PDA

View Full Version : Piston rings



chevynut
03-09-2016, 08:01 PM
I'm not an expert on engine building by far and I need some new rings for my 502. It's a new crate engine and I'm replacing the rings, mostly due to the low-tension oil rings in these engines. The bores are standard size at 4.466" and are in excellent shape since the engine has never been fired. I plan to have the block honed with a torque plate as recommended by Total Seal in my discussion with them at SEMA.

I called Total Seal again today and discussed my application which is a good, strong, reliable street engine. I don't plan to race my car, unless it's in an autocross down the road someday. I have studied their various offerings and got some more insight into the pros and cons of each ringset.

We first discussed their "gapless" rings and they recommended a gapless 1st ring instead of 2nd ring. I asked how important the gapless feature was for my application and the response was that I'd gain a little horsepower, but it wouldn't be that meaningful for what I'm doing.

So that left their standard CR5750 ringsets. They have a CR5750 that is for a 4.466" bore. Then they have a CR5750 5 ringset that's the same rings, but are file to fit. I assume the 5 means they're 5 thousandths oversize.

The rep I talked to recommended file-to-fit rings to make sure all the end gaps are perfect. I'm not sure I understand the benefits of doing that when we're probably talking a couple of thousandths difference when all is said and done. Are the regular rings made to have a perfect end gap only if the bore is a perfect 4.466"? I'm sure there's a tolerance on that too, but I don't know what it is. I know a wide end gap causes some pressure loss, but how significant is it? If the gap is supposed to be 0.015" how much difference in pressure or horsepower is there if the gap is .020"?

Here's what Total Seal says about their gapless rings:

" Conventional style rings when newly installed will show leak down figures of 7% or higher these figures can quickly exceed 20% or higher after a surprisingly short period of time. Gaplessrings on the other hand when newly installed typically show leak down figures of 2% and lower and should remain the same throughout the life of the engine."

It sounds like a good idea for an all-out race engine where you want to squeeze every last HP out of it, but I'm not sure it's worth the cost for a street engine.

So do I go file-to-fit or not? It seems like a lot of work to file 32 individual rings if it's not really necessary. I want to do this right, but not get anal about it. ;)

Rick_L
03-10-2016, 06:14 AM
My one experience with the "gapless" rings years ago showed no improvement over normal rings. It did give better leakdown readings but I think that's just a mirage that makes you think the ring set is better than it is. I'll say this - I have no idea if they've changed the gapless design over the years. The ones I used were a standard ring that had been cut down with a step so that a thin oil ring type ring could sit on the regular ring.

As for filing the rings to a precise gap, I always did it on a race engine but never on a street engine. The effect of a tight ring gap is probably gone in 500-1000 miles or less. I don't know how much power a tight gap gets you, but I'd guess 0.25% or so.

I am confused as to their statement about normal rings opening up the gap faster than a file to fit ring. That doesn't make any sense.

FWIW you typically don't file to fit the oil rings. Only the top and 2nd rings. So there is only 16 to do.

The expander is what's critical on the oil ring. It's what gives the ring set its tension and drag - and that's what determines the amount of oil control.

markm
03-10-2016, 06:22 AM
Honestly, I doubt you are going to drive your car enough for any of this to matter. I certainly don't see you side steeping the clutch at 5000 rpm and shifting at 6500 rpm like I do at times. FYI, my 396 has stock replacement cast rings.

chevynut
03-10-2016, 07:48 AM
Thanks for the feedback. So the standard rings are probably the way to go to save time and still do it right. If I recall correctly when I file-fitted the rings on my Grizzly ATV I also had to do the oil rings because the gaps were below spec. I think they were Wiseco rings. I thought file-fitting was a pain in the ass but I did buy a ring file/grinder for it so I can do it if it makes sense.

You're right, I probably won't be dumping the clutch at 5000 RPM and the engine redlines below 6500. But I don't see what that has to do with the rings anyhow. It'll get to redline if I want it to with either choice. ;)

markm
03-10-2016, 04:15 PM
But I don't see what that has to do with the rings anyhow. It'll get to redline if I want it to with either choice.

