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Guest Message by DevFuse

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Fixing a ruined bolt hole with JB weld?

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10 replies to this topic

#1 nickolai


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Posted 22 April 2011 - 09:31 PM

82 EA81

One of the bolts for my water pump sheered off in the block. Tried an easy out with no luck. Then I tried drilling it, and to make a long story short, I totally butchered the hole. It's probably 8 or 9mm wide now when it should be 6mm.

So this is my next idea: fill the hole with JB weld, then bolt on a bad water pump, and use it as a guide to drill a new hole into the JB weld, tap some threads into it and be done.

Does anyone see any problems here? Is there something better to use than JB weld?

#2 WoodsWagon


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Posted 22 April 2011 - 09:40 PM

I've also heard of greasing the threads of a bolt, filling the hole with JB and running the bolt in. When it hardens, tighten the bolt.

#3 lostinthe202


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Posted 22 April 2011 - 10:29 PM

Use a threaded insert.

Go to Mcmaster.com and type in item number 93715A610

This is an M6 which you'll have to verify if it's the right size for you. The great thing about this kind is that unlike helicoils you don't need any special tools to install them.

You will need a tap for the external thread of the insert, in this case an M10-1.25 which you can get from Mcmaster as well.

Good idea on using a bad waterpump as a drill guide if you have one handy to help ensure your hole ends up in the right place.

Good luck!


#4 Ricearu


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Posted 22 April 2011 - 10:36 PM

+1 on insert. The jb can't hold real torque. Its a plastic. Use the insertt and if its a water jacket bolt, use sealant when you install it and the bolt

#5 idosubaru


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Posted 22 April 2011 - 11:40 PM

another option would be to tap the existing hole with the largest tap that can fit in there and then drill out the water pump hole for a larger bolt to match the new threads.

i would do the easy fix - timeserts, helicoil, whatever brand who cares. fantastic and easy fix. remove the radiator/condensor if you have to get access to the bolt or rent/borrow/buy a right angle drill. you can get cheap right angle adapters, just depends how much room you got to work with.

it's really easy, don't sweat it, it feel really weird the first time drilling into an engine block...seems all wrong, but it's fine.

if you don't have much room, shear your drill bit in half and use a right angle drill adapter. i've had to do that before. drill bit locked TIGHT and BRACED in a vice and (with glasses on) wail it as fast as you can with a hammer to shear it. i've always had them go bouncing across the floor but find them.

don't waste your time with JB weld. while there's lots of anecdotal experience that seems to encourage folks to try it, it's low percentage on stuff like this. do it right and be done with it.

#6 ShawnW


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Posted 23 April 2011 - 12:58 AM

I would pull the engine to do this surgery if you haven't installed an insert before. I would also practice on the old water pump before trying.

#7 Loyale 2.7 Turbo

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Posted 23 April 2011 - 01:14 AM

Let me Kindly Suggest you to Read my Write-up about re-thread in Aluminium:


it Has pictures and I Hope it could be very Helpful...

Kind Regards.

#8 nickolai


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Posted 23 April 2011 - 08:09 PM

Thanks for the replies and ideas.

The engine is currently out of the car. (and torn apart)

This is what happened with the drilling: As I tried to drill out the steel bolt, I kept slipping and ended up drilling into the softer aluminum around it, especially to one side. So not only is the hole too big, but it's off center. This is why I didn't immediately put a heli coil in it. (Sorry I should have mentioned this before.) I did try to tap the hole at a bigger size, but it's crooked-the bolt doesn't stick out at 90deg.

Since the hole has threads (something for the JB to grab onto), and I have the right size heli coils, would it be strong enough if I put a heli coil into the JB?

#9 Ionlyhave3suubs


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Posted 23 April 2011 - 08:58 PM

A fix that has worked for me on a similar application, seems similar to the one mentioned by Loyale 2.7 turbo.

You already have a hole sounds like the bit started walking off the side of the bolt and got into the softer aluminum.

Possible solution: go ahead and clean up the hole by drilling it out to round again the next size that is big enough to make a round hole but no larger than absolutely necessary. make sure it is at a 90 deg angle. then tap it for the appropriate sized bolt for the new hole. screw the bolt in then cut it off flush with the rest of the surrounding surface, I suggest either a die grinder with a cut off wheel or a 4" angle grinder. I recommend using a grade 5 or grade 2 bolt (either will be harder than the aluminum). Next bolt on your "bad" water pump as a guide. Then get a short section of hard brake line just small enough to go inside the factory bolt hole in the water pump. About an inch or so of line should do the trick. Next get a drill bit just small enough to fit inside the piece of hard line. Stick the hard line through the "template hole" on the "bad" waterpump, then stick the bit through and start drilling slowly. The harder piece of steel beside the bolt should reduce the tendency of the bit to walk and the brake line section should help keep the bit from cutting sideways and help keep it straighter. If you really want to get fancy, you can use your JB weld to glue the line to the bit leaving only about 1/8 " or so of the tip of the bit exposed. It will further help reduce "walk".

After you have your nice straight hole in the center of the old bolt, start drilling larger sizes until you get your optimum size, then tap or helicoil (or other similar product) as appropriate. Using "left twist" bits may even extract the bolt.:banana:

#10 idosubaru


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Posted 23 April 2011 - 09:02 PM

since the engine is out, if you have any competent machine shops they'll fix this properly for $30-$70 depending on rates where you live. this is chump change for them, done that before as well. i suggested one of our down under members to do the same thing earlier this year and $35 later he was done.

is the remainder of the bolt out? if not, what i did (with water pump bolts before too), is to drill the hole that you "slipped" off into big enough to tap the remainder of the bolt into it and finally fall out.

then you can repair it properly. once the bolt is out, unless you mangled all the way around the hole then a helicoil should take on it's own. you probably only mangled it to one side hopefully?

you could still helicoil to a larger sized bolt. the larger sized bolt helicoil will be much larger if it's a hole you can drill out on the water pump housing.

also - once you get the bolt out, you could test and see how much thread is left in the original hole. the holes are not the same depth as the bolts -they are longer - so sometimes part of a fix is using a longer bolt to access those never used threads.

another option would be to drill an enormous hole and tap it - like a 12/1.25, but really short. shear/cut/tap a bolt to fit into it, cut a slot into it with a hacksaw or die grinder so you can use a flat head screw driver to install it. it's almost like you're "filling" it with an insert instead of welding it in. use lock-tite and screw it in, then drill and tap inside the bolt shaft you just screwed in.

i would not rely on JB weld at all, but it's not going to hurt (or help) if the rest of the repair is done well. there's a few options to do it and do it once.

good luck.

Edited by grossgary, 23 April 2011 - 09:05 PM.

#11 idosubaru


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Posted 23 April 2011 - 10:38 PM

here's a guy that just had JB weld not hold for more than a couple days:

it's a really low percentage solution on engine blocks in my experience personally (0%) and watching others try it and not work. the larger point though is there are many other ways to fix this that would be 100% successful, that's the bottom line to me. but i hate doing something twice.

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