Cam Lobe Staining

[ctwo]

A guy is worried about the staining he's found on his cams. Says he cannot feel any marks and they are glass smooth. I't just a couple out of 8 intake lobes. All others, including exhaust are nice and shiny.

Any ideas? Something go wrong with the hardening process or is this possibly nothing to worry about?

[John Hasler]

I think that is the oil additives coating the steel, which is exactly what they are supposed to do. What do the cam followers look like?

[Harold_V]

A guy is worried about the staining he's found on his cams. Says he cannot feel any marks and they are glass smooth. I't just a couple out of 8 intake lobes. All others, including exhaust are nice and shiny.

Any ideas? Something go wrong with the hardening process or is this possibly nothing to worry about?

Most likely it's just not making full contact with the lifter. Not all that unusual, in fact.
If hardening was the problem, I expect the cam would be destroyed. If you've ever seen a cam that fails because of hardness issues (either from a lifter or from the cam), I think you'd agree.

H

[wlw-19958]

Hi There,

If you've ever seen a cam that fails because of hardness issues (either from a lifter or from the cam), I think you'd agree.

Yeah, I've seen that. What is unusual in this case is the
high point on the lobe is stained too. This implies that
the lifter/tappet or rocker follower isn't making good
contact with the cam lobe. Normally, the pressure from
the valve spring on the valve train components (at full
lift) should cause the cam follower to wipe with enough
pressure to prevent staining from forming on the high
point of the lobe.

If this is happening only on a couple of lobes, I would look
into the valve train components and the lubrication delivery.
The staining is caused by heat interacting with the oil on
the cam. Some staining is normal but if one area of the
cam shows significantly more staining, this could be an
indication of greater heat build-up in that area. A
significant amount of the heat dissipation for the cam is
through the oil.

Either that, or valve train components don't make any contact
and hence, there isn't any wiping of the lobe and the deposits
are allowed to build-up excessively.

Good Luck!
-Blue Chips-
Webb

[John Hasler]

If the staining was due to the cam follower was making intermittent contact the high spots would be shiny and the low ones stained. If it was making no contact at all surely the machine would fail to run properly. Thus if the cam is uniformly stained and the valve operates correctly the cam follower is probably maintaining uniform light contact. Isn't that what you want?

[wlw-19958]

Hi There,

Thus if the cam is uniformly stained and the valve operates correctly the cam follower is probably maintaining uniform light contact. Isn't that what you want?

But, that isn't how it works. As the valve train opens the
valve, it compresses a spring. As the spring is compressed,
the pressure on the valve train goes up. Therefore, it isn't
uniform by design.

Good Luck!
-Blue Chips-
Webb

[John Hasler]

Ok, continuous. The point is that if the cam follower is always touching the cam it is doing its job.

[ctwo]

There is supposed to be a point where the valve doesn't touch the cam lobe. I think the cam is fine but would agree there could be an oiling issue around there.

This is an early valve check so wear may not generally be observable at this interval.

Thanks

[Harold_V]

There is supposed to be a point where the valve doesn't touch the cam lobe.

Only if the engine in question has mechanical lifters. Hydraulic lifters maintain constant contact, albeit at light pressure.

I think the cam is fine but would agree there could be an oiling issue around there.

I don't think there's an oiling issue. If there was, it would manifest itself by destroying the lobe and follower/lifter. Note that there's an almost perfectly shiny area on the right hand side in the picture provided. That indicates, to me, that there is contact, but that the lobe on the cam is not ground parallel to the surface making contact, although very close. I believe that's the reason for the discoloration.

This is an early valve check so wear may not generally be observable at this interval.

I fully expect that if oiling was a problem, the area that displays shiny would show signs of gulling. Take a look at the mating surface to see if there's signs of wear, although I expect there isn't. If it's a lifter, and it's spinning properly as it operates, I expect you'll find the center slightly discolored, while the outer edge will be polished from contact with the lobe.

I could be wrong.

H

[spro]

H. You could be wrong but I don't think you are. The pattern is repeated upon the next shown cam lobe. We don't even know what engine this is.

[ctwo]

This is overhead cam and there is likely a shim and bucket sitting on top of the valve. The owner is panicking over finding new cams or getting these reground. I suggested he just rub them with some scotch brite and reinstall them, and check them a bit early on the next check. I was just interested in the color pattern on the lobes. It reminds me of my Lufkin height gauge base.

[spro]

There is the fact that some engines had hydraulic lifters/ cam followers With mechanical adjustment to final clearance. It is possible that these were inserted upside down so that the adjustments were more easily done under the cam covers.