My comment was intended to go along with this one from Rick

As for filing the rings to a precise gap, I always did it on a race engine but never on a street engine. The effect of a tight ring gap is probably gone in 500-1000 miles or less. I don't know how much power a tight gap gets you, but I'd guess 0.25% or so.

JT56
03-11-2016, 09:14 AM
Mine are file fit Total Seal with a steel top ring on my application. Your not running a power adder (nitrous or boost), so gapless makes sense.

chevynut
03-11-2016, 09:36 AM
Mine are file fit Total Seal with a steel top ring on my application. Your not running a power adder (nitrous or boost), so gapless makes sense.

JT, please clarify. Are you saying you recommend I go with their gapless rings? Why?

JT56
03-11-2016, 01:39 PM
For you application, I would do the gapless. A street application where tight seal is the most important. Less blow by. Most racing applications use file fit rings, so there can be less friction which is cuts down on hp loss. Also those engines that use power adders (nitrous and boost) it allows expansion of the rings when heat from nitrous or boost is inside the cylinders.

Rick_L
03-11-2016, 03:09 PM
Obviously more than one school of thought on this.

chevynut
03-15-2016, 06:26 AM
I've read a lot of stuff on the internet that says NOT to use gapless rings in the second groove of the piston, and that the second ring gap should be wider than the top ring gap to relieve pressure. Apparently this is a well-known thing (not to me). Also, most input I read says gapless top rings really don't help either....but they don't hurt. They do cost a lot more. So, I'll plan to use conventional rings.

I have another question....can I just keep the first and second rings I already have and just replace the low tension oil rings with standard tension? Someone posted on a different forum that you can buy rings individually. I don't know what brand of rings my engine has in it so maybe that's not a good idea to mix brands, and full Total Seal sets aren't that expensive at $140.

Rick_L
03-15-2016, 02:50 PM
I used to buy rings for race engines in separate sets for each location, but it's not that common for OEM stuff. Total Seal is probably one of the possibilities for that.

There's not really any style, design, or brand relationship between the top two rings and the oil ring set. On an oil ring you just choose bore diameter, groove dimensions, and standard/low/ultra low tension.

The recommended ring gap is determined by piston design and material. For instance, a hypereutectic piston warrants a bigger second ring gap, and forged piston warrants a smaller second ring gap compared to a typical stock piston. Usually the top ring is gapped at .004" per inch of bore diameter, but this too may vary. You need to find out if that engine has traditional OEM pistons, or hypereutectic. Or find what the factory shop manual says the gaps should be.

chevynut
03-15-2016, 05:07 PM
The pistons are JE. They're forged and there is a "JE700" on the underside.

So you're saying I could just buy a set of 8 oil rings and be fine? I'd feel better if I knew what brand rings they used in it so I knew what type and quality they were. Maybe I'll just sell the whole set on eBay as OEM GMPP crate 502 rings and see what I can get for them.

Now I have another dilemma. I asked the guys at the shop if I needed to balance the engine and they're not sure. I thought for sure they'd know. I have read that the 454 and 502 are both externally balanced (I know aftermarket cranks are available to internally balance them). I bought a GMPP flywheel for it and it has the OEM damper, and all other parts are OEM. The flywheel is made for the ZZ and RJ 502....do I need to get it balanced? It's another $175. :(

Rick_L
03-15-2016, 05:28 PM
A couple of comments on gapless rings and gap.

When I tried the gapless rings in the second groove, I was running .043" wide rings and gas ports in the top groove (race engine). No availability for gapless rings there. I felt that the gapless second rings masked the leakdown performance of the top rings, which was what really counted.

No matter the location, the "gapless" ring set needs to have two gaps set. Same guidelines as traditional rings. You basically need enough gap to keep the ends at the gap from butting under heat and pressure. When the gaps butt, you have big problems, the ring seal being the first.

I don't understand your concern about the OEM rings unless you just want to be sure that you don't duplicate what you had.

