How to trim the oil piston ring coil?

[genscripter]

I've already sized my top and 2nd piston rings ok. I'm working on the oil rings, and unlike most of the oil-ring tutorials on the net, the IDI oil-ring setup is different. It has a concentric wire inside the coil, that it surrounded by a ring housing.

I can grind the ring housing no problem down to the spec. But I'm just wondering about the inner coil? Can I pull out the concentric wire, then grind the coil down a few ten-thousandths? But unlike the outer housing, I can't get a really exact measurement in the bore to find the gap.

I bought oversized rings so that I could grind them to the exact min spec. Everything is good, except on how to grind or resize the coil inside the oil-ring assy. I bought 030 over my size (limitations on what was sold.... I had to choose from Standard or 030 and nothing in between). I originally bought Standard as per the cylinder skirt spec dims, but when they arrived, they were already above the max piston ring gap spec. So I'm using these oversized ones, and gapping them accordingly. Any advice would really help me out. I know the coil expands and shrinks in the groove, but I would think a ring that is designed for 030 over would be too large for the compression to handle. I'd say it would need to be ground down at least some point. But how do I measure the gap on this wiggly oil ring coil?

 

[Thewespaul]

You should be able to snip enough of the oil ring off to get to the minimum spec

 

[genscripter]

Thanks.

But how do I make sure the gap is right? the coil compresses and shrinks and expands in the bore. Am I just measuring it from it's most relaxed size in the bore?

 

[Thewespaul]

Do you have the oil ring that came out of the engine?

 

[genscripter]

I have the old oil rings. They are slightly different but pretty much the same radius. I'm just going to run the new coils uncut. the ends have slightly higher frequency than the middle, so i assume grinding that off would make them less functional. I assume that when I compress them with my piston installer tool, it'll mush the coil a little. But that's probably by design.

 

[spg]

Using a larger bore size ring and filing the end gap to fit will give you more cylinder wall drag than what is desired. A slightly larger end gap is less of a problem than to much ring tension. As the engine gets to operating temp the ring gap gets smaller.

 

[genscripter]

Using a larger bore size ring and filing the end gap to fit will give you more cylinder wall drag than what is desired. A slightly larger end gap is less of a problem than to much ring tension. As the engine gets to operating temp the ring gap gets smaller.

I totally understand what you mean. I guess my concern is, how do guys like R&D IDI Performance run 2nd rings down to .018 - 0.024" then? Wouldn't that be crazy cylinder wall drag? http://www.idiperformance.com/store/p46/Total_Seal_2nd_Compression_Rings.html

If installing in a worn bore, extra care need's to be taken to file the gaps properly. Ring gap need's to be filed to between .014" and .020" on the 6.9, and .018" to .024" on the 7.3. On an engine with wear, the rings need to be gapped to the tightest part of the bore.​