Anyone ever broken a crankshaft?

[travelair]

I finally tore into my '96 3.1 liter and discovered the crankshaft to be broken. It sheared outboard of the main bearing nearest the right wheel. I waited too long to replace the lower intake manifold gasket and was afraid running the diluted oil had only damaged a bearing. No such luck.

The engine failed while accelerating through 30 mph. Afterward, it ran at idle only, with a loud banging noise. It was towed home a year ago and has sat since.

A month or two before the incident, the oil pressure light would come on at idle with warm oil and would extinguish above idle.

What would cause a crankshaft to shear in such a way? The engine can be turned by hand now and I don't understand what could've interfered with it to cause this damage.

[maxwedge]

Probably seized in the rear main bearing, pull that cap and look.

[travelair]

I'm done messing with it today but I will try to pull that cap. Will the oil pump get in my way? I don't remember seeing an obvious way to pull that bearing.

This is all for posterity at this point. The body of the car is in poor shape and it is not worth salvaging. I plan to give it to a local junk yard but was just wondering what caused its downfall.

[NeonKnight]

write free on it and give it to some poor teenager lol. have the kid fix it, maybe give him some morals in life. hahaha. or even a Mechanic Student.

[cadgear]

Originally Posted by NeonKnight

write free on it and give it to some poor teenager lol. have the kid fix it, maybe give him some morals in life. hahaha. or even a Mechanic Student.

Not a bad idea, actually. GTC where I'm taking my GM ASEP classes at welcomes GM donations, especially engine or transmission parts. You probably get a tax writeoff too, I'm sure.

[travelair]

I have my answer. Bearing siezure did not occur because the engine can be turned over by hand with the spark plugs removed.

An engineer friend of mine thinks the mild knocking for the last 20,000 miles weakened the casting causing the failure due to metal fatigue.

[maxwedge]

The engine turns over by hand because the crank is broken? Can you turn both broken halves?

[travelair]

Yes, I can turn both halves together. Although it is broken, it still fits together well enough to turn by hand. It did idle for short periods, albeit loudly and roughly, after the incident.

[maxwedge]

You would think it would take a catastrophic event to break a crank 4k neutral drop, seized bearing , broken block at the webs, very unusual. I broke a crank at 7500 rpm's, 130 mph , in a hemi S/S Plymouth, but that is a different issue.

[travelair]

Here's what happened:

42,000 miles: Titled car in my name and noticed coolant in oil.

45,000 miles: Used additive "liquid copper" in coolant advertised to stop head gasket leaks.

45,001 miles: Engine started knocking.

48,000 miles: Replaced lower intake manifold gasket.

65,000 miles: Crank failed.

Procrastination caused me to run the car too long with diluted oil. Then the additive poured through the leaking gasket and plugged oil passages causing further bearing damage.

All along, I thought the knocking sound was the lifters. Funny about hindsight.

[maxwedge]

Now I see, that is the catastrophic event I mentioned!

[tblake]

the "liquid copper" blocked oil passage ways? You didnt notice an oil pressure light come on or anything? Thats why whenever something goes wrong, I dont try the cheap easy fix first, I do it right the 1st time. Not saying that was stupid to try the liquid copper, but if it really does do anything, the effects arent going to last very long, and the head gasket/intake leak will just get worse and worse.

[meuhus]

Originally Posted by tblake

the "liquid copper" blocked oil passage ways? You didnt notice an oil pressure light come on or anything? Thats why whenever something goes wrong, I dont try the cheap easy fix first, I do it right the 1st time. Not saying that was stupid to try the liquid copper, but if it really does do anything, the effects arent going to last very long, and the head gasket/intake leak will just get worse and worse.

i agree with tblake
should have changed that head gasket
the only thing i would use stop leak for is a radiator leak
and then that should only be a temporary thing

[travelair]

The oil pressure light is simply a "low pressure" light. The pressure wasn't low enough to trigger the light at higher RPM's where the damage was done. I don't think it comes on until around 7-10 psi. So, in theory, I could have been driving down the freeway at 12 psi and never known it. An oil pressure guage is the only way to know.