piston groove

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aaronk785

aaronk785

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I'm freshening up my 340. My top ring groove in the piston measures .083. Is this to loose for a 5/64 ring. Second groove is at about .079. Thank you.
 
I didn't even know they wore out like that, that's a shame.
 
That's less than .005" larger than 5/64. I don't know if that's out of spec, but it seems like a small amount of wear. Does anybody have the spec on it?
 
RustyRatRod said:
That's less than .005" larger than 5/64. I don't know if that's out of spec, but it seems like a small amount of wear. Does anybody have the spec on it?
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I’ll see if I can find the Chrysler spec because I believe there is one, but when the ring, especially that big, heavy one is that loose in the grove it looses seal every time the piston changes directions and it will just continue to beat the ring groove out of it. That’s why some of the power adder stuff has hard anodized top ring grooves.
 
Ok, the 73 FSM manual calls out .0015-.0040 for the compression rings and .0002-.0050 for the oil ring. EDIT: I see by the spec the OP is right on the high side. I’d have a hard time letting that go unless it’s just a dead stocker that won’t see a lot of miles or you just don’t have the money to change the pistons.


28F25016-19C6-49AB-8417-6EA5939656F5.jpeg
 
yellow rose said:
I’ll see if I can find the Chrysler spec because I believe there is one, but when the ring, especially that big, heavy one is that loose in the grove it looses seal every time the piston changes directions and it will just continue to beat the ring groove out of it. That’s why some of the power adder stuff has hard anodized top ring grooves.
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I'm not disagreeing. I'm wondering what the spec is. It stands to reason if the ring is 5/64, then the groove has to be bigger, because there is clearance. That's why I am wondering what the spec is and what the tolerance is.
 
RustyRatRod said:
I'm not disagreeing. I'm wondering what the spec is. It stands to reason if the ring is 5/64, then the groove has to be bigger, because there is clearance. That's why I am wondering what the spec is and what the tolerance is.
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See post 8. I tree’d you by...two minutes LOL.
 
I’ve read where guy have had the top re grooved bigger and used an oil ring as a spacer. So about .020 bigger. What do you think?
 
aaronk785 said:
I’ve read where guy have had the top re grooved bigger and used an oil ring as a spacer. So about .020 bigger. What do you think?
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If you can keep the groove flat and round when you machine it, then that would work. I would think that’s going to be almost as expensive as new pistons.
 
I guess 10 years of 7000 rpm shifts and 3300 on interstate adds up. They are just trw 2316 pistons. Think I will just get new pistons at .040 and have it rebored the extra .010 and start off fresh. I’m just a cheap *** some times.
 
That’s a good plan it will give you opportunity to go to a lighter piston and ring combo because, it sounds like it needs it.
 
Hi all. I just read an article by weseco pistons on ring grooves. They say you don’t want more than .018 behind the ring because it takes to long for the pressure to build and push out on the ring. The last several sets of rings I have bought have a narrower top ring horizontally. So now I have over around .040+ behind the top ring. They just started doing this awhile back. Just got my short block together and read this. Why would the ring companies do this. And should I worry about it.
 
aaronk785 said:
Hi all. I just read an article by weseco pistons on ring grooves. They say you don’t want more than .018 behind the ring because it takes to long for the pressure to build and push out on the ring. The last several sets of rings I have bought have a narrower top ring horizontally. So now I have over around .040+ behind the top ring. They just started doing this awhile back. Just got my short block together and read this. Why would the ring companies do this. And should I worry about it.
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Depends on what you expect. For me, I expect the rings to fit the grooves and not have all that wasted space behind the ring. The real seals by compression pressure dropping dow the face of the piston, hits the top of the ring and then goes across the ring to the groove where it gets behind the ring and forces the ring against the cylinder wall.

Gas ports (horizontal, vertical or gas ported rings) all allow the gas pressure to get behind the ring quick, to get the seal quicker.

Either the pistons are machined incorrectly (very unlikely IMO) or the rings are just cheap pieces that are low performance.

I’m not wired in a way that would allow me to let what you have slide. Many others would run them and never think about it.

You have to decide who you are and then live with it.
 
Yes. I wonder where I can buy full width rings. Sealed power and Hastings are the new style narrow top ring. Same part no. Just a different top ring. What is their thinking?
 
Just found KB makes a set with a full width top ring. Damn I don’t want to take my engine apart. Oh well at least it’s not in the car.
 
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