As for the balancing, internal vs. external balance does not matter. The engine still needs to be balanced to a tolerance. Chevy has never produced an OEM engine 454" or bigger that wasn't externally balanced. You have two choices on the balancing. Deluxe is to convert it to internal balance. Proponents of this say that although external balancing gets you correct rotational balance, the weights hung on the ends of the crank make it like a noodle, and placing the weight closer to the other rotating/reciprocating components avoids some of that. You will need one or more tungsten weights in each counterweight on the crankshaft, and it will cost you far more than $175. Your other choice is to have the shop "refine" the factory balance to a tighter tolerance. I don't think that's worth the money unless you change some components in the rotating assembly (rings don't count as a change).

chevynut
03-16-2016, 08:28 AM
When I tried the gapless rings in the second groove, I was running .043" wide rings and gas ports in the top groove (race engine). No availability for gapless rings there. I felt that the gapless second rings masked the leakdown performance of the top rings, which was what really counted.

I read a lot of stuff where guys who seem to know a lot about engines say a second ring that seals "too well" can allow pressure to build between the top and 2nd ring, causing the top ring to lift off of the piston groove and "flutter", losing it's seal. Apparently it's been proven to happen by researchers. So the common thinking is that the second ring gap should be larger than the first ring gap to prevent that from happening. That's apparently also why it's no longer recommended to use a gapless second ring.


I don't understand your concern about the OEM rings unless you just want to be sure that you don't duplicate what you had.

I really don't have a concern about the OEM top and second rings, only that I don't know what brand and quality they are. My intention was to address the oil rings, which I have been told are low-tension rings and need to be changed. I didn't know you could buy only the oil rings separately. I have no proof that they're even the original rings, except I was told this was a crate engine that's never been apart and never run and that looks to be the case as far as I can tell.

I don't want to have an oil-burner, and doing the torque plate hone and replacing the rings hopefully will ensure that I don't. The guy I talked to at the Total Seal booth at SEMA actually worked at GM and worked on the ZZ/Ramjet 502 and was very familiar with it. He convinced me I needed to do this and confirmed everything I have been reading over the years. He said GM wouldn't let them address this problem in this 502s. I just hope I can get the honing done without causing too much piston clearance or some other problem. I read that it can be done without affecting the bore size because the torque plate causes slight bulges into the bore which is what is being removed.


As for the balancing, internal vs. external balance does not matter. The engine still needs to be balanced to a tolerance. Chevy has never produced an OEM engine 454" or bigger that wasn't externally balanced.

Yes I have confirmed that the 502 is externally balanced as I thought it was. It kinda bothers me that the guys at the shop didn't know that. They're about the only shop in the area that does this kind of work and they have a good reputation. I have the original damper that came on the engine, but I sold the flexplate and bought a GMPP flywheel meant for this engine. I did some reading and found out that if the flywheel is made for the engine, you're okay with the balance.


You have two choices on the balancing. Deluxe is to convert it to internal balance.

Not going to happen. ;)


Your other choice is to have the shop "refine" the factory balance to a tighter tolerance. I don't think that's worth the money unless you change some components in the rotating assembly (rings don't count as a change).

That's what I've pretty much concluded after searching the internet for info yesterday...thanks for confirming that. Sounds like it would be a waste of money for my application but it couldn't hurt. I'll probably not do it unless the guys at the shop find some issue with the engine.

markm
03-16-2016, 09:11 AM
I find it strange you worry so much about choice of pistons and nothing about balance. At my friends shop all serious all serious builds of 400/454 are rebalanced internally.

chevynut
03-16-2016, 09:26 AM
To re-balance this internally would require a different crank, harmonic balancer, and flywheel. This engine is already balanced to factory specs...externally. This engine would have run just fine the way it was before I tore it down. I've already explained why I'm doing this...it's to try to minimize the possibility of oil consumption and to clean it up internally since it's been sitting so long. Not going to internal balance it.....period. Millions of engines run great externally balanced.