B25SS Piston

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Cocker Cox
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B25SS Piston

Post by Cocker Cox » Thu Sep 17, 2020 5:21 pm

Hi, All,
Finally got the NOS standard piston for my B25SS, but surprised to see the circlip access slot is on the left not underneath. Any thoughts!
631B4F18-1EBF-4A8A-8288-C073DCCE6E52.jpeg

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malcward
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Re: B25SS Piston

Post by malcward » Thu Sep 17, 2020 6:37 pm

Never seen that before, where did you get it from.
Cheers Malc

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Re: B25SS Piston

Post by Cocker Cox » Thu Sep 17, 2020 6:53 pm

D8E2EEAD-D304-4C30-82DE-C2565AD8A339.jpeg
From an Australian supplier, although a piston with the same slot was on a US site, together with the packaging (see photo)

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Re: B25SS Piston

Post by Cocker Cox » Mon Sep 21, 2020 4:14 pm

Just to put this one to bed, I showed the piston to Roger Taylor, BSA specialist and owner of RTS Racing, who confirmed that the piston was genuine Heppolite BSA NOS, very well made and nicely weighted. He also said the position of the gudgeon pin clip access slot was not that uncommon, and also that the Starfire piston someone had replaced the SS original with in my bike’s engine was not only a non-Heppolite poor quality aftermarket one, but was also shagged... the piston rings rattling up and down in their slots. Glad I went to the expense of sourcing a replacement, then!

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Re: B25SS Piston

Post by JB » Mon Sep 21, 2020 10:22 pm

BSA had the capacity to make their own pistons in house and genuine BSA made pistons were diamond turned and of high quality. Triumph on the other hand bought theirs in, mainly from Hepolite; yet all 250's were made at Small Heath so you'd expect even the Triumph's 250's to be a BSA marked piston?
Here's a picture of the new old stock +1mm piston I fitted to my B25T that is not the same as your new old stock one?
B25 NOS Piston.jpg

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Re: B25SS Piston

Post by Cocker Cox » Tue Sep 22, 2020 7:25 am

The SS piston didn’t have the side recesses, so yours looks like a Starfire item (it’s exactly the same as the damaged piston I took out of my 1968 Starfire in 1969... see photo). The parts number for the +1/2mm Starfire piston is 40-973 and for the equivalent SS/T piston is 71-1803, so if you have a photo of the other side of the gudgeon pin you can check. I’ve seen NOS Starfire pistons sold as SS/T items on-line (they're much cheaper than the one-year only SS/T item). The difference in CR between the two (10:1 Starfire as opposed to 9.5:1 SS/T) is not visually discernable as far as I can see, but the piston design is. I doubt very much that Triumph fitted a different piston to their versions as they had no input into its production apart from styling it differently. I know that BSA produced their own pistons in the 50s but I doubt very much that they did so by 1971. Also, BSA owned Triumph, so why would they source pistons for the same engine, built on the same Small Heath production line, from Hepolite if they already made their own?!
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Re: B25SS Piston

Post by kommando » Tue Sep 22, 2020 8:16 am

You cannot apply logic to the relationship between BSA and Triumph, they were separate organisations and rival's even when told to act the opposite.

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Re: B25SS Piston

Post by Cocker Cox » Tue Sep 22, 2020 8:37 am

True, but when the same manufacturer makes all of the engines to their own design by the same workers on the same production line, I think it’s safe to assume that all of the pistons came from the same source! Whatever, the 1971 piston didn’t have the side recesses....

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