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FBODYFirebird · 10-01-2006, 12:19 PM

here's a more thorough writeup, most 3800 series have a normal sounding slapping noise during cold startup "yes it's normal" 5W/30 oil will help , because it flows better and quicker when cold...

the fix: replacing the wrist pins and cylinders

* Iron blocks, or aluminum blocks with iron sleeves.
* Aluminum pistons, period.
(The above excludes exotic ceramics, and the old Vega 4-cyl that had a skeeveless aluminum block with silicon embedded in the cylinder walls for toughness.)

* MANY engines have piston slap upon cold start-up; most do not, yet they still have two different metals.

* 'Different alloys' isn't a definitive explanation of GM 3.1/3.4 60* V6 piston slap.

2. The ORIGINAL GM 60* V6 was the carb'd 2.8 (used on late 70's Citations, and '85 Jeep Cherokees).
Then came the 3.1 and 3.4 (plus some goofy specialty engines, and now the new Caddy CTS line of DOHC's)

* The 2.8's never had piston slap.

* The 3.1 is an 8mm stroked version of the 2.8, and the pistons were shortened 4 mm (~3/14") to fit within the cylinders.
* That material was taken off the skirt at the bottom of the piston, and it still projects into the crankshaft a bit at BDC.

* Bottom line: The 3.1 and 3.4 pistons are so short that they 'wobble' a bit until the skirts heat and expand enough to fit snugly.
For *some* V-6's, this wobble causes noise (piston slap).
* * *

It only takes about 15 seconds for the aluminum piston to expand from the heat of combustion, and the engine should ALWAYS be treated gently during this warm-up due to lack of lubrication at the bearings.

10-01-2006, 12:19 PM	#3
FBODYFirebird Banned Join Date: Aug 2006 Location: Beachwood Posts: 73 iTrader: (0)	here's a more thorough writeup, most 3800 series have a normal sounding slapping noise during cold startup "yes it's normal" 5W/30 oil will help , because it flows better and quicker when cold... the fix: replacing the wrist pins and cylinders * Iron blocks, or aluminum blocks with iron sleeves. * Aluminum pistons, period. (The above excludes exotic ceramics, and the old Vega 4-cyl that had a skeeveless aluminum block with silicon embedded in the cylinder walls for toughness.) * MANY engines have piston slap upon cold start-up; most do not, yet they still have two different metals. * 'Different alloys' isn't a definitive explanation of GM 3.1/3.4 60* V6 piston slap. 2. The ORIGINAL GM 60* V6 was the carb'd 2.8 (used on late 70's Citations, and '85 Jeep Cherokees). Then came the 3.1 and 3.4 (plus some goofy specialty engines, and now the new Caddy CTS line of DOHC's) * The 2.8's never had piston slap. * The 3.1 is an 8mm stroked version of the 2.8, and the pistons were shortened 4 mm (~3/14") to fit within the cylinders. * That material was taken off the skirt at the bottom of the piston, and it still projects into the crankshaft a bit at BDC. * Bottom line: The 3.1 and 3.4 pistons are so short that they 'wobble' a bit until the skirts heat and expand enough to fit snugly. For some V-6's, this wobble causes noise (piston slap). * * * It only takes about 15 seconds for the aluminum piston to expand from the heat of combustion, and the engine should ALWAYS be treated gently during this warm-up due to lack of lubrication at the bearings. Last edited by FBODYFirebird; 10-01-2006 at 12:29 PM.