Look at the top of the pin bore,not a scratch on it,from what I see. If it had of hit a valve ya would think it would have a flat spot in it before it snatched the top off of the piston.

 

I would not expect a cast piston to show signs of a struggle at all. This is what they do when they experience contact. As someone mentioned before a foreign object could have caused the damage as well, the evidence would be in the pan but the bent puishrod is a tell.

 

It's possible the PR got bent after the top got yanked off the piston. From the looks of things it wasn't shut down right away.
These are not cast pistons they are hyper-u-crap-itc they may be cast but there is a difference.

 

Hypereutectic means they are super saturated with silicon and they can be brittle, they are still cast.
When contact occurs a cast piston can and will generally shatter. A forged piston can withstand more, but the end result can be the same though the piston will tend to stay intact in the areas around the point of contact. A hole in the cylinder is a typical result. A sleeve can often fix it up.

Exhaust valves can be problematic. The use of full teflon seals can also really dry up the guide which may cause trouble.

The above is merely speculation by all and can be harmful and dangerous as we don't have the assembly in hand to look at. It is for this reason I am going to refrain from posting further on the subject. The builder should have an opportunity to inspect it and determine cause of failure.

I can tell you one thing, I'd bet every engine builder who participates here would love just once for a guy to bring in a box of blown up parts and tell them they were hanging it out for all it was worth when it blew all to hell. There would likely be a healthy discount on the repair.

 

Ya know they do make cast pistons without the silicone,don't ya.
Yea I started building engines about 40yrs ago and have only used 2 sets of hyper-u-crap-tic and both blew the pistons out of them.
That's why I wouldn't run them in my lawn mower.
Exhaust valves are not a proglem unless the piston hits them. If that was so it should have blown up on the dyno,huh.
Max piston speed with a3.500 stroke and a 5.7 rod@7000 is 4083FPM and there is no way those pistons are rated for that.

 

But that is never when they break, is it?

Rich

 

I hope that silicone is not put into a piston as it would quickly melt. Silicon is the element added to pistons to reduce wear and scuffing. It is used in varying ammounts depending on the application. As far as I am aware silicon is combined with aluminum in all pistons whether cast or forged. The percentage of silicon is what dertermines whether it is a "hyper" eutectic, eutectic, or low silicon piston when discussing cast. 2618 and 4032 contain different ammounts of silicon as well.

Federal-Mogul did extensive testing on their hypereutectic line as they were being developed. One of their test mules was a 750 hp small block with a fogger system to prove their viability in the perrformance market. Some cup teams were also experimenting with them at the time as well. The clearances were so tight that the pistons had to be installed with torque plates on the engine and it could no be rotated without the plates or cylinder heads bolted on. This was the supposed advantage, better ring seal and control with light weight. Hypereutectic pistons when installed and tuned with the proper care are a viable affordable choice in a performance engine. They just leave a smaller margin for error.

I do not agree with your assesments (or your math) and I'll leave it at that.

Take care.

 

amen to that. hyperutectic pistons dont just break by themselves. i've seen them withstand some pretty amazing abuse. hell, i've seen el-cheapo cast pistons withstand some pretty crazy stuff!

 

My take on HE pistons: fine for certain OEM applications and stock type rebuilds. Not for high performance, from what I have seen. As far as this particular piston, I think it was defective. Maybe the manufacturer can analyze it?

Rich

 

I can't count how many people have blown out their Hyper-u -crapnic ring lands with blowers installed at only 550rwhp...this is not a timing issue, this is that fact that a cast(because YES it is still a CAST piston) cannot handle the cylinder pressures that are created.

You seem to be the one person that I have heard say these kind of things about hyper pistons, hell - why even make forged pistons then? I guess JE and Mahle, wiseco, CP etc should just go out of buisiness because "chapter 11" fedral-mogul and KB are going to take over the performance piston market.....................

 

If ya don't believe the math then get ya a calculator and tell me where I'm wrong!!!!!!
Kinda makes ya wonder why the factory has a 5500RPM? limit on these engines.
When ya start getting over 4000FPM ya need preminum parts and that means FORGED pistons or they will ****** the top right off the piston Exibit A in this thread.
At 5500 the max speed is 3208 Gs are1960
At 7000 the max speed is 4083 Gs are 3180

 

Here's my try at the $64,000 question:

Piston rings were either improperly installed or gapped wrong on that piston. All during break in and dyno time, piston ring is wearing a groove in the cylinder wall. Engine is installed, fired up, and is idling without a care in the world. Groove in cylinder wall finally reaches critical mass, bottom edge of piston skirt catches the ridge in the wall on the downstroke, force of the crank rips the piston pin out of it's bore and subsequently splits from the crown which at this point is still unharmed. Once piston skirt is annihilated and piston crown and rod end is free within the bore, upon upstroke the rod end comes up and hits the bottom of the piston crown like a pool stick hitting a ball, and sends the piston crown flying to the top of the bore where it promptly crashes flush into the exhaust valve, bending the pushrod. I would say that the smaller half of the piston crown in the pics is the half that was broken off at the point on the piston where the valve made contact. After the crown is broken and can no longer hold itself flush in the bore it is free to tumble around which is indicated by the mauling in the ring lands. Hole in cylinder wall was probably poked through by the rod end; either that or the larger half of the piston crown got wedged between it and the cylinder wall on the next upstroke and the rod used the piston crown to poke the hole.

 

Pretty good assessment but not enough run time to groove the walls.
Everything else sound right.
If the rings butted it would take out the ring lands which may have weakened it to the point of snatching the top off.

 

3.48 * 7000 = 24360 inches per minute = 2030 feet per minute. You only count the stroke once, stroke.

 

Calculate Piston Speed



Enter your Stroke (in inches) and RPM of your engine

Stroke:

RPM:

Your Piston Speed computed from your RPM of 7000 and Stroke of 3.5 inches is 4,083.33 feet per minute.