Motor swap, need help

Discussion in 'GM Powertrain' started by TheGMC, Dec 7, 2012.

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  1. TheGMC

    TheGMC New Member

    Im in the process of swapin out the motor on my 88 gmc heavy half ton, its a 350 5spd. and has a ton of blow by, and leaks about a quart from the main seal every 10min at idle. im looking for a motor for it, and have had no luck with a used tranny, but i need to know if anyone knows if its a four or two bolt main? been a while since i tackled a motor swap. thanks guys.
  2. tbplus10

    tbplus10 Super Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    Without casting numbers to go by anything at this point would be a guess.
    And my guess would be 2 bolt main since trucks of that vintage normally didnt get the 4 bolt main unless they were 3/4 or 1 ton or had a factory performance package of some type.
  3. TheGMC

    TheGMC New Member

    can i find out with casting numbers? i know it was the first year of the efi, ive only ever done 2 bolt main motors. but i found a motor for it from a 90 thats a 4 bolt main.
  4. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    Sounds like you found a winner. Whether it's a 2 bolt main or 4 bolt main doesn't matter installation-wise. I agree with Tim that it's most likely a 2 bolt main if the motor has never been swapped. Also, the bottom ends of the 350 have been the same pretty much through their entire run if I remember correctly, so as long as you don't need a manual fuel pump provision (it sounds like you don't) then any 350 block should work.
  5. TheGMC

    TheGMC New Member

    So installation will still work and it will run fine?????? the motor i found is a 4bolt. I just dont want to have to do this again.
  6. tbplus10

    tbplus10 Super Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    Yep, like Christopher said the big difference will be fuel pump, now would be a great time to put an electric one on anyways.
  7. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    with him having EFI (TBI) he should just have the in-tank electric fuel pump.
  8. moogvo

    moogvo Moderator 1000 Posts 100 Posts



    That's correct. However, you should attempt to locate an engine that was from an '88-'95 to make it a "drop in" and '96-'99 if you don't mind swapping externals. There is a difference in the way the rear main seal is installed in the pre-1988 blocks that might cause a problem, IIRC.
  9. tbplus10

    tbplus10 Super Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    Should, but 87/88 model trucks were odd they had some old and some new parts and it wasnt always the same since they were the first year for GM's new platform and the last year of the old platform.
    Some of the heavier GM trucks of that era came from the factory with carburators and mechanical fuel pumps, some also came with external electronic pumps. He'll have to determine what he has on his truck.
    Some of the early generation TBI systems used a mechanical fuel pump before GM figured out their fuel starvation issues.
  10. Crawdaddy

    Crawdaddy Moderator Staff Member Platinum Contributor 1000 Posts 100 Posts

    Ah, I didn't realize they used mechanical fuel pumps on some TBI setups.

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