Weird cam wear. Whats the cause?

[Chris142]

Last year a friend of mine installed a rebuilt 4.3 Chevy v6 in a customers S-10 blazer.

The engine has a roller cam and lifters (factory type).

24K later the customer brought the truck back saying that it was not running right and was noisey.

We traced the complaint and the noise to the cam. It has worn into a stop sign shape on all lobes! It has jagged bumps with a dip between each.

The lobes closer to the timing chain are worn more than the ones towards the rear of the engine.

I've never heard of anything like this. I've seen the roller stop rolling and ruin one lobe but nuthin like all 12 lobes.

The rollers appear ok.

Any ideas?

 

[jthorner]

Two thoughts come to mind:

1) Possibly a defective cam which missed the surface hardening step of the mfg. process. Although I have not seen this personally, I have heard of it happening.

2) Oil starvation where for some reason oil was not getting to the lobes. I'm not familiar with that engine design, so I don't know what the oil path is.

John

 

[Dan4510]

I would say problems with hardening process of the cam too.

Dan

 

[TooSlick]

Sounds like the rollers weren't rolling and you were getting sliding contact between the "noses" of the cam lobes and the rollers. Peak loads are when the lobe is pointed right at the roller, so the wear pattern is more pronounced in the center and you have a "U" shaped profile across the nose of each cam ....

A picture would makes things much clearer?

TS

 

[AV8R]

Since the engine is a rebuilt, the cause of the cam problem could be almost anything, from the wrong valve springs or rocker arm ratio to a cast cam blank instead of steel. High revs with low spring pressures (from re-using old valve springs) can cause lifter bounce and a washboard-like wear pattern which would be aggravated by a cast cam or insufficient lubrication. This is a case for total warranty, not just repair, as the bearings have likely embedded a lot of metal.

 

[Chris142]

Here's more of the story. The engine is 12k over the 12000 mile warranty. The shop that rebuilt it wont do anything. my friend is eating everything on this deal.

We pulled the pan....Bearings look fine, no scratches. Cam bearings look fine too.

He had another 4.3 in the back that was a real smoker but unrebuilt. Pulled the cam and lifters from this engine and put them in the engine in the Blazer making sure to put the lifters back on the same lobes.

I dunno if that matters with a roller cam or not but we done it anyway.

Got it running with fresh oil and a Wix filter, took it to DelTaco for lunch. Drove it back and changed the oil and filter again.

At no cost to the customer since we are such nice guys.

 

[DavoNF]

Chris,

What sort of oil was used in this motor? I have heard that any heavily friction modified oil will cause problems such as this.

A local oil I use, Penrite, states categorically on the label "non-friction modified".

Food for thought.

Dave

 

[TC]

DavoNF: I'm not sure about that one... Here in the U.S., friction modifiers are typically required to meet the "Energy Conserving" labeling requirements. While they aren't primarily meant to reduce wear, they do reduce friction, thereby increasing fuel efficiency. Wet clutches used in some ATVs, motorcycles, etc. may not function properly if friction modifiers are present since they'll reduce the clutch's "grip." That's the only warning I've seen against friction modifiers.

Here's a brief definition of friction modifiers, per Lubrizol, a primary supplier of motor oil additives: "In effect, they make oil more slippery by reducing the friction between moving parts. This both reduces wear and improves fuel efficiency." http://www.lubrizol.com/PasCar/default.asp

 

[Chris142]

We have no way of knowing what oil the owner runs. It left the shop with 10w-40 Chevron.

I think that the rebuilder didn't harden the cam after it was reground. The shop that rebuilt it has been getting a lot of complaints lately from several other shops we talk to.

Only time will tell if it eats another. If it does we will know that it has a major defect somewhere and deal with it accordingly.