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Things were going slowly but well on my install last night until I sheared off the passenger side motor mount bolt while putting everything back together (at about midnight - sigh). Here are the key questions on my mind this morning:

  1. Will I be able to extract the bolt with a standard big box vendor-issue bolt extractor (?
  2. If so, how big should the pilot hole be (i.e., how big a bit will I need for sufficient grip)?
  3. Am I likely to need to re-tap the bolt hole?

Any other warnings or suggestions would also be appreciated.

Adding a little more info: the bolt is on the forward side of the passenger motor mount. This is the bolt closest to the manifold crosspipe. The bolt is sizeable with a 14 mm head (or it did have such a head). I have plenty of access but it is a grade 8 bolt so just drilling a tap hole is a chore. As yet, I haven't managed to get enough torque on an extractor to back out the remains.

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    How big is the bolt diameter? Is it broken on the block side of the motor mount? How much access do you have?
    – mikes
    Commented Jun 10, 2012 at 20:07
  • @mikes, check the answer below for what I had to do.
    – Bob Cross ♦
    Commented Jun 11, 2012 at 17:10

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The short answer is: none.

A grade eight bolt that's broken off in the engine is almost certainly not going to extract in any conventional fashion. There's just too much torque on the threads. If you're going to drill a pilot hole big enough to get a grip on the remainder of the bolt, you're basically going to have to drill with a huge bit.

Instead, the shop will end up drilling an overlarge hole, removing the carcass of the bolt and inserting a helicoil. That will create a new threaded surface for the replacement bolt to grab.

Note: "removing the carcass of the bolt" is not an easy step. It's just as much trouble as drilling the pilot hole: there's still an obnoxiously tough bolt chunk where you want to put the replacement threaded insert. This sort of drilling makes all kinds of metal shavings that will cling to human skin and do monstrous damage to a human eye. Basic safety glasses are insufficient.

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  • That last sentence implies you found out the hard way - is it all sorted without injury now?
    – Rory Alsop
    Commented Jun 11, 2012 at 21:04
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    @RoryAlsop, everything is fine: I paid a $200 be-more-careful fee to the shop. The signal that I needed to stop trying to solve this on my own was when my safety glasses started becoming opaque with nasty spirals of razor wire.
    – Bob Cross ♦
    Commented Jun 11, 2012 at 21:09
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If there is sufficient metal surrounding the bolt so fitting a larger bolt will not impact structural integrity centre punch it (so your drill bit won't slip)-drill it out and tap a new thread in 3 stages to accept a larger bolt.Use a pilot hole then ever larger drill bits.Not applicable in all cases;but one option that has stood the test of time

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