What caused this carnage?

[thehueypilot]

One forged piston (#4) in my 427 stroker motor. It looks like an explosion happened on top of the piston ring and blew the piston land up? Any guesses as to what caused this? No NOS was used in the death of this piston.........
I sent these photos to CHP for their input and ask them if I could get one replacement piston and one ring set. Crossing my fingers for a positive response.

 

[brianj5600]

What are your ring gaps? Odd for a non power adder. Did those pistons have the TW intake valve pocket? CHP's seem to lift where the crown gets thin at that valve pocket. The top ring must have butted up to lift the crown like that.

 

[thehueypilot]

The second ring is a "zero gap" piston ring and the top has the standard 0.010" gap. The piston has the standard valve relief and the TW valve relief on intake side only and that is where it let go. There is no cylinder wall damage at all and no broken/bent rings.

 

[pabear89]

Was the top ring gap at the position of damage?
The piston/wall gap may have been alittle tight on that cyl.

PB

 

[brianj5600]

.010 seems really tight. .016 is about what I've seen recomended. If they are all that tight, I would adjust them all or you may have more trouble. Mine are like .024 or .026 IIRC (future turbo) as per speed pro for power adder. It seems weird running them that big, but that is what the sheet recomended.

 

[gsxrken]

Other than too tight top rings, those pistons look maybe too clean. What are your air/fuel ratios like on that chassis dyno? When it comes to gnarled pistons, Detonation is like the boyfriend of the victim... usually the culprit.

 

[brianj5600]

Other than too tight top rings, those pistons look maybe too clean. What are your air/fuel ratios like on that chassis dyno? When it comes to gnarled pistons, Detonation is like the boyfriend of the victim... usually the culprit.

True that. Detonation=heat=rings butting

 

[10secgoal]

Mine are like .024 or .026 IIRC (future turbo) as per speed pro for power adder. It seems weird running them that big, but that is what the sheet recomended.

Yeah, I'm at .027 Total seal recmended it for power adder.

Huey...you can tell by looking at the rings if they touched. All the way around the rings you'll see a wear pattern. Nice and even. if it's not detroyed, and they did touch, you'll see that wear pattern get even bigger. It'll look half again as big, or so.

 

[thehueypilot]

The top ring is at the same position as I took it out showing no damage. The A/F ratio was 12:1 recorded by a wide band oxygen sensor during the run with the timing set at 10 degrees. The ring has an even wear pattern all the way around and the cylinder wall looks normal. I wonder if the double valve reliefs had anything to do with it? I'm thinking manufacturing defect? If the ring ends met would not the ring break since it is made out of iron and very brittle?

 

[classic boost]

.010" is WAY too tight for a top gap! how in the world to you consider .010 to be "standard"?!?
total seal calls for .0065" x bore for their top ring.

 

[thehueypilot]

.010" is WAY too tight for a top gap! how in the world to you consider .010 to be "standard"?!?
total seal calls for .0065" x bore for their top ring.

0.0065" is tighter than 0.010"..........the .010" comes out of the factory manual but I bought this as a short block assembly and all I did was audit the torques and installed it w/o taking it back apart. It ran for over two years with no issues. The piston looks clean because I cleaned it before I took the pictures so it would photograph better. It had a layer of black and brownish soot on the top. I still have not heard from CHP.......customer service?

 

[classic boost]

0.0065" is tighter than 0.010".

.0065" times bore. .0065" x 4" = .026".
i'm sure chp set it up in the ballpark. you're pistons are textbook example of rings butting. it seems strange that it would last 2 years before giving up.

 

[rbohm]

i wish you had taken precleaning pics and posted those, but that looks like detonation damage to me. your cylinder pressures are too high, either due to compression ratio or ignition lead, or the fuel you are using has too low an octane, or your O2 sensor is giving you wrong readings.

 

[Dbeck002]

Seems like the force exerted on the ring lands came from the bottom up. I would imagine the ring gap was to tight and caused the tip ends on the piston ring to want to push on eachother, only to go nowhere but break the weakest part of the piston at that point, the ring land directly above the splice.

Was their any debris inside your cylinder?

 

[thehueypilot]

Yes, there was some melted pieces in the cylinder but the ring gap was not under that spot. CHP actually called me back and said that all pistons will fail at that area (intake valve reliefs) under detonation. He said the ring gap was set to approx. .018 - .025" and they will sell me one piston and one ring for a fee. He is still reviewing the photos........but said he thought it was caused by detonation. I only ran 93 octane and timing to the edge of detonation (by ear) and reduced by a tad until I could not hear it. The piston tops were black so I believe the A/F meter is correct but..............it does not monitor individual cylinders so that one cylinder could be leaner than the rest?

 

[brianj5600]

I've heard that CHP builds a sloppy motor. It sounds like they don't even know what they set them at. With 0 gap seconds I guess top gaps are not critical unless they are tight. I would put the ring in it's hole and check it. I don't think I would put the motor back together w/o checking everything.

 

[gtss]

Just my two cents worth but... detonation is the answer I have always recieved from most all engine builders, it seems to be their first line of defense because then it is not their fault.
And having said that, any and all cases of detonation I have ever seen, have always had more of an eroded/burnt away look to the damaged area. Almost as if the metal of the piston has been burnt away, and I don't recall seeing a single case where the piston top looks pushed up as yours does.
I tend to believe that it is more of a ring gap issue, binding when hot then the ring actually pushed up on the piston top, and it would make some sense that it would break at the weak area near the valve relief
Gord

 

[thehueypilot]

I went out tonight and installed the top ring into the bore and I got 0.028" cold. I still think the generic "one size fits all" multiple valve reliefs caused a stress riser at the spot it broke. You can still see a crack running inside the deepest valve relief. I will be talking to them tomorrow because the replacement piston must match the weight of the old one otherwise it will throw my balance off. They did tell me that they keep the records of all engines and balance results. Thanks for the input!

 

[10secgoal]

What are the chances of finding the pulg that came from that hole ? Does it have black specs on it ? Do any of them ?

 

[65ShelbyClone]

I only ran 93 octane and timing to the edge of detonation (by ear) and reduced by a tad until I could not hear it. The piston tops were black so I believe the A/F meter is correct but..............it does not monitor individual cylinders so that one cylinder could be leaner than the rest?

"Only" ran 93?

I find it really hard to imagine a n/a 10.5:1 engine detonating bad enough to wreck a forged piston like that. If detonation killed it, the top of the piston would look at least a little sandblasted. To me, it seems like the piston snagged the cylinder and pulled the edge of the crown off.