Originally Posted by BBCMudbogger
Anybody here have any rod bolt failures? I know a guy that lost a rod bolt last weekend ARP wav-locs in a big chevy the bolt failed at idle.
The bolt was already failed, it just came apart at idle.
You need to look carefully at the bolt and the cap. Bolts fail for lots of reasons but the most common is in bending. If the cap was walking around under load it puts a bending stress on the bolt. The bolt in the failure zone will have rows of shiny ridges followed by an abrupt tear. The flat mating parts of the cap and rod will have places where the material look dull and perhaps scared.
A bolt that's just ripped apart with a jagged tear probably backed off, look for again for dull marks and or scaring in the cap to shank interface and also under the bolt head to cap. This would also indicate the cap is squirming around and caused a loss of clamping force which then allowed the bolt to back out a little to where it got hammered on till it broke. This is mist likely a failure under the head where the previous failure is more likely in the shank close to where the thread start. Though a bolt that lost its clamping force might also fail in the shank, but it will most likely be a sudden rupture.
This is also more common to rods that have the big end resized as this tends to bend the bolts as they're torqued up. It's also common in aluminum rods that have been run too many passes.