Piston Rings A7 1949

[namloop]

Hi to all
Have just waited for and received a set of rings for my 62mm +20thou pistons.
The box says 63mm - I saw this after it took an hour with the compressor to get one piston in - once in it wouldn't move.
One side of the box says in handwriting A7 BA 67-0090/+20 - the other 63mm
They are GPM.

I am sure they are wrong - that being the case, any suggestions of suppliers - especially my Australian site watchers?

Can Bantam rings be used given they are the same size?


Our problem here of course is a 3 week turnaround in ordering to arrival!

Many thanks
Stephen
Gold Coast.

[Brian]

Sounds like the box is incorrectly marked, 63mm is +.040"

Definitely can not use Bantam rings.

If you ring C@D Autos in the UK and pay with VISA card you should have a set within ten days. Here in AUS you could try Modak but be prepared to mortgage your house to pay for them.

[bikerjohndavies]

You could always use a file on the end to reduce the size. I would put each ring in the bore about an inch down from the top and measure the gap. Gently use the file to give around a 8 thou gap when in the bore and you should be OK.

[BSA_54A10]

You could always use a file on the end to reduce the size. I would put each ring in the bore about an inch down from the top and measure the gap. Gently use the file to give around a 8 thou gap when in the bore and you should be OK.

Well actually you can't , well not for long any way.
A piston ring has a specific curvature so that it exerts the same pressure all the way round.
Cutting down an oversize ring will cause uneven pressure on the bore acccelerating bore wear and in particular ovality.
The rings will also wear unevely and you run the risk of the ends of the ring wearing so thin that can be disslodged from their groves ( not pretty )

Now if it is week before the BSA Natioinal or International then you will be able to get away with it without too much risk but you won't gae away with pressing your luck for next years rallys.

[bsa-bill]

A piston ring has a specific curvature so that it exerts the same pressure all the way round.
Cutting down an oversize ring will cause uneven pressure on the bore acccelerating bore wear and in particular ovality.

Not sure about the ovality though BSA_54A10, this presumes the rings do not rotate - a subject where opinions differ, myself I'm not sure I know enough to have an opinion but like to play devils advocate whenever.

Interesting to think just how the rings are produced in sizes of 10 or 20 thou steps, from tubes of similar differing size or tube and ground to size - come on you gurus let the hoy poloy know how it's done