| Listed in parts books | Not catalogued by year yet |
PISTON SET +.020 (63.5mm) 5T 1939-57 - 7-1 COMPRESSION - Use CP161 for 9:1
Piston set, +.020 oversize (63.5mm), for the Triumph 5T Speed Twin 1939-57, 7:1 compression.
This is a +.020 oversize piston set for the Triumph 5T Speed Twin, covering the 1939-57 model run, sized at 63.5mm and built to the 7:1 compression ratio that Triumph used on these engines. The Hepolite/Wellworthy-style CP prefix on the part number is standard for piston sets of this era, not a Lucas or electrical item despite what the manufacturer tag on file might suggest.
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If you're after a 9:1 compression piston for the same bore and bike, the catalog note points you to CP161 instead - so make sure you know which compression ratio your engine was built for before ordering, since the wrong one won't suit your head and cam setup.
We don't have more detail on this one beyond what's in the catalog note itself. If you're not certain your barrels have already been bored to +.020, measure before you buy, and call the shop if you want us to confirm before you order.
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