Looking for opinions on piston ring gap

MalcolmV8

Well-Known Member
Established Member
Joined
Mar 27, 2003
Messages
7,353
Location
Tampa, FL
Hey Guys,

Piston ring gap seems to turn into a complex subject. First off this is the card I got with my rings that give you guidelines to where you should be at.

IMG_5123.JPG


As you can see for a medium boost application of 15 to 30 lbs on E85 they recommend bore x .007. My motor is .020 over so my bore is 3.5720. If you take 3.5720 x .007 = 0.025 ring gap.

Well I've run 0.025 ring gap in the past and it tends to have a lot of blow by. It pushes a lot of oil out the valve covers. Even my turbo'd Honda's ring gap was .025 and it blew a lot of oil too out the valve cover. Like a catch can full a week when it was my daily driver.

I was asking around and some on similar setups/power as me say they run .020 upper and .022 lower. I wouldn't mind running that as I'm sure it'll have a lot less blow by but I'm concerned with going to small because of course if the rings expand and bind up you're tearing it all back apart and possibly reboring or looking for a new block depending on the damages.

Then comes the topic of how do you measure ring gap? and what about with or without torque plates?

The good news is almost everyone I spoke to measures it at the same depth. About an inch down the cylinder using a piston upside down to press the rings in square. Use either the wrist pin or an oil ring on the piston to act as a stop and keep the piston square in the hole.

The bad news is torque plates. Some say it makes no difference, but the majority of people say it does. My local machine shop says torque plates open up the hole about .0001 only. Problem is he also fed me so much other BS I don't know what to believe and what not to from him anymore.
Searching on google trying to find an answer I found everything from .0001 to .0004 and one guy said he even measured .0008 difference which seems extreme to me.

Some guys say if they're shooting for say .020 ring gap they'll just file to .018 or .019 because once the heads are torqued on it'll open it up to .020. While others actually file to .020 etc. Everyone has their own method.

So my point is when comparing ring gaps its become apparent to me everyone's doing it a little different and we're not even comparing accurate numbers.

Thoughts?
 

SlowSVT

Well-Known Member
Established Member
Joined
Aug 7, 2004
Messages
8,272
Location
Los Angeles
I get nervous about tightening up the ring gap. Get that wrong and the block gets another visit to the boring bar. I think .025 gap top ring and .020 on the second ring is fairly standard on this engine. I don't have any experience with E85 which may allow you to pull the gap "in" a bit. Using a torque plate to gap the rings can't hurt but I wouldn't loose sleep over it even more so with an iron block. If it changed the gap reading by more than .001 - .002 the effect on the ring gap would be the least of my concerns.

Have you considered a gapless 2nd ring?
 

MalcolmV8

Well-Known Member
Established Member
Joined
Mar 27, 2003
Messages
7,353
Location
Tampa, FL
I decided to call Total Seal tech support and see what I got. Calling any manufacture's tech support is always hit or miss. You either get a dedicated knowledgable person who's been in the industry for many years who's very well versed and experienced in the industry or a phone monkey they hired to answer phones that doesn't know jack. I was very pleased to get type A.

He did not feel I should be getting much blow by at .025 and felt other factors were probably in play. The conversation of gapless 2nd ring came up. Something I had initially not even considered because my machine shop told me only for low HP N/A motors. Total Seal said that's complete BS and that 80% of all the rings they sell are gapless. He recommends only a 2nd ring been gapless on the street because the motor will pull so much vacuum with no ring leaks that you'll be sucking oil by the valve guides/seals and every where else possible unless you have very good valve job etc. He said motors that idle at 18 inches of vacuum will jump to about 24 inches of vacuum by going gapless rings. That's huge.

So by doing my 2nd ring gapless I'll drastically cut down on blow by, increase hp and efficiency a little too. Seems like a win win. $140 to purchase a gapless 2nd ring set or send back the set I have now with $90 and they'll convert them (or swap them out or however that works) and have them back to me in 24 hours. I think I found my answer :)

He also said he owned his own machine shop for 30 years and in his experience filing ring gaps without torque plates only opens up the gap .001. So if I'm shooing for .025 he said file to .024 and you're good.
 

