forth ring ?????

john mullen

john mullen

Senior Member
I am installing new 4 ring pistons in a 8rt .080 over. Can I loose the bottom oil ring or is it needed for stability. I know friction is heat and want to have less if possable
 
Pistons designed for it definitely need it. Three ring pistons are available but are expensive in the smaller sizes. There are some cast 3-ring types above .125 oversize but none below that aren't forged to my knowledge.
 
I have 3-3/8 4 ring pistons in my dragster, left off the bottom ring. Ran it hard for 2 yr's. 5500rpm every run. not a sign of blowby. Walt
 
the forth ring is to set the skirt clearance, if you don,t use it you will have to much clearance and will probably make a noise and wear the lower part of cylinder
 
Just leave the 4th ring off. It is an extra oil control ring and is redundant. It has no effect on skirt clearance, piston stability, etc. You and the engine will never notice the difference.
 
There is NO piston stability gained from a 4th ring. The 4th ring does NOT set piston clearance. It was for oil control back when ring technology was not what we have now. Think about it: Rings float in their grooves so cannot exert any "stabilizing" effect on the piston. To the contrary, the piston stabilizes the rings!
The three piece oil ring made that 4th ring obsolete and unnecessary many, many years ago!
Look at modern engines: No 4th ring in sight anywhere. 5W-30 or even 0W-30 oil instead of 30 or 40W. Much shorter connecting rods, so greater side loading on the piston skirts, which theoretically increases piston rocking, and thus poor oil control. 6,000-10,000 miles between changes instead of 2,000-3,000 miles. Yet, these new engines routinely go well over 200,000 miles and still do not need any oil added between changes.
Bottom line, toss out that 4th ring unless you insist on using a NOS ring set from the 30's or 40's.
 
Piston design had more to do with making the 4th ring obsolete than the ring design. Ford engineers changed designs on the pistons as technology allowed. They started with steel pistons due to reliability problems with the aluminum castings that were having problems in the infancy of aluminum use. Aluminum expanded faster than steel so they had a problem with that. Split skirt designs helped solve that problem but the length of the skirt caused problems with the amount of oil film that was being moved around that couldn't be controled by one oil controler ring. The 4th ring was a compromise that has lasted to this day for the small diameter long skirt piston designs.

Modern technology has solved the expansion problems but design changes have never caught up with an engine that is considered to be obsolete by 99% of American corporate bean counters.

Running without the 4th ring will function as was already mentioned but it is a lot like running any race motor. Close tolerance fit is not always desired when running an engine flat out and oil control can be less than that of a motor being dogged around town. For every day driving and reliability it would be advisable to stick with the time tested design unless technology steps in and provides an adequate solution. If a person wants to take the time to build a solid reliable motor, why not utilize a piston that is designed for that purpose rather than take the risk of having problems.
 
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Why do Silvolite, Sealed Power Egge and others still make 4 ring pistons today??They are definitely not nos. Both sealed power,grant,hastings and perfect circle all still manufacture 4 ring sets for that 4 ring piston.You have to fill the groove with a ring.
 
40 Deluxe has very clearly stated the underlying rationale for deleting the 4th ring. In addition, good engine assembly practices will eliminate excessive oil throw onto the cylinder walls. So, it is very important to pay attention to rod big-end clearances, especially side clearances. Also, a windage tray could be added but that's probably overkill.
 
What was not mentioned in the rational was the length of the skirt on most modern engines as well as the bore diameter. Modern pistons have very short skirts and bore diameters are generaly a little larger.

Modern pistons could be made for a flathead with standard bores clear back to the 221 with 3 1/16 bore but no one makes them. Only the 3 5/16 & larger bore types are currently manufactured other than the forged type 3-ring pistons. The forged ones require a good bit of clearance with the cylinder wall due to the expansion coeficient of forged aluminum.

The amount of oil that is splashed on the cylinder walls is hard to control, especially when you have the piston squirt type con rods.
 
Ronnie said:
Why do Silvolite, Sealed Power Egge and others still make 4 ring pistons today??They are definitely not nos. Both sealed power,grant,hastings and perfect circle all still manufacture 4 ring sets for that 4 ring piston.You have to fill the groove with a ring.
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The piston manufacturers make stock replacement pistons and adhere to the original design, because its easy and that's what the market expects or accepts. Doing anything better might require some real engineering. For example, Egge makes both the early 3-ring flat-top 221 pistons and the later 4-ring 221 domed pistons. Egge also makes cast 3-ring pistons but only in the larger overbores, +.125 and larger.

This is an interesting discussion.
 
John R said:
The piston manufacturers make stock replacement pistons and adhere to the original design, because its easy and that's what the market expects or accepts. Doing anything better might require some real engineering. For example, Egge makes both the early 3-ring flat-top 221 pistons and the later 4-ring 221 domed pistons. Egge also makes cast 3-ring pistons but only in the larger overbores, +.125 and larger.

This is an interesting discussion.
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The question is about the 4 th groove being left open with no ring.We all understand why the piston design is where it is. The quality of castings and design has improved greatly no question about that. It still requires that the groove must have a ring installed in it on that style of piston.Not about a 3 ring piston or a 4 ring piston and their advantages.It not as simple as it appears to just eliminate a ring and leave the groove empty because it is presumed to have no effects on engine performance.
 
The piston manufacturer decided that the design of the piston required 4 rings. If you know more about the design of the piston than the engineer that designed and tested the piston in the engine, then leave out the unnecessary rings.

If you have to ask the question, you should install all of the rings.
 
TomO said:
The piston manufacturer decided that the design of the piston required 4 rings. If you know more about the design of the piston than the engineer that designed and tested the piston in the engine, then leave out the unnecessary rings.

If you have to ask the question, you should install all of the rings.
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Yup :D
 
Whoa! No one has explained WHY "You have to fill the groove with a ring.". What will happen if that bottom groove is left empty? The ring cannot stabilize the piston in any way. It has nothing to do with piston clearance. With a modern three piece oil ring, proper clearances, cylinder wall finish, etc. one oil ring will do the job.
 
I'm with 40 Deluxe. One modern three piece oil ring installed above the piston pin is all you really need. Why do all those companies still make four ring pistons? Probably because the molds and tooling are paid for. Everyone has an opinion, do what makes you comfortable.
 
I'm afraid the only acceptable explanation for the 4th ring would have to come from an engineer that is long dead. I'm no engineer but I have made mistakes in the past with oil control rings that cost me a lot of time to correct. Now days if I need information on something I get it from the manufacturer of the product at hand if possible. If not possible, then I ask someone who has done it before with acceptable results. Nobody likes to do anything over especially when it is a business arrangement.

If you must use only 3 rings on a 4-ring piston, go ahead. I just can't figure out the logic since the rings available aren't all that modern. It would just be easier to buy some 3-ring pistons to start with.
 
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