[Diy_efi] vortec engine piston noise?

[Shannen Durphey]

"Slap" occurs at idle also.

Been in the repair side of the business long enough to know.

For 50 years GM made engines that didn't make piston noise until
something went wrong.  Now, suddenly, the explanation is that they
need more clearance around the pistons?  Nope, sorry.

Same story with wristpin failures though.  Never saw a wristpin fail
in a stock engine in forever.  Then suddenly the 2.2's fail left and
right.  Engineering changes, material differences, software based
redesigns all contributing to the issue.

300 hp out of a 350 ci+ engine is childs play with today's parts, not
a "delicate balance."   GM is trying something different (again) and
this time they made a "boo-boo."  

366 truck engines see more heat than any pickup engine.  I worked for
the phone company when they'd get so hot at high idle as to melt
plastic parts in the engine compartment.  Lotsa fires then, too. 
Funny those pistons haven't "slapped" in, ohh..., forever.  I can tell
ya why, though.  Think about the piston and skirt combined length. 
Know when piston slap started becoming super prevalent in the
smallblocks?  When the zz series of motors came out.  It wasn't just
the lifters that did the tapdance in those engines.  The short skirt
hypereutectic slugs gm used made a ton of noise.

Hmmm.... Severe duty pickup motors?  Some see it.  Most don't come
anywhere near to "severe duty" usage.  

If you spend 20 to 30 thousand and up for a truck, ain't no way you
should accept anything like the kind of noise these engines are
making.  Doesn't matter how harmless it is.  Think for a minute how
much work GM (and their techs) put into fixing brake squeal on the W
bodies in the middle to late 80's.  That noise was nowhere near as
obnoxious as what's coming out of the engines now.  But they've
decided not to eat the cost of this?  

It's not uncommon for a tech to spend hours chasing wind noise,
suspension squawks, and things as stupid as "loose dashboards"  These
are often issues that most techs would agree are petty and well below
the "harmless" level.  I have yet to hear of or see a GM bulletin
saying that gm will not do the work to address these customer
concerns.  Hell, they're willing to spend money fixing paint problems
for years after the paint peels off, but they won't install a new
engine?  

Funny how Chevy warranty time has _always_ paid squat for major engine
work.  Remove, disassemble, inspect, overhaul, and replace an entire
engine in less than 12 hours?  They sure as hell don't want the techs
to diagnose an engine problem very often.  And they better not expect
a guy to do much "inspecting" in the process.  R&R, Bang out -n- bang
in, hurry up and get this warranty work out as fast as possible to get
some real money into the service bay.  Happens day after day in
dealerships across the country.

Nice diag on the carbon noise, if that was it.  The water trick works
well, and it's a great old fix that lotsa folks don't know about.  But
that's not the case with the new chebbys.

Think for a minute what happens at trade in time when you have a noisy
engine.  There's no dealer in the country that's going to give you
reasonable money for your truck if it's making a noise like the
engine's coming apart.  Doesn't matter how "harmless" is it
mechanically, it's not appealing to anyone.  The noise has now done
actual damage to the resale value of the vehicle.  Except that the
claim of "no dealer in the country" isn't quite accurate.  See, if you
want another GM vehicle, the GM dealer will give you something decent
on your trade since GM has instructed them as to how reliable the
engines are even with that noise.  Nice side benefit of not replacing
the engine.

Does the restaraunt you eat at tell you how you're getting your food? 
Does the store you shop at tell you what the clothes you buy will look
like?  Does the real estate agent tell you what house you will accept?

Justify dealers' claims that they don't need to bring the car up to a
customer's reasonable expectations.
Until everyone else's car makes that noise, mine better be quiet.

Shannen

mike katz wrote:
> 
> --- 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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