SlowSVT

Well-Known Member
Established Member
Joined
Aug 7, 2004
Messages
8,272
Location
Los Angeles
Yea, I consulted Total Seal before I purchased them. I think I have an iron top ring and a SS gapless 2nd.

Moving the gapless to the 2nd groove will also protect the 2 piece ring better not directly exposing it to the heat and combustion pressure.
 

MalcolmV8

Well-Known Member
Established Member
Joined
Mar 27, 2003
Messages
7,353
Location
Tampa, FL
Nice. I have a steel top ring which is what was suggested to me for high HP. My rings are also moved down the side of the piston some .050 (custom ordered pistons) I believe to reduce exposure to combustion.
 

01yellercobra

AKA slo984now
Established Member
Joined
Oct 5, 2005
Messages
21,128
Location
Cali
I had the stainless upper and gapless second ring in my big bore set up. IIRC the gap was .025 top and .022 second. Only oil issue I had was the leaks from gaskets. With stock heads and Ford GT cams my vacuum was 21 or 22" on my boost gauge.
 

MalcolmV8

Well-Known Member
Established Member
Joined
Mar 27, 2003
Messages
7,353
Location
Tampa, FL
I had the stainless upper and gapless second ring in my big bore set up. IIRC the gap was .025 top and .022 second. Only oil issue I had was the leaks from gaskets. With stock heads and Ford GT cams my vacuum was 21 or 22" on my boost gauge.

Appreciate the feed back. It sounds like the way to go. I already mailed back my 2nd set of rings to Total Seal for conversion :)
 

MalcolmV8

Well-Known Member
Established Member
Joined
Mar 27, 2003
Messages
7,353
Location
Tampa, FL
OK more confusion. So there's a mod motor group on FB with thousands of "smart" guys or many who profess. I don't know them of course, perhaps some of them are really smart?

Anyhow they're telling me 2nd gapless ring is a big no no. It should be top ring only that's gapless and 2nd ring standard gap. They say a 2nd ring been gapless causes a pressure build up between the first and 2nd ring causing the top ring to flutter and you loose power.
 

NastyNate420

Member
Established Member
Joined
Mar 17, 2009
Messages
930
Location
Jersey Shore
OK more confusion. So there's a mod motor group on FB with thousands of "smart" guys or many who profess. I don't know them of course, perhaps some of them are really smart?

Anyhow they're telling me 2nd gapless ring is a big no no. It should be top ring only that's gapless and 2nd ring standard gap. They say a 2nd ring been gapless causes a pressure build up between the first and 2nd ring causing the top ring to flutter and you loose power.

I have heard this as well. I dont have any real world experience tho.
Hopefully someone who does will chime in.
try searching on yellowbullet.com
 

SlowSVT

Well-Known Member
Established Member
Joined
Aug 7, 2004
Messages
8,272
Location
Los Angeles
OK more confusion. So there's a mod motor group on FB with thousands of "smart" guys or many who profess. I don't know them of course, perhaps some of them are really smart?

Anyhow they're telling me 2nd gapless ring is a big no no. It should be top ring only that's gapless and 2nd ring standard gap. They say a 2nd ring been gapless causes a pressure build up between the first and 2nd ring causing the top ring to flutter and you loose power.

Malcolm

I am no expert on piston ring design but this one has me scratching my head.

The rings rely on the sudden combustion pressure which forces the ring to the bottom of the land where the gas pressure can get behind the ring and force it to seal against the cylinder wall. Put the gapless ring on top and the lower 1 piece ring below it won't get as much blow-by pressure to seal it. Having two .75 mm rings stacked on top of one another won't be as robust or transfer heat to the cylinder wall as well as a 1.5 mm one piece ring under the punishment of a supercharger. I don't ever recall anyone (including Total Seal) advocating running a gapless ring in the top slot in a supercharged engine. Take two oil control rings that sandwich the wavy separator thingy and you pretty much got a 1.5mm gapless ring and this tech thinks that should take the brunt of the combustion protecting the fat 1 piece ring below it.
 

Nightmare302

OhChuteRacing Owner
Established Member
Joined
Jan 11, 2004
Messages
1,824
Location
Lawrence Kansas
I have heard this as well. I dont have any real world experience tho.
Hopefully someone who does will chime in.
try searching on yellowbullet.com

I'm in the same boat, I have zero proof but have been "told" by "experts" that I trust. However, who knows at this point. I've found my own way so far on my build lol.
 

