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I Need Engine Swap Info for 1986 GMC 4WD

Discussion in 'The Garage' started by Dave1, Feb 10, 2005.

  1. Dave1

    Dave1 Registered Member

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    My 1986 GMC 3/4 ton 4WD pick up truck "M" series carbrueted 350 with 203K miles is sick with blown head gasket(s) and maybe cracked head(s). I am trying to determine the most economical way of getting the truck back on the road.

    Because of the high mileage and engine wear, a total rebuild of this engine is needed, but is very expensive. Before doing that I would likely buy a new GM crate motor as it is only slightly more as expensive than the rebuild job but both are very expensive options. A rebuilt long block from a parts house is the next least expensive option. A good used replacement engine, if one can be found, will likely be my least expensive option.

    My question is, what year/make/model used GM engines would bolt right into my truck, fit my AC and accesories, with the least amount of alterations and expense? What can I expect to pay for a good used engine?

    Thanks for any info.

    Dave
    davisalf@aol.com
    Central Florida
     
  2. diesel4me

    diesel4me 1 ton status Premium Member

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    a lot of them fit...

    An engine from 1973-86 would be the best ones for your 86,anything newer things change rapidly(EFI,vorteck motors,etc) --too avoid a lot of hassles its best to find one the same year or close to it,the older motors will fit,but you will have to swap all your old stuff like smog parts and manifolds,etc to complete the swap...naturally the older the motor,the more likely it needs work or doesnt run that great..you should be able to score a 350 from an 80's truck or Impala that got T-boned or rear ended from a boneyard for 300-500 bucks,that would be the cheapest route..a new crate 350 from GM runs around 1100-1500 bucks at most dealers,you have to match the motor to the vehicle for the full waranty to be valid though....:crazy:
     
  3. Dave1

    Dave1 Registered Member

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    I would susspect a used engine in the 73-86 year range would have tons of miles and may not be in the best of condition itself. I would hate to buy another just like the one I have. I was hoping some of the newer year range engines would be a good replacement and an easy swap so as I could get one without lots of miles on it. Guess not.

    Maybe a used engine is not such a good idea after all.

    Dave
     
  4. 90blzr

    90blzr 1/2 ton status

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    I am sure you could find a good runner in the for sale forum here. I THINK you can also use the 87-91+350s. Just swap intakes.
    Most guys who are selling good runners on this board are straight up and wouldnt do you wrong.
     
  5. diesel4me

    diesel4me 1 ton status Premium Member

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    newer engines will work too

    A later motor will work in your truck,but its more work because you will have to change more stuff--I'm familiar with the older 87 and down trucks,the others on here can help you more with questions regarding the newer trucks--usually its easiest to put back an engine thats nearly identical to the one your truck came with...
    there are still some good running used 350's around,just the other day a friend called me and said his grandmothers 83 Impala was up for sale $200 bucks!)due to her husband passing away,it had only 35,000 original miles--my friend sold it to the next guy he called after me,I would have bought it if I had the cash,even though I dont really need a motor right now..:crazy:
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    An older post here said that GM doesn't have the "M" replacement engine anymore.

    The later engines use a one piece rear main seal, that means another flexplate/flywheel as they aren't interchangeable with older engines. Besides, head to intake bolt pattern changed from earlier motors too.

    Exhaust manifold fitment is another issue. Old SBC's won't work with the log style 7 bolt manifolds that were common in the 80's, which your truck probably(?) has. Same exhaust ports and all, but where the manifolds "dump" and that 7th bolt hole causes problems.
     
  7. dirtwarrior17

    dirtwarrior17 Banned

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    I just finished my 79 block to 88 k5 swap. i had to grind the ac bracket to fit the holley manifold but now it fits just fine.

    A newer motor will work for your truck all the way past the vortec stage as long as the heads aren't vortecs.
     

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