Cam Damage
 

Well, almost all of the parts that have come out of my 3.6 have looked great (dimensional checks to follow). Then I pulled the cams and found damage to one of the lobes on the #2 cylinder. I've attached some photos. Any idea on the type of failure we're looking at here? The rocker arm looked ok. Is it possible that I could have inflicted this damage myself while pulling the cam out of the cam housing?http://forums.pelicanparts.com/uploa...1331577457.jpg
http://forums.pelicanparts.com/uploa...1331577563.jpg

No, it wasn't you. Classic lubrication issue. Probably because of the low ZDDP in modern oils. You rarely saw this in the past. Now, seems to show up all the time.

I would have to agree that the quality of the oil contributed to the failure pictured.
We are finding that additional preparation to engine parts in these older engines is needed to ensure reliable performance.
We are using more coatings (DLC, dry film and ceramics) and treatments like cryogenics to compensate for missing oil components and the lower quality of manufactured parts.

Not sure which side that is, but my friend has a good used one. (only one, not sure if it is left or right)
Give him a call at 609-298-2277. Tell him Pete told you to call, he'll give you a good price.

Pete

Thanks Pete. Not sure what I want to do yet on cams; but, I may use this failure as an excuse to go back with RS cams in the car. This cam came out of the left side of the motor, so it is not the one with the power steering drive.

Hi Ernie,

This isn't uncommon any longer and due to several things, one of which is using oils containing insufficient levels of ZDDP.

The other big contributing factor is improperly finished rocker arms, right from the Factory. We are seeing a lot of rocker pads that were not ground flat & parallel with the rocker shaft bores. This puts asymmetric pressure on the camshaft lobes as well as the rocker arm pads which increases wear.

Add both of these issues together and its a recipe for these kinds of problems.

IMHO, its imperative that all rocker arms, new or used, get checked & trued before putting them in service to avoid camshaft problems. We do this in-house now after QC issues with some subcontractors.

Your cams need to be either repaired or replaced. If you have them repaired by hard-welding, the pads should be hard-chrome plated to prevent failures.

This pitting I have seen many times on 3,6 liter engines.

For example my camshaft:
http://www.porsche-foorum.org/album/...l_IMG_0339.jpg

But have it not seen it on right camshaft, only in left 1-2-3 cylinder row.

By my mind will be there some engineering problem.

Or has somebody seen same pitting on right camshaft?

I might have my geometry wrong but - doesn't the right side intake open rockers in a "bind", left side "pulls" the rocker open. I think this might be one reason one side compared to the other have different wear patterns.

we see this all the time in the VW world now. besides the fact that lifter quality has turned to poo. it has gotten to the point that if you don't buy CB lightweight lifters or equivalent then your screwed on top of the fact that zddp is absent from most oils these days....:mad:

Someone needs to come up with a roller rocker (not rocking roller ;-) upgrade for our cars.

Surly it can be done. Obviously a market for it.

Chris

73 911 E

there was a past post or thread discussing the possibility of a roller rocker, some very smart and experienced people looked at this and concluded it is not possible, the exact features or dimensions that are part of the limitation, I don't know, I don't think it was mentioned but it was awhile ago.

I believe Aaron @ Rennwerks put considerable time into the proposition of rollers for 911 engines with the conclusion that it was not worth pursuing further.

roller rockers
 

Aren't the roller rockers the Detroit iron crowd use, or the VW aircooled guys use, rollers which depress the valve? Pushrods do the other end of things.

While that roller setup might be helpful for something (less parasitic friction? less wear on valve tips?), and I am sure it is because otherwise who would mess with it, what is suggested here is that the rollers bear on the cam, no?

Does any rocker do that?

The roller rockers convert the sliding friction to rolling friction (which with steel on steel is pretty low). So they help a lot when there is marginal lubrication. It's like going from a bushing to a bearing.

Walt, most roller applications in "Detroit Iron" include the lifter as well as the rocker. The lifter follows the cam lobes while the rocker moves the valve stem, both in an attempt to reduce wear and friction. It's referred to as a "roller cam" and the profile of the lobe is changed to accommodate the roller lifters. Push rods connect the two roller parts.

Ah, now that you mention it, I hadn't thought of the roller lifter part of it.

By joining things with a push rod, the normal valve lash adjustment can be maintained.

Given how well the elephant's foot seems to work, would there be any useful gain by putting a roller on that end of a Porsche rocker? You could use lash caps for adjustment. I can't see that one.

So perhaps the attempts were using a roller on the cam? Which meant not only designing a roller rocker, but also trying to figure out how to regrind cams to make it work and take advantage of things? No wonder this hasn't been done to the point of products.

One of the improvements with roller rockers on Detroit iron is the switch from a stamped rocker that pivots/wobbles atop a stud, to an actual pivoting action via a roller shaft. The 911 rocker already has this pivot feature with the bushed rocker arm and rocker shaft setup.

One advantage of a roller cam follower in old style push rod engines is that the opening/closing ramps can be steeper and thus getting the valve open sooner and closing later without rapid wear which occurs with flat cam followers. Many modern OHC engines use rollers on the cam end of the rocker but I'm not sure if there would be space issues etc in our aircooled engines. I think, but am not sure, that later water cooled Porsche engines use a roller somewhere in the valve train.

A quick glance at the parts catalog for the 996 Cup car's motor did not show even a cam follower, much less any rockers. As best I can tell from the catalog, the cams open and close the valves directly. Unless I missed something in the parts diagrams.

The old Jaguar 6's used a direct cam follower pushing directly down on the valve stem.
They have problems too with the newer oils.
I believe the real answer is in the direction of an additive for the oil, perhaps to increase the ZDDP factor.
We used to add Wynn's Friction Proofing to all racing VW engines right off the bat when building them.
I don't know if it's still available...or maybe something else might be.
I have looked at the geometry of the rockers to put a needle bearing in the tip (cam side) and it might be possible...but the diameter would have to be small...and the pin size going through it would be too small to carry the load.
The other problem is the valve cover....higher ones would help with clearance...so the cost factor goes up a lot.
Bob