MalcolmV8

Well-Known Member
Established Member
Joined
Mar 27, 2003
Messages
7,353
Location
Tampa, FL
Malcolm

I am no expert on piston ring design but this one has me scratching my head.

The rings rely on the sudden combustion pressure which forces the ring to the bottom of the land where the gas pressure can get behind the ring and force it to seal against the cylinder wall. Put the gapless ring on top and the lower 1 piece ring below it won't get as much blow-by pressure to seal it. Having two .75 mm rings stacked on top of one another won't be as robust or transfer heat to the cylinder wall as well as a 1.5 mm one piece ring under the punishment of a supercharger. I don't ever recall anyone (including Total Seal) advocating running a gapless ring in the top slot in a supercharged engine. Take two oil control rings that sandwich the wavy separator thingy and you pretty much got a 1.5mm gapless ring and this tech thinks that should take the brunt of the combustion protecting the fat 1 piece ring below it.

Russ I don't claim to know the specifics either but everywhere I'm going now I'm finding gapless top ring only. 2nd ring gapped equal or bigger to top ring. Pressure build up between rings appears to be a real thing and causes the top ring to flutter or loose seal.
Another issue I've seen is keeping the oil down and prevent any from entering the combustion chamber and causing detonation. Apparently a gapless top works perfect for that too as the 2nd compression ring essentially doubles as an oil ring too.


Yup basically the same info I'm finding too. Gapless top ring. It leaves me confused why the Total Seal tech was telling me 2nd ring gapless. Unless he was just having an off day and said the wrong thing but wow what a mistake to make. I tried calling back today but they're closed so I'll have to wait till Monday.
 

SlowSVT

Well-Known Member
Established Member
Joined
Aug 7, 2004
Messages
8,272
Location
Los Angeles
Russ I don't claim to know the specifics either but everywhere I'm going now I'm finding gapless top ring only. 2nd ring gapped equal or bigger to top ring. Pressure build up between rings appears to be a real thing and causes the top ring to flutter or loose seal.
Another issue I've seen is keeping the oil down and prevent any from entering the combustion chamber and causing detonation. Apparently a gapless top works perfect for that too as the 2nd compression ring essentially doubles as an oil ring too.



Yup basically the same info I'm finding too. Gapless top ring. It leaves me confused why the Total Seal tech was telling me 2nd ring gapless. Unless he was just having an off day and said the wrong thing but wow what a mistake to make. I tried calling back today but they're closed so I'll have to wait till Monday.

Malcolm

I have no experience with gapless rings but did my homework before deciding whether or not to run them. In the end I came away with the impression the advantages outweigh the disadvantages in most situation for our intended use. This pressure build-up between the lands seems plausible but what is the bottom ring have left to do while the 2 thin stacked rings are taking the brunt of the heat and pressure? There is more to this story placing the gapless ring in the top land in this engine which has a few of it's own downsides in my opinion.

Pose the question in mod fords. I am sure Ed Eshaider will chime-in. I've discussed this topic with Ed more than a few times. He has a lot of first hand experience running Total Seal gapless rings and I don't think he will advocate running them in the top slot in a supercharged application on a street car.
 

MalcolmV8

Well-Known Member
Established Member
Joined
Mar 27, 2003
Messages
7,353
Location
Tampa, FL
I thought I'd come back and update with my experience with gapless rings for others that may be searching on the subject. I went with a gapless top ring.

Pros - It seals so well. I quite literally get 0% leak down.

Cons - It seals so well. Since day 1 of firing up this motor it's burnt oil, lots of it. I'm talking about 1 quart every 250 miles or so. Piston tops are black, exhaust looks like diesel soot, O2 sensors get trashed to non working in about 800 miles, plugs look oily, wet on threads even on a few of them.

I pulled the blower / intake (No PCV system, only breathers on valve covers) and the intake runners were covered in oil. The intake valves have had so much oil on them that in approximately 800 miles there's oil caked on them like an old oil burning engine would. I called Total Seal and they said the vacuum produced the the gapless rings is so strong it will pull the oil right past the valve guide seals if they're not in impeccable condition. My heads were just serviced and worked on at the engine build. Valve job, new exhaust seats, ported and of course new seals. None the less I began stripping things down and painstakingly changed all 32 valve seals in the engine bay. I cleaned the head thoroughly with brake cleaner and compressed air and installed each new FelPro seal with a dab of silicon to seal the base and prevent oil from been sucked between the guide and the head.

