Piston ring spacing

Frank Miller

Frank Miller

Well-known member
Just one of those nagging questions in my head. I have always read that you should not line up the ring gaps. I also have read, although not in a Ford manual, that you should keep the gaps off the thrust areas. That part would make sense but I was thinking any pressure escaping through the top ring will create a a fairly equal pressure in the chamber between the first and second rings. While I would never put an engine together with the gaps lined up I was wondering if anyone ever did or heard of a problem because it was done? Is the spacing more for piston stability? I figure there are people here with more engineering knowledge that I have that might make sense of this.
 
Old Smokie in his book said 4 Oclock and 8 Oclock for the top rings. I've been doing that for years and so far never had any problems. I'm sure there are many other ways to do it as well.
 
You stagger the gaps accordingly as per various types of info.After the engine is running the rings slowly rotate in the bore due to the honing pattern left on the walls.The statement about gap's at the thrust side really doesn't hold water as the rotation will at some point in time have a gap that is indeed at a thrust side.

R
 
So given that why stagger them at all? Or care about a starting position. I searched the web and could not find any explanation for the reason for staggering them.
 
Frank Miller said:
So given that why stagger them at all? Or care about a starting position. I searched the web and could not find any explanation for the reason for staggering them.
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I think you have answered your own question. :D

Or the age old answer that's the way we always do it.

R
 
If the rings start out lined up the compression will be wishy washy for a while plus you stand a chance of slotting at the gaps if the engine is run hard. The heat escaping at that point can groove a cylinder or piston if it stays that way too long. Why take that chance after doing all the hard work? If they align themselves running, there isn't much to be done about it but during assembly there sure is something that can be done. I'd stagger them.
 
Will the compression be wishy washy? The area of the openings stay the same. They will just be slightly further apart. I thought about them grooving the cylinder but they would need to be lined up withing about .020 for that.

As Ronnie said that's the way we always do it. I guess there are a few other things I do for the same reason. No time or money to experiment. Especially when it is just as easy to do it either way.
 
Ronnie, Thanks for finding that. Very interesting how minor the importance of end gaps on new rings. This is a classic example of how something we had done since the beginning of the combustion engine is not really that necessary. No one needs to abandon the practice or their preferred method because it does not increase the time for assembly but if someone forgot to do it there is no need to ter it back down. I do like to check all rings in the bore to ensure I have the right size. And I will continue to stagger them because that is how I've always done it.
 
Fe26 said:
A free burial at sea, how could one refuse...;):)
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Isn't that a classic one hard not to chuckle at that.I can't say that I have heard that one before.It is a keeper if I can remember it."LOL" :D

Nothing like a great sense of humor.We need all we can get.

Regards

R
 
I've been gapping mine at 4 and 8 o'clock for 50 years and have never had a problem. Probably will keep doing it. If one of you adventurous guys want to put around $2000 into your rebuild and line up the gaps we would all be interested in the outcome. We'll be behind you all the way - way behind!
 
Ronnie - Very interesting article in the link you posted. The logic is impecable and certainly is contrary to what many of us were taught.
 
Some folks overthink things right into the ground. Rings wear and eventually there is blow by. The whole idea about rebuilding an engine is to make it last as long as possible. I work in an industry where we take compression tests every 100-hours or one year (whichever comes first). When the compression is low on a given cylinder, we don't just take it off right away. If there is no evidence of valve leakage which can be audibly noted at the air intake or exhaust pipe with 80 psi being piped into the cylinder, there will usually be pressure comming out the crankcase vent. We run the engine again enough to get it good and warmed up then we shut down and do another compression test. If it is back up in the normal range we go on down the runway with it. If it is still low, (less than 65 psi with 80 psi input or 15 psi split with any of the other cylinders) we then take the cylinder off and repair it.

I've removed cylinders and put the rings back in the bore and found the gaps to be a lot more than they were when we sized them to fit at overhaul. The gaps grow with wear and ring gaps do align at times but seldom stay that way for long. Rings are generally replaced because they are worn out or broken not because of the gaps. If a person wants to purposefully align the gaps at overhaul, be my guest but a gas will pass through the path of least resistance and cause a small amount of compression leakage. Small as it may be, it's still a leak. Why not at least start out with minimal leakage then let natural accurances take there course. Break in is an important step in the life of an engine. If the rings start wearing in with staggered gaps maybe they will stay that way longer. How fast they turn or how long they stay aligned are unaswered questions and they are questions that the science hasn't answered yet. At least not to my satisfaction.
 
