Thanks 41eclipse and all others who responded to my previous concern about the piston noise. This was my first installation of forged pistons and rods due to piston land breakage on stock pistons. I did the whole bottom end with new main and rod bearings. I was impressed with the quality and engineering of the engine. No major problems, execept when I started it, it sounded like hell, then as it warmed up it seemed to disappear. Is that really normal with forged pistons and what are the long term effects?

Thanks again!

Piston slap is normal with forged pistons. Some people get it, some do not. Pistons expand with heat which varies based on things like build and silicone quantity. This means when the engine is cold there is some extra room in those cylinders for the piston to make some noise before they expand enough to fit the bore properly. If you search a lot of different places and different cars you will find piston slap is a common thing. It is worth doing the research on just so you know what is going on.

I have the same thing with my rebuilt motor. When it is cold the slap is pretty loud. Once it warms up it gets a little quieter but it is still there. It freaked me out the first time we started my car and I heard it, but it seems to be normal.

I'm the piston slap king, especially on those cold january 38deg winter mornings. It does subside with a few trips thru the gears. I like it. I pull up to a dodge ram diesel and we sould alike (cept mine sounds like munchkin and theres sounds like a big rig).

I'm so glad to hear this. I've had this noise ever since I rebuilt my engine last month, but had NO IDEA what it was. I kept telling people it sounded like a diesel engine in the mornings when I first started driving, and they looked at me like I was crazy!! :)

yea, it all has to do with the silicon content of your pistons. High silicon pistons will slap around a while, but their strength is very good, whereas lower silicon pistons will not have much heat expansion but they are weaker. just think of your slapping as a reminder that your pistons have very high strength!