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sr20 drop-in cams. re-shim needed?

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  • sr20 drop-in cams. re-shim needed?

    Noob question here. Working on a friend's SR, and all his shims went flying and rocker arms got dislodged after attempting to start it. I wasn't part of the rebuild process. Supposedly the head was just decked and everything put back to spec (with stiffer springs). lifters were also bled.. but even if they weren't i'd just think you'd get some tapping and not dislodged shims/arms. valve lash should not be different.

    Just want to know.. when people do drop in cams (specifically BC 264), do they typically reshim? I'm looking at the writeups, like http://www.frsport.com/Installing-To...0DET_t_35.html, and it doesn't seem like they even consider reshimming, nor do most "driveway tuners". Shouldn't the base circle of these be close enough that you don't need to reshim?

  • #2
    I definitely didn't re-shim when I put my JWT S3s in. It's important to make sure that if any shims come out, they go back in the exact same spot, though.
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    • #3
      Just changing out cams, if the shims arent upset, and are correct then no change is needed, as they only set the rocker parallel to the camshaft lobe with a hyd setup.

      If they do get out of place or a valvejob is done, or uneven wear is visible on the camshaft lobes, the head needs to be properly reshimmed, as you will get uneven wear from the rocker riding improperly on the camshaft.

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      • #4
        well cleaning up this mess is gonna suck for the owner. lots of shims and shim guides went flying. not only are the shims in random order now (requiring reshimming obviously), but probably worse - several shim guides were broken into pieces. one or two of which have not yet been recovered.

        how could this happen? worst thing would be to put this bad boy back together just to make another head shim/rocker arm salad. let's give him the benefit of the doubt and assume he started with a functional head. i know he didn't do a valve job. just new springs and retainers. does changing springs/retainers change valve lash? are aftermarket retainers different thickness and seat height than oem?

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        • #5
          I, honestly, have never heard of this happening... the rocker arm would, more or less, have to fly up and the shims are just sitting on the retainers so they could definitely come off.

          Did they not push the rocker arms onto the HLAs all the way? Maybe didn't assemble the springs / retainers properly?
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          • #6
            it sounds like bad,

            The base circle on any "new" (as in not a regrind) cam should be the same so shims shouldn't be a different spec,

            To get an SR to toss the rocker arms you need to float the valves or have completely flat HLA's

            could be that the motor was timed incorrectly, I would take the opportunity to remove the cams and rockers and pressurize each cylinder to make sure you don't have bent valves,

            With the valves closed and the piston at TDC or BDC you should be able to apply pressurized air through the spark plug and hear where the air leaks out from, aslong as you only hear air from the oil cap and dipstick tube you are OK if there is air crossing the throttle body (pitch will change with opening and closing TB or if there is air leaving the exhaust ports you have real issues,

            unfortunately my money is on incorrect cam alignment.
            I am SKULLWORKS

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            • #7
              yea, thanks for the input. having all the rockers move like this makes me think it's not just flat lifters. leaning towards some mechanical interference as well.

              this "refresh" is project fail up to this point. bunch of random parts (especially the head), lots of ppl having their hand / suggestions in it at different stages of the teardown/assembly, low low budget, and a non mechanically inclined nor technically savvy owner. it's a long road ahead for him, unfortunately. just trying to help him not make the same mistakes twice, i guess. it's also hard to get first hand information due to so many parties involved, and the owner not really knowing what effing happened. sigh... he should've just left things the way they were... running and stock.

              i've got a leak down tester. all the cams are out now, so each cylinder could be tested as it sits. (not tdc, just the random resting spot after the mechanical crunching sounds, haha). if it has significant leak without cams it's time to pull the head. otherwise next step would be measure for new shims, take the pulled lifters and re-bleeed them, buy replacement shims, reassemble, triple check the valve timing, and start it. hopefully those missing metal bits don't get past the oil pickup screen. eek.
              Last edited by gawdzilla; 02-27-2012, 03:38 PM.

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              • #8
                yeah you are gonna be facing bent Valves


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