I think you missed the point. The article ronnie posted dispels a lot of myths. You should read it. My understanding is that the larger end gaps are not responsible if the ring is sized properly. When they get worn they lose their force against the cylinder wall which is responsible for the blow-by.
 
Piston rings don't really start out with a lot of force against the cylinder wall. Some rings are designed to apply more force during the compresion stroke due to their design and the piston design. Wear does cause blow by. Cylinder wall wear, piston wear, and ring wear. Best you can hope for is that they all wear evenly and slowly. Or at least as slow as possible given the ambient conditions. On the question about stabitlity, the rings don't provide much stability. Most of that is provided by the skirt.
 
rotorwrench said:
Piston rings don't really start out with a lot of force against the cylinder wall. Some rings are designed to apply more force during the compresion stroke due to their design and the piston design. Wear does cause blow by. Cylinder wall wear, piston wear, and ring wear. Best you can hope for is that they all wear evenly and slowly. Or at least as slow as possible given the ambient conditions. On the question about stabitlity, the rings don't provide much stability. Most of that is provided by the skirt.
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The oil ring is the biggest offender of drag in all passenger car engines.Most if not all passenger car engine designs now have incorporated a new low tension oil ring that is very efficient and has removed the greater amount of drag and friction,due to their new design.And as well is able to have better oil control.Cylinder wall finishes are now more stringently adhered to also reduce drag.The manufactures have also gone to narrower metric ring packs to help in reducing drag.

R
 
Awhile back I read comments in a cycle magazine by a fellow who used to race the old Triumph triples. He would find the ring gaps aligned when he tore an engine down for rebuild. He attributed this to cylinder distortion when hot, especially the middle cylinder. It seems the cylinders would go oval when hot and since ring tension against the cylinder wall is not even (because of the gap), the ring gaps would migrate to one particular position in the oval cylinder (I can't remember if it was the large part of the oval or the small part.) Think I'll see if I still have the article tomorrow.
Plus, I'm willing to assemble my next engine with the gaps aligned on the compression rings. I'm not sure about the three-piece oil ring. Having the expander ends and both rail gaps all in a line may not keep the expander ends butted together properly. Then again, it fits so close together in the cylinder there's probably not enough room for anything to shift out of place.....Thinking about it, why not line up all the gaps in half the cylinders and stagger them in the other half?!! That's what I'll do! Then run a leakdown check on the engine stand and again after a few thousand miles of run time.
 
My theorey is when any pressure is put through a ring gap then yhe space below it is at that pressure. Pressure will be released as the gap in the lower ring allows. Like turning on a faucet to a hose filled with water. Whether it is 50 or 75 feet long the water will pretty much flow at the same time. I know there are friction losses in the hose but I do not think you would notice a significant difference.
 
40 Deluxe said:
Awhile back I read comments in a cycle magazine by a fellow who used to race the old Triumph triples. He would find the ring gaps aligned when he tore an engine down for rebuild. He attributed this to cylinder distortion when hot, especially the middle cylinder. It seems the cylinders would go oval when hot and since ring tension against the cylinder wall is not even (because of the gap), the ring gaps would migrate to one particular position in the oval cylinder (I can't remember if it was the large part of the oval or the small part.) Think I'll see if I still have the article tomorrow.
Plus, I'm willing to assemble my next engine with the gaps aligned on the compression rings. I'm not sure about the three-piece oil ring. Having the expander ends and both rail gaps all in a line may not keep the expander ends butted together properly. Then again, it fits so close together in the cylinder there's probably not enough room for anything to shift out of place.....Thinking about it, why not line up all the gaps in half the cylinders and stagger them in the other half?!! That's what I'll do! Then run a leakdown check on the engine stand and again after a few thousand miles of run time.
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The rings will indeed align themselves in a out of round bore and they usually stay that way.The ring design is usually what determines this.The tips of the ring are referred to as the points.Some manufactures have what is called positive points or droops which actually to a small degree exert outward in there installed condition due to this design.With this design type as the rings rotate and the points come to the out of round cylinder they align there and usually remain there as the points are now in the middle of the oval to speak.In order to rotate any further the ring points now have to bee compressed to travel further this is now preventing the ring from rotating any further.There are also some rings that have negative points and they droop inward to a small degree when compressed.Many times during the tear down of an engine when looking at the ring face at the points you can observe a wider wear pattern at the points due to the positive style droop of the ring.This wear pattern is harder to see when the rings are worn to a full face contact.The opposite condition is observed with negative points. These conditions have been observed at the large ring plants ( Hastings Sealed Power or Perfect Circle)as they all use research and development dynos that run engines to develop new ring styles.The world of ring design has come a long way from the day of the birth of Henry's first flat engine.

R
 
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