Ring gap? Olds 455 .030 over forged pistons

« **on:** April 12, 2015, 03:18:25 PM »

I'm putting my olds together now abd I'm having a problem finding the correct end gap for my rings. They are the "vintage" e-243k 30 type rings the 2nd ring has a slight chamfer while the top is square. Is there something a jet boat likes more over a street end gap?

« **Reply #1 on:** April 12, 2015, 03:56:03 PM »

Have you looked at Mondello Web site I believe he set his ring gaps top 20 to 22 and sec is 22 to 24

« **Reply #2 on:** April 12, 2015, 08:06:38 PM »

Quote from: bronco1 on April 12, 2015, 03:56:03 PM

Have you looked at Mondello Web site I believe he set his ring gaps top 20 to 22 and sec is 22 to 24

I'll look thst up no bro thanks man!

« **Reply #3 on:** April 12, 2015, 08:11:10 PM »

Your welcome

« **Reply #4 on:** April 12, 2015, 10:25:20 PM »

Ring gap is a product of circumference, ring material, and intended application. The ring lands are the hottest running porting of the piston because of the friction generated at the ring/bore interface. As the rings heat, they expand. This expansion is along the circumference of the rings and causes the ends to come into contact with each other, applying force to the cylinder walls and against the lands of the piston.

Ring seal is a function of the rings outer geometry interacting with the bore diameter, not the end gap. This means that combustion gases are not going to leak through the the gap, run around the outside diameter of the piston ring land, and then down through the next ring gap. There's just not enough time in 1/42 of a second at 5000 RPM. The goal, when optimizing an engine combination is to get the ring ends to just close up and contact within .001, but not actually touch. That requires a lot of trial and error along with teardown and inspection until right.

I would strongly suggest looking up the ring manufacturer's recommendation for end gap in thousandths of an inch per bore diameter for that specific ring. Then add the suggested amount in the event of supercharging and/or nitrous oxide, even if it is planned in the future.

It is better to error on the large side rather than be too tight.

Good luck,

Joe

« **Reply #5 on:** April 13, 2015, 04:07:09 PM »

Quote from: Flusher on April 12, 2015, 10:25:20 PM

Ring gap is a product of circumference, ring material, and intended application. The ring lands are the hottest running porting of the piston because of the friction generated at the ring/bore interface. As the rings heat, they expand. This expansion is along the circumference of the rings and causes the ends to come into contact with each other, applying force to the cylinder walls and against the lands of the piston.

Ring seal is a function of the rings outer geometry interacting with the bore diameter, not the end gap. This means that combustion gases are not going to leak through the the gap, run around the outside diameter of the piston ring land, and then down through the next ring gap. There's just not enough time in 1/42 of a second at 5000 RPM. The goal, when optimizing an engine combination is to get the ring ends to just close up and contact within .001, but not actually touch. That requires a lot of trial and error along with teardown and inspection until right.

I would strongly suggest looking up the ring manufacturer's recommendation for end gap in thousandths of an inch per bore diameter for that specific ring. Then add the suggested amount in the event of supercharging and/or nitrous oxide, even if it is planned in the future.

It is better to error on the large side rather than be too tight.

Good luck,

Joe

If you read nothing else from what he said (all good info, btw)... remember this part. It is far better to have an end gap .010 too large than .002 too tight.

Wish I could find a link to a study the OEMs did back in the 70s when they were playing ring end gaps and their effects on emissions. I read it a few years back and found it interesting. Basically they found no significant change in blow-by or compression leakage up to somewhere around .070" end gap. Totally counter-intuitive, but that's what they found.

Being that jets run for prolonged periods of heavy load and WOT (both of which make heat) I 100% agree with Joe that the gaps should be on the loose side. The Mondello specs listed above would be good in a mild street car but in a jet run upper at .026-.028 and 2nd ring at .028-.030.

« **Reply #6 on:** April 14, 2015, 11:33:15 AM »

The "Practical Olds" article recommended .022 top and .018 for second ring for a jet boat application.

« **Reply #7 on:** April 14, 2015, 11:43:48 AM »

Also remember that in a jet boat application, with a "normal" cooling system, the two front cylinders run cooler than the rear two cylinders. So to say you need to err on the side of caution cannot be stated enough.

If you have ever seen "bad day" posts from folks with blown up chit with portions of the top of the piston broken at the ring land, that was a result of either detonation or ring bind.

You should have increased piston to wall clearances, so ring gaps being close is not all that critical, open them up and be safe.

I am a .020 upper .025 lower person myself when it comes to a big Chevy. I cannot imagine an Olds would be much different.

