shrink fit sleeve for stripped main stud
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  1. #1
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    Default shrink fit sleeve for stripped main stud

    hello everybody. this is my first post so if this is in the wrong place please feel free to move it.

    ive come across a very frustrating issue with an aluminum engine block and im picking at straws here on how to fix it.
    my issue is that the engine is to use ARP main cap studs which are to be torqued to 90ft/lb. one particular hole just continues to strip out before reaching the finish torque. first it stripped the aluminum threads in the block, then it stripped the helicoil, then pulled the BIGSERT out from the outside aluminum threads.
    ive got maybe a .08" wall on 2 sides so i cant really drill it out and try a third time thread repair which im not even sure they make... in order to have this tig welded i would have to cut the block out from the side and have the hole filled and have the block patched once the hole is filled. id really like to try and avoid cutting the block up that much if i can find another solution first.

    my next thought was to turn down a stainless steel sleeve and shring fit that into the aluminum hole and use either loctite 608 or 640 similar to how cylinder sleeves are installed. my only concern is that i have little experience in engneering this sort of thing and am worried that the sleeve might be "pulled" out by the reciprocating forces of the crankshaft.

    any thoughts on the shrink fit sleeve idea would be great but im open to any other suggestions i can get as well.

    the stud is an ARP 10x1.25 thread and yes ive checked the torque wrench as well. all other holes ended up fine except this one...

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    First off I think the toque value is to be applied after the cap and nut is installed. The kits I have installed in LS blocks have a non threaded portion at the end of the stud to prevent the stud from bottoming the threads out in the holes in the block. Screw them in til they stop after your repair and do not torque until crank and caps are placed. Nothing is gained by bottoming a stud out in a hole extremely tight except misery later.

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    I have made a lot of thread inserts out of grade 8 bolts sometimes gr5 or 8.8 metric.
    Works well just Loctited in place.Making your own allows a choice of grip length.
    You may have some porosity in that spot.I don't think a shrink fit in aluminum for a smooth od thread insert is a good idea and neither a stainless one.
    Normally in aluminum I'd use a coarse thread but if you use a long enough insert a fine thread would work and allow for a thinner wall insert;a 1/2-20 might be to close.Looks like your wall is only about 9/16" thick?

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    If the alloy is only 2mm thick in part of the bolt hole,I say forget it ,and go on to plan B......can the hole be drilled deeper?.. ally needs about 3x bolt dia to hold torque....There is no way a force fit wont break out the thin part,and any normal V threat exerts a bursting force,you would need a square or butress thread......there is not enough metal left for any thread.

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    No way that shrink fit would hold the insert in thin wall material where even the threads are stripping.
    Unless there is enough "meat" to drill the hole considerably deeper your block is boogered for good. And even then you would need one extra long ARP stud..

    Might be just easier and cheaper to ditch the old engine block and get another one depending how exotic block you are working on.

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    I'm confused by the idea of using a fine M10 thread on a stud in an aluminum block in the first place. Usually studs for Al engines are coarse thread on the "insert" side, with fine threads on the nutted ends. Is it possible you got it backwards, and tried inserting the wrong end of the studs?

    And are these head studs or main caps? Can you post a picture of the damaged hole?

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    The torque value is for the nut. The stud is installed by hand. Torque values are usually based on the premise that the stud and nut or threaded hole are similar material. Where either has dissimilar strengths, The less strong governs the tensile stress applied to the fastening system. A stud or cap screw threaded in to a blind threaded hole will bottom or seize at the end of the internal threads, continuing to apply torque will damage the threads of the less strong member.

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    If you stripped the inserts out, you are doing something profoundly wrong. One could assume that there might have been something wrong with the original thread, but the new one too?

    What engine is it?

    What is your process for torquing the stud?

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    Just to be sure: the proposal is to drill the threads out of the aluminum threaded hole, and fabricate a steel
    part which is ID threaded for the original threads, and the OD of which is a smooth surface, and install that
    via adhesive or shrink fit, into the aluminum?

    If that is so, you have two problems to contend with. 1) the thermal contraction of the cast aluminum
    block is far larger than the steel insert you propose. As the engine heats the shrink goes away. 2) doubtful
    that an adhesive bond would have enough surface area to resist the extraction force that happens when the
    nut is torqued to value. And honestly that's a WAG.

    My gut feel is, don't do this.

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    I agree with the others who say a threaded insert is not going to hold. Can you weld up the hole and start over? As others have said, I believe you are trying to install the stud wrong. It is bottoming out and jacking out the threads.

