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 Post subject: Piston ring end gap
PostPosted: Thu Apr 22, 2021 10:20 am 
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4 BBL ''Hyper-Pak''
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Joined: Sat Dec 12, 2020 1:53 am
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Car Model: 1974 Dodge D100
Hello all,
So I am building my short block and am installing the pistons. The block is .060 over I have been checking the ring gaps and everything seems to be within spec besides two of my first compression rings. They measured about .025. The motor is naturally aspirated with a about 8.3 to 1 compression. Is this something I should be concerned over?
Thank you


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 Post subject: Re: Piston ring end gap
PostPosted: Thu Apr 22, 2021 11:42 am 
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Joined: Mon Oct 21, 2002 11:08 am
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Location: Blacksburg, VA
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Some people would probably agonize over that. Personally, I would just run it. The loss will be minimal.

What is the factory gap range spec again? Did your engine builder check and fit the pistons to the bores? Are the other ring gaps (2nd rings) for those cylinders in the factory range?

Lou

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 Post subject: Re: Piston ring end gap
PostPosted: Thu Apr 22, 2021 12:19 pm 
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4 BBL ''Hyper-Pak''
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Joined: Sat Dec 12, 2020 1:53 am
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Car Model: 1974 Dodge D100
Factory spec is .010 to .020. But I've heard of people running up to .030 with forced induction or nitrous. Yeah everything else seemed to be good. Just those 2. I assumed wider was better than more narrow.
I would assume they did, I got the pistons and rings from them. They had opened the 1st and 2nd ring packages to test them as well I assume.


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 Post subject: Re: Piston ring end gap
PostPosted: Thu Apr 22, 2021 1:23 pm 
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Turbo EFI
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Joined: Wed Oct 12, 2005 9:00 pm
Posts: 2077
Location: kankakee IL
Car Model: 80 volare, 78 fury 2 dr, 85 D150
Mine worked out to .012 on all the top rings and .020-0.024 on the 2nd rings and though within spec I was worrying about the gap on top rings being too snug. Running Mahle moly coated in mine, which was only opened up to 20-over, not the 60-over yours was


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 Post subject: Re: Piston ring end gap
PostPosted: Fri Apr 23, 2021 6:01 am 
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Should be just fine. The only thought I had was that the pistons may be too loose in the bores. You could double check their work with feeler gauges (IIRC), as per the factory service manual.

Lou

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 Post subject: Re: Piston ring end gap
PostPosted: Fri Apr 23, 2021 10:43 am 
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Turbo EFI
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Joined: Wed Oct 12, 2005 9:00 pm
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Location: kankakee IL
Car Model: 80 volare, 78 fury 2 dr, 85 D150
I dunno about the op, but mine ended up where a 0.002went in alongside the piston pretty easy, but a 0.004 wouldn't go at all. I'm sure I coulda forced/jammed it in.... Feeler gauges about a foot long, and slid in alongside the piston upside down from the top. Sticker and paperwork in the piston box said a thou-and-a-half was what they wanted, I'm a little over that. But the notes are straight and round, so it oughtta be alright.


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 Post subject: Re: Piston ring end gap
PostPosted: Sun Apr 25, 2021 12:37 pm 
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What kind of pistons OP? The hypereutectic (sp) require double the gap of forged or cast.

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 Post subject: Re: Piston ring end gap
PostPosted: Tue Apr 27, 2021 7:23 pm 
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4 BBL ''Hyper-Pak''
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Joined: Sat Dec 12, 2020 1:53 am
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Car Model: 1974 Dodge D100
I'm not sure how to test the clearance between piston and bore. Its pretty close. Definitely can't fit a .004 at least on the skirt sides. On the side with the piston pin, I can get moreI don't know I haven't tried but it seems like the gap tapers off from the skirt side and slightly gets wider as I move 90° to the pin side.
I belive they are just cast. I was told they were over sized factory replacements. Silvolites.


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 Post subject: Re: Piston ring end gap
PostPosted: Tue Apr 27, 2021 7:46 pm 
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Aren't Silvolites hypereutectic?

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 Post subject: Re: Piston ring end gap
PostPosted: Tue Apr 27, 2021 8:00 pm 
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Turbo EFI
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Joined: Wed Oct 12, 2005 9:00 pm
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Location: kankakee IL
Car Model: 80 volare, 78 fury 2 dr, 85 D150
I believe they are plain old cast.....I still have the paper that came with my new set. hafta look at it tomorrow.

and OP, many pistons are "cam ground" not perfectly round.
did you start the feeler gauge slightly first then slide the piston in while you also slid the feeler gauge?
Mine too,,,,,,, I could get a 0.002" in fairly easy alongside the piston, but a 0.004" was a "no go"
my long feeler gauge set skips 0.003" for some reason
sounds like they clearanced your cylinder bores, the same as mine.


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 Post subject: Re: Piston ring end gap
PostPosted: Fri Apr 30, 2021 8:44 pm 
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4 BBL ''Hyper-Pak''
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Joined: Sat Dec 12, 2020 1:53 am
Posts: 29
Car Model: 1974 Dodge D100
Yeah mine was similar. I found the box they are cast pistons.
First start is coming up. I gotta figure out proper break in. There is alot of opinions on oil and additives.


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