Rare Competition Triumph Pre Unit 500cc Twin with Grand Prix square barrel & head, carbs, magneto- sold

Rare Competition Triumph Pre Unit 500cc Twin with Grand Prix square barrel & head, carbs, magneto- sold


Rare Competition Triumph Pre Unit 500cc Twin with Grand Prix square barrel & head with a pair of Amal carbs and magneto.

This is a rare chance to buy a competition all-alloy square barrel / head engine. I have never seen one before. I have seen a few images, but never stood next to one until now.

So, 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.

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.

  • 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.

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.

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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