Why Did the Connecting Rod in an Ultra-Light Vehicle's Engine Fail?

[manuni]

Hey Guys,
Please help me out.
Q. The connecting rod of a newly developed internal combustion engine for ultra-light vechicle failed catastrophically during testing, damaging the crankshaft and smashing the engine block into two. An emamination of the fracture surfaces revealed that the cause of failure was fatigue and that the crack had initiated from the root ofone of the conrod threads.
I've begun my own investigation by carrying out some preliminary finite element analysis. By doing so, l was able to find out the distribution of hoop stress around surface of pin hole.

I need to write a full-detailed report about too many points but am mostly struggling with
1- cause of cracking,
2- any recommended modifications.
3- justification for the recommended modifications.

Please help me.I am seeking for details on those points.
Many thanks

Regards
xx

 

[minger]

Conrod bolt torquing is one of the most important torque specs on an engine. I've often heard that when doing it yourself, it isn't too safe to do it with one torque wrench three times (torquing, backing off, 3x) then checking with 2 other torque wrenches.

Do you perhaps have a picture of the conrod, also maybe a picture of a good one so we can critique the design?