Broken Cam - Why does it happen?

[pocket-rocket]

The Intake may have been leaking internally months ago etc, since then the bearings have been slowly deteriorating.

Coolant instantly starts to destroy the babit etc, but the damage may take time before it shows itself.

JMO

I've seen this first hand. The van ran for over a year after a bad intake gasket leak before bearings failed.

[kerno]

Checking the remaining section of cam is an excellent idea!

I'll pull the broken section of cam out and look at it today. If it is scored, the problem had to have begun before it broke.

Where does the LIM usually begin to leak? I'd guess it is at the coolant passages from the intake to the head, but have anyone seen a problem with the gaskets or do they come out looking OK, but leaking??

[Weatheralls Auto]

I certainly agree that coolant diluted oil would not lubricate well and I would be more comfortable blaming it on a leaking intake manifold if I had found any water in the oil on this engine.........

The Intake may have been leaking internally months ago etc, since then the bearings have been slowly deteriorating.

Coolant instantly starts to destroy the babit etc, but the damage may take time before it shows itself.

JMO

[CNCguy]

How does the rear journal look on the broken cam. If all bearing damage was done after the cam broke, the rear journal would look good as it wasn't turning without oil. The broken cams I have seen had damage to every journal which would indicate bearing failure prior to and the cause of cam failure.

[kerno]

I certainly agree that coolant diluted oil would not lubricate well and I would be more comfortable blaming it on a leaking intake manifold if I had found any water in the oil on this engine. The oil had about 1000 miles on it and I checked both the drain pan and the engine pan for water residue and did not find any. Nor did I see any evidence of gasket failure or a coolant path by the gaskets. But there was lots of bearing material in the oil, since the previous owner limped the car some short distance, not knowing that the oil pump had stopped when the cam failed. The intake showed no evidence of having been removed recently, so I doubt that the bearings had been hurt and the cam scored done prior to the last oil change, but that possibility does exist.

Hopefully, swapping over to a 3500 with the smaller coolant passages and improved gaskets will avoid any leakage problem. But I've also played it safe and ordered a solid cam for the engine.

[geoffinbc]

I don't think anyone with an otherwise good motor has had a cam break. The problem starts when the LIM gasket leaks and coolant mixes with oil. Now the lubrication is destroyed and the bearing and cam journal get more and more damaged. If you catch the problem early you will limit the damage if you get to it too late or never fix it all it is just a matter of time before the bearing catches the cam lobe and they weld themselves together and it snaps the cam. The front and rear cam journal have the most load on them so they are most likely the ones to go first.

[bszopi]

Cam is assembled by slipping the lobes on the hollow shaft and then forcing an object (metal ball) through the cam, therefore enlarging the cam shaft.

There are probably a dozen or so reasons why it could happen, as a hollow tube is much easier to shear than a solid core. Stop rotation (or inhibit rotation) on one side while the other side is still rotating will cause it to snap.

[Weatheralls Auto]

I never saw one snap all the years I worked in Dealer, seen several last 2 years in my own shop.

I think age mixed with lack of lubrication and heat causes it.
Driving with a leaking intake, coolant on bearings, vehicle over heating etc, will all have an effect on it.

Just because it has decent oil in crankcase now, doesn't mean it always has.
JMO

[IsaacHayes]

Bearings seizing up due to poor lubrication... Such as coolant in the oil from a leaking lower intake gasket. My motor is well over 220,000 miles and I beat on it all the time, and have yet to have the cam break... It's plenty strong as is, it's just when lubrication fails and a bearing seizes, the cam is first to snap.

[kerno]

Maybe I missed it in my search, but what are the theories on camshaft breakage? Most people here say they seem to break off the last section, which stops the oil pump and leads to bearing failure. The hollow cams appear to be made by shrinking the lobes onto a tube, but what makes the tube fail?

Not changing the oil or very thick oil in cold weather leading to higher oil pump loads seems reasonable, but the one I'm looking at broke on a 90 degree afternoon with dirty, but decent oil.