How to deal with a cored thread?

[mountainmachine]

Ok so refitting a bolt on a 300tdi engine and the bolt was just turning, not tightening past just a bit more than finger tight, torque wrench was set correctly at 45NM and it never go close to that as no effort was required, so removed said bold to see that it has cored the internal thread of the aluminium block its in. Bolt was all cleaned up and perfectly usable before.

Now problem is we need this bolt to be able to go in and tighten as its the timing belt idler pulley bolt.

Now i know in some industries they use something called a 'Heli-Coil' dont know if thats how its spelt or something.

As in like this:
http://coolercasesuk.co.uk/showthread.php?t=1211

But basically need some options as to what we can do and where we can get the stuff to do it.

 

[jug]

thats not a good bolt to thread

the quick and easy option is to drill it out and then use a tap and die to rethread it, then use a bigger bolt. the other option is to get a helicoil and then drill your hole out and rethread it, then screw the helicoil in and use the original bolt. i would only do that if i had to use the same size bolt for a good reason, such as a bigger one would not fit through the pulley's hole (which may be the case).

 

[mountainmachine]

i would only do that if i had to use the same size bolt for a good reason, such as a bigger one would not fit through the pulley's hole (which may be the case).

Exactly the case! A bigger bolt could be accommodated by boring the idler hole bigger, but not really ideal!

 

[custard]

you may get away with retapping on the same size die depending on how mauled it is.
i did this on a wishbone/chassis hole that was not tightening and it worked