Crank Bolt, It’s Not M8 x1.25 |
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Crank Bolt, It’s Not M8 x1.25 |
Mblizzard |
Aug 18 2019, 06:28 AM
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#1
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Advanced Member Group: Members Posts: 3,033 Joined: 28-January 13 From: Knoxville Tn Member No.: 15,438 Region Association: South East States |
This not a stock crank. The stock is M8 x1.25. I am sure this is some variation of the AA 78 mm crank but the bolt into nose of crank is clearly not stock.
As near as I can tell it is a M7 1.25. 1.0 is too coarse to start. Anyone know for sure what the threads are on these cranks and where to get the bolt? Type 4 store online has the stock bolt. |
porschetub |
Aug 20 2019, 12:53 AM
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#2
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Advanced Member Group: Members Posts: 4,701 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
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. |
Superhawk996 |
Aug 20 2019, 04:52 AM
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#3
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914 Guru Group: Members Posts: 5,827 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
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. |
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