Would blow by cause engine to throw a rod?

Blow-by itself is unlikely to directly cause an engine to throw a rod. Blow-by is the leakage of combustion gases past the piston rings into the crankcase. While excessive blow-by indicates significant engine wear and problems, it's not the *direct* cause of a thrown rod.

A thrown rod is typically caused by:

* Rod bearing failure: This is the most common cause. Worn or damaged rod bearings lose their ability to properly lubricate and support the connecting rod, leading to seizure and ultimately a thrown rod. Excessive blow-by can contribute to *increased* wear on the rod bearings due to the increased pressure and contaminants in the engine oil, but it doesn't directly *cause* the failure.

* Over-revving: Spinning the engine far beyond its designed RPM limits puts immense stress on the connecting rods and crankshaft, leading to failure.

* Insufficient lubrication: Lack of oil or low oil pressure deprives the bearings of lubrication, leading to overheating and failure.

* Pre-existing damage: A cracked connecting rod, a fatigued crankshaft, or other internal damage can predispose the engine to throwing a rod.

* Manufacturing defects: Rarely, a manufacturing defect in the connecting rod itself could lead to failure.

In short: Excessive blow-by is a symptom of a badly worn engine, often indicating problems that *could* eventually lead to rod bearing failure and a thrown rod. But it's the underlying issues (wear, lack of lubrication, etc.) that are the direct causes, not the blow-by itself.