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Piston Slap

18 years ago

1992 Geo Tracker 1.6 litre 8 valve engine with 88K it has what can only be described as diesal sound when it's cold

i researched it abit and i believe that i have piston slap can anyone confirm that and explain what piston slap is and if it is going to grenade my engine??

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Comments (6)

jemdandy
18 years ago
Piston slap happens when the piston is too small, possibly from wear, or from replacing the rings and cleaing up the bore, but not replacing the pistons. On worn engines, the tops of the cylinders and pistons may become worn on one side.

You may hear piston noise when cold and it may dimish as the piston heats. (However, other engine noises can behave the same way.) Often, piston slap is not heard at light engine load, but will appear when pullng a hill in the lower rpm range, or pulling away from a stop, say in the 1000 to 1500 rpm. It suddently comes on as the accelerator pedal is pressed and dissappears if the accelerator is backed off. It has the sound of a bunch little elves hammering on the side of the engine block. I suspect that piston slap will be 'heard' by the knock sensor and it will retard the ignition.
kalining
18 years ago
Unless you know exactly what piston slap is and have heard
it before you will be guessing FOR EVER. Have someone hear
it that knows what piston slap is. Sticking valves will
sound the same when you never change oil on time or let it
go for over 6000km or use the wrong oil. Piston slap in most of the small engines is normal because they use up to
4 different metals when the upper part of the engine is
built. It goes away when warm. G.M. had so many problems
with piston slap in the 3.1 that they rebuilt the motor
under warranty sometimes making it worse. Then they started
replacing motors. Didn't work. They took out bad motors
and put in bad motors. The 3.1 owners were told to live with it. My 3.1 is still slapping with 543,921 kms. on it
and still going strong.
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shelbyscott
Original Author
18 years ago
thank you both for the feedback. I had taken it to 3 different mechnics one said it was a exhaust manifold leak the other said that it was piston slap from overrevving the engine during the winter months and one thought that the cam lobes were wore. I adjusted the valve lash i bought a mechnic's stethascope i put new plugs cap and plug wires in it i retarded the timing which quieted it down abit but i didn't like the idle with the retarded timing. i bought and installed a oil pressure gauge 80 psi cold and around 40-45 warm. it runs like a champ it just has that annoying tick when it's cold???
john_g
18 years ago
Have you considered that more than just one of them is correct?

An exhaust leak at a manifold can make a "ticking" sound.

Piston slap occurs engine cold, but usually goes away as the pistons heat up and expand to fit the bores. Pistons because they expand faster than the block actually have to be smaller when cold to allow for that expansion, that's why they can slap when cold.

Retarding the timing is a mistake. Set it back to where it belongs.

Some engine noises can be almost impossible to identify. The worst thing that can happen is you tear the engine down and you do not actually find anything out of spec, nor worn. When that happens you end up putting the engine back together only to hear the noise is still there. So basically if it's not causing any other issues, let it tick, and drive the thing. There will be little difference in the cost to repair it next year, or the year after when it breaks fully and forces your hand. At least then it will be able to see what the noise was....
shelbyscott
Original Author
18 years ago
thank you
shelbyscott
Original Author
18 years ago
You make a very interesting point: Just drive it and it won't cost you anymore to fix it later than now. That is
good advice I guess that when it comes to my daily driver
i would like it to run well. This rig does run well i
have a issue with it's milage one fill up it gets nearly
30 mpg the next it only gets 18?? same type of driving
i'm gonna save up for a new O2 sensor and see if that helps
thanks again

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