How to fix mild pre-detonation on forged pistons.
The subject pistons are Wiseco pn 6595M85
+14 cc dish pistons w/ H.D wrist pins
03-07 Evo VIII
The pistons came into my shop with slight damage around the thin wall of the eyebrow on the outer edge.
They were hung on Eagle rods.
To me it looked like hot spotting and pre-det.
Notice the damage on the outer edge of the piston?
the first step is to remove the piston from the rod.
That is done by removing the C clips from the wrist pin bores.
Be careful not to bend or deform the clips, or you will have to order a new set form the piston manufacture.
Next is to mic the piston to make sure it is within spec.
Next using a small burr I ground away the damaged aluminum
After that I used a flapper wheel to smooth any rough spots and to remove the galling
I also removed the sharp edges (90*) that was from the machining of the piston when it was first made to help eliminate and more hot spots.
Next the pistons were glass beaded clean.
Now to maintain balance, the piston were weight matched within .2 grams
Next I checked the balance on the rods, starting with the small end.
After all the small ends were matched.
I balanced the overall weight of the rod, also keeping the balance with in .2g .
Now it was time to hang the pistons on the rods.
I start by installing one of the clips in each piston.
After that is done, I oil the wrist pin bores in the piston.
Also oiling the small end of the rod.
Then oiling the wrist pin
Then sliding the wrist pin through the piston and rod, Making sure the piston faces the proper way on the rod.
The last step is to install the other wrist pin clip and making sure that all clips are seated in their grooves and the rod floats smoothly on the wrist pin.