Ring seating, heat transfer

[Truckedup]

My understanding is a lot of piston crown heat is transferred from the rings to the cylinder walls....If the rings, I would assume primarily the top ring, don't seat fully there is a possibly of piston galling or seizure..Sometimes this may be confused with lack of cylinder to piston clearance or even detonation.
Are all modern rings pre lapped so they seat almost instantly? Can I assume that the least expensive cast iron rings are not lapped and require a longer period to seat fully? So if the only option is cast iron rings then try to avoid high engine loading for a longer period?

[Newold1]

Simple solution, use moly faced top rings in a properly finished cylinder and quick sealing and normal heat transfer should not be a problem. Buying cheaper cast iron top rings is not worth the breakin issues they can create. This works for most mild NA engines but other ring types are needed for other boosted and power adder situations. In most builds, poor or improper cylinder bore finish is the number one cause of poor ring seal and ring life period!!

[PackardV8]

Current cylinder wall finish techniques and good quality rings have made the old break-in process no longer necessary. Even rebuilder rings seat instantly.

We once tore down a Chrysler Marine flathead six which had run for forty years, sometimes for hours at full throttle. Two cylinders had chrome rings which had never seated.

[engineguyBill]

Simple solution, use moly faced top rings in a properly finished cylinder and quick sealing and normal heat transfer should not be a problem. Buying cheaper cast iron top rings is not worth the breakin issues they can create. This works for most mild NA engines but other ring types are needed for other boosted and power adder situations. In most builds, poor or improper cylinder bore finish is the number one cause of poor ring seal and ring life period!!

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Proper cylinder bore preparation and good quality piston rings will seat effectively. And yes, properly seated rings will transfer piston crown heat to the cylinder walls.

[hoodeng]

As the previous three guys have pointed out ,bore finish is paramount as well as geometry ,torque plates are now accepted as the standard to ensure in service distortion is almost non existent ,even old engines that would have been manufactured without surface compression and fastener distortions catered for will benefit from torque plates, we also plateau finish bores as a standard machining step. I used to send my bores out over 25 years ago,the stuff i was getting back precipitated my purchase of a boring machine and hone,,, i happened to walk into the machine shop i used then unannounced and saw emery cloth wrapped around the hone head to finish my bores!!!! they told me the material of the bores was that hard it was the only way they could get the finish i expected without wearing out their stones,,what rubbish.

All the major ring manufacturers will use best tech even on their base product cast rings ,these rings are the cheapest alternative they manufacture ,that is not to say there is anything wrong with them ,they are perfectly suited to service in standard duty engines that they specify them for. If an engine manufacturer has used a treated ring as standard fitment, use the same type of ring at overhaul, if an older engine has had as cast rings installed as OEM you can use the same again with confidence, although a better grade ring will not necessarily give a performance advantage it may give longer service ,but considering how often we do rings in a street engines life,high end rings are a bit of a luxury for base model work.

For years i have been asked to do bores off engines that i do not normally service ,i can do them, all the customer has to do is give me the torque plates to suit and the job is done no problem, when the customer tells me they are not important or that it is only one job and not worth the investment i tell them there are other machine shops out there that should be able to make them happy and at a lower cost!

These days you can get plate flame cut and slash ground as cheap as chips,you can even email a drawing to them,there is no excuse,even if you go shares with like minded friends.

Cheers.

[modok]

A cast piston taht is open behind the oil ring, with wide rings on it, the rings will be doing a lot more cooling than if you have a forged piston and skinny rings.

[Sparksalot]

It's nonsense that the primary heat loss from the piston to the cooler cylinder is though the piston rings. Slap yourselves upside the head.

[Truckedup]

It's nonsense that the primary heat loss from the piston to the cooler cylinder is though the piston rings. Slap yourselves upside the head.

Ok, explain why not...

[naukkis79]

Ok, explain why not...

Small contact from ring to cylinder and even smaller contact from piston to ring. And ring itself absorbs a lot of heat from combustion gases and from friction to cylinder wall. And there's a lot of oil-filled surface between piston and cylinder where heat has much less restricted path to cylinder wall.

[Keith Morganstein]

It's nonsense that the primary heat loss from the piston to the cooler cylinder is though the piston rings. Slap yourselves upside the head.

These rings also play a major role in the heat transfer process between the piston and cylinder wall.

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[Keith Morganstein]

Hastings rings are pre-lapped, including plain cast rings.

[engineguyBill]

It's nonsense that the primary heat loss from the piston to the cooler cylinder is though the piston rings. Slap yourselves upside the head.

Wrong! As was stated in the beginning posts, primary source of heat transfer from the piston crown to the cylinder wall is through the compression rings. Heat is then transferred to liquid or air cooling system and ultimately to the atmosphere. Even thin rings transfer heat from piston to cylinder wall quite effectively.

[engineguyBill]

Hastings rings are pre-lapped, including plain cast rings.

All major ring manufacturers currently lap their rings at the factory. This lapping operation is checked periodically to make sure that the rings are "light tight", meaning that no traces of light are observed leaking through between the outer surfaces of the ring and the fixture ID.

[nm9stheham]

Torque plates have been mentioned. But for more mundane engines bored/honed without them, there are going to be cylinder distortions when assembled that presumably need to be worn down. So the idea that all break-in processes are 'instant' in those cases does not seem likely, and some extended break-in time would seem to be the reality. If you look at the bores of such engines after some running, you'll often see areas around the top of the bores where the honing marks are more worn, which presumably were the high spots resulting from the torquing of head fasteners.

[modok]

What the rings don't touch....is another issue.
what I would consider "rings seating" is about what the rings do touch.

When the rings touch the cylinder and they SCUFF, the raised edges of the scuff marks only serve to hold the rings off the wall.
A Good cylinder surface is fresh material shaped in to provide boundary lubrication. It's about oil, and about oxide.
Old hands will say something like "exposing fresh material, open the pores of the metal" maybe something about work hardening, and....if that's right or not, I don't know, but basically that the right kind of ideas. The surface of any metal is oxide, so you need to make a surface conductive to lubrication with oil, and conductive to forming a new oxide layer.