.030 340 With KB Hyper Pistons, Ring Gap Info

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340doc

340doc

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Ok, so I have a .030 over 340 going together. I'm used to using file fit rings. My question is for those who have used the KB Hyper pistons. How did your ring gap come in? Being that these pistons require a larger gap, did you have to file a standard .030 non file ring? According to KB's chart I need a .027 top ring gap. Thanks.
 
I don't like having such a big gap but hyper piston's require them. We built a 400 chevy and had a .028 gap and he overheated it and it scuffed the wall hard probably close to pulling the top off the piston. The piston is a lot smaller at the top putting more heat on the ring, that is why you need a big gap.
 
yep ring is closer to the top and the hyper materiel does not suck the heat out of the ring
you most likely can start with standard gap rings and file them
but more important (IMHO) is to get a ductile or better top
hyper gap when running is about the same as forged
 
I believe KB says .006" per inch of bore for naturally aspirated rather than the "usual" .004. More if it's going to be driven hard. So I'd go around .028 for the top, and probably .24 on the 2nd.
 
moper said:
I believe KB says .006" per inch of bore for naturally aspirated rather than the "usual" .004. More if it's going to be driven hard. So I'd go around .028 for the top, and probably .24 on the 2nd.
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Yes .0065 per inch of bore. I'm going with a moly ring. I'm hoping someone chimes in and can let me know if they had to file a regular .030 ring to hit those numbers. Otherwise I'm searching for a .035 over ring.
 
IIRC, yes we had to file the top KB moly rings that came with our .020" over KB 340 pistons. Piston-to-bore fit was set in the normal range fit for these pistons, nothing special.
 
nm9stheham said:
IIRC, yes we had to file the top KB moly rings that came with our .020" over KB 340 pistons. Piston-to-bore fit was set in the normal range fit for these pistons, nothing special.
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Thanks, this is what I was hoping to find out. Do you remember what the second ring was at?
 
I’m file fitting my KB243 rings a little bit. Just a hair more than suggested.
 
340doc said:
Thanks, this is what I was hoping to find out. Do you remember what the second ring was at?
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Sorry, not off the top of my head... I won't be able to get to our notes for at least a week to see if I made notes on that. I don't recall touching them....
 
I never even try and run the ring gaps down at the min spec with the KB hyper pistons.
I’ve used them a bunch of times, never any blow by issues.

They’d be at .030 if I was doing it.

.020-.022 for the second ring.
 
Wyrmrider said:
easier to get ductile in .035 over
just saying
cheap insurance
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I agree but I'm having a hard time finding a file fit ring for a 4.070 bore. The KB's take the stock size 5/64 ring, not the more popular 1/16 ring. I started another post about that.
 
PRH said:
I never even try and run the ring gaps down at the min spec with the KB hyper pistons.
I’ve used them a bunch of times, never any blow by issues.

They’d be at .030 if I was doing it.

.020-.022 for the second ring.
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Are you able to get by without the .005 over ring then?
 
340doc said:
I agree but I'm having a hard time finding a file fit ring for a 4.070 bore. The KB's take the stock size 5/64 ring, not the more popular 1/16 ring. I started another post about that.
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Cannot ANY ring can be a 'file to fit' ring LOL? Am I missing something here? Why not start with the standard KB rings for that piston in +.030? 4000AM8070 for moly top ring. (No ductile in that size in their catalog unfortunately.)

If you go with a .035" ring a stuff it into a .030" bore dimensioned for a hyper, that is going to be tightening the ring gap.... and (I think) would be increasing the ring tension over what is necessary.
 
340doc said:
Yes .0065 per inch of bore. I'm going with a moly ring. I'm hoping someone chimes in and can let me know if they had to file a regular .030 ring to hit those numbers. Otherwise I'm searching for a .035 over ring.
Click to expand...

Because the usual gap the stock replacement rings come with is based on the factory spec - either ring will work. A plain "+.030" ring will not need to be filed as much.
 
You can file standard rings, just set them to the recommend gap.
Make sure you have them a little more than KB recommends. Because your bore can have some taper.
 
.028 top ring
.018-.020 2nd

The top ring is spaced higher/away from the others...it gets the heat 95% .

However...It wont hurt adding .004 to the 2nd ring, so do it it however you like.
 
moper said:
Because the usual gap the stock replacement rings come with is based on the factory spec - either ring will work. A plain "+.030" ring will not need to be filed as much.
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That what I was wondering. I didn't want to buy a plain .030 ring set and find the gap too large. Standard ring gaps are usually large to make them error proof.
 
sireland67 said:
You can file standard rings, just set them to the recommend gap.
Make sure you have them a little more than KB recommends. Because your bore can have some taper.
Click to expand...
I know they can be filed, I just was worried about them coming in too big out of the box.
 
nm9stheham said:
Cannot ANY ring can be a 'file to fit' ring LOL? Am I missing something here? Why not start with the standard KB rings for that piston in +.030? 4000AM8070 for moly top ring. (No ductile in that size in their catalog unfortunately.)

If you go with a .035" ring a stuff it into a .030" bore dimensioned for a hyper, that is going to be tightening the ring gap.... and (I think) would be increasing the ring tension over what is necessary.
Click to expand...
Yes any ring can be filed. Most standard ring sets have a built in larger gap to make them error proof in various situations. I didn't want to buy a standard .030 over set and find the gap too big out of the box
 
340doc said:
Yes any ring can be filed. Most standard ring sets have a built in larger gap to make them error proof in various situations. I didn't want to buy a standard .030 over set and find the gap too big out of the box
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Interesting... I can't say I have found that to be the case for fresh bores, properly sized. They always seem come pretty close to standard spec.
 
nm9stheham said:
Interesting... I can't say I have found that to be the case for fresh bores, properly sized. They always seem come pretty close to standard spec.
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That's good to know. I'm gonna order the KB moly rings and hope for the best. Comments seem positive. Thanks to all!
 
340doc said:
That what I was wondering. I didn't want to buy a plain .030 ring set and find the gap too large. Standard ring gaps are usually large to make them error proof.
Click to expand...
Buy/use the ring sized for your bore, .030 over bore....030 over ring set, file fit them... there is plenty of room to open them up...the 2nd is usually just right or .002 tight.
If I'm reading what I think im reading...Do not use standard size rings on a .030 bore!
 
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