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    The OP needs to answer some of the questions put forth in the responses. What block of what displacement and who made it? He may be polishing a turd.
    Joe

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    unfortunately this block is a 1 off currently and would cost me about $3k to replace and a 4 month lead time in doing so. yes ive only installed the studs into the block hand tight and final torque value was applied to the nut once everything was in place. unfortunarely this is the second to last stud in the torque sequence. to be clear, the id threads of the insert arent whats stripping, its pulling the od of the inserts out of the aluminum casting. the last insert pulled out with the stud and was a pain in the ass to get off the stud since it was cold formed with the stud.

    the engine block is a hyundai theta ii out of a 2010 genesis coupe.

    i believe this section of the block was just a crap casting since nothing but the actual aluminum in the block is being damaged.

    the arp studs have a 1" thread length that goes into the block. ive got about .3" of the original threads which say below the insert depth and is still usable though i doubt .3" is enough thread for much of anything.

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    total depth of the hole is roughly 1.750". the original threads in the block were 10x1.25 and the arp studs are 10x1.25 on both sides. only difference between the sides is one has an allen hole to set the studs in by hand.

    would it be better to make an insert out of 6061 to try and keep the expansion similar?

    this idea only came to me by the mothod of cylinder sleeve installations. i wasnt sure if there was a way to adapt that process to this scenario.

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    If no car guy but if it's pulled out the original threads, a heli-coil and a big-sert I doubt very much a pressed in sleeve will work.

    Would an aluminum insert with a fine O/D thread (internally threaded for your ARP stud) with a matching I/D thread in the block?

    Can you post a picture?

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    Quote Originally Posted by ryan953267 View Post
    unfortunately this block is a 1 off currently and would cost me about $3k to replace and a 4 month lead time in doing so. yes ive only installed the studs into the block hand tight and final torque value was applied to the nut once everything was in place. unfortunarely this is the second to last stud in the torque sequence. to be clear, the id threads of the insert arent whats stripping, its pulling the od of the inserts out of the aluminum casting. the last insert pulled out with the stud and was a pain in the ass to get off the stud since it was cold formed with the stud.

    the engine block is a hyundai theta ii out of a 2010 genesis coupe.

    i believe this section of the block was just a crap casting since nothing but the actual aluminum in the block is being damaged.

    the arp studs have a 1" thread length that goes into the block. ive got about .3" of the original threads which say below the insert depth and is still usable though i doubt .3" is enough thread for much of anything.
    Not familiar with that engine but some engines are famous for stripped threads like GM Northstars.
    What is the manufacturer recommended torque for the bolts?

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    A press fit bushing could pull out and then tighten against the cap. So you'd THINK you have proper torque on a cap bolt, but you'd have a loose bushing in a hole.

    I think your plan B is the path. But (forgive my ignorance) can't you use a Mig welder to fill the hole from the outside?

    BTW, whole engines (the 2L turbo) are on eBay for 2600 or so. But if you want a newly rebuilt engine I understand trying to make this work. That said, that casting may just be crap and will never hold a properly torqued bolt. Sure sounds like it.

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    Welding will undoubtedly distort the main bearing housing bore next to the repair, requiring a line bore or line (shudder) hone....
    Decades of proven repair on threads in aluminum automotive applications would be to make a thick (relatively) walled threaded insert out of 642 bronze.....
    Stronger than the aluminum at holding threads and has similar expansion rates....
    Sounds to me as you have passed that point....
    Pressed or shrunk sleeve will not work.....fools errand!
    Welded repair will kill the heat treatment of the repaired area making the parent material at the fix gummy and with lower tensile...you already (apparently) have issues at that location...
    Might not get better with welding.

    If this was the last one on planet earth and worth millions...i would try the welding route....must carve open the cavity to allow full penetration all the way to the bottom of the original threads...
    If this block is used chances are that the material is oil impregnated, often needing the welder to weld then grind out the bead till the oil is cooked out....might take several passes to get a good
    low porosity weld....Some would run that weld using helium (pure) and running the electrode DC.....Yea i know that is not what the books say, but for some castings it works better, giving
    better penetration, with lower overall heat to the surrounding structure......

    Weld should be run in short bursts, peened between to reduce distortion....expect to line bore the mains after completing the weld, if you get a reliable thread repair that holds torque.....

    One additional note...the torque value that ARP is quoting, reflects the torque needed to bring the stud material into its elastic point (some stretch) ....May mot be able to get that with the base
    material of the block...that as you have discovered is the limit.....I would use the original makers factory torque spec. as a better guide.....

    You need to find a welder that is experienced in this realm.....at this point it has moved past the "rookie fix it" route..

    Good luck!
    Cheers Ross

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    why cut hole in block to weld it? if you can get at it to tap it for inserts someone can weld it. there are weird angle tiny torches.

    I hate tapping welded aluminum. good luck.

    shrink fit on a thread insert near a thin wall.... no way in hell.

    can you go much deeper? a longer stud there would be far preferable.

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    the block had custom ductile iron cylinder sleeves installed which is why im intent on saving this block rather than getting a new motor. i have a spare oem block so i guess i have to weigh the cost/reliability welding vs the cost of removing the sleeves from this block and installing them into the other. the welder i went to was going to cut down the side to fill it due to the overall depth of the hole. i only weld for small home projects do i took his word on how it had to be done. .

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    Your block is shit. Get a different block. Stop throwing good after bad. It's an expensive hobby.

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