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So I speaking with a service advisor at Ford in Austin TX regarding issues with a GT350. His comment was that Ford is issuing or issued a owner memo saying some piston slap may be audible and is normal. This is from 9/11/17. Can any of the gt350 owners confirm that.. Thanks!
may exhibit a rattle or rapping type sound during cold operation at light loads and speeds from Idle- 3000 RPM.
The noise will be most noticeable during light acceleration in the 1500-3000 RPM range and may also be noticeable in the 800-1200 RPM range with neutral throttle blips.
This sound is caused by the piston motion in the cylinder bore.
This is an inherent characteristic of the forged aluminum pistons utilized in this high performance
reaches operating temperature the noise will diminish, although it may still be noticeable even when fully warm.
There are no durability concerns with this sound."
The characteristic is because of the aluminum pistons, they expand as they heat up. If the pistons fit snug like traditional pistons when cold, as they expanded from warming up, you would have too much friction and just burn up the cylinders.
Anyways, I guess Chevy had the same issue in models that used aluminum pistons. Was never a big long term deal.
Im pretty sure this is also exactly what the 2018 5.0 "tapping" noise while cold at idle is.
Car starts and sounds fine then idle goes to normal and I can hear a tapping from the lower end of the engine I have some videos of it. It doesnt happen when warm and goes away completely when warm.
Piston slap occurs during initial cold start-up, resulting from piston-to-wall clearance which disappears as the piston gets hot. The steel inserts molded into pistons (aluminum) are there to allow uneven expansion circumferentially as the piston heats, stopping or minimizing slap until operating temperature is reached.
Slap usually remains audible (in a normally-worn) engine no longer than about 10 seconds, max.
Ford's "slipper-ground" pistons are actually not perfectly round, when cold. As they heat up, the inserts exert forces which make them become round during regular operation, thus reducing or eliminating "slap" when cold start-up occurs.
Heres what a GM engineer said about piston slap : "Are you talking about piston slap during the first few minutes of warmup..?? If so...that is what it is. Nothing to fear or nothing really wrong...just the piston noise until the piston warms up to fill the clearance to the bore. Pistons rock as they cross TDC where the thrust load from the rod angularity shifts from one side to the other. This makes noise. Harmless..but it is the source of piston slap in most all situations. To prevent this, pistons are designed with long, tapered, flexible skirts so that they can be fitted very tight in the bores when the bore and piston is cold. The taper of the skirt and flexibility of the skirt then prevents scuffing when the piston is hot. Also, the piston pin in OEM production pistons is always offset to one side....it is NOT in the middle of the piston. By offsetting the pin in the piston, artificial thrust load is created to control the piston "rocking" as it crosses over TDC. Unfortunately, all of the above control techniques, common in past model engines to the extreme, create excess piston mass, cause friction and cost power and fuel economy. With the desire to build in as much power and free-revving capability and to improve fuel economy as much as possible thru friction reduction these design features are pushed in the other direction on modern engines. Piston pin offset has been reduced over the years to a bare minimum today to reduce the thrust load generated and reduce friction. Pistons have been lightened up considerably by shortening the skirts. This creates less rotating/reciprocating mass which is good for power, free revving capability and fuel economy. Light weight pistons are great but the skirts, by necessity, are short making it hard to make them both strong and flexible and the shorter ckirts make them more prone to rocking. Unfortunately, when the performance and fuel economy oriented pistons are run cold they are very prone to "slap" until they warm up to operating temperature. The piston designers and development engineers are always treading the fine line between piston slap cold and friction and power/fuel economy loss when the engine is warm. It is possible that you are hearing piston noise from an engine that is on the "high limit" for piston clearance so that it makes some noise cold. The good news is that the condition is harmless and that engine is probably a little more powerful (due to less friction) than a "quiet" counterpart. The bad news is that...it makes noise cold. As an example of what the piston pin offset can do, it was common back in the early 70's to turn the pistons around "backwards" in the large displacement Chrysler engines to gain power. Those engines had large piston pin offsets to create thrust load to control the piston slap. So much thrust load and friction was created that just turning the pistons around in the bores was often good for 10 HP. The engines were very quiet with the pistons in correctly and they slapped like crazy, especially when cold, with the pistons reversed so as to reverse the pin offset. Racing engines do not have the pin offset and thus the pistons slap like mad...but no one hears them over the open headers...LOL. The noise is an annoyance but will not hurt anything and the engine is fine. I don't remember if that engine had full floating pins or not but they can also cause some ticking just after start. Same sort of deal...the "correct" clearances in floating pins will cause clicking after startup for 30 seconds or so. To prevent the start up noise, the floating pin clearance must be kept so tight that the pins are almost press fit again."
I've never had a car that's done it... Also, if it were normal, then ALL the cylinders
would have it. That's not the case, as you saw from the small video above. Only
two of the eight cylinders were effected.
This is what it does to the piston skirts & cylinder:
Those, you can feel when you run your fingers over the damage, both the skirt and cylinder walls.
There is another tapping noise the Coyote 5.0 makes, after you change the oil for the first time.
Ford has an additive that stops it, but you have to add it every oil change.
If you want to test for actual piston slap? It is a long process, unless you know what # it is.
You pull the plug on each cylinder, one at a time, pour a tablespoon of oil into the cylinder,
put the plug back in, start the car, and listen. When it stops, is when you found the one that
is slapping. If it's more than one, the interval will be slower. You repeat on each cylinder to
see which ones are doing it. It won't be all of them, and that's why it should not be normal.
IF they say it is, so be it, but I would not own a car that does it. It's a wear factor fail just
waiting to happen.
Last edited by 08'MustangDude; 09-29-2018 at 12:20 AM.
09-12-2018, 05:34 PM
PISTON SLAP IS EXPECTED???
