Re: Flywheel cap screws

Pete Twissell

It is worth noting that the strengths indicated by bolt grades are minimums, and that there are a lot of very dodgy manufacturers who will mark bolts as whatever they want to sell, regardless of properties.
At work, we once bought a batch of "Unbrako" bolts. After some failures and an investigation, it turned out they were marked "uMbrako" (my capitalisation) and they were fakes.

On Sat, 20 Feb 2021, 11:46 Mark Dunstone, <mark.dunstone@...> wrote:
Yes, to all that.  My experience with propellor bolt breakage:   I had 8.8 MPa ‘high tensile bolts’, and perhaps they were, but they were also very brittle.  After around 150 hours 4 broke in flight, necessitating an out landing in a rape seed paddock. With a wood prop these bolts are not torqued much at all.   Changed to 3,2Mpa bolts which easily handle the minimal torque, but are malleable rather than brittle, and the problem was least for the next 600  hours when the VW conversion was replaced with a Jabiru.  When investigating this (after the out landing) I noticed I could have purchased 8.8MPa bolts that could be bent and which weren’t brittle.

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