GT

Sent from my SCH-I545 using SoCal Jet Boats mobile app

« **Reply #8 on:** April 14, 2015, 11:45:37 AM »

GN7 (RIP buddy) did a great write up on this year's ago. I will look for it and link it here.

GT

Sent from my SCH-I545 using SoCal Jet Boats mobile app

« **Reply #9 on:** April 14, 2015, 01:39:18 PM »

I'm the 1st to admit I run my gaps loose... probably a couple thou looser than needed. It's a precaution thing to help protect people from themselves and keep them from coming back and saying I didn't build their engine right when in reality they were out being stupid with the motor. So far so good, no one has come back with damage related to ring end gap yet *knocks on wood*.

FWIW, a couple thou looser on the 2nd ring is said to promote ring stability and keep the top ring from fluttering. Pressure that gets past the 1st ring then gets caught between the 1st and 2nd rings and can cause the 1st ring to become unseated. A larger 2nd ring gap allows an escape path for that gas and helps keep the 1st ring seated. An accumulator groove between the rings on high-end pistons helps relieve the pressure as well. Read a tech article on that years back and have adopted that method since.

« **Reply #10 on:** April 14, 2015, 02:39:28 PM »

I wrote my post incorrectly and have since corrected.

The ring gaps are set so that the maximum cylinder pressure retention and least gas pass is achieved.

I used to be a huge fan of cast iron rings years ago, they cut in in about an hour and lasted quite a while. Since the introduction of chromoly and hybrid rings, iron has somewhat become a lost technology.

Cylinder finishes have also changed quite a bit in the last 20 years.

I was also always told the higher the ring land is on the piston the tighter the gap should be. That always seemed counter intuitive to me.

Maybe someone can tell me why. My suspicion has always been to prevent pressure build up under the top ring, but that is just a guess. My Venolia pistons only have about .2" of upper land above the ring. Whereas the JE version of the same slug is .325". That is what brought it up.

I will say that the Venolia's are coated.

GT

« **Reply #11 on:** April 14, 2015, 03:35:43 PM »

Quote from: GT Jets on April 14, 2015, 02:39:28 PM

I was also always told the higher the ring land is on the piston the tighter the gap should be. That always seemed counter intuitive to me.

Maybe someone can tell me why. My suspicion has always been to prevent pressure build up under the top ring, but that is just a guess. My Venolia pistons only have about .2" of upper land above the ring. Whereas the JE version of the same slug is .325". That is what brought it up.

I will say that the Venolia's are coated.

GT

That's interesting. The only thing that comes to mind is perhaps the JE, with its low top ring, is designed for forced induction while the Venolia is more of an NA setup? That would explain the wider gap on the JE as well? Just spit-balling here as this is the 1st I've heard of that. Would be interesting to know the theory behind it.

« **Reply #12 on:** April 15, 2015, 07:31:15 PM »

Subscribed

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« **Reply #13 on:** April 17, 2015, 09:58:53 PM »

All good stuff boys! I just ordered a set of sealed power rings for my block should get them in a few days haven't been on here for a while been working my ass off haha I'm gunna get info for that ring set and it makes sense to lean more towards a little extra than have a major problem on down the road .

« **Reply #14 on:** April 17, 2015, 10:06:42 PM »

Ps I decided to go w a diff ring thats,why I have em on order again lol spend that money ha

« **Reply #15 on:** April 26, 2015, 11:49:24 AM »

Ok so I got my rings in. Same ones so I'm going with them haa must be a sign anyhow I have .022 for my top and .019 fir my second which fits one of the comments here maybe I'll shoot for getting my second at around 022 as well that's pretty middle of the road and would cause a problem I'd think

« **Reply #16 on:** April 26, 2015, 03:39:01 PM »

I can't find the Sealed Power documentation online and I can't seem to put my hands on my engine assembly records for the time being. From the Mahle catalog, since these are the last pistons/rings that I installed:

For .078 / .0625 / 1.5mm thickness - per inch diameter of cylinder bore

Top ring
.004 NA
.0045 NA race only
.005 N2O street
.007 N2O race only
.007 turbo/supercharged

Second ring
.0045 NA
.005 NA race only
.0055 N2O street
.0065 N2O race only
.006 turbo/supercharged

If you have a 4.1560 bore, gaps would be:

Top ring
.0166 NA
.0187 NA race only
.0208 N2O street
.0291 N2O race only

Second ring
.0187 NA
.0208 NA race only
.0229 N2O street
.0270 N2O race only

According to Mahle, "Most of the second ring gap recommendations are larger than the top rings. Recent testing has proven that a larger second ring gap increases the top ring’s stability allowing for a better seal. This larger “escape” path prevents inter-ring pressure from building up and lifting the top ring off the piston allowing combustion to get by. Many engine builders have reported lower blow-by and horsepower gains at the upper RPM ranges with the wider second ring gaps. Also, almost every new car made is using this inter-ring pressure reduction method to lower blow-by and emissions and to increase engine output."

