[Diy_efi] vortec engine piston noise?

mike katz ecmhacker at yahoo.com
Tue May 21 18:18:19 GMT 2002


--- steve ravet <sravet at arm.com> wrote:
> If anyone has some concrete information on the
> piston noise problems
> with the new Chevy vortec truck engines, like what
> causes it, how it's
> diagnosed, what it sounds like, etc., can you get
> back to me directly?
> 
> thanks,
> --steve


I think you guys worry too much. 

First off I don't care what anybody tells you piston
slap occurs under engine load, not idle. Most of what
you guys are hearing is valvetrain noise. Roller
lifters and changes with the valvetrain weight makes
those things seat faster. I listened to the noise on
this link
http://www.angelfire.com/tx5/gmpistonslap/index.html
That is NOT piston slap.

Piston slap sounds like a bad bearing, but the knock
is a higher pitch and goes away after heavy loading
when the piston gets really hot.
It shows up when the motor is cold and about 1/4
throttle or more and does not change in intensity with
more loading. Bearing noise does that.

You are driving trucks, not cars. The motor has to be
designed with more piston/wall clearance due to  high
engine loading. You would be twice as mad if your
motor seized every time you towed a boat or camper up
a steep grade.

Piston slap is also harmless to the cylinder bore. It
will only cause minor (if any) scuffing to the piston
which will NOT hurt it.

Loose is fast. When building a race motor, the
clearances are set loose as well. 454 truck motors are
known for this kind of problem. 
It also comes from carbon loading due to lack of heat
to clean the piston off. So when they say drive it
hard, they mean it. A quick way to clean up carbon
loading is with a squirt bottle full of water. With
the engine up to temp, run it around 2500-3500 rpm and
squirt a little water in the intake. It will steam
clean the piston.

Enjoy your trucks, they are not on the verge of
breaking. It is a delicate balance to get almost 300
hp
out of a stock motor and still make it quiet, but yet
see severe duty.

Mike

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