Rare Competition Triumph GP Gearbox + big bearing engine, Grand Prix type square barrel & head, carbs, magneto – SOLD

Rare Competition Triumph GP Gearbox + big bearing engine, Grand Prix type square barrel & head, carbs, magneto – SOLD


Gone to France

Rare Competition Triumph GP Gearbox and big bearing engine with Grand Prix type square barrel & head, carbs, magneto

This is a rare chance to buy a competition all-alloy square barrel / head engine with the even rarer gearbox. These are currently only available as a pair. 

If you are building a Triumph Grand Prix, or an evocation, then here’s your chance. Of course it’s not as cheap as a regular 5T / T100. It will make all the difference to your build though. I might even consider some prewar or pre unit parts as part of the deal. But I need at least half of the price in payment. Also, it’s your responsibility to get your parts to me.


The gearbox is definitely a Triumph GP gearbox. Aside from the normal unique number stamped on the main case, there are three letters stamped inboard. They are “R-NB”.  The special stamps are for the rare Triumph Grand Prix motorcycles. Triumph produced less than 200 GP bikes. R = Grand Prix and NB relates to the fact that it used Needle roller Bearings.

As this is a very rare and sought after GP gearbox, I would prefer to sell to someone who will be using it in a Triumph GP. It can be used in other Triumph rigid framed bikes, including the Trophy.

This particular GP gearbox was dispatched to Humphrey & Andrew on 24th September 1948.

Please have a good look at the images. The main case has a cast number T264A. The gearbox has a unique number: TE07040.


  • The box has the selector indicator and the casings are OK and free of cracks or welds. It clicks through the gears.
  • The clutch adjuster mount is still in one piece. (They are usually broken off). However, it will need a little welding to make it secure. It comes with the clutch arm.
  • Both mountings are good.
  • It turns over freely. You will have noticed that the gear lever has been turned through 180 degrees. Presumably, the last owner actually used it for competition as intended.
  • The sprocket teeth look OK. Sprocket number is T471.

Overall, this is a nice Triumph Grand Prix gearbox. If you happen to have a Triumph GP motorcycle, you are very fortunate and this original GP gearbox would be a great asset.

It’s being sold as a gearbox needing rebuild as I haven’t opened it up, it even though it turns fine.


Now…. I’m not suggesting that this is a factory Triumph Grand Prix engine (they were made in 1948-50). It’s clearly a race-developed 5T engine. For those that wanted to be really competitive, they followed the Isle of Man Senior TT winner for 1946. They bought a war time generator, that was supplied by Triumph to the War Department.. They took the all-alloy top end and bolted it straight onto either a 5T or a T100. Hey presto! They had a high performance, lightweight, 500cc Triumph Twin. I believe that the head is off a wartime generator.

  • The cast number on the cylinder head is E2481
  • All fins are good
  • Engine cases have matching numbers
  • The carburettor inlet manifold appears to be the works type.
  • The pair of Amal carburettors are 376/68 and 376/6
  • The magneto is BTH
  • Engine number is shown in the images. The stamped numbers suggest that this is a  1946 5T. However, as the engine cases match and the fact that it has a Big Bearing case, I would suggest that this engine is actually from the mid 1950’s. You decide.

Triumph competition department were a bit slow to catch on as the 1946 Isle of Man Senior TT entry was allegedly a private entry ridden by Ernie Lyons. I say allegedly, as Freddie Clarke, Head of the Experimental Department, helped to develop the privateer’s bike engine. Triumph eventually produced less than 200 Triumph Grand Prix motorcycles as a limited edition production in 1948 and phased the run out in 1950. They replaced it with the race specification Tiger 100.

If you look closely at this engine, it has clearly been used for competition. Parts are wired up and the carbs caps are covered. It has the rev counter drive assembly in the timing cover. It is being sold as an engine that requires a complete rebuild. It does turn over and the timing gears are there.

These race-spec 500cc Twins were also used in many makes of race cars. Even the 1950 British Grand Prix support race was won by Frank Aitkens with one of these engines.

Come and view it. Check it over yourself.

More pictures are available.

International shipping available. Please ask. Shipping is charged separately from the item. 

Combined shipping available if you buy more items at the same time. 

Viewing: Please come and check it over before you buy. It is at PE28, near St Ives in Cambridgeshire.

Shipping: I usually ship to most destinations. If you don’t see a price, please ask. Thanks. International shipping available.

Collection: If you don’t want it shipped, I have plenty of space. If you can’t collect for a while, it’s not a problem. However, I will need to be paid very soon after the sale. Thanks.

Payment: Good old fashioned money on collection is preferred. I can accept payment through PayPal or by bank transfer as well. I can receive payment in euros.

Import Taxes: Please note that IMPORT DUTIES are not something I can control. If you are buying from outside the UK, there is a chance that you will have to pay import taxes. Import taxes vary from country to country. If there are charges to pay, it is the buyer’s responsibility to research the cost and pay the duties. The price that you see on my advert is for the item and not the item plus whatever taxes might be due.


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