Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
Assuming there is no backing expander, Davids photo looks like Cord rings with a filler spacer to moderate the number and the friction. Use as oil rings, more benign.
When I first got my Seven into use away from home, close neighbours were Lester Reader who owned the Rubber Duck and his colleagues, all of whom had recently grown out of Sevens and Seven specials. They reckoned steel expanded rings robbed Sevens of power, and considered Sevens went best when worn out! Unfortunately I did not know enough at the time to quiz them extensively.
i am amazed that Cord rings were suggested for diesel engines, which rely very much on the operating priciple of conventional comp rings. I am surprised Cords rings still made. Might be more helpful if they made ring spacers as these now seem unavailable , making it difficult to renovate old pistons.
Joined: Aug 2017 Posts: 1,746 Threads: 42
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Location: Malvern, Victoria, Australia
From memory Cord Rings were described as causing 'fumonial wear likened unto a barrell' or similar- was it in the old Special Builders Guide ?
Joined: Aug 2017 Posts: 1,715 Threads: 47
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Location: Auckland NZ
Car type: 36 Nippy, 31 RM, 38 Special, 24 Works Rep
I worked on an engine fitted with cord rings, I was quite surprised to find the damage they caused was, as Tony suggests "fumonial" when compared to regular rings. This was even more sad when you learn that the engine had been built at great expense with a fresh 60+ rebore, new pistons, big valves etc only a few years previously by a professional engine builder, by the time the owner realised he had a problem and came to me the damage was done and the block was scrap. I have not used cord rings myself, whilst they may be of use in an extremely worn engine to extend its life by a few miles it would appear not a great idea in a good engine.
Black Art Enthusiast
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
11-11-2021, 06:53 AM
(This post was last modified: 11-11-2021, 06:59 AM by Bob Culver.)
For any youngsetrs still hanging in there Cord rings were not flat. Could therefore distort to accomodate oval bores. The normal operating priciple of a ring, that the gas pressure acts behind to apply wall tension, is more or less forsaken. Used in worn engines with collapsed split skirt pistons the rings were agitated severely. Thay supposed to block gas leakage just by the number of gaps. What really went on when used as comp rings who knows? I was astonished they stayed on the market so long and certainly not now. Bore top wear is largely associated corrosion; mid bore wear is more simple wear, often attributed to lube problems.
All rerings were not desperate short term measures. Our family 1952 minx by 40000 had the 4th ring fitted but burned pint in 300. My father fitted new rings (no honing) with a spring rail oil ring and when sold at 120,000 still not using original oil.
Joined: Jan 2019 Posts: 1,567 Threads: 20
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Location: Bala North Wales
Car type: 1933 RP Standard Saloon
I have no idea what rings were fitted to the pistons that were in my car when I first had it. The photo I posted was one of the pistons I replaced when I put new pistons in to cure little end knock. I kept the three 'good' pistons just in case.
I posted it just to demonstrate that the composite oil control ring should be fitted to the upper oil control groove.
Joined: Aug 2017 Posts: 3,329 Threads: 372
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Two have now confirmed that on the touring Seven pistons, these ring springs that come in the sets definitely do not allow a fit (i.e. for both ring spring and oil control ring) in the bore. So if you buy any, just respect the typed note, but that is the reason!
For novices like me, rings are also pre-gapped, so worth bearing in mind if you are contemplating trying to re-assemble between rebores rather than do a complete rebuild.
Joined: Mar 2015 Posts: 5,442 Threads: 231
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Did a note come with these, from the supplier, explaining that the ring spring should be discarded Jon?
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Yes indeed, as per original post and above.
As I said above, it is just nice to know exactly why otherwise you never learn anything.
Steve H mentioned that another cherished suppliers stock come like this and confirmed.
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
As above it is essential the ring can push down flush with the piston face. Seems like cannot with the spring hence advice to discard. Pre gapped rings were popular with the Trade and eliminated one more source of botched workmanship. But irksome for those seeking minimum gaps. If rough finished generous gaps become even bigger with bed in. However engines run merrily with quite large gaps.
