New engine knocks/rattles under load

[Roubian1]

Hey guys, I am having a problem with my '01 Explorer with the 4.0L V6, so I thought maybe somebody here could help diagnose it. Here is the situation, I had the engine rebuilt at 115,000 miles because my timing chains were rattling like hell. The redid the entire engine, including replacement of the lifters. About a month after getting the car back, whenever I start the car there is a terrible rattling/knocking coming from the engine. The rattling only happens when I accelerate or put a load on the engine. If I have it in park/neutral and rev the engine, it doesn't happen at all. The rattling does go away after 5 minutes of warming the car up and driving it. The rattling kind of sounds like detonation. I took it back to the shop and after they looked at the car for a few days they said it's piston rattle/slap. They said it's normal, nothing they could have done because everything was in "spec" when they built the engine blablabla and to just let the engine warm up before driving. However, I am getting a little sick of having to warm my truck up every time I want to drive it. What do you guys think? This wasn't a problem before and I find it hard to believe that they pistons and bore would have changed that much where now the piston slap would occur. When they rebuilt they just honed and put in a set of rings. It's really starting to irk me whenever I drive my truck. Maybe it's the cold weather?? On one of the days we had a hot day it didn't seem to happen. Could it be something with the MAF or EGR causing the engine to run really lean when cold? Any assistance is greatly appreciated!

 

[vroomzoomboom]

new engines should not have piston slap! if they did everything to spec, that shouldn't happen. if they tell you that's normal for a new or rebuilt motor, ask them to start there cars up, and why there's don't do it. i think they took to much out when they honed the block. ask them if they have the spec sheet, or build sheet from you motor, if they don't, then tell them how is it that you know everything is to spec. . i know if that where me, and i had to lay down a few g's for a newly rebuilt motor, i would be pissed!