Engine: Piston Ring Fit

[MARSHALLR]

I have been looking at some of the past threads on piston ring fit. The book says .008-.016 end clearance. This is a 289 bored 20 over. I ordered my parts from SI. The end gaps I have measured are running .015 to .020. Do I need to order rings from someone else, or is this a "normal" dimension? Any ideas will be greatly appreciated.

Thanks
Marshall

[bezhawk]

If you are using hypereutectic pistons, they call for a few thousandths more. I set mine to .017 and they were fine. No big blow by or oil consumption.

[GinettaG12P]

If you set the gap of the second ring a bit greater than that of the top ring, it helps the top ring seat by reducing pressure below the ring.

[Dan Timberlake]

I'd use them, after checking ALL the end gaps, and spend an extra 20 minutes final cleaning the cylinders over again scrubbing with ATF or motor oil on clean white rags.
Did you use hot soapy water and a stiff bristle brush to clean the honing residuals out of the bores?

Do you have a good ring expander to help install the compression rings on the pistons?

http://d3hdkr4fllgwps.cloudfront.net/ats-1941.jpg

[Bud]

The end gap on the rings depends on the ring manufacturer. My preference for rings in a stock engine are Hastings as I have had good results when using them. It is also possible that the cylinders have been bored a bit large which will give you a larger than recommended end gap. My advice is to measure the bore size to determine that the cylinders are bored correctly before condemning the rings. That being said, a few thousandths extra gap on the rings shouldn't cause a problem. Bud

[5brown1]

So what is solution if the gap is too large?

[Dan Timberlake]

Based on no recent experience (last millenium) I would not expect any passenger car rings to have much tighter end gaps out of the box.
Others with much more useful recent experience may well have knowledge of gap trends among different ring manufacturers

Hastings Master catalog here -

http://www.hastingsmfg.com/Master_Catalog_Pdfs/Master2012.pdf

page 10 recommended ring end gaps for 289 Studebaker bore 0.012-0.022 inch
Only ring set for 259/289 = Set 630 on page 197
Page 362 says that V8 set 630 uses rings 032/126/860 with barrel faced plain iron top ring
AND that Chevy 194 6 cylinder set 666 uses the same rings, but set M666 uses a barrel faced moly ring. (ring types on page 5)
If the top rings are not available separately ( open stock, used to be at least from Sealed Power/Speed Pro) I'd be inclined to consider even buying 2 sets of Chevy moly rings.

if I was desperate for tighter gaps I'd look into "5 over" rings ( 25 over in this case) and file to fit, but they are probably only available in sizes ( ring material, style and facing, bore, width, oil ring tension) to fit engines used in competition.
+10 rings are likely to distort too much in a +20 bore and fail a light test, AND require removing about 0.030 inch from each compression ring, AND the oil ring tension would be pretty high, and hard to accurately reduce.

Std bore was 3=9/16" = 3.5625 inch.
+ 20 = 3.5825 inch
+ 25 = 3.5875 inch nominal bore

I'd expect modern rings with some hi-tech facing, running in a nicely finished and properly cleaned bore, using synthetic oil after breakin to maintain close to the as-installed gap for a long time. Unlike a basic iron ring whose gap might open up several thousandths over the first few hundred miles.

[PackardV8]

You haven't given enough information for an exact answer. For modern hypereutectic pistons, that .015"-.020" end gap is correct; maybe even a bit tight. For old school 259" full skirt pistons, it is on the high side, but not totally wrong.

I'd never use the .008" low-side Studebaker Shop Manual. That's too tight. If the engine were to be mis-timed enough to overheat, the rings might butt and disaster follows immediately.

The Keith Black calculator for hypereutectic pistons calls for .023", because with a high ring placement and a close piston-to-wall fit, the ring sees more heat.

Your manufacturer probably aimed for the safe end of the middle.

So what is solution if the gap is too large?

Today's rings are manufactured to such exact tolerances, it's rare to find a set which is outside the spec. If the ring gap is found to be larger than anyone's recommendations for that bore diameter, get a new set of rings. If a second set is the same greater than desired end gap, it becomes a DIY. If one wanted to get exactly what the Studebaker Shop Manual recommended, it becomes a "file fit" situation. Since our OP is concerned his for the .020" bore are too large, he'd order the .030" oversize and file them to his preferred .008"-.016" end gap. However, to remove that much material, one would need a power ring filer.

While we're on the subject of piston rings, I was just told by our warehouse moly rings are NLA for our V8s. What rings and who's brand did SI provide?
jack vines

[Flashback]

Stay over .010 and use .025 as a top number. Street engine ?

[Mike Van Veghten]

Jack wrote -
""I'd never use the .008" low-side Studebaker Shop Manual. That's too tight. If the engine were to be mis-timed enough to overheat, the rings might butt and disaster follows immediately.""

This isn't exactly gosple either..
I receintly bought a set of Total Seal rings for my stock bore Stude engine, they recommended (for "their" rings)...at that small bore, .006"/.008" (top ring) for a naturrally asperated engine, no nitrus. Remember, this small bore (3.562 vs. a 4.00"), there is less material to expand. So, there "can" be a tighter gap with less chance of butting on the small bore ring because there is a lot less material to expand and close up the gap.

The Total Seal company use different gaps for a different "group" of bores, for blown vs. unblown, for nitrus vs. no nitrus and for cast vs. hypereutectic vs forged.

There are many different materials that are used for piston rings today. Each has it's own expansion rate.

One cannot blanketly say anymore, .004" gap per inch like used to be done. Maybe for a Hastings like ring that hasn't changed in the last 40+ years, but not for a modern ring.
Plus, most higher quality ring manufacturers also...make a .005" oversize ring for file fitting to each cylinder.

Mike

[Dan Timberlake]

Hi Mike,

Perhaps different instructions come with your ring set, but there is some gap info at the Total Seal site here-

http://www.totalseal.com/Techpage.aspx

About 40% of the way down the page there are some ring end gap tables.
If using the gapless ring in the top position on a gasoline powered street car with 3-9/16 inch bore the chart seems to say 0.0065 X 3.562 = 0.023 inch ring gap.
After doing a search for "minimum" on that page It is still unclear to me if that is the minimum.

"Street, strip, circle .... Gas, Alky, E85 .... Bore X .0065"

=====
According to that page if the gapless ring is used in the 2nd position it would be 0.0045 X 3.562 = 0.016"

[MARSHALLR]

Thanks for all of your valuable input. This is a street engine. I bought a complete engine kit from SI including 20 over pistons; but, I can't really say what type of pistons they are. Sounds like I'm in good shape for a street engine so I will go with what I have. I did wash the bores with soap and water. I used the "white rag" method for cleanliness. I also installed an R1 cam from Phil Harris.

Will let you know how it all turns out.

Thanks Again
Marshall