Got a question for you guys that have a 383. I get slap sound when my motor is cold but it goes away when it gets hot. the motor was done by Speedmotive in LA. Its coming from the pass side I thing its one piston that is to much clearance . Had the heads off after I first started it because of a noise that turn out to be windage tray being hit by one of the rods.couple of the bores look like the skirt was slapping bore. the motor only as 800 miles on it. Is some of the new coatings would help I would tear it down and have it done. What do you guys think?

 

Like you said, it sounds to be excessive clearance for that piston....Iv'e seen it a hundred times on builds where things weren't checked very well, or that it was noticed, but nothing was done about it....if it's not too excessive, and goes away quick during heat up, It could be fine for it's normal life without causing any adverse problems... some forged pistons have a higher rate of thermal expantion and require greater cold bore clearances to compansate in which they most all knock when cold, but your only hearing it on one side with possibly one piston so it dosn't sound intended and known about, and you would think that they would have mentioned it when they were building it for you since it's bound to be noticed(but who knows)..... And just how excessive things are, is really impossible to know without checking....it "could" be too much for any coating to make even the slightest difference sound wise...many guys who run coatings do it so that they can run even tighter bore clearances to cut down on even more piston rock and sound than normal ....IMO, I'd find out the exact recomended clearance for your pistons from the piston manufacturer(not the builder) ,then check exactly what you have clearance wise, then contact the builder if it's a big problem.........joe

 

Thanks for the rely . But how many .000 can be added to the skirt on a case like this? does the coating come off with wear? the pistons are srp . I know when my 350 was new it had some piston slap but that was stock . I ran a addtive and the noise when away after a month or so . I dont know it just bugs me with this kind of piston which has the wrist pin being in the oil land area. The pistons are -16 srps.

 

hmm... this is why I built my own motor. No offense though, I know not everyone can build a motor. I actually didn't know crap about them until I did this one for my bird. I noticed that my mahle pistons had a really short skirt. I was expecting mine to slap becuase of this, but I was pleasantly supprised when I fired her up and nothing! The pro mags are way louder than anything else in the motor for me. I beleive coatings wear off. I dont think you can add metal to the piston or the hole in order to take up clearance, you would have to punch it out to the next size and get the next size pistons too. Its a bummer dude. Otherwise, live with it. The brand new chevy trucks have short skirts on the pistons, and we see them in the shop all the time for the slapping. Nothing you can do about it.

If it drives you nuts, bitch at the builder! See if they will do something for you.

 

i got the same thing happening to me. my builder also told me that it was "slap" from having and extra .001 cut into the bore. here's what i was told from the builder:
it's normal, happens to a lot of engines that are stroked. i had to bore extra out to allow for clearance.

here's what the piston company told me (keith black):
the pistons are designed to expand into the overbore size. there shouldnt need to be any excess taken out to compensate for expansion. also, if the piston rings are cut right there shouldnt be a problem any way.

so, what i gather is either the builder was lazy and just decided to do it the "old fasion'd way" to get it together and get it out...or he made a mistake and cut too much out, when he couldnt fix it he decided to put it back together any way. my opinion any way.

my next buildup will be another LT1 that I do on my own...or an LS1 383 from slp...havent decided yet. but either way, i'm going to do it all myself.

oh, another person told me i might have a failed lifter, since it's only at low temps...i'm in the process of getting new rockers/lifters/pushrods/guideplates to find out.

 

Again thanks for relys. No this is a expandion issue. A stoker piston as a every short skirt so the piston really rocks back and forth when cold. I quess call speedomotive but I know their answer, oh no block was done with cc machine the bores are all the same. The only way to tell is to pull the motor and check the clearance my self.