Broken Cam - Why does it happen?

[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.

[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.

[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

[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.

[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.

[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.

[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.

[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

[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??

[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]

The autopsy results are in and the victim died of lack of lubrication. The back half of the camshaft had lightly scored journals, but the rear bearing looked very bad. I was not able to remove the section because it has a spun cam bearing floating on it between the journals and the edges of the bearing are hammered so it won't easily let me remove the cam. So, the back half of the cam goes to scrap with the block.

But my conclusion is that in spite of no evidence of leakage, there must have been enough leakage to kill the oil and then the engine.

If you have a decent running 3100, the best choice is probably to fill the radiator with oil. It may not cool as well, but the bearings will sure last longer.

[pocket-rocket]

You could put the front half of the cam back in and smack it with a hammer to drive the back half out through the flywheel side if you really wanted to get it out.

[robertisaar]

If you have a decent running 3100, the best choice is probably to fill the radiator with oil. It may not cool as well, but the bearings will sure last longer.

that's one way to tell a leaking LIMg to fuck itself!

[pocket-rocket]

that's one way to tell a leaking LIMg to fuck itself!

I actually lol'd reading both of your guys' responses, lol. Keep 'em coming!

[kerno]

I'm new to the forum, but I'm not new to engine building. I grew up on both big and small block GM engines. All of 'em had the same cam in block with pushrods, stamped metal pans, leaking rear main seals, double row timing chains and valve covers that never really sealed. As a result, when I bought a super clean 1999 Malibu with a 3100, I knew the engine was DOA, but I was pleased to see the changes in the design of this engine family. Things like the 2 piece intakes with part of the intake serving as the valve cover surface, the cast aluminum structural pan and the fulcrum rockers are a depaturer from the "old ways" of GM.

But as proof that you can't teach an old dog new tricks, what's with the cut off distributor driving the oil pump? That's been a GM theme forever. What a steaming pile that is! Why not do a crank driven gear type pump like the rest of the world? How about the same old timing chain and gears with no tensioner? To take the slap out of it, they just tossed ln a couple guide rails on the inside.