Announcement Announcement Module
Collapse
No announcement yet.
258; 4.2L straight 6 engine question Page Title Module
Move Remove Collapse
X
Conversation Detail Module
Collapse
  • Filter
  • Time
  • Show
Clear All
new posts

  • 258; 4.2L straight 6 engine question

    Hopefully this is a quick question for this forum.......

    We have a '77 CJ5 with the stock 258 in it. We've been having engine problems now for about 4 months (very long story) and have replaced just about everything except the engine itself.

    I recently came across two rebuilt engines that I couldn't refuse. Problem is one is a '87 - '90 long block that has a crank for a serpentine damper--meaning I'd have to replace the alternator and water pump pulley. The other engine is a drop in replacement short block. Here are my questions as I try to determine the path of least time and cost:

    1) Will the '87 - '90 head (off of the long block) fit on the stock short block? This would preclude me from having to change out all of the pulleys for the serpentine belt. I've already determined that;

    a. The stock (metal) valve cover will not fit---requires the plastic one.
    b. the stock timing chain cover will not fit

    2) If the answer to #1 is "no," then does anyone have an estimate on how expensive it is to modify all pulleys to accept a serpentine belt?

    Thanks--I'd really like to get this thing drivable again.......

  • #2
    Wait a minute, I think a 258 is a 258 they should have the same length block if they are both 258's. Maybe I misunderstood you.

    Comment


    • #3
      I believe you're right about the length of the block. What I'm not sure of is whether or not the bolt patter on the newer head is the same as the '77 stock. Also, the question comes as a result of comparing the casting numbers. The 87-90 casting number falls in to a different category raising my concern that the head may not be a direct replacement on both blocks.....

      Comment


      • #4
        it should bolt right on. 258 is 258. i've swapped parts from a 73 258 onto a 86 with no problem

        Comment


        • #5
          Great!

          Thanks

          Comment


          • #6
            Originally posted by rippin YJ View Post
            Wait a minute, I think a 258 is a 258 they should have the same length block if they are both 258's. Maybe I misunderstood you.
            Short block is just the block, rotating assembly and cam. Long block is usually a complete assembly including the head, valve train, water pump, oil pan etc. Has nothing to do with the actual "length" of the block

            Comment


            • #7
              Roger that.

              Ultimately, I'm trying to avoid having to go with the serpentine set up by using the long block. I'd like to swap the head from the long block and put it on the existing re-built short block. Before I tore down the long block though, I wanted to see if anyone else has done this to ensure that the bolt pattern and all ports etc were still the same.......

              Based on what I've heard thus far, there shouldn't be any issues in making the swap.

              Comment


              • #8
                Early 258's have 1/2" head bolts. Later models, I'm not sure what year, have 7/16" head bolts. I think Clifford Performance has sleeves to make them work on eachother's block, but I'm not positive.

                A 4.0 HO head would be your best choice. Your intake will work, but the exhaust would need work. It's "supposed" to gain you 40hp by swapping.

                Good luck,

                High5

                Comment


                • #9
                  Thanks much High5. I guess the saying "nothins easy" still holds true. Course it is a Jeep!

                  Cheers

                  Comment


                  • #10
                    Originally posted by High5 View Post
                    Early 258's have 1/2" head bolts. Later models, I'm not sure what year, have 7/16" head bolts. I think Clifford Performance has sleeves to make them work on eachother's block, but I'm not positive.

                    A 4.0 HO head would be your best choice. Your intake will work, but the exhaust would need work. It's "supposed" to gain you 40hp by swapping.

                    Good luck,

                    High5
                    Had the same problem with 351 heads on 302s. To prevent blowing head gaskets we had to step way from the stepped bolts, sleeves, and drill and tap the block for 1/2" thread. Here I would have the bolt holes opened up in the heads to prevent head gasket failures around the sleeves.

                    Comment


                    • #11
                      You could just swap the crank dampner to the v-belt style and replace the water pump(serpentine pump runs in the reverse direction of a v-belt pump) and use your v-belts. Seems like that would be easier than swapping the head. I did the reverse and converted a v-belt engine to a serpentine set-up. I already had a harmonic balancer puller(they're cheap) but I had to buy the installation tool.

                      Comment

                      Working...
                      X