2003 Mach/Maruader 4.6 bent rods

[Spdjunky]

So I tear apart my Mach engine this week to start going through it. The previous owner who was a mechanic said it had a light tick on the drivers side. (30k miles ish)
I assumed it was the 7-8 cylinders head problem due to heat.

I pull the heads apart, no problems with the valves or seats. Ok good....

Rotating the engine there is a drag. Long story shorter, piston 8 has the lip below the pin missing, the rod is bent, and the piston is rubbing on the crank counter weight. WTF I thought.

So I pull apart the Marauder engine (60-90k miles) to check it and maybe use a piston and rod, and low and behold piston number 5 has the same problem and bent rod!!

So I've known a few people who have built and roasted a modified 4.6. Is this faily common?

In 2003 and 2004 4v NA engines ran a small dish, almost a flat top. Looking through the internet, earlier model 4.6 pistons that had a larger dish, did NOT have a lip below the pin on the side.

So this is the start of gathering information. Does anyone have any first hand experience with this or any speculations?

 

[Svt Fox]

I wish I did! I will be watching your thread with great interest.

 

[Spdjunky]

So it appears both both rods were bent from fluid in the chamber. The most likely culprit is a leaky injector. since both motors are lower miles and in good shape.

I formed an opinion that due to no return fuel line that the injectors are subjected to more pressure or at least holding pressure longer and they may bleed off easier.

I assume this since I've never heard of a 5.0 doing this or a 4.6 on a return style system.

The only guy I know that blew up a 4.6 had it pretty stout and did not have a return fuel system....


I'm good either way as I have enough parts to rebuild a warmed over 4.6 and enough to build the hp monster later.


Any other ideas?

 

[Speedtospare]

Do you think an leaky injector dropped enough fuel in there to hydro lock the cylinder and bend the rod? Did the oil smell of fuel? I have tons of passes and street use on my eaton swap mach/aviator setup. I have the hyper pistons, powder rods, and non forged crank. Was pulling 11.50's@121 with 9PSI and never had a problem thus far. My research on various sites has led me to believe that they hold up to about 475 WHP and 7000 rpm, before bending.

 

[Spdjunky]

Your correct on the HP numbers, I've heard the same thing.

Hydralocking is much more damaging then HP or RPM.
The scenarios that would likely cause it would be when the engine is not being ran. With the engine just sitting possibly overnight, the pressurized fuel system would bleed off through and injector. The shops I spoke with said its not even uncommon for the starter to bend the rod with the fuel in the chamber.

I just don't see it being as common in the older systems we run with a fuel regulator and a return line. I would think it would slowly bleed off past the regulator instead of through the injector.

 

[Speedtospare]

Glad I went with a new fuel system. Had a 302 hydrolock on me at idle. I was lucky, no damage. New head gaskets and I was ready to go.

 

[Spdjunky]

Why did the 302 hydralock? Injector or bad head gasket seal? Which head gaskets were you using?

 

[Speedtospare]

Head gasket let go. Fel pro gaskets. cant remember which number of the top of my head.