My son has 2003 impala. A knocking noise has gotten worst. A mechanic said it was the piston and needed a new engine. Cars runs great except or noise. Can it be something else?

Pistons can't be removed from the bottom. Head has to be removed for the piston to come out and the piston has to come out to remove the connecting rod. Instead of sleeving a cylinder its way cheaper to have it bored .001, .002, or .003 and just get an oversized piston.

All due respect John, I have done it. Not on an Impala, but a 350 cid Blazer, drop thr pan, granted it's not easy, take rod cap bolts off, rod cap, turn engine by harmonic balancer and breaker bar on bolt, when it's in the right position you can pull the entire connecting rod and piston out and re-assemble the same way backward.

Then your engine wasn't a factory installed engine. Engines cylinder walls are tapered to the point where the bore at the very bottom is smaller than the piston. Very very few enginee allow for the pistons to be removed from the bottom and reinstalled there. None of them are going to allow this to happen with the crank installed because of the counter weights. Only racing specific engines will do this. I got on Bing to look up the info you typed and nothing came up for a Chevy 350 being able to have pistons removed through the bottom. If you can find a site please put it on here I would love to read it.

Hi John, that engine did not belong to me, it was in a Blazer that was owned by the owner on the company I worked for at the time. He had more money than he knew what to do with, so I don't know what he had done to it, as a matter of fact is was not factory, you are right on-- he had several custom cars, a dragster he liked to tinker with and I was in his 8 car garage and he asked (told) me to help him. I did find it odd that the piston was just round with no skirt, the ring compressor was the biggest problem room-wise and we got in in from the bottom. I made an assumption that that could be done on a factory engine, my bad- shouldn't have made that assumption. It was a 350 block, that I do know. But never asked what he had done to it...he reminded me of Tim Allen...more power!! I don't know of any web site but I will take a look, This guy was on the cover of "Hot Rod" magazine in 1993 or '94 with an article inside. It was framed in his office. I will try to see if I can find the exact month of the issue, long time ago-- and there is an outside chance I can show you that-- for what it's worth. Good day my friend, you taught me several things I did not know on this topic and others in this forum.

PS...since you educated me on that it make my first post dead wrong. So I will delete it for that reason. All that was a long time ago--I left the Air Force in 1984 and went to work at that place....there are no civilian jobs working on F-16's.

Some high end racing engines are designed that way due to tendancies to melt rings. The intent was to be similar to a quick change rear end. Hand full of bolts and in a few hours you're back on the road/strip/track.

PS Thank you for your service.

Yeah, he was, maybe still is, an off-road as well as track amateur racer. He abused such fine machines .. pushing them over the red-line --it made me cringe but as I said he had (has) so much money he didn't care. I really don't want to name the company but he had 110 trucks...all Kenworths, and they were always gone, on the road, never more than a dozen or so in the yard for service. In other words successful. Anyway, he didn't have to really work, just count money other people made for him, so he was always tinkering with his cars and/ or racing them, with his own mechanic traveling along in a KW and 45 foot trailer with a complete shop in it. And thanks. sincerely for the acknowledgment..I almost stayed for 20, should have, but 1971 to '84 got me 13 years and a small, very small pension but now at 59 it really helps albeit how little., never got deployed to V-Nam though but the 56th Fighter wing and 61st squadron... we kept them at ready--- was needed in Phoenix, Luke. Sure got off topic but thanks again

a piston noise is not something that is mistaken for something else. the bearing has worn out which creates a larger space between the connecting rod and crank shaft. that causes a knocking sound.