So as I have been paying more attention to my engine I have noticed since its been cold I get the piston slap either until it idles warm, maybe 5 minutes during which it gradually decreases, the most of the decrease happens within 30 seconds, or I start to drive away. So much info on this out there, conflicting opinions and such! I had an olds alero with the 3400 that did it just not as much, I drove it for 400k miles so GM3100 - piston slap, is this really an issue to be concerned with at all? it is a low end sound and is not valve noise, I know its the slap, and when warm it is completely gone and it is as quiet as a Cadillac.
I personally do not think it is an issue, annoying yes, but I don't think it will cause any harm as long as it is just the cold engine Piston slap. From what the GM Engineers tell me it is caused buy a combination of 2 things. 1-the loose tolerance between the aluminum block and the piston when both are cold. As both parts are aluminum they both expand to take up the tolerance. 2-carbon build up on the upper surface of the pistons. They tell me it causes a slight imbalance of the piston as it does not build up equally, so the piston tends to lean to the side it is heaviest on. Then when the engine heats up to operating temp the tolerance tightens up and the "slap" goes away. My wifes G8 with the 6.0 LS engine has recently started having a slight slap when cold and the air temp is below 40F. The engineers told me the biggest hassel is Corvette owners, the LS1 engines were the most prone to the condition, and the Corvette owners were the 1st to complain about it. They do an upper end clean and it fixes the issue for about 10,000 miles, then it comes back after the carbon builds back up. They claim it is an annoyance not an actual problem.
thanks, metal knocking gives me the heebie jeebies, but I seem to think you are right, there were just some folks out there saying it could ruin cylinder bore and piston skirts, I rebuilt the top end I want to hold on to my short block lol
dude, this wasn't a complaint...... just a question on if this was ok to roll with, thanks for the good advice...
I had a Renault 5 (LeCar) that had a habitual piston at connecting rod slap. I religiously idled it from cold for about 10 to 15 minutes. Then, turned it off and waited awhile. After that, it ran quiet, once everything expanded to near operating temperature. I owned the car for years and drove it up and down through Europe without any problems. Clearances are designed for the excessive coefficient of aluminum expansion. My other cars didn't have the piston slap. But, I always warmed them up the way I did with the Renault
It was odd that it rattled up a storm when I put mobile 1 10-30 high mileage synth oil in it, my alero loved it, this car hated it, kinda noticed it came on quickly, well apparently this car just prefers regular old dinosaur juice 5-30 seems to have quieted down alot.
I think the newer models did something with teflon to quiet the aluminum pistons up, top still chitters for a few but all my vehicles without overhead cams and timing belts did that
Oh, I know, but since we're talking about what people think, you'll always have some who are disgruntled. Not that I am; I have a 2000 Buick Century with a 3100, and I always thought the noise was an errant tappet, despite the 83K original miles. There are some things that just cannot be engineered out immediately, but given time, some fairly ingenious fixes come along. Ford Modular engines had bad piston slap when they first debuted, but in time, the powertrain engineers got a handle on it; it's still there, but just not as much as there used to be.
We bought a 2003 Buick Century with 3100. It started making noise within a couple of years. The dealer replaced all the pistons under warranty with the "new, improved" ones. The mechanic told me what the improvement was but its been so long ago that I forget.
Right, but it's low-mileage piston slap that the OP is concerned about. If my Century had the pistons replaced under warranty by the original owner, would I confirm that at the local dealer? I simply want to make sure about its cold start noise.
