Piston oil holes

I was wondering if anyone's ever recevied a set of forged pistons in which the valve-reliefs cause the bottom/inside of the piston to cover the oil-holes drilled in the oil ring groove?

Wierd part is that it's only 2 of the holes that are problematic, and for the most part, they did break through to the piston innerds... only 1 piston seems like the aluminum bent out a bit, instead of drilling out.

The other problem is that 6 of the pistons are perfect, and one has 2 raised bumps where the holes should be... and the last one looks like it was "close". The holes are there, but one has a "cling-on" or "hang nail" situation going on. I sure as hell don't wanta install a piston that might shed a metal flake that size (probably 2 mm by 1mm oval).

1) Is it safe to CAREFULLY shave the flake out? Any reccomendations on tools? (should I use a small drill bit and do it by hand?) :eek:

2) Would 6 oil ring holes, and 2 non-holes be acceptable in a piston for high-performance use? I don't like the idea, but I'm also hesitant to try and drill on my coated, foreged, Wiseco 18/23* pistons. :think:

Anyone seen this before? I can't imagine I just "happened" to be the first. :p

From your description, the drill didn't quite break thru (raised bumps), or wasn't quite sharp enough and it pushed out the metal. The hangnail is a typical drill burr, especially from a dull drill bit.

My observation is that someone didn't check/inspect and deburr the pistons properly during manufacture. Since we are in the precision machining business (not pistons!), I'm surprised at the sloppy work by Wiseco. Sure CNC machines are nice, but things still need checking with the Mk I eyeball.

If you bought the pistons complete with coating from Wiseco, you might contact them first and question them. They should rework the holes for your gratis. If it were our parts, we would pay shipping both ways. If they were coated after Wiseco sold them, that's probably not an option.

To do it myself, I would use a new drill bit turned by hand, maybe in a small chuck removed from a hand drill, to remove the burrs and finish the holes. Try number size or fractional or metric drills to get the correct size. There's probably no coating in the ring grooves anyway, and coating on those oil holes isn't important.

It's probably better that the drill didn't quite break thru rather than go too far thru and hit the valve relief area!

Originally posted by OldSStroker
From your description, the drill didn't quite break thru (raised bumps), or wasn't quite sharp enough and it pushed out the metal. The hangnail is a typical drill burr, especially from a dull drill bit. Yep, that's what it looks like (guess I should take some pics and post them).

My observation is that someone didn't check/inspect and deburr the pistons properly during manufacture. Since we are in the precision machining business (not pistons!), I'm surprised at the sloppy work by Wiseco. Sure CNC machines are nice, but things still need checking with the Mk I eyeball. Yeah, kinda suprised me too. I thought it may have been a Left or Right piston thing, but the two pistons are one of each. Looking at the drilled holes, all pistons have excellent machine work with clean holes at the other 6 locations, but it looks like the 23/18* valve reliefs and a 1.20" compression height makes the 2 holes nearest the wrist pin a bit challenging to punch through. From my perspective, I can't imagine they looked at the inside of these 2 pistons and thought they were ok... but granted, the rest of the pistons and the other details of these 2 pistons are amazing. Maybe this isn't such an issue in standard 23* valve reliefs, or in larger compression heights... just strange looking.

If you bought the pistons complete with coating from Wiseco, you might contact them first and question them. They should rework the holes for your gratis. If it were our parts, we would pay shipping both ways. If they were coated after Wiseco sold them, that's probably not an option. I bought them from a friend of mine who changed directions on his build up. I'll check to see if the coatings are Wiseco or 3rd party.

To do it myself, I would use a new drill bit turned by hand, maybe in a small chuck removed from a hand drill, to remove the burrs and finish the holes. Try number size or fractional or metric drills to get the correct size. There's probably no coating in the ring grooves anyway, and coating on those oil holes isn't important. Yeah, I originally thought of a Dremel, but I just about crapped my pants when I thought of it skipping even once. The aluminum shouldn't be too hard, and I KNOW it's damn thin, the bumps shown are exactly where and shaped like the end of the drill's edge. A sharp drill bit from the back should leave a natural chamfer to boot.

It's probably better that the drill didn't quite break thru rather than go too far thru and hit the valve relief area! Yeah, I'm pretty sure that's how the deptch was choosen in the CNC program. The tip of the drill sticks forward a bit and the other edge of the drilled hole only breaks through to make the oil hole a pass-through.

Thanks for the feedback, I feel a little better about trying this if I have to.