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. |
Superhawk996 |
Aug 18 2019, 01:02 PM
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#2
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914 Guru Group: Members Posts: 5,869 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
Useful trivia on ISO metric fasteners and trying to figure out what you might have if unknown.
M6 x 1.00 fastener will be drilled with a 5mm drill then tapped. M8 x 1.25 fastener will be drilled with a 6.75mm drill then tapped M8 x 1.5 fastener will be drilled with a 6.5mm drill then tapped M10 x 1.5 fastener will be drilled with a 8.5mm drill then tapped. See where this is going? You can gauge a metric hole (approximately) by the size of drill rod that will just barely fit into the tapped hole. From there you can roughly infer the bolt size and pitch. At which point I'd find that tap and see if it runs in easily. If not, don't force the tap unless you're sure you have the right one or you'll have a complete mess on your hands. Highly doubtful you have a M7 x any pitch fastener. That would be a very uncommon size for automotive use. If you really think that is the case, check with the crank supplier. Don't get me started on British machinery and Whitworth fasteners. (IMG:style_emoticons/default/chair.gif) Digital calipers and a thread pitch gauge are a must for working on old stuff in my opinion. |
Mblizzard |
Aug 19 2019, 09:27 AM
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#3
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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 |
Useful trivia on ISO metric fasteners and trying to figure out what you might have if unknown. M6 x 1.00 fastener will be drilled with a 5mm drill then tapped. M8 x 1.25 fastener will be drilled with a 6.75mm drill then tapped M8 x 1.5 fastener will be drilled with a 6.5mm drill then tapped M10 x 1.5 fastener will be drilled with a 8.5mm drill then tapped. See where this is going? You can gauge a metric hole (approximately) by the size of drill rod that will just barely fit into the tapped hole. From there you can roughly infer the bolt size and pitch. At which point I'd find that tap and see if it runs in easily. If not, don't force the tap unless you're sure you have the right one or you'll have a complete mess on your hands. Highly doubtful you have a M7 x any pitch fastener. That would be a very uncommon size for automotive use. If you really think that is the case, check with the crank supplier. Don't get me started on British machinery and Whitworth fasteners. (IMG:style_emoticons/default/chair.gif) Digital calipers and a thread pitch gauge are a must for working on old stuff in my opinion. OK so did a lot of checking. 6.5mm drill will fit into current hole with a little movement. Not much. OD of M8 bolt 7.90mm tap 7.99mm as best I can measure. There is a clear point (slightly shinny where bolt has rubbed) where a M8 bolt hits a lip in the crank. See below Hard to see but there is a clear difference in the size of an M8 compared to the threads in the crank. The lines exaggerate that difference somewhat but it can seen with the eye. Best I can tell the crank has a number 780B 180435 that brings up no results when searched. |
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