I had a bolt break off in my aluminum engine block. I've been able to get
the broken piece out of the block, but the threads were damaged. Now I need
to repair this...
The original bolt was an M8x1.25x100mm of #8 hardness. If I put a new bolt
into the hole, it does grab but is VERY loose and not suitable to hold it's
braket in place.
I was hoping to find an M9x1.25x100mm bolt, but no luck. I then tried to
locate an 11/32"x4" bolt and again, no luck.
So now I figure I can drill this hole out a bit and cut threads for a
Does this sound reasonable?
My biggest issue is clearance. I had to use a 90' drill to get the broken
bolt out. There is almost no visibility to see if the hole is straight. The
bracket that mounts here does not have any critical tolerances.
Your plan or Mr Meehan's helicoil will both work. My objection to your
plan is your intent to introduce an SAE bolt into a metric engine. The next
person to work on the engine will be using metric tools on this bolt.
With the poor location the helicoil may be the better bet.
If it's that hard to access you might have a heck of a time trying to
properly install a helicoil insert.
If the bracket is not something you anticipate having to remove and
replace often I'd give a try to using JB Weld to "glue" your new M8x1.25
bolt into that buggered up hole.
Use a Q-tip and solvent to clean out the hole and the new bolt threads
as best as you can, then slap on some JB weld and drive the bolt in as
tight as you dare to without stripping the hole.
That's worked for me and it might for you too, and if it doesn't, you
can start from scratch again.
I often use Jeff's idea but use a separate stud and nut. After a good
cleaning, smear the hole and stud with JB Weld or similar epoxy and screw
the stud in until it bottoms out. Let it set up for 24 hours, install
washers as desired, install nut and tighten. It makes a stronger and
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