Rod Bearing Load Estimate for 90 ft-lbs Torque Starter Motor

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The discussion centers on calculating the rod bearing load when a 90 ft-lbs torque starter motor stalls, with calculations suggesting a peak load of 166,844 lbs on the rod bearings, which raises concerns about the feasibility of such a load. Participants debate the assumptions made regarding starter motor torque, cylinder pressure, and the effects of hydraulic lock and pre-ignition on engine damage. It is clarified that the load on the rod bearings will be limited by either the starter torque or the cylinder pressure at TDC, emphasizing the need to consider the crank advantage near TDC. Additionally, the conversation highlights that higher torque starters may not necessarily resolve issues if the engine is already experiencing damage at lower torque levels. The complexity of multiple cylinder engines and shock loading effects on bearings is also acknowledged, indicating that real-world conditions can significantly differ from theoretical calculations.
  • #31
A “comparative novice speedfreek†or a computer chip “over-clocker†is NOT an engineer.

They are individuals abusing the technology.
They have no concept of reliability engineering.
They are pushing beyond the SOE to destruction.

Economics and reliability are critical to engineering.

I agree with you 100%
My aim here is to quantify the possible bearing loads in the aforementioned scenario to point out the folly of such engine modifications. Knowing the torque of the starter motor, I suspect it will depend on on 3 more things; location of spark BTC, cranking speed, & the time interval from spark to combustion. If anyone has insight into that last item, (or the characteristics of the combustion process with regard to this) please contribute.
 

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