In many of the discussion here low bearing wear as indicated by low lead readings in UOAs is considered the holy grail. However, I submit that bearing wear is not usually the life time limiting factor in the automotive engines I've seen.
Yesterday I was visiting with one of my car buddies and had a look at the Ford straight 4 motor he is rebuilding in his shop. The trigger for the rebuild was low compression and high blow by. Tear down indicated worn rings and marginal valve seats.
This got me to thinking that in most cases of engine tear down this is what I've seen as well. I do this kind of thing as a hobby, not as a profession so my sample is less than 10 motors, but bearing wear out or failure has never been the thing which caused these engines to need rebuilding. Valve train wear and cylinder/piston wear have always been the trigger points. Generally one installs new bearings as a matter of course.
However, it seems that for most engines we should be concerned first about the metals used in the valve train, rings, pistons and bores and only secondarily about the bearing metals. These are surfaces which are generally not pressure lubricated.
For most engines this would mean that iron and aluminum would be the ones to watch most closely.
Comments?
John
Yesterday I was visiting with one of my car buddies and had a look at the Ford straight 4 motor he is rebuilding in his shop. The trigger for the rebuild was low compression and high blow by. Tear down indicated worn rings and marginal valve seats.
This got me to thinking that in most cases of engine tear down this is what I've seen as well. I do this kind of thing as a hobby, not as a profession so my sample is less than 10 motors, but bearing wear out or failure has never been the thing which caused these engines to need rebuilding. Valve train wear and cylinder/piston wear have always been the trigger points. Generally one installs new bearings as a matter of course.
However, it seems that for most engines we should be concerned first about the metals used in the valve train, rings, pistons and bores and only secondarily about the bearing metals. These are surfaces which are generally not pressure lubricated.
For most engines this would mean that iron and aluminum would be the ones to watch most closely.
Comments?
John