TheSamba.com :: View topic

Sat Jan 02, 2021 9:50 am

can any of ya'll describe what piston slap or maybe its skirt slap?( now im not sure what what the term is exactly..) anyhow, does it have a specific sound?

Sat Jan 02, 2021 9:53 am

Luckily, I’ve had neither.
Sorry, I can’t be of more help.

Sat Jan 02, 2021 9:56 am

Like a rattle kind of. What pistons and rods are you running? Non-offset rods and narrow pistons are more likely to cause it.

Sat Jan 02, 2021 10:02 am

Drive a 2000 or there abouts Chevy 5.3 or 6.0 liter pickup engine with some miles on it when it is first started cold.
My 2000 GMC has piston slap when cold for about 200 ft out the driveway.
It's quite noticeable but hasn't caused any harm in the 15 years We've owned it.

It's just a rattle sound that changes with rpm and then hopefully goes away as the piston warms up and expands.....It only takes a little bit of heat to stop.

Sat Jan 02, 2021 11:22 am

most of the time it sounds like a diesel if you get rid of the clicketyclack sounds.... or kinda like a hallow sound like a base ball wacking around in a wooden bucket.or steel can... one of my old motors I used some nascar pistons in13.8 cr. and they were to be set up at .009" min clearance...and thats what everybody set them up at so they would survive the race....what a ficken noise motor that was. I had bought many sets of those pistons at a great deal. si I started expearaminting with clearances...first down to .006" worked great and better ring seal. the next was a motor for my brother, I set his to .0045" pretty darn quiet. I of coarse use torque plated and sunnen ck10 honed super fine. big clearances also crack skirts.I milled away almost a inch eact in 4 places of cracked skirt off those first set of pistons .set them about .005 and never had any issue with them.and quiet also. those pistons were shit for the most part, early to mid 70's nascar stuff. way to heavy. and pin way to low. low pin also makes more piston rock witch transulates in to slap,noise and ring seal issues. I didnt mind they were oh so cheep.and once I figured the right clearance they worked great, the lightening also helps.could of taken another 100 grams out if I had taken the time to do so. I think I still have one hear somewhere. I made lotsa $$$ with them. when I sold all my racing stuff 2 years ago a few sets still in boxes went away.I probably should of rote the right clearance on the boxes.....
pistin slap isant usualy a slap sound. thats probably a bearing.or busted skirt.or skirt hiked up and you get slapped for looking. :shock: :wink: :roll:

Sat Jan 02, 2021 11:47 am

heh heh " slapped for looking up the skirt". good one.

and i built a 2021 last year that sounds like it has a rocker adjusted out to far and clickin, just a little louder than normal.
now before yall ask.. stock heads, hd single springs, stock vw rockers on solid shaft. 110 cam ( yeh yeh, i know. i just had it laying around ) p&c were used, honed & re- ringed. i didnt check clearance. i dont remember mfg but the pistons did have the reeeeeally thin upper ring, took me forever to find a set of rings. " A " pistons and stock vw rods. ive checked valve lash couple a times and the rocker shim clearance is good.
honestly i dont really care about the noise , im just curious and the other day piston slap popped into my head. cant say ive ever heard it before ...

Sat Jan 02, 2021 4:46 pm

I ran one of those piston slap Chevy trucks for the company I worked for for 4 years. To me it sounded like bad lifters or in VW terms a really loose valve lash but louder.

Sat Jan 02, 2021 7:06 pm

According to Tom Wilson's, "How to Rebuild Your Volkswagen Air-Cooled Engine" book, he describes Piston Slap on pg. 12 as a a "dull, hollow sound... difficult to hear over the engine mechanicals... easier to hear while driving." The first chapter describes quite a few sound-related diagnostic steps prior to deciding on a rebuild.

I've seen this book mentioned quite a few times in addition to the Bentley manual as good resources to have.

Sun Jan 03, 2021 8:41 am

I have had Chevy LS engines which had the piston slap at first when started, and it was like a lower note tapping sound. Had a straight six that was tapping when I got it. It sounded like a lifter or rocker arm tapping. I adjusted the valves ( hydraulic ), and it was still there. Then I pulled the lifters out and disassembled them to clean them. Put it back together and the noise was still there. Finally pulled the engine apart and number 5 cylinder had scuffed and had .015" clearance. So there are times when you can't tell a piston tap from valve train. IMO

Sun Jan 03, 2021 1:41 pm

Sounds like a noisy rocker for a few seconds on warmup.