Lotus Elan

Piston ring orientation

PostPost by: jono » Mon May 16, 2022 9:22 am

My oil control rings (which I'm re fitting) have no 'up or down' marks and one side has a very obvious bevel edge - would I be correct in saying that this edge should point down?

...these are the deep rings with slotted recesses and the separate spring oil retainer which fits behind

Cheers

Jon
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PostPost by: nmauduit » Mon May 16, 2022 10:56 am

as for the oil control rings the thin part of the bevel is usually on top, the rationale being that on its way down the ring will scrape the oil back to the sump and on its way up it would glide on the cylinder surface...
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PostPost by: jono » Mon May 16, 2022 3:33 pm

Sorry, I'm not sure I was clear.

One face of the ring has a square outer edge/arris and the other face has a pronounced bevelled outer edge/arris - are you saying that the bevelled face should be uppermost?

The ring is not a 'keystone' in cross section (it perfectly square)
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PostPost by: nmauduit » Mon May 16, 2022 4:09 pm

jono wrote:Sorry, I'm not sure I was clear.

One face of the ring has a square outer edge/arris and the other face has a pronounced bevelled outer edge/arris - are you saying that the bevelled face should be uppermost?

The ring is not a 'keystone' in cross section (it perfectly square)


I'm not sure I understand where the bevel is if the ring is perfectly square... the bottom ring is usually made of 2 very thin blades...

in any case, if in doubt, I would attempt to check the installation recommendatinos of the ring or piston manufacturer... rings should be marked on the face that goes up (chamber side)

as for the general principle :
https://www.performancemotorsports.eu/support/instructions-terminology/piston-ring-tech/

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PostPost by: jono » Mon May 16, 2022 4:44 pm

This ring is not a two part - it's as shown here and it uses a separate expander spring behind the ring.

Unfortunately I do not know the ring manufacturer as these are +30 year old pistons and rings.

In the photo I have placed the ring with the bevel (or perhaps better described as a 'chamfer') at the bottom
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PostPost by: promotor » Mon May 16, 2022 6:57 pm

jono wrote:This ring is not a two part - it's as shown here and it uses a separate expander spring behind the ring.

Unfortunately I do not know the ring manufacturer as these are +30 year old pistons and rings.

In the photo I have placed the ring with the bevel (or perhaps better described as a 'chamfer') at the bottom


Jono,

The reproduction rings you get now have two chamfers on them - they are both on the top side of each "micro-land" of the type of oil rings similar in design to yours in the photo.

So, the chamfers face upwards, and the sharp edges (ie non-chamfered) face downwards to scrape the oil back into the sump.

If you only have one chamfer (can't really tell in your photo how many you have) then the chamfer would still want to face up and the sharp edge face down to scape oil back into the sump.
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PostPost by: jono » Mon May 16, 2022 7:36 pm

Al,

That's perfect thank you and makes good sense now you explain it.

Oddly enough I have a new set of Goetze rings for a spare engine and the oil rings, though the same format, have no chamfers on either face!

I only have one chamfer and have set it to the bottom so I now need to correct that before I assemble the engine - glad I checked!

Thanks again

Regards

Jon
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PostPost by: promotor » Mon May 16, 2022 7:50 pm

jono wrote:Al,

That's perfect thank you and makes good sense now you explain it.

Oddly enough I have a new set of Goetze rings for a spare engine and the oil rings, though the same format, have no chamfers on either face!

I only have one chamfer and have set it to the bottom so I now need to correct that before I assemble the engine - glad I checked!

Thanks again

Regards

Jon


You're welcome, jono.

I've just checked a few different new old stock pistons and they have the chamfer(s) in the same orientation, and the rings have "top" marked on them so we can be confident the manufacturers' all agree they're meant to be that way!
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