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Motor General

Piston Rings ?

PISTOL GRIP
Moparts Member
Posts: 219
From:
Registered: Apr 2002
posted 07-01-2002 04:12 AM

are they good? i'm stuck with a set, so i need to know if i need to save up to get a good set. it's for a 70'340 bored 30
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gregsdart
Moparts Member
Posts: 1343
From: Mn USA
Registered: Jan 2001
posted 07-01-2002 04:43 AM

If file fitted properly, good for 9.365 at 143 mph in my book!
Just measure the end gap by squaring the rings in the new cylinder bore 1/2 to 3/4 inch down. You can use a piston with an old ring on it, just turn it upside down. If the ring seems too big, and it probably will be too big to go in the bore as shipped, put the ring in the filer and take a little off, till it will fit in the bore for measuring. Use a feeler gauge to measure the end gap, and be Very cautious when filing the new rings, sneak up on the desired gap a little at a time. Also, the top rings are harder than the second rings, and the amount that comes off for filing will very greatly, and also due to not being able to "feel" How much tension we put on the rings during filing, the amount removed can vary each time. Rule of thumb is .004 per inch of bore for top rings, .003 for second rings. Or, for a small block, go .016 top, .012 second for a forged piston. By file fitting the rings on A new motor, blow by is reduced. Quoated numbers in HOW TO BUILD HP show about a 30 hp gain on a 350! So it is worth it!
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68_340_Cuda
Moparts Member
Posts: 418
From: Ottawa, Ontario, Canada
Registered: Nov 2001
posted 07-01-2002 10:45 PM

Be careful, if they're 1/16 340 Speed Pro file fit rings they should have a low tension oil ring that aren't very good for the street.
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info provided by members listed above

Ring gap for H116CP pistons, file-fit type

Diplomat360
Moparts Member
Posts: 360
From: Windsor, Ontario, Canada
Registered: Jun 2000
posted 05-13-2002 01:10 PM

Hey Folks!
I plan on doing the ring end-gap work this week on my 360, .020" over engine.

I'm not sure about the gaps though, the machinist says 16-18 first ring, 22-24 second. That seems awfull high to me.

This is normally aspirated street engine, 10:1 CR, Sterling H116CP hyperutectic pistons.

The rings are SealedPower file fit type, moly.

What are the recommended gaps?

Thanks!
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ZIPPY
Moparts Member
Posts: 4364
From: Detroit suburbs MI USA
Registered: Jan 2000
posted 05-13-2002 01:37 PM

For hypereutectic pistons I would use this chart:
http://www.kb-silvolite.com/speclear.htm#CHART
More ring gap info from KB pistons, via the magic of copy and paste---I find the comment I made bold kind of interesting:

Top Ring End Gap is often a major player when it comes to piston problems. Most top land damage on race pistons appears to lift into the combustion chamber. The reason is that the top ring ends butt and stick tight at TDC. Crank rotation pulls the piston down the cylinder while leaving at least part of the ring and top land at TDC.

Actual end gap will vary depending on the engine heat load. Lean mixture, excessive spark advance, high compression, low capacity cooling system, detonation and high Hp per c.i. all combine to increase an engines' heat load.

Most new generation pistons incorporate the top compression ring high on the piston.The high ring location cools the piston top more effectively, reduces detonation and smog, and increases Hp. If detonation or other excess heat situations develop, a top ring end gap set towards the tight side will quickly butt, with piston and cylinder damage to follow immediately. High location rings require extra end gap because they stop at a higher temperature portion of the cylinder at TDC and they have less shielding from the heat of combustion. At TDC the ring is above the cylinder water jacket.

If a ring end gap is measured on the high side, you improve detonation tolerance in two ways. One, the engine will run longer under detonation before ring butt. Two, some leak down appears to benefit oil control by clearing the rings of oil build up. Clean, open oil rings are necessary to prevent oil from reaching the combustion chamber. A small amount of chamber oil will cause detonation and significant Hp loss. The correct top ring end gap with KB pistons can be 50% to 100% more than manufacturer's specifications. The Special Clearance Requirements for KB Pistons chart gives minimum recommended top ring end gaps based on expected operating combustion chamber temperatures. For 2nd ring end gap follow ring manufacturer's specs.

