Piston slap is cause by excessive clearance between piston and bore
and there is no fix short of a rebuild with properly sized pistons. GM
has 10 or thousands of engine out there with this problem and the 5.3
is the worse it seems. Because of the amount of them and what it would
cost to fix them all, GM has been saying that it is okay. You could
reduce the noise but not using 5w30 oil in it and using 10w30 minimum
(15w40 is it is bad) but other than that not much else you can do
short of a rebuild. It will get worse with time.
No it is caused by the shorter skirt on the new design piston. Nothing
to do with bore sizing. The shorter piston skirts allows the piston to
rock slightly in the bore until it heats up a bit. The "fix" is simple.
Start engine and drive the truck. I haven't seen one yet that had any
damage from it.
There is no particular fix, unless you want to take the engine apart
and have the pistons hand fitted to each cylinder. It's an annoying noise,
but I have yet to see any engine damaged because of it. And we are
going on 8 years now.
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