Again, this is Mahle guidelines and Sealed Power are probably different. There are also discrepancies between manufacturers as to which gap (top or 2nd ring) is larger.

I also seem to recall that the gaps were opened up an additional .XXX per 100 horsepower of nitrous, but I can't find that number right now.

Good luck,

Joe

« **Reply #17 on:** May 03, 2015, 06:13:56 PM »

Well its a,short block now I left the gaps at 22 I'm pretty sure it will be fine. Maybe if this,was a crazy monster I'd have gone different. So my next question is everything turns over great no deep scratches in the cylander s no noise or scraping sound but I notice a faint faint almost pencil line in the cylander s I'm guessing this is the actual ring gap showing? Its not a scratch just more of a faint rub. Is that normal?

« **Reply #18 on:** May 03, 2015, 06:27:05 PM »

Did you deburr the ends of the rings after filing? Did you oil the rings and pistons before installing?

« **Reply #19 on:** May 03, 2015, 07:31:19 PM »

Quote from: Flusher on May 03, 2015, 06:27:05 PM

Did you deburr the ends of the rings after filing? Did you oil the rings and pistons before installing?

yes and yes I inspected them and made sure everybody freely moved and "clocked" the rings as,well. It appears the slight Shiney rub spot is at both sides so I'm guessing it's where the gaps are. I used w d 40 to lube up the cylander and the rings. I heard it helps them seat.....

« **Reply #20 on:** May 03, 2015, 07:33:15 PM »

Let me explain how slight it is lol u have to look through the reflection of the cylinder to catch the line. Like really closely look

« **Reply #21 on:** May 03, 2015, 08:50:28 PM »

Quote from: che77y on May 03, 2015, 07:31:19 PM

I used w d 40 to lube up the cylander and the rings. I heard it helps them seat.....

IMHO, WD-40 is too thin to properly prevent micro-welding of the rings to the bores and ring lands. I would also worry about it diluting your oil on first fire. I have always used the same oil as will be run during break-in to lube everything that doesn't specifically get assembly lube applied.

I have heard that sprinkling Ajax into the carb during break-in helps to seat the valves, but I would never know because I would never try that.

« **Reply #22 on:** May 05, 2015, 06:36:59 PM »

Quote from: Flusher on May 03, 2015, 08:50:28 PM

IMHO, WD-40 is too thin to properly prevent micro-welding of the rings to the bores and ring lands. I would also worry about it diluting your oil on first fire. I have always used the same oil as will be run during break-in to lube everything that doesn't specifically get assembly lube applied.

I have heard that sprinkling Ajax into the carb during break-in helps to seat the valves, but I would never know because I would never try that.

Knowing that opinions vary... I've used WD40 on anything from a 60hp Chey Luv pickup to a 700hp turbo small block... no problems

« **Reply #23 on:** May 05, 2015, 10:55:02 PM »

I couldn't do that to mine.

I couldn't be part of helping someone do that to theirs.

To each their own. Who am I to tell you how to build YOUR project? That is why I said, "In My Humble Opinion" instead of accusing anyone of doing something wrong. It is just that, MY opinion. I had to speak my peace.

My mentor always said, "I won't help you, but I will watch you do that to yours. And if you find a better way, I'm open to change."

My only intent was trying to save a brother some grief. I look at all the money paid for parts and machine work by myself AND others, then I read through the carnage threads...

Respectfully,

Joe

P.S. The last time someone told me to do something like this, I called my ring manufacturer (C&A) to ask. They said, "Get your parts back and walk away from that shop, whoever told you that is a F'n idiot!"

« **Reply #24 on:** May 06, 2015, 01:51:56 PM »

Well at least you called me an F'n idiot respectfully... so, uh... thanks?

I never claimed my way was "better" than yours or that you were doing it wrong so get off your high horse. All the money you and others spend at machine shops... thank you... as manager of a shop that's been around 71 years I appreciate your support of the industry. However, also as a guy who has been around the block a few times I have a clue about what I'm talking about from 1st hand experience, not just reading or talking to sales guys (which I also do but also have experience to take that all with a grain of salt). It's the inexperienced guy that sees only black and white, right or wrong. The true expert knows the shades of grey, and obviously that isn't you.

WD40 is fine for what he's doing for this particular application.

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