I know the piston slap comes up a LOT, and i don't mean to post a repetitive thread... but I haven't really been able to find any info on fixing it...

Hell, i'm not sure that i have it. everyone elses seems to go away, mine sticks with the truck the rest of the day. patient: 4.8L 2wd, 99+ ECSB, Auto.

Start engine, takes 2 secons or so, then KNOCK KNOCK KNOCK like marbels in a can. then dies down after engine heats up.

But heres where mine is different from what i've seen called the piston slap. when i put it in gear and start to move, the knock comes back. when going around people, say grocery store, i'll try to go real slow and let the truck idle through parking lots to avoid the knock... because once i give it gas the knock picks up again. I don't think it's tranny related though because it does it just fine in park, neutral, or in gear. also, when parked on hills it's real loud.

took it to 3 muffler shops, and 3 mechanics now. nobody knows. closest was yesterday, zeroed the sound in around the dip tube, but seems unrelated. the other guess from yesterdays mechanic who drove it an spent 2 hours with it... was maybe the oil pump rubbing on something.

But overall he says the engine is in great condition (140,000 miles) and i should ignore it because it's no big deal.

nice guy, but this knock is a pain in the ***. if it is piston slap, whats required to get rid of it? can this engine ever be slap free?

 

140.000 miles. Yeap a nice forged rebuilt will get rid of it.

 

I was under the impression that moving to forged pistons made piston slap even worse. Reasoning behind it was because of the shorter skirts and being denser (due to the forging). The thermal expansion rate was supposedly higher on the denser forgings because its made of atoms which expand at the same rate as hypereutectic aluminum pistons, but since theres more fo them packed into the same space, the thermal expansion and contraction is more pronounced.

This is just what i heard, but it makes sense to me. Id like to hear other views on the matter...

Anyway, Theres nothing you can really do with a 140K mile motor except try changing to different oils. Id just ignore it as its probably not harming anything anyway.

 

Tolerances of piston skirt to wall are tighter on a forged setup.

 

Sure, I can see that source of slapping being eliminated, however I thought the differences in thermal expansion were the real culprit (excluding defects like you stated above).

 

It's been knocking (or slapping) since December/January and i haven't seen any changes in power or drivetrain action at all so i'm not really worried about it. but the truck is almost paid off and i was thinking about rebuilding the engine for performance anyways soon. just wanted to get some ideas of good replacement parts to make sure I don't bring on a new slap down the road.

thanks guys,

 

Most reputable shops should be able to whip you up a nice shortblock. Im looking at the SDPC 402 in particular for when the time comes.

 

I'm pretty sure forged pistons have to have the most clearance (because of thermal expansion as mentioned before), then hypereutectic need less clearance, then cast can run the least.