Ring Options of 1/16" or stock 5/64" are offered on most of the KB Series. The 1/16" option reduces friction slightly and seals better above 6500 RPM, while being considerably more expensive. Stock (usually 5/64" compression rings) work well and help with the budget. Please see the Numerical/Ring Reference
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Jim Phipps
Moparts Member
Posts: 111
From: Burnsville,MN
Registered: Feb 2002
posted 05-13-2002 02:47 PM

Be careful. The H116CP's have the upper ring land lower on the piston then the KB's. This is why the KB's need such as large end gap, they see more heat!
I will have to look up what I gapped my H116CP's at (CRS syndrome), but I do remember they are about the same or the same as stock cast pistons. Call a dealer or distributor of the Federal Mogul. They should have recommendations for you to follow.
Jim
P.S. I will try to find my old paperwork and update this later.
Cut and pasted from FM site:
Speed-Pro’s cast hypereutectic material is a relative newcomer to the performance market, and has several attractive features. Our hypereutectic pistons operate perfectly with standard ring end gaps, and have conventional ring land locations. When compared to traditional cast pistons, which are not designed for performance use, the hypereutectics are significantly stronger, particularly in the highly loaded ring land, skirt and pin bore areas. Our FM244 Alloy contains 16.5% silicon, and has excellent tensile and fatigue strength. This material’s improved thermal characteristics, it’s greater hardness, and the increased resistance to scuffing permit tight bore clearances which help minimize noise on cold engine start up. This quiet operation, along with a lower cost are the primary advantages over a comparable forged piston. These pistons are an excellent choice for street performance, for “claimer” oval track engines, and for bracket racing use. They will also work well in moderate supercharged applications, and are suitable for towing and marine use.
CHECKING COMPRESSION RING GAPS
top
The following chart shows the SAE recommended Automotive compression ring end gaps. These recommendations are followed for the majority of the ring line unless a certain application requires deviation from the chart. These deviations are noted in the ring section. It is unnecessary to adjust end gaps in most cases. Our ring end gaps are measured in precise gauges that are accurate to .0001" for the diameter for which the rings are intended. Remember -when fitting rings to cylinder bores, every .001" change in bore diameter changes the end gap by approximately .003" Example: A bore .002" greater than the base diameter increases the ring gap by .002" x .003" = .006".
Cylinder
Diameter Ring Gap
Recommendations
2.000 - 2.999" .008 - .016"
3.000 - 3.999" .010 - .022"
4.000 - 4.999" .012 - .025"
5.000 - 6.999" .016 - .035"

I would calculate the top ring gap to be 20 * 0.003 = .006 plus the minimum recommended of 0.012, so you're looking at 0.018". I think your machinist knows what he is talking about!

Hope this helps,
Jim
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ZIPPY
Moparts Member
Posts: 4364
From: Detroit suburbs MI USA
Registered: Jan 2000
posted 05-13-2002 04:31 PM

.015-.020 for the KBs vs .012-.025 for the FMs isn't much difference IMO.
You're most likely safe going .018-.020, its all a judgement call on how likely the ends could butt together and that's relative to how hard it will be run, and the conditions it's run under.

I don't think .018-.020 is too loose, but having said that I have gone as tight as .014" in a very mildly built 360+.030 with cast pistons with no problems. I have also done another similar .030 over cast piston 360 and used .020" top ring gap, and it ran no better and no worse.

So my feeling on it is this:
Does the tighter ring gap actually do anything? Probably not much.
Does it increase the chance of the ends butting together, and possible damage? Yep.

Your mileage may vary...
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todd440
Moparts Member
Posts: 821
From: lapeer,michigan
Registered: Jan 2001
posted 05-13-2002 04:34 PM

Jim is right on here. The federal mogul and sterling h-series pistons have the ring lands much lower than KB pistons. This means the piston will take more of the expanding heat, instead of the rings.
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Diplomat360
Moparts Member
Posts: 360
From: Windsor, Ontario, Canada
Registered: Jun 2000
posted 05-13-2002 07:00 PM

Thanks guys.
I was aware of the difference between the KB series of pistons which have a top ring land in a very high position and the Sterling or probably what is the majority of the other pistons as well. Because of the higher heat at that top ring location KB recommends bigger gaps. This is not applicable to my situation however.

It is actually not so much the top ring gap that I question but rather the second ring gap. The machinist says .020"-.022"...the SealedPower file-fit ring instruction sheet says:

1) top ring: .016" - .018"
2) second ring: .010" - .012"

Now, that second ring gap seems kind of tight...but heck...I don't really know...the machinist calls for a lot of gap.

Considering the effect the oil has on detonation once it gets in the combustion chamber I am leanning towards to smaller gap.

OK, now how about occasional nitrous use? How will these numbers change then?

Thanks for your suggestions everyone!
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UCUDANT-1
Moparts Member
Posts: 842
From: Las Vegas Nevada
Registered: Jan 2001
posted 05-13-2002 07:24 PM

Bigger gap for Nitrous. Example KB calls for a .030 gap in a .030 over 340 with NOS, without NOS .026
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info provided by members listed above

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