On May 6, 8:26 pm, johngd...@hotmail.com wrote:

I thought issues like that were a thing of the past, from before
computer controlled machining.

The piston slap noise is not the result of relaxed piston-bore production
tolerances.  The noise is the result of shorter piston skirts.

Piston slap is common on lots of engines these days. In an attempt to
maximize fuel economy, engineers have worked to reduce piston to bore
friction. This has been done by reducing the piston's skirt length
(think height of the piston) and optimizing the piston to bore
clearance for a warmed up engine. The 3.5L V6 has aluminum pistons and
iron liners. They expand at different rates, plus the pistons are no
cooled directly, so they run hotter than the bores. Since aluminum
expands at a higher rate than iron (steel), the piston to bore
clearance is greater when the engine is cold. This increased clearance
along with the shorter skirt allows the piston to rock slightly in the
bores. As a piston passes top dead center and bottom dead center the
trust angel of the rods change direction. This causes the piston to
shift angles in the bore. The pistons shift so that the bottom of the
skirt swings from one side of the bore to the other (opposite side of
the piston now rides against the bore). If the piston is slightly
loose in the bore, the piston can build up enough speed during this
shift that it strikes the opposite side of the bore with enough force
to generate an audible noise. Many older engines (including Toyota
engines) had so much lifter and chain clatter that you could not hear
this noise, even if it was present. And many older engines ran tighter
clearances, which reduced the noise when the engine was cold, but
increased friction and hurt fuel economy. And many older engines had
longer piston skirts that limited the piston's angle changed, but the
longer pistons were heavier and had higher friction, again decreasing
fuel economy.

I think every manufacturer is hearing complaints about piston slap.
Even with really good machining techniques, there is some variation in
piston to bore clearance. When you are trying to run at the perfect
clearance, a few are going to miss. In general if the piston slap
noise goes away shortly after you start a cold engine, it is nothing
to worry about. If the noise persist after the engine is warm, you
probably need to have an expert check it out. It might not be piston
slap at all.

Same basic engine. I would expect it to behave in the same manner.
This is really nothing new. A couple of years back when I was shopping
for a pick-up I test drove three V8 Tundras. All three exhibited
marked piston slap noise when started. The salesman told me they all
did that and not to worry. Interestingly Ford replaced thousands of
engine for this same concern - I guess Ford owners just weren't used
to the rap rap rap of quality. I did not buy a Tundra in the end. I
ended up with a Nissan Frontier - which makes the piston slap noise on
cold morning....errrrrrrrr. I've learned to live with it.

Ed