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Thread: Cracked Block Options

  1. #1
    Join Date
    Apr 2005
    Location
    Mesa, AZ
    Posts
    300

    Default Cracked Block Options

    Well in an effort to find a knocking sound in my engine I found a bigger problem. The block is cracked on the number 4 main. I need to have it together by June 30th because I need my vehicle off my dad's land(he is closing his business).

    I don't daily drive it and intend to use the vehicle for offroad use someday...

    Here are my two options:

    1) Drill under the crack to try to stop it, and lock'n stitch the block. Extend my girdle to number 5 main. Drive it until it starts to leak coolant into oil or vice versa and drop in a 4bt when it fails. Any ideas how long it may last?

    2) Try to get my old 6.2 block machined with about one week left to build and install it. Tie the girdle into number 5 main and hope it never cracks. It doesn't look cracked and it should last if it isn't cracked(I hope). It does have rust in the cylinders, but I hope it only needs to be bored over .020" so I can use my pistons from the new cracked engine.

    Any suggestion?

    -Thanks,
    Kyle
    '83 Blazer, DB2 built like 4911 by Accurate Diesel, 6.5 oil pump, 6.5 turbo injectors, 82 6.2 block, 6.5 heads, serpentine, gm-4 turbo with turbo master, timing gears, custom stud girdle, lower compression
    Pics: http://s153.photobucket.com/albums/s205/kkarlson_photo/

  2. #2
    Join Date
    Feb 2008
    Location
    N.Delta, BC, Canada
    Posts
    182

    Default

    Kyle, I suggest that you go with the 6.2 block if it has no cracks.

    I would pull ALL the main caps, clean them with solvent, spray them with the red crack penetrant, and then use the crack developer which is white. All the cracks will show up pink. It is surprising what can appear right before your eyes... deeper cracks will been seen outside of the main caps such as this one pictured below...



    If you have a crack-free block, use it.

    I am having a cracked block repaired by a shop who specializes in this work. They guarantee the job. It is similar to your lock'n stitch, but they mill out the cracked bolt area on their lathe and machine-in some inserts. It costs around $100 per crack. My block has 3. I have 2 more blocks also with 3 cracks each. They will be repaired next if I am happy with the work.

    My experience is that 6.5's run with cracks... flexing and growing. They will certainly fail at some point, if nothing else fails first.

    Bore your 6.2 block.. and I would not rush anything when it comes to building your power plant properly. Tow your vehicle somewhere you can work on it if you need more time.

    The thinner #2,#3, & #4 main caps are thin and develop cracks due to the 12mm bolt holes and inadequate strength. They moved to 10mm diameter bolts in later years to decrease this problem.

    Typical girdles tie the 3 weaker mains together... such as below picture and is adequate. The girdle is a good idea. In my opinion, its not necessary to tie this girdle into the #1 and #5 mains.



    Good luck .
    Last edited by JetBoater; 05-17-2008 at 10:09. Reason: typo

  3. #3
    Join Date
    Sep 2001
    Location
    Lubbock TX, USA
    Posts
    4,194

    Default

    I think you need to do as described above.

    From the pictures you posted in the 6.2L forum, the scoring in the bores will really lead you do at the very least hone them out. It looks like you had inadequate clearance in the bores for the pistons. Saw this (to a less degree cyl's 6 & 8) in a semi-recently torn down splayed engine of mine. This was due to inadequate clearance as well with the KD pistons. The pistons were coated, the machine shop and I agreed to use the piston diameter measurement in the Mahle book. The measurement with the coating was tricky (why we used the book measurment, added the .004"). In the end the coating was pretty rigid and took up the clearance and lead to some scoring, or we still didn't get the right measurement due to the coating. None the less, we'll hone out .0005 - .001" (wipe, cleanout light marks) and put it back together eventually. So, get this next block bored with the pistons in hand the right way this time and get real measurements off the skirt. These things vary!

