Ring sizing question
Thread Starter
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Senior User
Joined: Jun 2014
Posts: 446
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From: Denton, TX
Ring sizing question
Okay,
I’ve got a bit of a head scratcher. I took apart my 82 351w and while it’s apart decided to hone the cylinders and replace the rings. This engine has 92,000
miles on it and everything appeared to be close to spec. and in good shape so I just purchased some standard sized rings. After honing, the ring gap was .025 about 1/4 - 1/2 of the way down on all 8 cylinders. My manual says the gaps need to be .010-.020 so I decided to buy some rings that are .010” larger than standard, which I thought would put me right in the middle of specs.
Here is where it gets weird. The larger rings have no gap at 1/4 of the way down the cylinders, and that’s as far as I can get them. Same on all 8 cylinders. Zero gap whatsoever.
How could this be? I measued multiple times and have actually tried two different standard sets and two different oversized sets. Two different brands.
I know I’m missing something, but cannot figure out what it is. I would love to take the block and get it bored out but that’s not an option.
I’ve got a bit of a head scratcher. I took apart my 82 351w and while it’s apart decided to hone the cylinders and replace the rings. This engine has 92,000
miles on it and everything appeared to be close to spec. and in good shape so I just purchased some standard sized rings. After honing, the ring gap was .025 about 1/4 - 1/2 of the way down on all 8 cylinders. My manual says the gaps need to be .010-.020 so I decided to buy some rings that are .010” larger than standard, which I thought would put me right in the middle of specs.
Here is where it gets weird. The larger rings have no gap at 1/4 of the way down the cylinders, and that’s as far as I can get them. Same on all 8 cylinders. Zero gap whatsoever.
How could this be? I measued multiple times and have actually tried two different standard sets and two different oversized sets. Two different brands.
I know I’m missing something, but cannot figure out what it is. I would love to take the block and get it bored out but that’s not an option.
Moderator
Joined: Jan 2001
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From: Virginia
You need to buy rings that are the correct size, not oversize. If you want to file the gaps yourself, buy the proper size rings for the bore that are "file to fit". These are the proper size and are made for you to adjust the gap.
FTE Emeritus
Joined: Jan 2006
Posts: 2,288
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From: springfield Missouri area
Your thinking is off on the sizes. It is bore size(diameter of hole) so a .010 oversize is .010 inches bigger in diameter. So that would be like putting a 5 inch diameter stick in a 4 inch diameter hole. Bigger won't fit. You could always get a set of the gapless rings if they still make them, haven't looked for years. Total Seal is the brand. They don't have a gap. TOTAL SEAL PISTON RINGS
Thread Starter
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Senior User
Joined: Jun 2014
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From: Denton, TX
Thank you all for your help. As I am searching online trying to find some rings that are file to fit, I see some that have a ring thickness of 1.5mm,1.5mm, 3.0mm instead of the 5/64,5/64,3/16. I assume these are not acceptable to use with my factory pistons? The only file to fit rings I can really find that aren't 10 times the price are 1.5mm.
I am still not real clear on why the math doesn't work on the factory bore piston rings I tried vs the .010" larger. I realize that it is wise to get standard size and file them. However, in doing so, am I not just filing them to be a certain amount larger than the factory ring? If I had a .025 with the standard, shouldn't I have .015 with the rings that were .010 larger?
I am looking for the file to fit, I just don't understand the difference. I also see some rings that are 4.005. Are these file to fit?
I am still not real clear on why the math doesn't work on the factory bore piston rings I tried vs the .010" larger. I realize that it is wise to get standard size and file them. However, in doing so, am I not just filing them to be a certain amount larger than the factory ring? If I had a .025 with the standard, shouldn't I have .015 with the rings that were .010 larger?
I am looking for the file to fit, I just don't understand the difference. I also see some rings that are 4.005. Are these file to fit?
Thread Starter
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Senior User
Joined: Jun 2014
Posts: 446
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From: Denton, TX
Your thinking is off on the sizes. It is bore size(diameter of hole) so a .010 oversize is .010 inches bigger in diameter. So that would be like putting a 5 inch diameter stick in a 4 inch diameter hole. Bigger won't fit. You could always get a set of the gapless rings if they still make them, haven't looked for years. Total Seal is the brand. They don't have a gap. TOTAL SEAL PISTON RINGS
Obviously, the answer is no. But I do not understand why.
Fleet Owner
Joined: Jan 2004
Posts: 26,007
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From: Brentwood,CA
Simple answer, because to use .010 rings you need to bore the engine .010 over. I don't advocate DIY honing because you are not going to get the correct RA finish like you would on a sunken or similar machine. Use standard rings it's all you can do in your case. Also make sure to buy engine correct rings and don't get hard face moly rings they won't bed properly.
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Post Fiend
Joined: Feb 2008
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From: St Albert, Alberta
You can't use over sized and file them to fit as the arc of the ring is not the same as the arc of the bore. Using over size rings in a smaller bore will lead to uneven piston ring pressures which could result in broken piston rings and will result in uneven cylinder wall wear..
The correct way is to buy rings that need to be filed to fit. Even better is is to measure the bore and see what it is exactly and get the right rings.
You will gap the rings at the bottom of the bore which will have the least amount of wear and gap them tight .010" in your case, this will help cover up some of the bore taper...
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Thread Starter
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Senior User
Joined: Jun 2014
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From: Denton, TX
I am having trouble finding any rings that are file to fit that are the correct widths. Everything I am finding is 1.5mm instead of 5/64. I know those are very similar in size, but are they okay to interchange with factory pistons?
Thread Starter
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Senior User
Joined: Jun 2014
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From: Denton, TX
What are going to be the ill effects of just installing standard sized rings and going with the slightly out of spec gap? I do not have a lot of money to drop into this vehicle. I want it to run strong and be dependable, but its really just a town cruiser.
Fleet Owner
Joined: Jan 2004
Posts: 26,007
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From: Brentwood,CA
No not unless you want broken rings.
Post Fiend
Joined: Feb 2008
Posts: 5,831
Likes: 121
From: St Albert, Alberta
Here is some good info .
Hastings 139 Piston Ring 4" Bore Cast Rings Chevy, Ford, Chrysler, AMC | Northern Auto Parts
Hastings 139 Piston Ring 4" Bore Cast Rings Chevy, Ford, Chrysler, AMC | Northern Auto Parts
Moderator
Joined: Jan 2001
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From: Virginia
There may be a formula somewhere that you can plug in your difference in gaps, and figure out the bore wear. Like was said, consider the bottom good where the oversize ring was touching.
Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
Use standard iron rings in the standard size. Your ring end gap is what it is. You either go the full way and do a proper rebuild with machine work or do a re ring. In the case of the re ring I normally don't associate strong and dependable in the same sentence. Its Its normally done for vehicles you are looking to flip.