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#1
16-12-20, 16:08
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The idea behind these screws was that if you cranked the engine over with a hydrolock , these bolts would shear , and not the whole cylinder would be pushed from the crank case , and create more irrepairable damage
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#2
16-12-20, 16:16
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After re reading I am thinking this too. Bob as you said no other damage was done.
__________________
Jordan Baker RHLI Museum, Otter LRC C15A-Wire3, 1944 Willys MB, 1942 10cwt Canadian trailer
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#3
16-12-20, 16:19
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That may have been the idea but in real life the cylinder gets detached from the crankcase causing lots of damage. I have seen the results and the eight bolts were still OK.
David
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#4
16-12-20, 18:51
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If you start the engine, i.e. mags on with hydro lock, you will likely lose a cylinder or two.
If you crank it over with mags off, you will probably see the benefit of the shear screws.
__________________
Adrian Barrell
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#5
17-12-20, 03:28
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From the photos, it looks like a classic fatigue failure to me, affecting all the bolts. If so, it is an age-related failure as it takes a certain number of stress cycles to grow the fatigue crack across the bolt to the point the remaining intact area is not strong enough to withstand the tensile load and the bolt fails.
A characteristic of fatigue failure is the fracture surface shows a relatively smooth area with fine, often crescent-shaped lines spread across it. The remainder of the fracture surface has a rougher crystalline appearance, which is caused by the sudden final tensile failure. Bob, can you post a close-up photo of the fracture surface, the closer the better? Malcolm
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#6
17-12-20, 03:50
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If my 216 Chev or Ford flatty goes bang-stop it's 'oh shit' (been there, done that). I expect if the same occurs on your radial R975 that takes it to a whole new level.
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#7
17-12-20, 05:13
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Tank, you just stop and hold up traffic. Aircraft, yes it takes you to a whole new level, alright.
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#8
17-12-20, 05:30
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Quote:
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#9
17-12-20, 03:48
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Some good ideas here... I like the idea of conventional cap screws and tapered washers..but have not found any in the 5/16 size yet. It would be easy to make a tapered washer or even have custom bolts machined. I am not sure about the idea that these bolts are intended to shear off under hydrostatic lock up. I am sure that that is one situation where they might fail.There is no mention in the detailed OH manual about any such intentions.
I do have an engine which was badly smashed up inside due to oil in the lower cylinders, when it warms up I will pull it apart and check out the crank gear and related parts. Sorry, I cannot post any other photos but you will note there is a similar pattern of failure on them all. As failures go this one is certainly less traumatic then lots of other types, provided no other issues resulting from this, turn up. Last edited by Bob Phillips; 17-12-20 at 04:12.
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