I am rebuiding a V-6 Fuel Injected motor that I bought from the neighbor, and he said it was "hammering like hell." I pulled the heads and they looked ok. Then I looked down each of the cylinders and one of the pistons had broke. When I pulled it out, the connecting rod was bent. By looking at it, I decided that the piston broke because when the rod bent, it shortened the path and was hammering on the Crank. My question is, what makes a rod bend? I've heard some silly stuff from our local shops here, but would like to get to the bottom of it before we replace the piston.

 

coolant leaking into the cylinder would do it....

 

Also fuel; also ingesting flood water.

 

I thought maybe it was coolant leaking in because one of the other cylinders has corrosion spots in it, but the one that bent was perfect, and also had the usual carbon left on it. As far as the fuel part, would that be a stuck injector? How would I go about testing it to make sure it isn't stuck?

 

Causes? My votes are:

Hyrdo-lock;

Wrist pin / pin boss failure in the piston;

Excessive thrust load / end play on crank;

Weak rods at high RPM with excessive clearances (like over-revving a loose stock bottom end).

 

Ok, well I checked the oil that was drained yesterday, and there are no signs of water or coolant. It doesn't smell a gas smell to it so I don't think it was fuel either. I guess that probably rules out the hydro-lock. I don't think it was a pin failure because the rod moves smoothly along the pin with hang ups and no scores of any kind. I'm leaning more towards a weak rod, but would appreciate if you could explain to me what

Excessive thrust load / end play on crank

means. This is the first time I've had problems like this and not familiar with a lot of things. Thanks

 

If the crankshaft has excessive play from front to back, the rods can be stressed in a direction that tends to bind the wrist pin in the piston, and bind the piston in the bore. Someting is going to fail first.

I'm not sure which bearing on a V-6 is the thrust bearing, but the rear (#5) main bearing on a V-8 controls the fore and aft movement of the crank in the case. Normal service limits for end play are about .006-.010". A manual transmission (actually, opening the clutch) tends to impart thrust on the crankshaft and will wear the thrust bearing surfaces, allowing more movement than the rods can tolerate. Automatic don't get this to the same extent, but can have thrust from clutch pack wear and torque converter swelling/damage.

 

as i seen it said above it probably filled up the cyl with water
you cant compress water so the rod gave

 

Just so those of you who were waiting for an answer. It took a little looking into, but it turned out the intake gasket broke around the water jacket and leaked coolant into the cylinder. So you guys guess right. Thanks for the help.