I expect someone ran a puller screw down into that thread as they were pulling the pulley off of the crankshaft nose. Should have screwed the bolt into the hole until it bottomed out on a spacer or direct on the end of the crankshaft so there was no damage to the threads. Last one I pulled was a hard pull!
You might do best to take a sharp drill bit and drill a 1/16" or so of the threads out before attempting to start a tap. You might also make some headway by tapering the end of one of your bolts on a grinder or even better threading it down in a lathe and see if you can get it to catch once you have drilled the first couple threads out.
I didn't remember that the bolt was left hand thread, but it's been a while since I pulled one. Any chance there was a change during the series? Maybe a regular thread bolt with a sheetmetal lock? I'll have to look in the SRB, but it's not handy at the moment.
Hi Team,
ccj has it right, too many times I caught people using a puller without the adaptor that has a protruding centering spike and a corresponding centre drilling on the opposite side to keep the puller bolt from doing this sort of damage.
I would do as ccj says as if you try and start a tap in the crushed down threads it will cut a new thread at the starting point of the damaged threads--I guess I am trying to say the damaged and undamaged threads are out of sync with each other and you will damage the good thread beyond use.
I would sharpen a suitable sized drill bit with very little cutting angle so it will not dig in too far and take out more threads than needed-- a better option would be a multi start core drill as they have less tendency to dig in.
At The Dealer we had torque wrenches that qould work in both directions for such left hand threads.
Some cheap ones I have seen at auto accessory shops are this type.
The torque value would be the same as for a comparable sized right hand threaded fastener.
Cheers,
Eddie B.
Even if things go to hell you can get LH helicoils as well as the taps from McMaster-Carr.
On larger bolt holes like that I have gently removed the damaged end threads using a Dremel tool or a tiny end grinder. Good luck with it.
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