The piston peices probably got pulverized into dust or very small fragments. It would not take very many revolutions, and the motor probably turned over hundreds of times after the piston failure. If there are any piston chunks left, they are down stream in the exhaust system.

As to the discoloration of the metal near the crack, many pump fuels will leave colored deposits. The crack could have been there a little while before the piston totally failed, allowing the fuel and combustion to stain the piston.
There is also plenty of discoloration on the skirts of the piston, too.

IMO, the 'deposits' on the failed area are not carbon from sustained running with a cracked piston. Any deposits are probably piston dust that fused to the area shortly after failure.

Both pistons failed near the exhaust valve. The exhaust side is hotter than the intake side (the intake gets cooled by the unburned fuel).

The theory that two pistons were dropped in exactly the same way and both got hairline fractures that caused premature failure in the same place really is grasping at straws. They both failed on the raised area near the exhaust port because that is the point where the piston was getting the most heat and abuse.

BTW, your coolant temp gauge is not really a gauge. It is designed to sit in the same place even when the motor temp varies withn a normal range. It is more like an 'idiot light'. It will only go to 'Hot' when the coolant temp goes way up. When it goes up a little, the 'gauge' does not move. And you can have violent increases in combustion chamber temps and pressures immediately when you put a load on the engine. It takes sustained load to raise the coolant temp substantially.

 

Ok so lets say all the valves and what not turn out clean and in good condition (I will take pics tonight and post tomorrow) what would be everyones next suggestion as to what is going on and where to start looking? Everyone here has somewhat the same reaction as everyone else I have shown it is an odd break and situation...maybe theres more then just pistons and valves and wrenches out there....I wonder...haha

 

I think that either the pistons had a casting flaw, or they were broken before installation, or the guy that installed them beat them into the cylinder with a metal hammer, or they struck the head, or they struck a valve, or they struck a foreign object that was ingested, or you've spun a bearing causing one of the above, or the piston was damaged before assembly.

Take a pic of the broken spark plug too please.

At the moment, my personal opinion would be to put the engine back in, replace your broken spark plug, and drive on. I'll give you another opinion when you upload the other pics.

 

you might as well pull the lower assembly apart and see how much crap is missing from your bearings and then wonder how much is in the crank.

 

I did this to my first GT motor with a 200 shot of N2O. I did have some det. marks from not enough fuel but my broken piston (and it looked just like yours) was caused by the wrong ring gap.

You weren't running a power adder though, were you?


I would have to say you prob. ran lean and seized it up and it broke off.

 

you mentioned that you ran a fram oil filter that is a no-no , they are known to collapse and cause oil starvation problems. Also your timing is controlled somewhat by the oil pressure as the timing chain tensioners are 'tensioned' by oil pressure; a collapsed filter could have caused a mis-timing issue which could have led to detonation.

I would agree with those that it was the wrong top ring end gap or very cheap pistons. but the ultimate cause was a LEAN condition that provided an elevated cylinder temp necessary to cause a ring to seize and pop the piston top off.
the missing part is in a zillion little pieces that went out the exhaust.

replace your bearings as they have been damaged (trust me I have seen this several times).

 

If the ring gap was originally perfect and the ends butted together under normal combustion, then the increased combustion temp under detonation can cause the ring to expand further causing it to **** in the bore and snap the ring land of the piston.

 

The rings are in perfect condition but yeah the top ring looks as though it didn't set you can just take it off easily with your hand no problem.

 

Yes....Detonation!

 

I'd agree again. The modular uses a pretty weak piston (and connectiong rod also). It is fine in most situations, but obviously you have some issues as does anyone who adds too much power adder. A near stock modular is not going to show the same kind of detonation damage as a race engine. I think if you post an a more performance oriented site you will get better answers. I like www.turbomustangs.com or http://www.nmraracing.com/

 

Anyone ever seen what happens to Keith Black pistons if you don't gap the top ring REALLY loose? Exactly the same thing. Ring ends butt and pop the top off. I've done it 4 times. Friend has done is a time or two with nitrous.

Not saying that it was the problem in this case, but a combination of lean mixture, detonation, cheap fuel (or old fuel...does the same thing) may have caused it.

In any event, it sucks!

 

As others have already stated, when you changed your exhaust and did not have it retuned, causing your lean condition, you broke your engine.

Your pistons failed from detonation (that sound of marbles in your engine under load), plain and simple. These hypereutectic pistons cannot withstand any abuse of detonation. You have 1 choice, replace the pistons and get it tuned.

 

Wow you seem convinced that you absolutely know the problem without ever seeing or hearing true evidence. Well how come the owner before me broke a piston in cylinder 3 long before I ever seen the truck or layed a finger on the exhaust smart guy? Seems to me like your one of those mechanics (tradewise or in your own head) that knows the problem right away without considering all the situations and possibilities. Sorry but I am getting pissed off with not being able to truley find out what the !@#$ is going on. Please read my first posting before you start stating the problem is "plain and simple."

 

Easy there cowboy, I've been building engines for over 20 years and specializing in these engines for over 8 years. The MP in my user name stands for Modular Performance .

 

Well then how do I go about tuning this thing where can I take and what do they have to do to tune it? Remap the timing maybe? How much is this going to cost me? To tell you the truth though I know tonnes and tonnes of people who have exhaust systems and I never heard anyone having to get their whole engine retuned because of it. i know the backpressure changed a bunch but I thought the engine automatically compensates for that kind of thing, just as it does for temp, elevation, etc.