[awes]

I melted a piston during engine dyno.
No idea what caused it.

Cylinder 4.

Newly put together. N/A. SRP forget pistons. Single plane intake. Rings carefully filed for NoS (but no NoS during dyno!)

Also cylinder 3 show a spot of about 2cmX0.4cm where the piston had started to melt. Heat spot is slightly to the intake side of the piston right at the edge.
Rest of the cylinders only show trace of good combustion.

Anyone with ideas what can caused this?

 

[novaracer1]

Detonation????

 

[Tubbed63]

Would have had to be some seriously massive detonation to destroy a forged piston like that. I say somebody fooked up and forgot to file the top ring on that piston. Broke the ring land then punched what looks like a round hole in the top of the piston. I also see where it was beat up by the ring land pieces.

 

[Real McCoy]

Did you have EGT probes in the headers when it was on the dyno? If so what was the EGTs of all the cylinders? Were 3 and 4 real hot? A vacuum leak could do that but the EGts will be way off.

 

[Lugnut79]

Looks like the pistons on my snowmobiles of the past when I had a vacuum leak. It always looked like someone drilled a hole in the piston. I'd have to agree with RM ^.:yes:

 

[jason snyder]

Dang , i would think the dyno operator would catch that before it melted down ! I also would think the dyno operator KNOWS why it melted down . WHAT does he say ?

 

[Granny 67]

Newly put together. Does this mean new pistons also? If they are from your old combo its a possibility you could of lifted a land when running the No2 and not noticed it. Hard to tell what happened first the lifted land or the torched hole. Most likely the lifted land as someone mentioned.

 

[The Big Al]

Did you have EGT probes in the headers when it was on the dyno? If so what was the EGTs of all the cylinders? Were 3 and 4 real hot? A vacuum leak could do that but the EGts will be way off.

My very thought.
A DYNO run with all the monitors hooked up would have solved this!
That is a lean condition, many things could cause this.


Al

 

[SMLBLK66]

Would have had to be some seriously massive detonation to destroy a forged piston like that. I say somebody fooked up and forgot to file the top ring on that piston. Broke the ring land then punched what looks like a round hole in the top of the piston. I also see where it was beat up by the ring land pieces.

X2, either that or the bore was off and to tight for the piston, but since the others look fine i would guess or agree that the ring was to tight and or the land was lifted whiched caused the rest of the damage. JMO.

 

[Camgrinder]

What octane fuel was it supposed to be?
Looks like it happened very fast. The sealing rings on the head gaskets dont look deformed. I would measure the crown thickness on a good piston in the are where the other ones failed.

 

[cody rusow]

did something catch on the top of the gasket? it looks like a mark. i agree about the ring catching . i was wondering the bore, stroke, rod length, compression height, gasket thickness, and how much it was decked? Thank you

 

[levisnteeshirt]

2 much timing

too much timing , not enough octane , not enough coolant flow ,,,

were you using an electric water pump on the dyno or a regular pump ??

 

[awes]

Thanks to everyone posting suggestions and ideas!
And I've very sorry I haven't replied to questions posted quicker. I did a long post, then my browser died and I didn't have time to rewrite at that time.

But here are responses to (most) of the questions.

Dart Littel M all machine work newly done, zero decked, 3.48x4.155 with 5.70 rods, Victor Jr heads (64cc before adjusting for the 4.155 bore), SPR forget 9cc dome pistons (new), 1003 gaskets (0.041 thick). Will give roughly 12.8 or something in static comp I think.
Ring gap 0.025 top 0.028 second.

No waterpump during dyno. Water supplied by the dyno rig.

"Conservative" timing during dyno.
V-Power with Octane booster. (104? octane RON).
(Will use race fuel when turning on NoS.)

Theory is, as some already said, that first the ringland broke for some reason, the hole is a secondary damage. Still no good theory for the ringland break though. Might be me f-ing up during assembly and broke a ring (not likely, but could have happed)!
The plug is seriously damaged (burned/melted) at the worst damaged cylinder. But that could also be a secondary damage of cause.
No readout seems to warn that this was on its way (the dyno guy use to have a headset to a mic for catching detonations.)

Oh well, block re-honed, new rings filed, 3 new pistons, shortblock together. Waiting for the heads that needed a little cleanup as well.
Hopefully I will be ready to race this weekend. Will keep my fingers crossed.