there is a ton of details... but not all that data is correct.
                  There is some confusing data on cyl heads and there is both internal and external oil drains depending on year and model, but all pre 1950 are 500s. But you can run into 4 fin and 5 fin heads. Unlikely yours is a 5 fin but they came in the 1950s and were for more compression and handled heat better.

                  The bolt pattern WAS 6 bolts at the cyl flange but then went to 8, But there is a base flange difference on some models so you CANNOT fit a 650 cyl on one without a lot of machine work.

                  It is possible to fit a later 1 piece crank and later rods with real bearing inserts. But in mid 50s they modified the cases to take heavier duty main bearings as well. (There is a tell tale lip below the timing cover) but not on prewar engines but there is some variables on the engine breathers as well.


                  • #10
                    Starting to get to know the Triumph took the clutch apart and cleaned up the steel plates all a bit gummed up, basket is worn where the friction plates are driven and these plates were well passed their best , so some new parts on the way.

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                    • #11
                      That clutch has seen better days,, the early ones are 4 spring, later are 3 spring. also many early ones used a brass thrust washer on the backside of the basket.

                      Did you check the clutch center shock absorber? Early Preunits used a big wound coil spring on the end of the crank to absorb shock to the drivetrain.. Later on (Alternator models) used a cush drive inside that clutch center. There is also a internal spider that controls a lot of things. (See the small screws?) so there is plenty of online sources on how to rebuild the clutch center but it takes some thought,, but inside should be a series of small rubber bisquits and they run on the central spider,, the back plate and sometimes outer plate can often be badly worn but its critical it works correct.

                      Lastly there is 20 small barrel shaped bearings behind that clutch center hub that the clutch basket rides on. I am always baffled how people manage with an open primary how to handle lube,, but based on the accumulation of sludge on the inner cover, clearly SOMETHING was used but I would say most of the primary is running on metal on metal most of the time.

                      Now,, I know its fashionable, to run that crusty period stuff, but to me, if you actually want to ride, a real benefit in many different ways would be to run a belt drive with sealed bearings, much less rotating mass (Surprising power boost) as well as functional.

                      I have run MAP kits on several unit Triumphs, they dont list one for a rigid but I heard you can get them,

                      The Bob Newby kits are spectacular and hope to try one out soon on a BSA,, but dont see one listed for a Rigid model..

                      But this place, I believe is a Tony Hayward kit, and he seems okay, but all his dont run a sealed bearing which I prefer. dont know if you can mod it to take one,, but even without a sealed bearing would be light years improved over what you got. YRMV

                      Belt Drive Kits MADE IN ENGLAND, Belts made in Germany. Also seeClutch Drum Page SynchroFlex Belt, Can Run Dry for racing use, but are not affected by the weather. Synchroflex timing belts deliver high outputs thanks to their high grade components. The Excellent bond between the hard-wearing polyurethane teeth and the galvanised steel tension members... Read more »


                      • #12
                        New clutch time: -

                        Spend some time stripping and looking at what I had, the friction plates had seen better days and the basket was worn where the plates are driven, not bad for almost 80 years but time for an upgrade.
                        Sourced a billet aluminium basket and new plates, also new needle bearings while were there it also got a new primary drive chain. The crush drive looked to be in good condition so was left alone.

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                        Next will be a look at the wheel bearings and brake shoes.....


                        • #13
                          Front wheel bearings found to be a bit notchy so up for replacement and spindle had a worn section so found NOS. The bearings look fairly normal but they were hard to source and some people had some fantastic prices 1 quoted over £100 per bearing....

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                          • #14
                            The early taper bearings are largely obsolete for these applications, I know Harley and others used similar but no interchange. Many people say they machine the wheels or use adapters to use modern/later bearings and I use a modern Sealed bearing in most Triumphs and replace any wheel bearing with new as a safety measure. (not worth the risk, and I buy them in bulk so last time they penciled out at around $6.00 ea which IMHO is good value for peace of mind)

                            But I recently put together some basket cases and discovered the axle OD is a different size for pre early 50s wheels and assumed a later wheel would still fit. On the 46, and 52 Rigids the later wheels wont fit as the axles are larger. Any chance you can mic or measure your axles as well as illustrate whats inside your rear wheel? The parts book shows a diagram but seeing the actual parts is helpful. I believe others would agree.

                            Thank you for posting these pix of the front wheel and bearings, again helpful.


                            • #15
                              Originally posted by Dexter

                              Holy crap, the roller spacing sure is 'interesting'. I'd try and source more robust alternatives directly via bearing manufacturers.

                              Originally posted by Dougtheinternetannoyance123
                              The early taper bearings are largely obsolete for these applications...
                              Properly maintained tapered roller wheel bearings can last hundreds of thousands of miles. It's one of the things I love about my '98 Sporty.
                              Last edited by Skjoll; 10-24-2019, 7:06 AM.


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