Announced in early Ocober 1928 was Triumph's first 350cc overhead-valve Model, the Model CO. Along with the accompanying side-valve Models CN and CSD these were an entirely new range of machines and Triumph's first to have a recirculating oil system. (As opposed the the previous 'total loss' system.) The oil was pumped from a tank mounted on the saddle down-tube via a gear pump in the crankcase. It was not a high-pressure system as we would know of today, but at least there was direct lubrication to the big-end and elsewhere, rather than places needing oil being dependant upon 'splash'.
The oil still wasn't fed to everywhere it was needed and the over-head valve mechanism required greasing.
Apart from engines and carburettors these three C-Series (as I refer to them) shared frames, gearboxes, tanks, wheels, mudguards; well, everything else!
In order to keep the bike relatively low the lower cross-tube, was raised up to clear the the Model CO's ohv engine. The side-valve models shared the frame type and looked a little strange with the engine sitting well below, but by having so many common parts Triumph kept the costs down, and today missing items are more easily located as it doesn't matter which of the C-Series models the part originated with.
If anything, these new models were 'over engineered' for frames were very substantial and wheels and muguards were quite wide. A 350cc ohv model could probably have done with a lighter frame, but as it was common it needed to be strong enough for the side-valve models to haul a sidecar; although I have seen a Model CO cope quite adequately with a sidecar and passenger.
The original 1929 sales catalogue pictures of the Model CO showed the oil pipes to the crankcase routed in a quite impractical manner, which is why above I show a 1930 model.
The 1929 models had 'standard' handlebars, while the 1930 models had Triumph's Patent 'clean' bars with a twistgrip at each end and the control cables ran through the bars and exitted at the centre, to be discretely routed away to wherever their other ends were to go. I great sales feature, and the 'out of sight' cables concept was appreciated by owners - until the nipple pulled off the throttle twistgrip on a dark wet night!
For the 1930 season the 350cc Model CO was paired with a 500cc ohv model - The Model CTT. Still in the 'C-Series' range with the shared frame parts, but the 'TT' came from the fact that it, and also the Model CO, had the very successful ohv head of the earler Model TT, designed by Vic Horsman.
Introduced in Australia in 1928, I believe, was 'dirt track racing', later recognised as Speedway. Many motor cycle manufactures saw an opportunity for sales of such a specialised machine, and Triumph was amongst those. So at the 1928 Motor Cycle Show Triumph showed their dirt track model, which was to become the 1929 Model RT. Using the 350cc ohv engine of the Model CO the machine was very much pared down without any unnecessary items. So, as were dirt track models, it had a single gear, just one footrest and no brakes. It was certainly available in Australia and New Zealand but I don't know whether any actually sold, and if so it is most unlikely that any have survived.
The Model CO was catalogued for the years 1929 and 1930, while the
Model CTT appeared for 1930 and continued to 1931.
Reliable engines in very solid frames.
Model CO 348cc overhead-valve 72mm bore X 85.5mm stroke.
Model CTT 498cc overhead-valve 80mm bore X 99mm stroke.
Another new Triumph 3-speed gearbox. Full of needle roller bearings!
These ohv models were very popular, and I am told by the owner of a Model CTT that it "pulls like a train".
Initially selling well it was a shame that later sales of these machines was to be affected by the Depression following the 1929 American Wall Street Crash.
7 inch twin shoe brakes front and rear.
Fuel tank capacities were increasing and the C-Series had 2½ gallon saddle tanks, with a separate oil tank of 4 pints in 1929 and 3½ pints in 1930 - a different design of tank.
From my current researches it would appear that production of the Model CO was probably around 2,500 and Models CTT around just 1,000.
Models CO still survive in Australia, Belgium, Britain, Germany, Holland, Ireland and New Zealand.
Models CTT still survive in Australia, Britain, Denmark, New Zealand and Romania.
C-Series frames and gearboxes have survived in the Czech Republic.
(Not possible to determine which models they came from.)
For more details, technical information, performance figures, and much more, you really need to refer to the booklet I have written covering these models.
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