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Thread: How far will a 6.2L bore?

  1. #21
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,282

    Default

    Just for the sake of argument.

    I would be hard pressed to go past .75mm overbore on one of these blocks.

    I had a 6.5 block sonic tested recently prior to a purchase. (That did not happen)
    We found that generally what you are showing here is just about right on the money.

    We did tests at 8 spots around the diameter and we did this in 1 inch steps starting at the bottom of the bore.

    The scarry part was the little pockets that are present where the core must have been uneven.
    We found one area on the upper 2 inches of a couple cylinders that had good thickness but then there would be a little pot hole if you will that was very thin.

    The block in question was already .75 over and needed to go farther.
    The basement was sound but I was very nervous about the bores.

    If we had gone on out with it we would have possibly hit water in a couple spots and maybe had failures after it was running.

    The seller insisted the block would go more but after doing the sonic I decided to pass on it.
    I would have liked to cut the sucker open but the seller was adamant on selling it as a good block. (End of story)


    I dont know if 6.2 blocks would be any heavier or have any more integrity in the cylinder wall thickness.

    Regardless I would cap the plan to overbore any of these at .75mm

    Far too much $$$ to find out down the road (No pun intended) that the sucker has issues.

    Sonic testing is not cheap but I have a friend in the business that was also interested in the 6.2/6.5 block thickness so he did this one on the house.

    I think we were just lucky to have found those pot holes because you could miss something like that real easy.

    Every 45 degrees around the hole and do it on the inch starting at the bottom and work up.

    Takes a bunch of time too.

    Hope this offers some insight into this bag of worms.

    Robyn
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  2. #22
    Join Date
    Mar 2000
    Location
    AB Canada
    Posts
    218

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    Quote Originally Posted by dieseldummy
    Cutting with an angle grinder kindof sounds like a suicide mission... A much better choice would be a band saw. If I had access to one I would have taken a cross-section of the block. There isn't much meat in the pan rail area for splayed mains. I guess there doesn't need to be since the idea behind splayed mains is just to spread the load out over the block more evenly. I'm still not certain it is worth it though...
    Please explain [ suicide misson ] does the noise or the sparks scare you.

    What is better, Trying and fail, or failing to try.
    98 GMC sierra 2500 ext cab 4x4 auto tr 6.5 td 252000 km. needs new engine, next project
    95 GMC sierra LE 2500 ext cab sh box 4x4 auto tr 6.5 td 328.000 km. my wife's truck .remote pmd on cooler
    89 GMC sierra SLE 1500 ext cab 4x4 auto tr 6.2 720000 km engine swap at 665000 km because of broken oil cooler line. 6 bolt wheels.
    Waldon wheelloader repowered with a 6.2 na

  3. #23
    Join Date
    Nov 2003
    Location
    COLORADO
    Posts
    723

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    The kickback factor is what scares me... there is a reason that stationary chop saws were invented. One wrong move and there is a good chance of injury. This is observation after spending a good amount of time running a big angle grinder. If I had a junk block laying around still I'd offer it up for someone else to try and cut up. John and I did our part in the cylinder wall thickness proof department... I'll let someone else do the pan rail thickness idea.
    white '93 K2500 started it all..
    red '94 K3500 old faithful
    black '93 K3500 daily driver
    '83 G20 conversion van
    '74 C65 truck diesel conversion...

  4. #24
    Join Date
    Mar 2000
    Location
    AB Canada
    Posts
    218

    Default

    Quote Originally Posted by dieseldummy
    The kickback factor is what scares me... there is a reason that stationary chop saws were invented. One wrong move and there is a good chance of injury. This is observation after spending a good amount of time running a big angle grinder. If I had a junk block laying around still I'd offer it up for someone else to try and cut up. John and I did our part in the cylinder wall thickness proof department... I'll let someone else do the pan rail thickness idea.
    OK, point taken, I'll have to find a block , then i'll do it
    98 GMC sierra 2500 ext cab 4x4 auto tr 6.5 td 252000 km. needs new engine, next project
    95 GMC sierra LE 2500 ext cab sh box 4x4 auto tr 6.5 td 328.000 km. my wife's truck .remote pmd on cooler
    89 GMC sierra SLE 1500 ext cab 4x4 auto tr 6.2 720000 km engine swap at 665000 km because of broken oil cooler line. 6 bolt wheels.
    Waldon wheelloader repowered with a 6.2 na

  5. #25
    Join Date
    Mar 2000
    Location
    AB Canada
    Posts
    218

    Default Mission acomplished:Rail pan area thickness

    Well it took a while looking for a block to cut open, did not find one so i decided to use my own web cracked 98 506 block.

    against diesel dummy's and others advice i used a 7" x 1/8 zipdisc on a 7" angle grinder to cut a wedge out of the rail area adjacent to the center web. i started with a angle cut 2" out and 2" deep towards the web, and than straight down beside the web till within 1/8 of the angled groove, and pryed the pieceback and forth till it broke free. the whole operation took less than 2 min to do. piece of cake, nothing to be scared of, no kick back occurred.
    but I am NO amateur with a grinder to start with.

    thickness of the metal from the surface of the panrail till the waterjacket is minimum 1 3/16 on the inside to 1 1/4" against the outside of the block, wich leaves enough meat in my opinion to drill a hole 1" deep staight down or at an angle for the outerbolt of a splayed cap or full girdle. It baffles me wy in the world GM decided to put the outerbolt holes in the place they are.

    I would put some pics on if i could find a way to do so, but for some reason they are to big and i can't get them smaller.

    Simon
    98 GMC sierra 2500 ext cab 4x4 auto tr 6.5 td 252000 km. needs new engine, next project
    95 GMC sierra LE 2500 ext cab sh box 4x4 auto tr 6.5 td 328.000 km. my wife's truck .remote pmd on cooler
    89 GMC sierra SLE 1500 ext cab 4x4 auto tr 6.2 720000 km engine swap at 665000 km because of broken oil cooler line. 6 bolt wheels.
    Waldon wheelloader repowered with a 6.2 na

  6. #26
    Join Date
    Jan 2019
    Location
    Homer
    Posts
    9

    Default

    After reading All of this valuable information I am wondering a bout the affect of core shift which may affect any block and any cyl wall.
    If I want to go to a big bore I get the block ultra sound tested at a good shop
    I do like where y'all are going here though as I am researching the rebuilding of my 85 CUCV original 6.2
    and am looking for the biggest safe bore I can use safely

  7. #27
    Join Date
    Feb 2000
    Location
    Montana
    Posts
    11,382

    Arrow

    Quote Originally Posted by 86 CUCV View Post
    After reading All of this valuable information I am wondering a bout the affect of core shift which may affect any block and any cyl wall.
    If I want to go to a big bore I get the block ultra sound tested at a good shop
    I do like where y'all are going here though as I am researching the rebuilding of my 85 CUCV original 6.2
    and am looking for the biggest safe bore I can use safely
    Glad you brought that up. As I mentioned earlier in this thread, I had heard from a couple South African and Australian members who reported longitudinal splits in the cylinder walls after boring a pre-599 6.2 block to std 6.5 bore dimensions. I thought at the time, and still do, that a core shift during the casting process may explain this.

    GM's maximum recommended overbore for either the 6.2 or 6.5 is 0.030", but most engine shops will be happy to do a 0.040" overbore, and you'll find a ready supply of 40-over pistons on the market. Personally, I'd look for another block, if at all possible, before going farther that 40. Jim

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