Stumped on 302 rebuild first run

Discussion in 'Technical' started by skiziks44, Jul 12, 2014.

  1. skiziks44

    skiziks44 Member

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    Fine folks,

    I finished up the rebuild of the 302 that I am going to drop in my Maverick.

    Have it setup on a run stand and fired it up then did the usual break in procedure.

    The Craigslist headers were good enough for the break in but were painted in paint that was not high temp, smoke galore.

    Everything went great with one problem. Number 8 is not firing enough to burn the paint off the header tube.

    Swapped the plugs between 7&8 no change.

    Swapped the wires between 7&8 no change.

    Pulled the valve cover and switched the rockers and push rods between 7&8.

    Watched the rockers go up and down all good.

    120 PSI for compression on 7&8.

    Put it back together and 8 still does not fire all the time.

    Put the timing light pick up on #8 wire and then #7 wire and get same RPM reading on each.

    Pull the carb and see if there is a blockage in the intake. Nothing.

    Pulled the intake and no blockage there.

    Pulled the header on that side and there is no blockage.

    Pulled the muffler from the header and no blockage there either.

    Double and triple checked the firing order and matched it to the cam, all good.

    Think I will put it back together and try a different distributor as nothing mechanical seems to be wrong.

    What have I missed?

    Thanks,
    Larry
     
  2. Bryant

    Bryant forgot more than learned

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    have you pulled the 8 spark plug wire while running?
    could the header tube happen to have better paint than the rest?
    did you use a temp gun on all the tubes to see if 8 is a substantial different temp?
    did the spark plugs look different on 7 and 8?
     
  3. skiziks44

    skiziks44 Member

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    Yes I did use a temp gun to verify that pipes were gaining temp and that is the only one that did not peg out the temp gun.

    The miss can be felt at the exhaust pipes too.

    The plugs look fine, not wet or anything.

    It is really very strange.

    Thanks for the input.
     
    Last edited: Jul 12, 2014
  4. groberts101

    groberts101 Member

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    what pressures are the other cylinders generating?

    The reason I ask is that 120 PSI is very low for a fresh engine and may indicate that the rings have very poor seal in those cylinders. If that is in fact the issue here.. and assuming you've gone through the entire checklist(especially ignition).. you can seal rings very quickly with a PCV valve hooked up to a sealed crankcase. In other words.. do not allow fresh air venting from the opposite side of the engine. Never good to run an engine under heavy load like that(especially at high rpm decel).. but it works great for sealing rings in no time. Maintaining 15-20 psi of "manifold vacuum pull" on the ring packs does wonders for break ins in these situations.
     
  5. 71gold

    71gold Frank Cooper Supporting Member

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    I would think 120 PSI would be good to fire that (or any) cyl. it may be low for a fresh rebuild but shouldn't be his problem...:huh:
    this is a no load situation.
     
  6. simple man

    simple man Member

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    Did you do the compression test on all of the cylinders? If just #7 and #8 are low, you may have a gasket leak between those two cylinders. I have found that just cause it's new, sometimes doesn't mean squat! Also see if you can spin both pushrods when #8 is on TDC. You should be able to. :)
     
  7. baddad457

    baddad457 Member

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    If you have a flat tappet cam, I would pull the intake and then the pushrods and lifters to make sure they're not wiped before running it further. Also drain and inspect the oil before doing this, if it looks metal flaked, then definitely pull the intake, and lifters to inspect the cam.
     
  8. skiziks44

    skiziks44 Member

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    Thanks to everyone for the input.

    A little more information and background on this build.

    It is a 74 block that has been bored .30 over. It has a used set of TRW forged pistons that were inspected and sized before boring the block. A mild cam with hydraulic lifters. A Holley street dominator intake and an Edelbrock that is used to break in all new engines at my friends shop. The distributor is one of the single wire HEI types that was a good price but looks like crap and will be replaced soon.

    The engine was broken in on a run stand and then the oil was drained. It looked great without any metal flake in it at all.

    The compression test of all the cylinders cold with the intake removed are in the 120-140 range.

    Intake has been reinstalled and I will warm it up and do another compression test later today or tomorrow. After I check that all pushrods spin free on each cylinders compression stroke.

    Thanks again for all the input.
     
  9. baddad457

    baddad457 Member

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    Also check while the engine is running to see that all the pushrods are rotating while the engine is running. No rotation = wiped cam lobe
     
  10. skiziks44

    skiziks44 Member

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    Well maybe the gremlins just packed up and ran off.

    After re-stabbing the distributor and adjusting the plug wires I fired the engine back up on the run stand.

    All of the tubes on the headers match side to side and the paint on #8 has begun to blister off.

    I double and triple checked all of the plug wires before removing the intake so I can't believe that it was loose before.

    At this point I am just happy that it is running nice and smooth.

    For the heck of it I hooked up a vacuum gage to the carb and with the timing at 8 degrees and a idle of 900 or so will hold rock steady at 30.

    This is on an Edelbrock 1406 that is used by my friend to break in all of the engines he builds which are mostly Chevy 350s and 400s. It is a bit rich for the 302.

    Now that it seems to be running well I will rebuild the Holley 1850 and get things further dialed in while it is on the run stand before I drop it in the car.

    Thanks again for all the input and ideas that you all have posted.
     

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