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question about tapping holes...

Discussion in 'The Garage' started by colbystephens, Dec 22, 2006.

  1. colbystephens

    colbystephens 1 ton status GMOTM Winner

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    one of the bolt holes used to bolt the starter to my engine block is stripped. i think there's enough space in the clearance holes on the starter to run a 7/16 bolt instead of the 3/8 bolt. of course, i'll check before drilling.

    now, i've never tapped a hole before. when i run the tap into the block, will it just follow the existing hole so that i drill straight? or is it more difficult? i'm concerned about really messing myself up.

    thoughts, please.
     
  2. txfiremank5

    txfiremank5 1/2 ton status

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    I will be easier since there is a hole there already. Just watch it and make sure it stays straight. When you tap it, just thread the tap in a little and back up a little and go a little deeper etc, and repeat until you get the tap as deep as you want it.
     
  3. JEBSR

    JEBSR 1/2 ton status

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    After reading that I'm sweating.:haha: :haha: :haha:
     
  4. txfiremank5

    txfiremank5 1/2 ton status

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    Does it need a "not work or child friendly" title? ;)
     
  5. JEBSR

    JEBSR 1/2 ton status

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    Sorry to here that, but we where all there at one point:haha: just take it slow and easy:doah:

    But seriously, you can get a tap guide and use that. I would suggest you use a bit guide and a tap guide since you haven't done this before. It's not difficult but if you don't get it straight your somewhat screwed. Also check one other thing. How deep are the threads stripped? If it is on the first few threads, rethread the hole with a 3/8 tap and run a bolt that will use the entire threaded area. Also make sure you are using a shouldered starter bolt and not just a standard bolt.
     
  6. mechted

    mechted 1 ton status Premium Member

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    Also, make sure you use a lot of oil on the tap.... ATF, or motor oil work just fine.
     
  7. colbystephens

    colbystephens 1 ton status GMOTM Winner

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    thanks guys!
     
  8. rdn2blazer

    rdn2blazer 1 ton status Premium Member

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    I concur, get yourself a guide or make one if you can, and have the necessary equipment, I.E. a drill press that has a square head to the drill press table so the hole is straight.

    the other thing you can do if just the first few threads are damaged is to tap the hole to the bottom. use a a plug tap first to get to the bottom, then use a bottom tap to tap the last few threads to the bottom of the hole. then measure the depth and stick a bolt in that just does not hit bottom. it will gain you some extra bit of thread engagement. hope this helps.
     
  9. rdn2blazer

    rdn2blazer 1 ton status Premium Member

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    ........oh, and yes, its just like being with a woman, you want it good and lubed :D
     
  10. diesel4me

    diesel4me 1 ton status Premium Member

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    good advice,but....

    I wouldn't tap it for a 7/16" bolt!...starter bolts are special,with knurled shanks,plus you'll have to hog out the starter nose hole to 7/16" too,and that will leave only a few thousandths of an inch of "meat" ,and it will weaken it greatly..not a good idea ,especially on a diesel starter,that is under much more stress than one on a gas engine..I'd drill and tap it for a heli-coil,so you can use the stock starter bolts (usually 3/8",or 10mm)...a bigger hole in the block might weaken it enough to cause it to crack too!.:doah: :eek1: ..heli-coiled holes will not strip again,they use stainless steel thread inserts..:crazy:
     
  11. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    And don't use anything but a tap handle to turn the tap. Adustable wrenches, combo wrences etc are not a good idea. Almost impossible to get the tap to stay straight and you run a pretty good risk of breaking your tap. I broke a 3/8npt (pipe tap) once with a crescent. Thats a big ass tap by the way. Almost as big around as my thumb.
     
  12. lurtch-k20-(78-90)

    lurtch-k20-(78-90) Registered Member

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    I agree I started a thread not to long ago about a broken E-Z out, one is just as hard as the other, don't sweat it. BUT if You do break it that CRUNCHING sound you hear will ring in your ears every time you use a tap or ez out.
    One thing you might try instead of oil, use contact cleaner.
    I have tapped alot of holes in castiron even used a drill with a 1/4-20 tap and contact cleaner works great, but IMO you sould use a hand tap, and "feel" how it cuts
     
  13. Zeus33rd

    Zeus33rd Smarter than you GMOTM Winner

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    Depending on the app. there is no problem using a tap in a drill motor. My last job we used to tap ALOT of open (not blind) 10/32 holes in up to 1/2 thick material. We had 12v Makita cordless drills with taps in them. Drill the hole to the right size and run the tap through the hole with some lube...The hole was tapped in like 2 seconds. But, it didn't really matter if the tapped holes ran 100% straight or not. So it worked.
     
  14. roadnotca

    roadnotca 3/4 ton status

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    Hey yous guys, get real. I'm not familiar with the 6.2, but Colby will be "underneath" with no help from "tools", in the cold and working on his back. Get the heli-coil kit, drill, tap, insert coil, bolt-up starter, and don't spend any more time than that "thinking" about it. Fixing the starter bolt hole is exactly what that kit is made for! bangbangbang
    Oh yeah, :xmas:
     
    Last edited: Dec 22, 2006
  15. orangebeast74

    orangebeast74 Registered Member

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    I too would go with a heli-coil. I work in a machine shop and we use them all the time. They work great and you will be able to retain your stock bolt.
     
  16. Corey 78K5

    Corey 78K5 1 ton status

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    Colby if I remember correctly You have a 6.2 in your Blazer, right? I have seen several 6.2 motors where the block cracked around the outer starter bolt hole. The area around that bolt hole is pretty thin. I would suggest installing a helicoil and using the correct size bolt and make sure that you have the starter support bracket on your starter which is a must on 6.2's.....
     
  17. gmcburb1965

    gmcburb1965 clever user title

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    Yeah, heli-coil is the way to go here...
     
  18. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Better than a heli coil is a time sert. These are basically a bushing rather than a thread coil and they are a permanent repair unlike heli coils which can and do come out. Here is a link to their website. http://www.timesert.com/
     
  19. supersize75k5

    supersize75k5 OrganDonorRacing.com

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    i broke a starter bolt on a big block..


    rather than replace it with a regular bolt again, which will stress the hole when you tourque/tighten in.


    tap the hole with a 10 dallar tap kit from the parts store, use the handle, then use a stud or piece or all thread, some lock tight and a nut,


    this way the pressure is on the flat machined surface and not in the already small and maybe weak area.


    anyways, just another way to do it if the block is cracked and a bolt is risky:D
     
  20. Avery4jc

    Avery4jc 1 ton status Premium Member GMOTM Winner

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    ditto on the heli-coils...oh and in my opinion don't use the drill...for something this small just get the correct handle and use cutting oil on it...the last thing you want to do is use a drill and have it grab and pull itself in crooked...at least w/ a handle you can feel it pulling in and can make sure it's straight.

    BigJimmy74! Which one? I work at Precision Portable Machine shop...its good to hear from a fellow fresnan...

    EDIT: Found it... (Veco Technologies)

    -Avery
     

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