To make a long story short, I had this motor built a few months ago and have been working on gathering some parts, installing other parts on the car etc since then. Well, tonight I was getting ready to bolt the heads on and while cleaning the deck surface I realized a "flaw" with one of the pistons. The flaw is on the edge of the left side of the piston. These were brand new pistons from Wiseco, so now I'm stuck deciding how to handle this situation. I will be going to the machine shop first thing in the morning. My instinct tells me that the machine shop damaged the piston and that its NOT a defect, but obviously theres no way to prove that.
What I want to ask you all is what do you think of this flaw in general? What I'm left wondering is how much will this impact cylinder cc size and is the skirt damaged, but I can't see it without disassembly? Will the piston break worse once it sees compression/combustion?
How would you handle it and how much should I be concerned? Just looking for some opinions guys. I'd prefer some opinions from some motor guys with experience if possible. This motor will be a "max effort" build with a blower on it.
Thanks!

 

It doesn't look bad to me. If I was building a n.a 400-450hp engine, I would probably remove it. Make sure the are no cracks and use it. The missing piece is tiny. I don't think there would be balance problems. The difference in piston volume cc would also be negligible.
That said, "blown max effort engine", replace it!
Just my 2 cents

 

I'd be more worried about where the missing bit is....

 

Interesting. This does not make me feel too good about having Wiseco's in my car....

 

Doesn't look like a piece broke off ... looks like there was machining purposely done there for some reason. I'd call Wiseco and ask them if they do anything like this during manufacturing of the pistons.

 

Would have been nice to see another piston to compare to.
But it looks to me like that was done intentionally to break a sharp edge that might otherwise cause the piston to "burn" in that area.

I read about that over on yellow bullet. Especially with turbo builds. Wiseco posts there.

Just surprised they all aren't like that one.

Ron

 

RonssNova- In the first two pics you can see a comparison to another piston.

 

Definitely something chipped off. The fact that this is the only one like this should tell you this is not intentional. Any intentional machining to remove weight from that cylinder is usually done to the rod and not the piston, especially not the face of the piston. In fact, looking at the pictures, the chipped piston has sharper edges than the other ones, so it's not for reducing hot spots and predetonation. Looks to me like someone dropped it on the floor or something. It can be taken to a machinist to have them weld new material back in, but the material still won't be as homogenous as the original piston. If it was me, I would replace it.

When replacing the piston or getting the old one repaired: You never know if the rotating assembly was balanced weighing the rod/piston assembly or the rods and pistons separately, so you will need to bring them one of the rod/piston assemblies from another healthy cylinder to get the weight correct.

If you want to use this piston, and don't want to go back to the machine shop, there is still a good chance that everything will work out just fine. I would still take the piston out to inspect it with a microscope for cracks. Then smooth out the chipped edges with some sandpaper. This is such a small chip, that the balance loss may be negligible. Since it's an aftermarket rotating assembly, even if you throw off the balance a little, it will probably still be more neutral than the stock rotating assembly which has a manufacturing tolerance of like 13 grams. If you end up having vibration issues, you could use a strobe balancer and add weights to the flywheel or harmonic balancer to compensate.

 

Just as a follow up to this thread. I contacted Wiseco and they said this was done in house during the manufacturing process intentionally. I also found a thread on Yellowbullet about the same thing where Wiseco commented.
I ended up having the machine shop pull all of the pistons back out and machine them all down in the same spot. The material on the piston in that area is thin and my understanding is that it can fatigue and break off after some abuse.

 

While you had the pistons out I hope you had the machine shop take a fine hand stone and eliminate all the sharp edges on the area you machined away. That machined surface will be a great place for detonation to start unless you remove all the sharp edges.
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