Forged Redeye Engine Failure :( Why????

[Bobo]

Are you pointing out that it failed because of a lack of chamfer on bolt holes? I see no witness marks from the stud and washer on that bolt hole.

 

[16GoManGoHC2]

Are you pointing out that it failed because of a lack of chamfer on bolt holes? I see no witness marks from the stud and washer on that bolt hole.

No, but why does the surface were the hardened stud washer sat have such a pronounced indentation from the washer? This is a 4140 material billet cap, they’re not soft. How did just torquing the nuts down on the washers do this? Aren’t the washers there to kind of spread the nuts load bearing surface out a bit more and provide a nice smooth hard surface for the nut to spin against and not dig into the cap?

 

[Unholy707]

holes too big? Thermal expansion?

 

[16GoManGoHC2]

holes too big? Thermal expansion?

Nope
Expansion kind of sort of but not thermal.
The “parts” not up to the task are in the first picture, they did not fail but they did not do what was needed of them in this case, their part number was included for a hint. If there was 4 of them not 2 of them in at least caps 2 3 and 4 they would have worked. I’ve mentioned a few material types here, I’ll give another, 8740, it’s the culprit. What’s made from 8740 in the pictures?

 

[Unholy707]

The main studs

 

[Unholy707]

So we have cap walk/ fretting, but those hardened studs are supposed to prevent that?

 

[Unholy707]

So I guess 2 bolt main isn't going to do it (regardless of cross bolts) with the fastener. But if that fastener was used in the dart block with a true 4 bolt main cap, would have been fine? So the fastener is the culprit? Why?

 

[Bobo]

No, but why does the surface were the hardened stud washer sat have such a pronounced indentation from the washer? This is a 4140 material billet cap, they’re not soft. How did just torquing the nuts down on the washers do this? Aren’t the washers there to kind of spread the nuts load bearing surface out a bit more and provide a nice smooth hard surface for the nut to spin against and not dig into the cap?

Agreed that 4140 is a very tough material, I machine parts out of it all the time. It takes a lot of pressure to indent the flat bolt surface.
Was the 8740 not heat treated correctly?