The results? Not much changed. Did an oil change, topped up to full on dipstick and did approximately 260 miles and oil is just barely marking the bottom of the dipstick. I called Total Seal again and they now feel its my lack of PCV system. They say the 4.6 has a very small crank case area and the cavitation caused by the pistons suspends a great quantity of oil vapors in the air that will land on the cylinder walls and is more than the oil rings can handle. This causes it to go into the combustion chamber and burn. Total Seal feels that if I re-install the PCV system the oil burning problems will go away. I considered purchasing an electric vacuum pump and attaching to my valve covers but I'm not convinced this will do much of anything. The reason I deleted the PCV is because of the recirculated oil that gets into my blower's intercooler reducing heat transfer efficiency.

So I started searching google for gapless rings and oil burning and loan behold there's no shortage of links or complaints. So I started reading the many forum threads and info I could find. In the process I learned a lot more about how piston rings work than I previously knew and about how the combustion pressure actually pushes the ring outwards against the cylinder providing the pressure or seal for that ring. I also read up links and info on how into today's engines the 2nd compression ring is only 5 to 10% compression control and 85 to 90% oil control. Interestingly enough I found information that says the gapless top ring seals so well no pressure gets by it and the 2nd ring has no pressure to expand it out and press against the cylinder. Thereby rendering that 2nd ring's oil control useless and making you burn oil.

I found some theories and suggestions of using a Napier 2nd ring due to the cut design (looks like a claw with a reservoir) to aid in the oil control when the gapless top ring is not providing any pressure to the 2nd ring. It was just a theory though and could not find anyone who had tested it and confirmed success.

So at this point I'm pretty disappointed in my gapless top ring experience and will probably need to tear this motor back down and hone the block and re-ring it with conventional rings to fix this oil issue.
 

Quick Strike

Well-Known Member
Established Member
Joined
Sep 27, 2003
Messages
2,067
Location
PA
Malcolm, Have you done a leak down test on this engine? I m just wondering if the rings ever seated or if the machine shop finished the cylinders correctly for your rings.

I know crankcase evacuators really helped with pressure in my old NA big block. They work better with open headers and I know you are dealing with metered air here. Maybe a vacuum pump/separator would help more then you think if it is a pressure issue and not a ring seal issue.
 

MalcolmV8

Well-Known Member
Established Member
Joined
Mar 27, 2003
Messages
7,353
Location
Tampa, FL
Malcolm, Have you done a leak down test on this engine? I m just wondering if the rings ever seated or if the machine shop finished the cylinders correctly for your rings.

I know crankcase evacuators really helped with pressure in my old NA big block. They work better with open headers and I know you are dealing with metered air here. Maybe a vacuum pump/separator would help more then you think if it is a pressure issue and not a ring seal issue.

Leak down is 0%. The rings are seated and sealing amazingly well. I believe the problem to be the top ring not allowing any gasses or pressure to pass it and push the 2nd ring out against the cylinder. Hence no oil scraping from that 2nd ring. A vacuum pump wouldn't fix this.
Juiced46 apparently has this problem and tried rebuilding with different solutions to address it and make the gapless rings work and never could come right and gave up on them according to a response I got on mod fords. I'll shoot him a PM and see if he can chime in.
 

01yellercobra

AKA slo984now
Established Member
Joined
Oct 5, 2005
Messages
21,128
Location
Cali
Something reading your post just reminded me about. I ran my big bore set up NA for about a year. Around 2010-2011 IIRC. During that time I went to a dyno day. During the decel it shot out a decent amount of blue smoke. Enough I got concerned. When I got home I did a full compression test and every cylinder was over 180psi. I figured something happened with the PCV system so I deleted it. No one driving with me ever said anything about smoke like that again. So I figured it was fixed. Maybe it was the issue of creating too much vacuum and sucking the oil past the seals? My heads were rebuilt before I assembled the engine.

Now I'm feeling bad for recommending the gapless set up.
 
Last edited:

Users who are viewing this thread



Top