triumph 3T engine

[john.k]

Can a Triumph 3T or 3TA be changed into a 500 ....the unit one already has 500 barrels and head ,so maybe a crank and rods ?.........or does it need a 500 crankcase as well?........He s looking at two ,one a preunit ,one a unit (early)

[Rex]

3T and 3TA are very  different engines.
3T crankcases differ from the 500s and 650s, and the instant way to tell is the position of the PRV. On the smaller 3T's it's on the timing cover, on the larger engines it's on the front of the crankcase.
Unit engines (3TA and 5TA) use the same crankcases, but the 3TA usually has stamped steel con-rods rather than the 500's alloy jobs. Although some mugs say it's possible to ream out the steel con-rods to fit the larger gudgeon-pinned 500 pistons, I wouldn't do it for the longevity of the engine.
The unit 350 block is different to 500's, and can't be bored out to take the larger pistons.

[john.k]

The unit bike (said to be a 57) has already got 500 ally barrels and head fitted ,so assumes any conrod substitution /alteration has already been done......claimed it has 500 pistons .

[Rex]

Unit 500 with ally barrels? Sure it's not silver paint?
I don't think I've ever seen ally barrels for the smaller unit engines.

[iansoady]

I've seen someone making them on FB. But I suspect you're right it's silver paint - which was original for these engines. I think they loook better black though....

[john.k]

very interesting....I never knew that .......anyhoo ,IMHO the bike is somewhat overpriced ,I  dont want to have much to do with it .