I've seen both types of rods fail in both axis for various reasons. The critical buckling load is determined generally by the Rankine formula (or modifications thereof). Effective lengths for the rod are normally K=1 for the thrust axis and K=0.5 for the pin axis. But, the pin axis value is not strictly correct and could be as high as K=0.65 (the shape of the transition to the bigend strongly influences this).
Elastic or plastic failure may occur on either axis (or both) depending on rod geometry, cylinder pressure, rpm, etc.
An H-Beam rod is a convienient (for low volume) way to improve the strength in the possibly weaker pin axis for engines with high cylinder pressures and means you don't have to do a rigid analysis for each application which is time consuming and hence costly.
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I am wondering if some of these connecting rod and rod bolt issues are coming after bearings get hot and the heat on the rods is what may be fatiguing them? Is anyone checking these cranks for heat marks on them when there are failures?
At the end of the day even the most rigid analysis of a connecting rod is worthless if the rod and bolt are made from poor quality materials.
TTV Racing - Race flywheels, clutches, drive shafts and valve guides - over 5000 applications & custom one off's or production runs - made in England.
Suppliers to GT3, LeMans, WRC, Global X-Cross, WTCC, BTCC, F3 and more! Visit our Instagram Page!
I am not a Pro. But I think primary rod failures are extremely rare and occur due to defects in the metal (which may be acquired if the rods are nicked, or due to manufacturing defects, etc.) not to the cross sectional design. Obviously, rod bolts do fail, but I suspect even most of these failures are due to improper assembly or defects.