J engine ring end gap

Here's the response from Cliff at MTC:

"Here is what I know about the ring gaps being larger.

About 10 years ago we started noticing larger ring gaps coming in on rings this being from the company that supplies all the rings for MTC, Wiseco, CP, JE and several other piston company's some of our top engine builders where wondering why so we contacted the company from overseas and had a phone conference with me the owner and a top engine builder. They said when motors where reaching 300 to 400 hundred degrees in the bore the ring end was closing up to much causing head gaskets to leak so they changed materials and went with a larger gap. We have not seen any problems with the larger gaps in the past 10 years nor do our top engine builders in the industry. I am surprised that you got .011 on the top the sets I see all are about .016 top and .021 second right out of the box.

Just for the heck of it since I haven't done it here sine the gap changed back then I did pull a 72mm and an 83mm and did several packs of rings just to refresh what I know and did come up with still .016 top and .021 second."

The company that produces the rings is Nippon Piston Ring Co. (NPR),

They also produce / supply stock piston ring sizes to OEM and many aftermarket companies selling replacement rings for most Japanese engines, too.

Recently (within the last two years) we had to file all the top and second rings in a MTC 82 mm set for the late GPz, a Wiseco KZ1075 kit required the 2nds filed, A set for a CRF450 needed to be filed top and 2nd, so did a stock bore set for a CB350. A Z1 Ent. stock bore replacement set for my KZ-J had correct gaps out of the packages despite bores slightly on the "loose" side (all the rings were close to the tight side of the FSM specs). Same with a Wiseco set for a DRZ400. I still haven't run into a set of replacement rings were too big gap out of the package, not yet.....

When fitting cast iron rings in automotive engines, there was a well known "rule" - I remember it went - top ring 0.003" per every 1" of cylinder diameter (for example, sb ford and chevy were 4.000" bore, top gap = 4.000 x 0.003" = 0.012"). 2nd ring 0.004" per 1" diameter. Oil control rails 0.003"....

We used to build some very high output V-8's back in the 90's (like 840 BHP @ 9500 RPM on 332 CI, naturally aspirated), and having 2nd ring gap a little wide didn't show up on the dyno, cranking pressure, or in leak down tests....tight top ring gaps (and a tight fit in the groove) and all cylinders being sized properly, round and straight and properly finished (honed) were much more critical....

Hey Guys. Been away for a while. Too much work. But I finally got back on setting ring end gap.

Bottom line:

-- Wiseco (and almost all) end gap formulas say .012" top .015" 2nd for a street 72mm bore.
-- MTC Pistons explained the NPR ring company change to larger gaps and suggested .016" and .022" 2nd.
-- Wiseco support gives me a different answer, depending on who I talk to.

I had a chance to look at the old rings up close and saw shiny spots on both the top and second gap surfaces. Like they may have been slightly butting up against each other at high temps. The shiny spots were at the outer side of the gap surfaces -- right where the tightest spots are when measuring with a feeler gauge.

Anyway, I'm thinking going .015" top and .021" second. Any input would be greatly appreciated. Thanks.

Oh, also read on a Honda cars tech forum about NPR end gaps going larger out of the box. And they said it was done to accommodate hot-running air-cooled bikes, but it was done across the board so water cooled car guys have to live with the larger gaps.

Makes sense. Even though water cooled new cars and bikes are run LEAN thus higher cylinder temps. I'd go with what you know.
Steve

Since MTC says .016" top that's what I'd do.

Years ago Wiseco, who supplies rings to all the others, had the ring manufacturer open the ring gaps because too many people were assembling the engine without gapping them, then blaming Wiseco. Since then, the ring gaps have all been on the large size with no need to gap them.

Just weird that I have .011" on the top rings out of the box. Even bought another set and it's the same.

Formula says .012"/.015". MTC says .016"/.022". Think I should be safe at .015"/.021".

And if the shiny spots I'm seeing are from the ends slightly butting together, this should correct that.

.003" per inch of bore.

All the Wiseco and MTC rings ( both use the same ring supplier ) I have fitted over the past few years have rarely needed any gap adjustment and have dropped in with the gaps towards the wide end of the specs (especially the top rings).
Prior to this the rings would sit in the bore with the ends touching and would always need gapping.
The second ring gap always want's to be slightly wider than the top ring to reduce fluttering and increase ring seal.

zed1015 wrote: All the Wiseco and MTC rings ( both use the same ring supplier ) I have fitted over the past few years have rarely needed any gap adjustment and have dropped in with the gaps towards the wide end of the specs (especially the top rings).
Prior to this the rings would sit in the bore with the ends touching and would always need gapping.
The second ring gap always want's to be slightly wider than the top ring to reduce fluttering and increase ring seal.

Hey zed,

So what do you think of my situation? Wiseco formula says .012"/.015" (72mm bore/street), and MTC says .016"/.022" to prevent butting due to ring manufacturer change in materials years ago. I gapped them at .015"/.021.

Top rings were .011", and 2nd .019" out of the box.

Alex

It's the first time i've heard of the change in ring material although i did hear they tweaked the actual piston alloy for less expansion a few years ago.
We use MTC pistons in the turbo drag bike and set them using the same formula as for the Wisecos as they are the same rings and there is no indication of ring butting ( I give the drag bike gets regular top end strips and inspections.)
I would have gapped your top ring and left the second as it came out of the box but your gaps will be fine.

Hey zed, here's the quote again from Cliff at MTC:

"Here is what I know about the ring gaps being larger.

About 10 years ago we started noticing larger ring gaps coming in on rings this being from the company that supplies all the rings for MTC, Wiseco, CP, JE and several other piston company's some of our top engine builders where wondering why so we contacted the company from overseas and had a phone conference with me the owner and a top engine builder. They said when motors where reaching 300 to 400 hundred degrees in the bore the ring end was closing up to much causing head gaskets to leak so they changed materials and went with a larger gap. We have not seen any problems with the larger gaps in the past 10 years nor do our top engine builders in the industry. I am surprised that you got .011 on the top the sets I see all are about .016 top and .021 second right out of the box.

Just for the heck of it since I haven't done it here sine the gap changed back then I did pull a 72mm and an 83mm and did several packs of rings just to refresh what I know and did come up with still .016 top and .021 second."