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Hole in Piston Ring
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15-03-2023, 07:51 AM
On dismantling my Ruby engine today, I found a hole of about 1/8" diameter in one ring. In the photo, see the second ring on the right hand piston. Does anyone know whether this is a normal feature on a certain type of ring? It seems strange that this hole is not found on any of the other rings.
15-03-2023, 10:26 AM
(This post was last modified: 15-03-2023, 10:27 AM by John Cornforth.)
Hi
That is rather odd. The only "pegged" rings I have encountered are on two strokes, where you don't want the ring ends to clash with the transfer port so have to stop them from rotating. With those, the peg is offset so you only get a half-moon cutout in the ring so as to not weaken it too much.
15-03-2023, 01:22 PM
The style of rings suggests that the pistons were fitted a long time ago and re-ringed at some time. The Cords oil control rings are something I have not seen in a long time, and through the period I have used A7s (since 1959) all new pistons (except slipper type) had 2 compression rings and 2 oil control rings the upper one being above the gudgeon pin. The upper compression ring pictured appears to be fitted in a very worn groove, and the purpose of the hole is a mystery to me. It looks as though someone did the cheapest overhaul they could get away with.
15-03-2023, 06:53 PM
(This post was last modified: 15-03-2023, 06:57 PM by Graham Barker.
Edit Reason: I meant wriggled sideways in their guides,
)
Robert, thanks for that information. The last time I had an Austin Seven motor in pieces was almost 6 decades ago. So I need updating.
This motor was reconditioned 40 years ago by the previous owner and never used much since then. It produces light blue exhaust smoke when under load and seems to have an inordinate amount of blowby forcing a lot of oil out of the filler pipe and the tappet cover vents. It uses about a litre of oil per hundred miles. The gap in the ring grooves alongside the rings is 4 to 6 thou. The bores have negligible wear and I see from receipts that they had been rebored. It's a Ruby high compression engine and all cylinders give 100 psi on cold, throttle open compression test. Also all the valves can be wiggled sideways in their guides a little. Do people think that fixing the outdated ring setup would be sufficient to reduce the smoke and blowby or should I be focused on renewing the valve guides? (15-03-2023, 01:22 PM)Robert Leigh Wrote: The style of rings suggests that the pistons were fitted a long time ago and re-ringed at some time. The Cords oil control rings are something I have not seen in a long time, and through the period I have used A7s (since 1959) all new pistons (except slipper type) had 2 compression rings and 2 oil control rings the upper one being above the gudgeon pin. The upper compression ring pictured appears to be fitted in a very worn groove, and the purpose of the hole is a mystery to me. It looks as though someone did the cheapest overhaul they could get away with. 
15-03-2023, 09:05 PM
My advice is bite the bullet and do the job properly Graham. Those pistons are not a great design, the modern split skirt or slipper versions with narrow rings work so much better. The Cord rings cause excessive bore wear and sap power. If I were doing the job the block would be skimmed, honed/bored, new pistons, new valves, new guides, head skimmed, tappets refaced and profiled, and that's without looking at the bottom end which will no doubt need some remedial work.
Black Art Enthusiast
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