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4 bolt vs 2 bolt main

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  • 4 bolt vs 2 bolt main

    Ok all here is my final question I am sort of being forced to start my project early. My new wife doesnt like the wag series so she gave me an ultimatum. Either prove its worth or get rid of it. She is tired of the constant repairs and little things that always go south with it. (I guess I gotta get my vortec engine swap done asap. Here is my question.

    I have found a machine shop in my or close enough that has 350 and 454 vortec engines for the same price!!!!!!!!! Anyway the guy asked me whther I wanted a two bolt or four bolt main. I didnt know what the pros and cons of either one were so could any of you help?

    What are the pros and cons of two and four bolt mains? Two bolt versus four bolt.

    Remember I am building my rig to be the ultimate long distance/comfort/pimp wagoneer... It may need to do some occasional towing but not often and also some light to medium off-roading. (no heavy duty off-roading I have a new cj I just picked up for that!!!!!!)
    88 Grand wagoneer AMC 360 all stock
    89 Grand Wagoneer AMC 360 (Deceased)


    1. Electric Radiator Fan 10/15/11
    2. Cs-144 Alt 10/1/11

    All completed long ago (cannot remember when)
    1. TBI
    2. New fuel tank
    3. AW-4 Transmission
    4. Aluminum condensor
    5. Custom Gauge Panel

  • #2
    A 4 bolt has 4 bolts on the rear main and a 2 bolt, well has 2. 4 bolts are a little stronger in the bottom end but I wouldn't get too hung up about it if the price is quite a bit different. If they are the same or very near, I'd take the 4 bolt, but a 2 bolt is strong enough. Many good engines are 2 bolts, like Pontiacs for instance, except SD455's.

    So there really isn't much of a pro or con either way. There is no con to a 4 bolt or a 2 bolt and the pro for the 4 bolt is it's a little stronger.

    1989 Black Grand Wagoneer, BJ's 4" lift, ProComp ES3000's
    31x10.5x15 BFG AT KO's,MSD 6A,TFI upgrade,360,727,229,2.72 gears.
    2006 Dodge Magnum R/T
    2000 Jeep Wrangler
    1988 Cadillac Brougham
    1966 Dodge Monaco 500 383
    1965 Pontiac Tempest 326


    • #3
      What year engine? GM had problems with piston slap.
      2013 Mini Paceman
      1985 Jeep GW (coolant leak again!)
      1979 Ford Fiesta


      • #4
        2013 Mini Paceman
        1985 Jeep GW (coolant leak again!)
        1979 Ford Fiesta


        • #5
          It is my understanding that the stock 4 bolt offers nothing more than the 2 bolt except at high rpms. In other words, an off roader and daily driver that does not live much above 5000 rpms would not get any real benefit from a 4 bolt block but it certainly would not hurt anything to have one. All comes down to the price difference.
          In Process: 91 Wagoneer, D61/71 axles with 3.07 gearing, NV4500, NP205. Cummins 6BT.

          Back burner project: Crew cab M715, Cummins/Allison/Rockwell Tcase/Dana 61/Dana 71.


          • #6
            2 Bolt vs. 4 bolt in a street engine is a non issue.
            Chevrolet used 4 bolt bolt blocks in trucks mainly,
            if given a choice tkae the 4 bolt block, if asked
            to pay anything over a few bucks take the 2 bolt
            block. For the big question 454 vs. 350, well does
            mileage mean much to you ? Do you mind a few more
            issues with stuffing it in the slightly to small
            hole under the hood ? If no to both go for the 454 !
            I will pull a lot harder than a 350.

            Think long and hard about the reliability issue
            though, any swap is likely to be more unreliable
            than the factory setup just because the factory
            guys have had time to work out all the issues,
            where you are going to have to sort it all out on
            the fly.

            Mike D.
            Home of ADHD project list

            1977 J-10 Honcho 360-T15-D20
            1977 Cherokee WT 360-Th400-NP241 true-trac(s)
            1979 Cherokee 4 Door 258-T-18-D20
            1981 Cherokee Chief WT 360-727-NP208
            1972 K20 Suburban 350 SM465 205
            And the other stuff that gets driven


            • #7
              dont matter how many bolts its got the load is in the center of the caps ...........just get the thing running would you ????
              I\'ve seen gsmikie\'s video for the TH400 and thought it was just awful.watching a guy tear down a greasy pile of metal in a junkyard. it dosent have to be surrounded by water to be an island


              • #8
                4 bolt is supposed to be stronger and it's typically worth more money, but you'll never know the difference. I'm running 4 bolt mains in practiacally all my vehicles but that's just because I had them available and wanted to hang on to them so I can sell them to some sucker down the road who "thinks" he needs 4 bolts.

                [ August 31, 2004, 04:41 AM: Message edited by: HotRodYJ ]
                90 YJ,350 Chevy,700R4, NP231CHD with SS-SYE, SOA, HPD44 locked, 14B locked, 4 wheel disc,<br />38\" TSL/SX on H1 beadlocks


                • #9
                  Back in '68, Chebby increased the main bearing diameter on the small-block for some fool reason (was it 2.3 to 2.45" -- don't rightly recall). They soon found that the old 2-bolt cap no longer had enough meat on the sides to remain stable at high revs/loads, and devised the 4-bolt patch.

                  I was racing those motors at the time, regularly spinng the poor things past 9,000 RPM, and noticed that even the new 4-bolt blocks didn't hold up as well as the old ones. I had a guy machine some steel caps with slightly splayed outer bolts (Summers Brothers was doing the same thing at about the same time), and that helped. I later just started using the old small bearing block modified for a similar splayed 4-bolt cap.

                  Note that this was in the day when GM metallurgy was pretty poor -- just a couple of steps beyond Ford's pig-iron stuff. My first test of main caps back then was to drop them on the floor. The ones that didn't break were worthy of a magnaflux investment. They've improved quite a lot since then.

                  For your purposes, I'd guess that 4-bolt caps are pretty much irrelavent. They may help keep things more stable in low-rev, very high load conditions, thus extending bearing life a bit -- probably less than just using good synthetic lube. I suppose, given GMs way of doing things, that the 4-bolt blocks might also have other improvements as well, possibly making them more desirable, and probably not worth worring about below 6,000 RPM.


                  Disclaimer: All of my experience with SBCs is at least 30 years out of date.
                  "Carpe MaƱana".

                  '83 Wagoneer
                  360, .030-over, K8600 cam, Crane springs, ported heads, Edelbrock Performer, G.M. TBI, TFI, 3" exhaust,
                  T-18a/208, D44/AMC 20 w/ limited slip in both, 3.73s, 33s, BDS 4" springs, Rancho 9000 shocks, etc., etc.