Announcement

Collapse
No announcement yet.

Broken Rings and Piston

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Broken Rings and Piston

    Other than a combination of too much boost and compression, I'm trying to figure out what caused some damage to my motor. I have no idea how many miles were on the short block before I got it. It survived about three years for me under boost.

    Specs:
    350 SBC
    Performer intake
    750cfm TBI with 4 160 lb injectors
    291 heads, bowls cleaned up, port matched, chambers polished, 1.94,1.5
    unknown cam 510/510 lift
    L2256 forged pistons (9.7:1)
    HX55 turbo @10psi
    Air to water intercooler. The max temps I've recorded under boost were around 130F.
    2500 rpm converter, 3.50 gear, 3900lbs
    rev limited to 6k, rarely saw 5k. Usually short shifted into second around 4k. Street use only very rarely saw boost in third
    MS-II
    Solid 12.7 afr under boost.


    Cold Compression Test
    1 160lb 2 180lb
    3 70lb 4 180lb
    5 150lb 6 180lb
    7 160lb 8 200lb

    All of the pistons look normal in color and wear. The skirts and tops look good. The backs are clean. Some show some evidence of blow by on the second land. All of the driver side pistons had the top rings in five or more pieces. Number three was broken through the second land down through the pin hole and back up to the second ring land. The passenger side pistons and rings all look fine. The bores appear undamaged but the honing is all but polished away. Would the lack of oil break rings without scuffing skirts? I know this motor is a recipe for detonation but I never heard any, and it doesn't look like it. I didn't think 10psi through these heads would be enough to break a piston. What do you guys think?

    Thanks,
    Kevin





  • #2
    Re: Broken Rings and Piston

    was the left side head milled more than the right side head, some time in the past?

    Is it possible that a problem with an injector or wiring caused it to go lean on the driver side?
    My fabulous web page

    "If it don't go, chrome it!" --Stroker McGurk

    Comment


    • #3
      Re: Broken Rings and Piston

      sounds like it was pre ign maybe that side injectors are a tad weak
      as it's a dual plane intake, or one is dead or almost dead/clogged

      Comment


      • #4
        Re: Broken Rings and Piston

        The heads are measuring the same. I think I cc'd them when I polished the chambers. It has two injectors per side and the way the intake is, it looks like if an injector failed it would affect both sides of the motor. My injection setup is kinda hokey to say the least so I can't rule it out. The injectors are spraying through the boosters on a 750 DP. It looks like chugging fire hoses at idle, but it atomizes beautifully under load. I'll give the injectors a quick flow test tomorrow evening.

        Thanks,
        Kevin

        Comment


        • #5
          Re: Broken Rings and Piston

          If the tops of the pistons are not beat up from detonation, maybe ring gap was too tight. As I understand it, the top ring needs more gap for boosted engines.
          BS'er formally known as Rebeldryver

          Resident Instigator

          sigpic

          Comment


          • #6
            Re: Broken Rings and Piston

            Originally posted by Rebeldryver
            If the tops of the pistons are not beat up from detonation, maybe ring gap was too tight. As I understand it, the top ring needs more gap for boosted engines.
            x2 but why only one side..

            Comment


            • #7
              Re: Broken Rings and Piston

              Originally posted by Tazracing
              Originally posted by Rebeldryver
              If the tops of the pistons are not beat up from detonation, maybe ring gap was too tight. As I understand it, the top ring needs more gap for boosted engines.
              x2 but why only one side..
              maybe they just messed up on that one ring?

