piston slap experts

[bjones18]

Any experts on piston slap? I've read many forums (here and other) that place the blame on piston to wall clearance (pwc). Some threads which state .0040" pwc is great and .0055" results in slap. Just for completness, the other direction <.003" can rip the tops off the pistons (due to heat & ring locking).

Measuring my pistons (forged) and cylinders, I find it hard to believe 0.001" is the difference between slap and no-slap. OEMs have slap problems and if .001" were the cause... it is cheaper to hold .001" tolerance than deal with customer complaints.

Short skirts and light weight pistons seem to be more prone to slap. Is it lateral motion or rotational about the pin for the piston at the root of slap? Rigid body modes of the piston pushed laterally may cause some slap. These modes would be effected by piston weight/inertia and the "holding stiffness" from forces that resist "slap" motion including oil viscosity/film, ringland/ring friction, and pin/piston friction.

My question is... Is it possible that correct pressure build up between piston rings (due to differential ring gap) provides friction on the ring lands which helps prevent the piston from moving in a "slap" lateral direction? This must be understood under load and no-load conditions (is there slap for both conditions?). Ring flutter from improper differential ring gap would not provide stability to the piston.

Does anyone have experience with differential ring-gap (#1 #2 rings) affecting or not affecting piston slap?

 

[bjones18]

I am interested in continuing this topic if I can find others who are interested. It would be very helpful to hear from a few builders who know what their clearances started at (pwc, #1ring gap, #2 ring gap), what pistons they have and if they have hot/or/cold --- throttle-on/or/off piston slap (at what rpm).

I was able to solve crank walk on a 7-bolt with a history of walking... with a $15 set of parts and a hand drill. It cost me more than $15 to figure it out, cause I ruined a shortblock rebuild in the process. My second time through it worked fine.

I would like to look at piston slap if I can find people with slap information. I can't afford the time or cash to ruin engine(s) figuring this one out.