two ring piston experience?

[ZEROMAN91]

While everyone is on the subject of rings, could someone explain the difference between a Napier ring and the offset 2nd ring in some ring sets.

[bigjoe1]

The best way to describe the napier hook ring design is that the edge of the ring that is in contact with the cylinder wall is shaped like a meat hook. It does look like a dykes ring upside down. The contact area is very small, about one third to one half the normal contact area.It acts like a squeegy on the down stroke. I have used these with much success in the past. This would be my first choice for second ring types. JOE SHERMAN RACING

[Ron C.]

Joe, is it me or does the napier give anybody else trouble wanting to actually catch in the fix'd aluminum ring compressor when pushing them into the bore??
I usually have to switch back to my old steel ring compressor to get them in the bore.

Blessings........Ron Clevenger.

[Barry_R]

Wow - - check out the guys answering on this post - pretty cool! Good to see you on the board Dave! Back when I was at Speed-Pro (way back - just over a year ago...) we went through the 2 ring dance about every other year. It goes something like this...

You can reduce drag by dropping the 2nd ring. But doing so lets oil into the chamber. To dry things back up you bump the oil tension a bit - which in turn brings the drag back up. Net gain ends up really close to nil in many cases. Now that the landscape has changed quite a bit with the advent of high vac in the sump, and the risks are thus lower. It might be a better deal now than it was back in the day...

Reducing the radial wall thickness of rings has proven a very effective means of keeping bore contact without requiring high tension or drag. Using a seriously back cut 2nd, with or without napier, will reduce drag to darn near nothing while still retaining the desired squeegee effect. You can keep taking tension out of the oil expander too when using a reduced radial wall package - - even OE engines are very, very light these days.

The only limitations on reducing ring cross sections - both radial wall thickness and height - are those imposed by temperature, material and manufacturing limitations. On top rings this is a limiting factor where the heat can kill many rings (unless they are in an engine subject to frequent replacement anyways). On 2nds there is really no reason not to go really small - they all rely on point contact. The same is likely true to some extent on oils - but since the real tension is controlled by the expander design I suspect the rewards are pretty small too....

In my eyes, the risk/reward ratio still favors a three ring combo in any application where you have adequate real estate on the piston.

[ChrisU]

Ron,

Interesting you mentioned destroying the napier upon installation.

That coupled with the 'pride' total seal has on those things has given me a bad taste for them.... anyone have any help to offer so I don't scrap these things?

[RW TECH]

More taper angle on the compressor & longer straight section.

[ChrisU]

I knew you would respond

[RW TECH]

Couldn't resist so I had to respond.

So far no Napiers broken on my end, but they are tricky to get aligned into some of the tapered compressors.

Ran into this while working in experimental engine back in the 90's, when we were investigating use of Napier-style seconds for production. Actual fix at that time was what I described in the previous post. Seemed to do OK.

[ChrisU]

Maybe that and a little patience?

[cmw]

The problem of breaking rings on installation is easy to cure. Don't champers the top of the cylinder. As the piston comes out of the correct bore ring installer and if you have a champers on the top of the bore with a Napier ring or .8mm ring or smaller you will break it.

[Racer7088]

Yes I have seen many people break the iron napiers that are .043 or thinner. The steel ones are tougher and the bigger iron napiers (.047 and up) are not so delicate. I have never broken any of them in three years and maybe 300 sets but those smaller thinner iron napiers are much easier to break it seems.

Ron,

Interesting you mentioned destroying the napier upon installation.

That coupled with the 'pride' total seal has on those things has given me a bad taste for them.... anyone have any help to offer so I don't scrap these things?

[Racer7088]

Barry,

I think all you say is certainly true. The people I know in racing and from engineering are usually happy enough with the best three rings deals but want to shrink the piston even further or get the skirts up higher on the piston for other effects. Lighter is usually better as well but it is harder to make the two ring work unless everythings right.

Wow - - check out the guys answering on this post - pretty cool! Good to see you on the board Dave! Back when I was at Speed-Pro (way back - just over a year ago...) we went through the 2 ring dance about every other year. It goes something like this...

You can reduce drag by dropping the 2nd ring. But doing so lets oil into the chamber. To dry things back up you bump the oil tension a bit - which in turn brings the drag back up. Net gain ends up really close to nil in many cases. Now that the landscape has changed quite a bit with the advent of high vac in the sump, and the risks are thus lower. It might be a better deal now than it was back in the day...

Reducing the radial wall thickness of rings has proven a very effective means of keeping bore contact without requiring high tension or drag. Using a seriously back cut 2nd, with or without napier, will reduce drag to darn near nothing while still retaining the desired squeegee effect. You can keep taking tension out of the oil expander too when using a reduced radial wall package - - even OE engines are very, very light these days.

The only limitations on reducing ring cross sections - both radial wall thickness and height - are those imposed by temperature, material and manufacturing limitations. On top rings this is a limiting factor where the heat can kill many rings (unless they are in an engine subject to frequent replacement anyways). On 2nds there is really no reason not to go really small - they all rely on point contact. The same is likely true to some extent on oils - but since the real tension is controlled by the expander design I suspect the rewards are pretty small too....

In my eyes, the risk/reward ratio still favors a three ring combo in any application where you have adequate real estate on the piston.

[Strange Magic]

You will come to find that many comp records are set with engines that have 3 ring packages. E/AA was recently just set with a 7.74 pass and a 318 inch engine with a 3 ring package.

At one time two ring packages were the lick and now most all are back to 3 ring packages, with the exception of certain IHRA mountain engines.

The key to controlling oil is in the rod side clearence, piston drain back design, rail end gap and design, style of expander w/correct tension for the application and recently withing teh past couple of years that napier second which allows you to do some tings you couldn't do in the past.

Piston rings/styles and radial wall tensions are application specific and they are just as complex as camshaft design, but when you hit the nail on the head, not only can you make some serious HP but you can keep your chambers dry as well.

P.S. Dave, when you get a chance maybe you can get back to me on that question I posed to you on the phone and than again at PRI a year ago (piston weight related issue on two identical pistons at different times). I also faxed you over the information you requested at the time as well.

Thanks.

[dwilliams]

The problem of breaking rings on installation is easy to cure. Don't champers the top of the cylinder. As the piston comes out of the correct bore ring installer and if you have a champers on the top of the bore with a Napier ring or .8mm ring or smaller you will break it.

Exactly. I quite chamfering many years ago; I just run the burr knife around the bore to break the sharp edge, and I've never had a problem getting the rings in.

I also went away from the tapered installers to a corrugated band with an adjustable flip lever. I don't know who made it, but it's quick and easy, and it works on any bore size, well from 3.5 to 4.5, anyway.