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Thread: ring gap questions
          
   
   

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  1. #1
    TOW'D is offline CHR Member/Contributor Visit my Photo Gallery
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    ring gap questions

     



    I'm rebuilding a 1973 B-20 4 cylinder push rod Volvo motor that was bored .030 over. Tough as nails old "tractor" motor- no overhead cam shafts or timing belts or aluminum heads to corrode- just good old cast iron.

    I just got the block back from the machine shop with new cam bearings and hot tanked. Rods were checked and didn't need new wrist pin bushings
    everything is looking good.

    so today I cleaned all the engine parts---installed the pistons on the rods
    and started checking the pistons/rings
    Deves rings
    after reading the installation sheet that came with the rings
    I was measuring the fit of the top ring in the piston and I could not get .006 to fit between the ring and ring groove so that piston was still good .

    Then I noticed that the ring is the same size as the top of the piston seems to me that the ring should be bigger diameter
    It was too late to call the parts place tonight-
    my piston tops are 89.5mm(little more than 3 1/2") and the rings are 90mm
    there is almost a 1/2" gap on the rings uninstalled

    I'm pretty sure that they sent us the wrong piston rings-

    anybody know the correct ring gap for that size of piston 89.5mm or 3 1/2"
    I'm sort of remembering that it is .004 for each inch of piston does that sound about right
    .004 x 3.5= .014 ring gap

    How can I figure what size rings to order I've already told the parts place the piston size and maybe they just messed up and sent the wrong ring

    spiritual advice welcomed
    thanks
    hank

  2. #2
    R Pope is offline CHR Member Visit my Photo Gallery
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    Take 'em back. They screwed up.

  3. #3
    erik erikson's Avatar
    erik erikson is offline CHR Member Visit my Photo Gallery
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    Car Year, Make, Model: BLOWN 540 57 CHEVY
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    Quote Originally Posted by TOW'D
    I'm rebuilding a 1973 B-20 4 cylinder push rod Volvo motor that was bored .030 over. Tough as nails old "tractor" motor- no overhead cam shafts or timing belts or aluminum heads to corrode- just good old cast iron.

    I just got the block back from the machine shop with new cam bearings and hot tanked. Rods were checked and didn't need new wrist pin bushings
    everything is looking good.

    so today I cleaned all the engine parts---installed the pistons on the rods
    and started checking the pistons/rings
    Deves rings
    after reading the installation sheet that came with the rings
    I was measuring the fit of the top ring in the piston and I could not get .006 to fit between the ring and ring groove so that piston was still good .

    Then I noticed that the ring is the same size as the top of the piston seems to me that the ring should be bigger diameter
    It was too late to call the parts place tonight-
    my piston tops are 89.5mm(little more than 3 1/2") and the rings are 90mm
    there is almost a 1/2" gap on the rings uninstalled

    I'm pretty sure that they sent us the wrong piston rings-

    anybody know the correct ring gap for that size of piston 89.5mm or 3 1/2"
    I'm sort of remembering that it is .004 for each inch of piston does that sound about right
    .004 x 3.5= .014 ring gap

    How can I figure what size rings to order I've already told the parts place the piston size and maybe they just messed up and sent the wrong ring

    spiritual advice welcomed
    thanks
    hank
    Ring gap is based on application.
    Street,strip,drag,nitrous applications, blown applications,circle track etc.
    Bottom line is you have the wrong rings.

  4. #4
    HOSS429's Avatar
    HOSS429 is offline CHR Member Visit my Photo Gallery
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    are you trying to put stock bore pistons in a bored block ? you didn`t mention you had new oversized pistons or not
    iv`e used up all my sick days at work .. can i call in dead ?

  5. #5
    speedy55779's Avatar
    speedy55779 is offline CHR Member Visit my Photo Gallery
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    Car Year, Make, Model: 41 plymouth, 48 dodge truck
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    look at the piston ring box see if it says STD. or .030 anywhere on it. but since its bored .030 over your going to need .030 over rings and .030 over pistons. and denny has posted the right way to check your ring gap but otherwise the way you checked it you should get anywhere from .002 - .005 for checking the ring groove. I would think there would be some sort of specs & instructions with the rings but i could be wrong.
    Derek Doble

  6. #6
    TOW'D is offline CHR Member/Contributor Visit my Photo Gallery
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    The engine was rebuilt in the '90 and has just sat after a accident
    The pistons are .030 over
    I'm just refreshing it up for use in our VW 4x4 syncro Vanagon
    I'll put the rings in the bore but pretty sure they are wrong
    thanks for the input

  7. #7
    TOW'D is offline CHR Member/Contributor Visit my Photo Gallery
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    update on my rings

    I received the correct size of rings yesterday for our rebuild- The package said the rings were made on Jan 28 2008- nice having fresh ring to work with instead of "old" stock-

    They fit into the bore with only .002 gap and I'll have to file them to get the correct gap-
    The motor is NA fuel injected so nothing too wild about it
    what would better to shoot for when doing the filing of the ring gap
    .010 to .018 is what the paper that came with the rings showed.
    should we just go for right in between them say .014

    thanks
    hank

  8. #8
    techinspector1's Avatar
    techinspector1 is offline CHR Member Visit my Photo Gallery
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    I use the rule of thumb...0.0045" for each inch of bore (4.000" bore, 0.018" gap) with conventional cast pistons. Hypereutectics require more gap and use a factor beginning at 0.0065" for each inch of bore for naturally aspirated street motors.
    http://www.kb-silvolite.com/download...Automotive.pdf

  9. #9
    TOW'D is offline CHR Member/Contributor Visit my Photo Gallery
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    I got .016 to .022 from a Volvo site for the ring gap
    and filed the rings so I have a .020 gap
    read in 3 different places in each cylinder
    looks good to me so far

    Tomorrow I'm taking the piston/rod assemblies to a grocery store that a buddy runs to weigh them.
    Just to see how close they are.

    thanks for the help

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