Crank Bolt, It’s Not M8 x1.25 Options

[Superhawk996]

I might be a bit thick but you are talking about the fan hub bolt right?? if so just step up drill size to get to 8mm root diameter of 6.75 and tap to 8 x 1.25 no issue then.
Sharp drills and good taps are the key points here.
Mike read my new post on AA performance parts,good luck mate.

You're not thick but the details are in the math related to the thread forms.

The step up in drill size between 6.5mm and 6.75mm is only 0.25mm which is approximately 0.010" (i.e. not much). The previous threads would have been approximately 0.75mm from thread root to top of thread. So ideally you would need to step up to a fastener with a thread root of at least 8mm to clear the previous threads (i.e. M10 x 2.0, M10 x. 1.5, or M10x1.0 would all fit the bill).

The risk is that if the fastener was M8x1.5 the step up in root size to 6.75mm won't clear all the previous M8 threads. There would then be potential for intersections in thread forms between the 1.25 pitch and the 1.5 pitch. It would look nasty, be prone to cross threading and would be lot weaker than a proper heli-coil repair or tapping fresh to M10.

All theoretical since we don't actually know what this was drilled for.

I'm with Len, have the machine shop drill and tap it for M10.

[Mblizzard]

With lots of good advice from everyone and working with the Type 4 Store (they have been awesome) we decided to do a new crank just to be sure.

[Mark Henry]

(IMG:style_emoticons/default/agree.gif) Since it's new from T4store it's best to send it back and let them sort it.

[Mblizzard]

This is what it is suppose to do.