Help me me diagnose this piston failure

[TurboMatt]

'11 pro rmk, Silber Turbo, vipec , mtn tek fix kit on it approx 800 miles on the rebuild. I run straight 100ll at 10psi at high elevation and 5 psi back home. I felt like the sled was vibrating a little more than usual so I opened it up. Checked oil useage and it was 43:1 & I also mix 100:1 in the gas tank.PTO side has scoring on 4 corners, mag side looks OK but has excess piston to cylinder clearance. PTO side has fairly heavy metal transfer on the piston. Roughly Checking Piston to cylinder clearance with a feeler gauge I could fit .016 on PTO side and .008 on mag side. It wasn't this loose when I put it together. It was right in spec. Cylinder was a exchange from millennium when top end was put in and measured in spec so cylinder was like new. I feel like I warm the sled up very religiously. Run it up to 100deg always before driving it.

I'd also like to add, this is my second set of mtn tek pistons. the first set showed extreme wear on the intake side of both pisrons after about 600 miles. Both sides were the same. My is my sled eating fix kit pistons? I could post pics of those if needed.

How does my piston wash look to you?
PTO side pics:

 

[TurboMatt]

Mag side:

 

[Jeffdutch123]

Looks to me like your clearance was too tight to begin with. You say"in spec" but a freshly renicd cylinder with a forged piston and ten pounds of boost will need extra clearance from the start or it will get tight.

 

[TurboMatt]

Looks to me like your clearance was too tight to begin with. You say"in spec" but a freshly renicd cylinder with a forged piston and ten pounds of boost will need extra clearance from the start or it will get tight.

I believe mtn tek says .0055 for Turbo application. I was at .006"

 

[ez-ryder]

Cast Pistons are looking like a better plan for round three.

 

[diamonddave]

I think if you have had this happen twice, I'd be looking at replacing injectors and at the least, flow test and ultra sonic cleaning if you have auxiliary's with your turbo kit still.

We have has excellent luck with the MTNTK Fix Kit's.

 

[TurboMatt]

I think if you have had this happen twice, I'd be looking at replacing injectors and at the least, flow test and ultra sonic cleaning if you have auxiliary's with your turbo kit still.

We have has excellent luck with the MTNTK Fix Kit's.

I don't see any signs of deto, why do you say this?

 

[TurboMatt]

Cast Pistons are looking like a better plan for round three.

I ordered Indy Dan's top end kit today. I'll let you all know how it works out. I'm hoping to make one more trip out west this year yet

 

[The Bob]

Pretty sure he is using Polaris pistons again. Match the piston weights when you get them, as most are off from each other, maybe he does that before sending them.

Most boosted engine builders (not just sleds) steer clear of cast pistons. Polaris are cast.

 

[geo]

It looks a little lean for me but I don't know if this extra air you get from boost is the reason.

You didn't mention the head you are using.
What I found when I built my motor with Mntkt pistons is the piston crown was taller than stock pistons. This is a benefit with the silly squish dimensions in a stock head but with an aftermarket (at least the one I had) head, where the manufacturers try to match their squish angle to the stock pistons, the higher crown created a negative angle in the squish.
Meaning, the clearance is greater at the outside edge of the piston than it is at the inside edge of the squish band.

This creates pockets of trapped fuel mix that I kinda see on one piston. That would lead to higher crown temps and eventually skirt collapse, which one of your pistons shows. Bigger issue with forced induction than n/a too.

Probably not an issue with Indy Dan kit but a simple solder check for dimentions is a good habit with a rebuild and if using a billet head with domes, it's an easy fix on a lathe.

 

[TurboMatt]

It looks a little lean for me but I don't know if this extra air you get from boost is the reason.

You didn't mention the head you are using.
What I found when I built my motor with Mntkt pistons is the piston crown was taller than stock pistons. This is a benefit with the silly squish dimensions in a stock head but with an aftermarket (at least the one I had) head, where the manufacturers try to match their squish angle to the stock pistons, the higher crown created a negative angle in the squish.
Meaning, the clearance is greater at the outside edge of the piston than it is at the inside edge of the squish band.

This creates pockets of trapped fuel mix that I kinda see on one piston. That would lead to higher crown temps and eventually skirt collapse, which one of your pistons shows. Bigger issue with forced induction than n/a too.

Probably not an issue with Indy Dan kit but a simple solder check for dimentions is a good habit with a rebuild and if using a billet head with domes, it's an easy fix on a lathe.

Stock head
What do you see that makes you say Lean? Sled has been run on straight 100ll for most of it life.

 

[geo]

Just the wash Matt. Not enough carbon build-up for me. Carbon build-up shows some help from fuel to keep piston crown temps down.

The stock head squish dimensions leaves a lot on the table for performance (un-burnt useless fuel mix wasted) and less det help (only about half of the width is useful dimensionally). Most of the stock heads I have measured have .020" difference between ID and OD. Safe for N/A but useless for performance.
It's a hard head to jig up and cut for a N/A use and probably doesn't have enough meat in the casting to open up the dome enough for turbo use. Don't know, have'n tried.

You may find less piston issues (cooler crowns) and more power at less boost with a proper turbo dome head with proper squish clearance.
I set-up for .030" clearance but compression ratio desired is the bottom line.