4.3 High Incidence of Rod Bearing Failures explained...
#1
02-16-2012, 12:00 PM
4.3 High Incidence of Rod Bearing Failures explained...
Here's an interesting article on the 4.3s rod bearing failure issue.
4.3l V6 rod bearings
4.3l V6 rod bearings
As for 4.3 bearing damage. I was told by a bearing guy. That the reason for all the front rod and main wear is becaose GM went to the large pickup tube on the oil pump.
SBC chevies had no bearing problems since 55. Same with the 229 and many early 4.3's. All had the smaller inlet tube on the pump..
The reason, I was told, for the 4.3 problem, is when the engine is shut down. The oil naturally drains down to the pan.
When the engine restarts. The extra internal volume of the large pickup tube creates a large air pocket that takes just an instant more to overcome and in that time the front rod/main bearings get starved or a weak air/oil combo from the oiling system.
Causing just that little bit of wear. That plus the imbalance harmonics of this engine design really test the bearings.
SBC chevies had no bearing problems since 55. Same with the 229 and many early 4.3's. All had the smaller inlet tube on the pump..
The reason, I was told, for the 4.3 problem, is when the engine is shut down. The oil naturally drains down to the pan.
When the engine restarts. The extra internal volume of the large pickup tube creates a large air pocket that takes just an instant more to overcome and in that time the front rod/main bearings get starved or a weak air/oil combo from the oiling system.
Causing just that little bit of wear. That plus the imbalance harmonics of this engine design really test the bearings.
#2
02-16-2012, 12:04 PM
As stated early on in the link you provided, I bet a much higher percentage of rod bearing failures are due to prolonged LIM gasket leaks affecting oil quality as opposed to the diameter of the oil pickup tube. Not that bearing failures are a common problem to begin with. The title of this thread is somewhat sensational.
Besides, when you really think about it. How much air could there be? When the engine is off, there is quite a bit more oil down in the pan than when it is running; further submerging the pickup tube. It's not like the entire pickup tube would be drained. Even if there is 1" of air in the tube, the volume difference between a 3/4" pickup tube & a 5/8" pickup tube is very small (0.135in^3 per inch of air in the pickup tube).
Besides, when you really think about it. How much air could there be? When the engine is off, there is quite a bit more oil down in the pan than when it is running; further submerging the pickup tube. It's not like the entire pickup tube would be drained. Even if there is 1" of air in the tube, the volume difference between a 3/4" pickup tube & a 5/8" pickup tube is very small (0.135in^3 per inch of air in the pickup tube).
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