    Get in no hurry. Build the engine in a place where you can leave it while you're waiting for the right parts to arrive and for you to check everything. The truck can be moved by chain and trailer, believe me, I know, boy do I know...

    I like the Girdle idea. I do believe this is one MAJOR reason why the '97 (12mm outside main studded block) with piston spray block is still alive and making some insane RWHP out of a 6.5L and is still together, add .010" turned/polished crank to that same scenario (yikes). I never intended it to do what it has (budjet hi-performance engine). But at least a block I spent way too much money on to have splayed (out of another project) will get to be used somehow, probably this project.

    AMG P400 for the '95 Suburban after it's proven of course and 18:1 slugs are available for it (currently not).
    Last edited by john8662; 05-19-2008 at 20:09.
    1982 C10 SCSWB 6.5TD, mods too extensive to list. (13.69 1/4 mile @94.6 MPH) RACE TRUCK
    1982 C10 SCSWB 6.2NA, 2.73 700
    1986 C10 SCLWB 6.2TD 3.73 700
    1989 V20 SUB 6.2NA, 3.73 400
    1994 G20 VAN 6.5NA, 3.42 60E
    1994 K20LD ECSWB 6.5TD, 3.42 80E
    1995 K20 SUB 6.5TD, Wrecked, ran into by stupid teen.
    1995 C3500HD DRW 6.5TD, 12' Flatbed 5.13 80E
    1995 C3500HD DRW 6.5TD, 18' Rollback Wrecker 4.63 80E
    1994 C20HD ECLWB 6.5TD 3.73 80E Wifes Truck.
    1995 C20LD ECSWB 6.5TD 3.73 80E
    1995 K20LD SCLWB 6.5TD 3.73 80E
    1996 K30 DRW 6.5TD 4.10 80E
    1997 C10 Tahoe 2Door 2WD 5.7L to 6.5 Conversion Underway

  4. #4
    Join Date
    Oct 2001
    Location
    Granby, Missouri, USA
    Posts
    2,975

    Default

    Is this your '82 block that cracked?

    Casey
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  5. #5
    Join Date
    Apr 2005
    Location
    Mesa, AZ
    Posts
    300

    Default

    Yeah it is the '82. I do not think they are as good as they are supposed to be. I found a crack repair made for 6.2's by lock'n stitch. I think I will try it and get the engine together. In a couple years when I am done school I will pull it back apart and see how the crack repair has held up. They say they garauntee it or you get a full refund. It will be a good experiment, none the less.

    It won't see much driving now that I got a diesel vw rabbit. I should be able to check the crack with a borescope periodically after I repair it too. Here is the repair.

    http://www.fulltorque.com/

    http://www.fulltorque.com/ffbs.htm

    straight from the website:

    "Cracked bolt holes are now easily repaired and strengthened. Head bolt holes, main bearing bolt holes, starter motor bolt holes, the uses are endless. All bolts and other thread designs create radial spreading force when tightened. This frequently leads to cracked and stripped bolt holes in machinery parts.

    When a Full-Torque thread insert is installed into a cracked bolt hole in cast iron, the crack is automatically drawn together and reinforced by the radial drawing ability of the Spiralhook threads on the outside of the insert. As the insert is tightened into the hole that is threaded with a special tap, the insert is pulled upward and engages the upper side of the threads with the negative hook angle on the insert with the matching bottom side of the threads in the threaded hole. As it is tightened the surrounding metal is drawn inward and deeper into to the Spiralhook threads. "

    We will see...

    I might actually build a 4bt if this block does die on me to get better gas mileage and a proven strong engine.

    -Thanks for the advice,
    Kyle
    '83 Blazer, DB2 built like 4911 by Accurate Diesel, 6.5 oil pump, 6.5 turbo injectors, 82 6.2 block, 6.5 heads, serpentine, gm-4 turbo with turbo master, timing gears, custom stud girdle, lower compression
    Pics: http://s153.photobucket.com/albums/s205/kkarlson_photo/

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