              Comment


              • #8
                Re: Broken Rings and Piston

                Originally posted by 1988montecarloss
                Originally posted by Tazracing
                Originally posted by Rebeldryver
                If the tops of the pistons are not beat up from detonation, maybe ring gap was too tight. As I understand it, the top ring needs more gap for boosted engines.
                x2 but why only one side..
                maybe they just messed up on that one ring?

                o/p "All of the driver side pistons had the top rings in five or more pieces"

                Comment


                • #9
                  Re: Broken Rings and Piston

                  Originally posted by Tazracing
                  Originally posted by 1988montecarloss
                  Originally posted by Tazracing
                  Originally posted by Rebeldryver
                  If the tops of the pistons are not beat up from detonation, maybe ring gap was too tight. As I understand it, the top ring needs more gap for boosted engines.
                  x2 but why only one side..
                  maybe they just messed up on that one ring?

                  o/p "All of the driver side pistons had the top rings in five or more pieces"

                  to my mind that would make it more likely that Scott is right - put together one the right side one evening, the left side the next evening (or day).. easy mistake to make. Or, bore is a bit tighter on the left side?
                  Doing it all wrong since 1966

                  Comment


                  • #10
                    Re: Broken Rings and Piston

                    It can matter on a blow thru how its clocked
                    2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
                    First to run in the .90s .80s and .70's in SBN/A
                    2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
                    2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

                    Comment


                    • #11
                      I have been thinking about why only one side has shattered rings. Could be the builder file fitted one side and got lazy, or in a hurry when doing the other side. Could be as simple some of the rings were misboxed. Also possible, boost could be uneven side to side, more boost hitting one side of the intake. Though, thats something to discuss with the blower companys tech dept.
                      BS'er formally known as Rebeldryver

                      Resident Instigator

                      sigpic

                      Comment


                      • #12
                        I've never measured gaps on used rings, so I have no idea how they wear, but this is where the ones that survived were when the others broke. 2 was .032,4 was .036, 6 was .031, and 8 was .031. The previous owner likes nitrous so I assumed he had gapped them for it. He seems pretty meticulous but could have missed gapping the other side. I measured the injector flow by mass individually so my timing adds greatly to the uncertainty but I figured it would do for this test. Using the driver rear as 100%, driver front is 98.8%, passenger front is 96.4%, passenger rear is 99.0%. I have the injectors batched diagonally across the throttle body, 2 injections per cycle alternating. I can measure the pressure in the ports individually when I put it back together. I should find a set of blower pistons but it's hard enough to resist the urge to buy just one piston.

                        Thanks,
                        Kevin

                        Comment


                        • #13
                          I always thought busted ring lands = way too rich.
                          Life is short. Be a do'er and not a shoulda done'er.
                          1969 Galaxie 500 https://bangshift.com/forum/forum/ba...69-galaxie-500
                          1998 Mustang GT https://bangshift.com/forum/forum/ba...ix-to-4sixzero
                          1983 Mustang GT 545/552/302/Turbo302 http://www.bangshift.com/forum/forum...485-bbr-s-83gt
                          1973 F-250 BBF Turbo Truck http://www.bangshift.com/forum/forum...uck-conversion
                          1986 Ford Ranger EFI 545/C6 https://bangshift.com/forum/forum/ba...tooth-and-nail

                          Comment


                          • #14
                            Originally posted by JeffMcKC View Post
                            It can matter on a blow thru how its clocked
                            I agree.

                            linear to rotation gets the driver side more anyway..

                            and american v8s have two cylinders firing back to back on the driver side. Only 90 degrees separated.

                            then there is alignment of actual materials for strength... upside down one side, right side up the other.

                            I learned this with small boxer engines.. it is actually quite dramatic through the seasons. I go as far as equal pipes on an n/a engine.. not to be a hotrod.. but to help conquer strange things like this.
                            Previously boxer3main
                            the death rate and fairy tales cannot kill the nature left behind.

                            Comment


                            • #15
                              I've been looking at parts and need some help deciding. I can get a set of dished, forged pistons and rings for less than $400, but the 350 still just has a cast crank and stock rods. I already have a LA Ent Kryptonite crank and H-Beam Kryptonite rods with dished gas ported 8.5:1 JE pistons. It's a 4.155" bore with a 3.31" stroke. I have a two bolt 400 block to put it in. On either one, I'm going to ditch the double humps for a cheap set of 200cc-ish aluminum heads. The other option is a local junkyard has LQ4's for $1000, but I'd have to upgrade to an MS-3 to run it, and at least swap the pistons. What do you guys think?

                              Thanks,
                              Kevin

                              Comment

                              Working...
                              X