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Piston Disintegrated - Failure Analysis

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Stock OEM cast piston, rally racing application.

Almost completely stock engine, only modification is some mild upgraded cams.

Basically the piston just completely disintegrated, there's nothing left as shown in the pic.

Bits of it are in the crankcase and even wound up inside other cylinders! Bits must have been push out the intake valve and then sucked back up into other cylinders.

What are some possible causes? What's most likely or least likely?

"No description available."

What were the operating conditions when the first signs of failure occurred? That might provide a clue.

Possible causes:

Excess piston speed.

Excess heat (seized piston).

Non-compressible item in the combustion chamber (everything from a broken valve head, to water injestion).

Failure due to previous damage (detonation / burned piston).

What engine is it? Dont see many with a helical gear on the web - is it a bike engine?

I wasn't the driver, so I only have second-hand information about the circumstance.


Apparently it happened suddenly without warning. It was running fine, then sudden horrible noises and dead. It happened just after a gearshift, so revs weren't too high. Temps were all normal. I'll ask about potential water ingestion.

3 of the 4 valve heads in that cylinder were broken off, but it's probably unknowable if that was a cause or a result of the piston itself failing.

@Adam: It's a Ford Duratec 2.5l. That's the drive gear for the balance shaft, which we always delete on these motors.

"No description available."

pretty hard to conclude any type of reason for this failure, if it was running std pistons in a rally type application there is so many factors that could lead to a piston failure, don't rule out bearing failure that could have caused the piston to hit a valve or the head, even a bent rod can cause this, more pics may help tho is there anything left of the piston to get pics of ?

As a guy that road races 2L MZR / Duratec engines, I'm going with a broken valve head (it's happened more than once to me). But the 2.5L also needs to be kept to a conservative RPM limit (7000 iirc) due to the piston speed, if over-reved excessively, I could see piston failure happening.

I too have had a customer with a 2L NA duratec drop a valve, I dont know these engines well enough to know if it is the same series as this engine or not. It did have cams and springs but OEM valves, it wasn't a real screamer, I think it was run to around 7500 and only done a season of racing before letting go.

The first time it happened to me I got lucky, the valve parked itself in the intake port. Only dinged the piston:

Attached Files

This one has been racing for about 3 years, it had 20 events on it. Rev limit was set to 7200rpm and it hit that on a fairly regular basis.

@David: I'm curious what you redline the 2.0's at? I know they have a great rod-to-stroke ratio.

I normally run an 8000 RPM rev limit, but will go to 8400 in the lower gears if needed. Here are some notes I sent a customer 2.5L that I setup (I didn't build it, Mazda did!)

I just ran this piston speed calculator and the 2.0L with 83.1mm stroke, gives a piston speed of 76 ft per sec at 8400 RPM, vs the 2.5 (100 mm stroke) which has a piston speed of 76 fps at 7000 RPM.

So I think your 7000 is probably a good upper limit, and perhaps you would really want to target a top RPM of 6800 or so regularly.

That it bent a rod indicates there was something stopping the piston reaching full travel, whether it was initiated by a dropped valve or breaking up piston it's impossible to say for sure, but the number of replies with valve issues suggests that dropping one could be the problem.

I had a similar failure on an M104. Piston was in the sump. Tho that issue was the VVT cam timing was off.

Can you see any fragments that are sort of intact? If you can look if there are little tiney dots on there.

If you have some photos of the piston fragment edges i can help you figure out of it was a ductile fracture.

Other things could be the rod journal on the crank getting damages from oil starvation and that could affect piston hight.

You could also have had a blocked injector making go lean and took out the piston witg heat. In a rally application the engine would be dieing and driver would be none the wiser. Not the case here

Tho those canyons in the sleeve tells me this was happening for a while and no marks on the other side of the sleeve tells me something was keeping the rod agianst that sleeve.

From my view it seems the piston conta ted the valves. You dont get this level of bend for other objects. With the valve heads off it tells me the piston to valve was your culprit

If you have more photos of the fragments please post em up. I would like to see.

If piston melts. AFR related issue. If piston shatters valve contact.

Attached Files

Here you can see how a rod failure affects piston height

Attached Files

Here you can see melted piston off a mazda 1ZY with bad injector. It melted from high heat. If you look closley youll see some dots thats also from engine knock. Camera doesnt show it well

I cant find a photo of the M104 piston. It doesnt show any signs of the above 2 photos and looks almost new just that it is in a bunch of pieces like a jigsaw. It was very long ago unfortuantely

Attached Files

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