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Austinsevenfriends
Piston ring scuffing - Printable Version

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RE: Piston ring scuffing - Dave Mann - 30-01-2025

The engines we built 4000 to 18000 BHP if the piston rings were replaced the cylinder HAD to be honed followed by a 16 hour run in starting with 30 minutes at no load rising to full speed, the run in could be halved by using BP running in compound added to the fuel. I often wonder what happened to the 2000 gallons of fuel and running in compound when the works closed and was demolished.

RE: Piston ring scuffing - Hugh Barnes - 30-01-2025

Do I count 9 cylinders in vew, presumably making it an 18 cylinder engine. Is that an odd number or something that relates to a specific application?

RE: Piston ring scuffing - Colin Cooke - 31-01-2025

Hi All,

Enjoying this thread, as I'm currently in the process of choosing pistons for an engine build. I have a few questions:

Firstly, what is an acceptable ring groove width size. In the piston below, the 1/16" groove measures 1.67mm. Is this ok?
Very sorry for the mix of metric and imperial, but I believe 1/16" is 1.60mm.

Some useful size pistons that I have, also have a 3/32" groove. Would these be readily available? They are +0.060" pistons.

Finally - Several pistons that I have looked at, have had these 'piston ring assisters' (see picture). What is their purpose? Are they piston specific or ring specific?

I may end up just buying new pistons, but I'd much prefer to try to reuse some old ones. I'm not looking to break any speed records - cruising at 40mph is enough for me.

Appreciate any help.

Regards,
Colin

RE: Piston ring scuffing - Robert Leigh - 31-01-2025

The piston ring assisters are to increase the radial force of the ring in the cylinder. I don't know whether they are a standard part of that type of ring or whether they could be added to reduce oil consumption by giving a better seal in the cylinder. I have found them on pistons I have removed.

RE: Piston ring scuffing - Dave Mann - 31-01-2025

Yes a V18 driving an alternator for Bermuda Electric Light Company Hugh.

RE: Piston ring scuffing - Chris KC - 01-02-2025

Colin,

I have notes from long ago which state that the vertical clearance of piston rings in their grooves should be approx 2 -3 thou (measured with feeler gauges). They are worn out when this gap exceeds 6 thou (oil scrapers) or 8 thou (compression rings). Just how "worn out" might be a matter for judgement. If the car was running well I'd leave them alone.

As for availability, if our usual suppliers are unable to help, you could try Cox & Turner - they hold a wide selection, albeit it at a price.

RE: Piston ring scuffing - Colin Cooke - 03-02-2025

Thanks Chris.

I'll consider my options, but I'm out of the game for a few weeks.

All the best,
Colin