Wanted: A7 Pistons & Rings

[Biker Chris]

Greetings all,

During my Star Twin rebuild I find myself in need of the following, if anyone can help, please?

- piston rings +020 (Hepolite R3630/20 or BSA 67-88)
- pistons +020  (Hepolite 10030/20 or BSA 67-84)
Or high compression alternatives +020 (Hepolite 12502/20 or BSA 67-106/67-106)

I've seemingly scoured everywhere, including a few auto jumbles without much success.

It seems both high compression and 020 oversize parts are fairly allusive.

Any help would be great!

[limeyrob]

Any use?

http://www.klempfsbritishparts.com/PISTON--A7-BSA--020-0

Post from the USA is quite cheap, can be less than UK domestic but its very size and weight dependent. Its worth calling them if these are right.

[Biker Chris]

Cheers for flagging that one but it's part number is for the 51-68 variant with a 66mm bore.

I'm after the earlier 62mm bore +020 unfortunately.

[limeyrob]

This add is confusing, shows plus 60 but also lists + 20 in the text, perhaps worth a call.  Is this the correct bore?
I've just been through this with some -20 shells, STD, -10, -30 everywhere but no -20. Even UK suppliers who took my order then cancelled.  Found loads in the USA.  Makes sense because huge numbers of bike were exported.

[Swarfcut]

  Contemporary 5T Pre-Unit Triumph bikes have a 63mm bore, so surprisingly Triumph pistons will fit a Longstroke 62mm + .040"/1mm bore, even down to the gudgeon pin diameter, give or take the odd thou. From research I reckon some sellers list these two pistons as being the same, and even muggins thought he had found rare Longstroke pistons that turned out to be everyday Triumph. As always, there are variations in compression height of any pistons offered.

 Standard 63mm Triumph rings  will fit Plus 40 BSA Longstroke Pistons which also have ring thickness 1/16" /1/16"/1/8".

 Not much help in this case, but maybe of interest.

  eBay is probably the best source for choice, even contacting sellers directly rather than waiting for a listing to appear.

 Swarfy.

[limeyrob]

Doh, never posted the link.....

They are listing +60 but referring to +20 in the description, you never know they may have both.

https://boaspares.com/products/bsa-a7-pistons-1946-49-60-pair

[Swarfcut]

 Yup, listed as fitting a Triumph motor and two part numbers...BSA/Triumph. I reckon 45 thou running clearance is a typo, decimal point in wrong place.

[Biker Chris]

Doh, never posted the link.....

They are listing +60 but referring to +20 in the description, you never know they may have both.

https://boaspares.com/products/bsa-a7-pistons-1946-49-60-pair

Cheers, I'll give them a call but from the listing it's 63mm so I don't think it'll fit a 62mm+020 as that's 62.5mm.

[Biker Chris]

I've looked at just C10/C11 rings as they are 63mm STD, so 62mm+040 but I'd prefer to avoid a rebore if I can.

I'll look at the Triumph option too.

Ideally still looking for the BSA part numbers but it might be an alternative.

[Biker Chris]

The linked below would be perfect but awaiting stock...

https://draganfly.co.uk/shop/55043/piston-complete-71-long-stroke-a7-20/#10030/20

[Biker Chris]

Cheers for the help guys, a set of 7.5:1 +.020 high compression complete pistons came up on eBay so I'm all good without having to rebore to +.040!