Piston Slap

AFAIK it's not an issue for newer ones. Some 1999-2002 engines are the main offenders.

NJ Vike wrote

All of the new gen small block engines have this problem. It's fairly normal...and I doubt that you will get the dealer to do anything. Just drive the thing.

Ian

Not true, it was worse back then but can still be a issue today due to acceptable production tolerances to meet quotas and control costs. Using 10w30 instead of 5w30 will help and reserve 5w30 for temps consistantly below zero (F)

----------------- TheSnoMan.com

Thanks for the reply.

Why are they building engines like this?

Ken

Thanks for the reply.

I believe I have this and will change the viscosity on my next oil change.

Ken

I either have this or another engine issue. Having this in my Expedition, I'm kind of leaning towards the piston slap.

It's too bad because this is one nice vehicle.

Ken

Cost and time. Which amounts to cost and cost.

Not advertising or condemning this site,

but you can get some info here on piston slap. I believe it's just a little biased, but you can Google GM piston slap and get tons of articles.

Brian

Because They Know that PEOPLE will not do their Research before Buying a Vehicle,,,

one way to Guage a Vehicle's Quality, Is To Go around the to the Back of The DEALERSHIP around 8am and See How many Cars & Trucks are lined up For SERVICE ! The Service Department with the Shortest lines is The Vehicle You want to BUY !

And all those Cars ARE NOT Getting their oil changed, only About 10%

Brian,

Thanks for the link. I will look into it.

Ken

I thought they won award for quality from J.D.Powers & Associates? That much I thought I saw. Also, Consumer Reports gave it a "Recommended" I guess you can't believe everything you read.

Ken

This is nothing new. It comes up on the newsgroups every now and then, but the problem has been around for years.

There are many factors, but the main one is that GM and others went to short skirt pistons years ago in a bid for lower drag, better fuel economy...etc. The short skirt pistons will rock in the cylinder bore when cold and that's what you hear. Once the piston has warmed up and expanded to its normal running size, the noise goes away.

We have not replaced any pistons in the new gen v-8 small block in an attempt to correct the noise. Some other dealers do, but I think it's nothing but a patch anyway....the new pistons are the same design.

It doesn't affect reliability....it's just annoying that your nice new truck sounds like my 20 year old K-car.

Ian

Doesn't sound like a data driven decision to me.

Brian

If you look at a GM manual for 20 or 30 years ago on prodution tolerances on engine internals you will see that today they have a larger gap or spread as to what is acceptable than they did back then. If you have the misfourtune to get a engine that the bores are at the large end of the tolerance and pistons that are at the small end together in one engine they can slap/knock. Gone are the day when they would closely fit pistons to bore because labors costs are too high.

----------------- TheSnoMan.com

Really? Better dig out your 20-30 year old manuals and tell me what the piston to cyl clearance was. (production, not service) In the case of a 5.3 v-8 in 2006, the gm spec is:

a.. Piston - Piston to Bore Clearance - Production -0.036 to +0.016 mm -0.0014 to +0.0006 in

Look at that! A negative number! See if the 20-30 year old manuals come close to that tolerance!

Ian

I have looked and while I have not looked at a 06 spec recently I have older ones (05 on back). I nknew a few guys that used to work in GM engine plants in 60's through 80's and they told me how they used to take time to get it right and fit each part and get each bearing right one but that started to fade out in later 70's and by the today, the parts are slaped together whether they are the correct fit or not with no time to hand fit them like they did long ago when they would have pistions batches of different sizes that they would match to bore if need be. SOme blame shorter skirts which has some effect but the bottom line is "IF" they would take the time to fit them properly from day one there would be no slap but with todays labor cost making up about 70% of the cost of a vehicle they are hard pressed to use as little extra labor as possible. You can put spec in a book but following them is another matter at time and it would be interesting to tear down a engine that is slapping a lot and measure the bore and the piston. It is very very rare to see slap in a import motor because they spend more care and man hours building it.

----------------- TheSnoMan.com

................... I'm going to have to call you on this one. I have been at several GM engine plants to audit, and some of what you say is purely unsupported. First off, they have never closely fit piston to bore, because the bore & hone operations are not even close to the piston insertion operation. Each block is bored & honed to a specific tolerance +/-, which is audited every so often to make tooling adjustments & such. Later on, and after some other operations, the cases (blocks) are moved on pallets to the engine assembly area. After several more operations, the cases make it to the piston insertion area. At this point, pistons are inserted and capped. They always have been assembled this way, and they have never been custom "fitted", as you imply.

As far as labor costs, I believe you're off the mark here as well. The pistons are brought in fron a vendor, and therefore expected to be within a certain tolerance +/- as well. Take this tolerance and couple it with the variance in honing, and you can have quite a difference that will be purely a roll of the dice... As you put it,i the worst case, the large end of the tolerance. In this large tolerance situation, if the bore is too large, it is not because of high labor costs, because it would take longer to create a larger bore, than to retain a smaller bore in machine cycle time. The hone operation cycles for a certain time, then it moves on to the next hone station. Each station has a finer set of stones, and is set to a different tolerance. If labor costs were a factor, then bores would be tighter, since cycle time would be shorter.

Part of the current problem is piston composition. Basically, they just don't make them like they used to. Shorter skirts are the rave, but not when it comes to pistons. Then we have the pistom composition.. another stort entirely. Using your labor cost argument here as well in regards to piston size, you will also relaize that it would take longer to machine the piston smaller than it would be to keeping it larger. Thus, machine cycle time to machine the piston to the low/smaller end of the tolerance spectrum would cost more in labor.

Please understand that although a few thousandths only takes less than a minute to accomplish, but when we produce thousands of engines, a few minutes here & there add up to hours & days by the end of the year. These are several added days of time that are added to (IMHO: mistakenly) oversize the bore or overmachine the piston. So much for concern over high labor costs eh? Keep in mind again, that pistons have never been custom fitted to each motor, as you implied. I am in the engine plants.. I would like to know if you have been?

Regardless, with the new GM 100,000 mile powertrain warranty, any engine failure will be covered with model year 2007 and future models sold in the last half of 2006 an so on. This warranty applies to the same procedures & processes that have been in place. Nothing has changed with the motors. This does not mean that I accept the piston slap. It bothers me. But you did make an excellent suggestion regarding bumping up the oil weight. 5w-30 is the worst oil to run in these motors. I would run a 10w-40 in the winter weather and a HD-30 (straight 30) in the summer weather.

Ian,

Could I bother you to listen to this wave file on this web site,

? It's supposedly a GM motor with piston slap being recorded. The point of my asking you is as I know you have extensive experience at GM dealerships in the service department, I'd like your opinion on if this is a normal sounding motor that is considered to have piston slap.

Personally I've never had any of my GM vehicles with any piston slap noise, including my current 2006 5.3 liter. Nor have I ever heard one, hence my request from you.

Anyway, Ian thanks for all the service advise you give, and I hope you have a Happy New Year.

Brian

I wonder if GM and Ford are going to take into consideration that there are those of us that are going to go somewhere else for our next vehicle.

I will never buy a Ford again and if this turns out to be piston slap on the Denali, this will be my last GM product. I hope someone from GM is calculating this into the equation.

Ken