Striped Aluminum Hole

kopeck · Jan 5, 2010

I've got a crankcase that has a striped hole. The current bolt size is M8x1.25, could I just get an M10x1.25 bolt, and run a 8.8 drill down the hole and retap? I guess what I'm worried about is having enough meat to be able to get a decent cut with the M10 tap.

The bolt get torqued down to 18 foot pounds. The holes in the flange have quite a bit of play so the M10 should work, an M12 might be pushing to though.

K

C.R. · Jan 5, 2010

can you find thread inserts? Helicoil or something similar?good luck

kopeck · Jan 5, 2010

(quoted from post at 08:12:25 01/05/10) can you find thread inserts? Helicoil or something similar?good luck

I could I suppose depending on how big the insert is.

I suspect it would be a few sizes up, I don't have a ton of space to work with.

K

toolz · Jan 5, 2010

You could use a "step stud" if you needed to have an 8mm stud when done. These come in various lengths, and are 10mm on one end, and 8mm on the other. Were very common for rebuilding air cooled VW cylinder heads.

douglas carroll · Jan 5, 2010

fill with aluminum weld puddle ( heliarc ) then
redrill hole and thread

Bob · Jan 5, 2010

WOW, that's a LOT of torque on a little fastener going into aluminum!

Helicoil it.

Hole will need to be drilled to 8.3 mm, then tapped with special Helicoil tap. (About .327".)
Helicoil specs Go to Page 17

Spook · Jan 5, 2010

You should be able to helicoil the hole to the original 8mm size. Costs a few bucks for the stuff, but once you have it, you can do a lot of them.

kopeck · Jan 5, 2010

Sounds like I'm going shopping after work...

How much does a kit usually run?

K

Dean · Jan 5, 2010

The last one that I bought, about 18 months ago, was around $80.

Dean

kopeck · Jan 5, 2010

I'm assuming that was for more then one size right?

K

Anonymous-0 · Jan 5, 2010

A good aluminum welder could add a little more material as well. It's common to weld oil pans off of semi's and also to weld up the hole for the air valve on aluminum rims and drill another one in a different location. Dave

Anonymous-0 · Jan 5, 2010

18 ft pounds on a 8mm bolt?? must be 18 in. pounds

kopeck · Jan 5, 2010

No not 18, I had the head bolts number was stuck in my head.

15 foot pounds.

K

Dean · Jan 5, 2010

No. The quoted price was for a kit includinig specially sized drill bit, installation tool and several (5?) inserts of the same size.

Dean

kopeck · Jan 5, 2010

$35 bucks for the kit (10 inserts, a tap and a install tool) from NAPA. Add another couple for a drill bit (I bet I had one but why find out that I didn't and have to drive back into town).

Not cheap, but at least I'll be able to sleep at night.

It's not even my engine, that's why I think I'm so nervous about getting it right!

K

Dean · Jan 5, 2010

K:

You will almost certainly find the bit needed for the helicoil tap is a special, non standard size, hence the price of the kit.

Dean

kopeck · Jan 5, 2010

(quoted from post at 17:47:27 01/05/10) K:

You will almost certainly find the bit needed for the helicoil tap is a special, non standard size, hence the price of the kit.

Dean

Yeah, it was 21/64s or something like that.

None the less the hole outfit was under $40.00. They don't give them away that's for sure.

I installed it a few minutes ago. Very simple, no problems. Now I feel a whole lot better about that bolt. I hate to work on a friends machine and not get it right, it's one thing if I mess up my one machine, when it's someone elses...

K

MarkB_MI · Jan 5, 2010

Helicoil is by far the best solution. A lot of new aerospace stuff is helicoiled because it's resistant to cross-threading and can handle more torque that the same size fastener in aluminum.

However, for non-critical fasteners, you can fill the stripped-out hole with Devcon metal-filled epoxy, then drill and tap the filled hole. No good for high temperature, but acceptable in many cases.

Anonymous-0 · Jan 6, 2010

Friend had an import truck that had 6mm bolts holding the transmission top on.I tapped all 4 for 5/16 bolts, no more trouble.

Striped Aluminum Hole

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