Cam Scrape - is this the rocker's fault?

The Watson · 06-16-2014, 01:40 PM

Tore down cam housings today and found some abrasion on the #6 intake lobe of the cam. I realize this needs to be fixed or replaced, but I want to make sure I don't recreate the problem if it was caused by the rocker. Here are some pics of each. You can see some slight beveling on the top right - is this beyond normal and would it cause that cam damage? None of the rockers appear perfectly straight across the top edge, so I don't want to make something out of nothing. I would appreciate any comments on the condition of the rocker and the appropriate next step, if needed. Thanks folks.

HawgRyder · HawgRyder's Garage

Any two metals rubbing together WILL erode the surface.
Depending on the lubrication available...the wearing process can be slowed down a lot.
So...if the hardness of each metal is too close to each other...both will wear.
If the hardness of one is higher than the other...the softer one will wear more.
In a perfect world....nothing would ever wear out.
I always look for the "shearing" content of a lubricant (I may be wrong here)...but over the years...good oil...and sometimes the correct additive will work wonders.
Some additives work too well....we found out that adding Wynn's Friction Proofing to a new engine worked against us...it prevented the rings from seating for a long time.
In your case...of the cam shaft...the part of the lobe that shows the wear and pitting might have been caused by too thin a layer of hardness on that spot....the hardening process is not guaranteed to cover every millimeter with the same thickness or hardness...sometimes a contaminent will leave a small spot of weaker coating.
Also...valve springs...as pointed out by my very learned fellow Pelicanites...just right is good...too much...and you end up with what you have...damage to the lobe or rocker.
Bob

cgarr · cgarr's Garage

None of the rocker edges are straight, the cam does not ride near that edge.

Lapkritis · Lapkritis's Garage

Was the car parked for a long time? Sometimes you'll see pock marks from rust that rubs away when the engine is started for the first time in years.

JFairman · 06-16-2014, 06:49 PM

While your cam towers are off you can visually check that all the cam spray bar holes are clear and not clogged by spraying carb cleaner or brake clean into one end and holding your finger over the other end while spraying solvent into it.
Then using a rubber tipped air blow gun connected to an air compressor blast 120psi air into where the oil line connects to the cam tower.

Cgarr does a great job resurfacing and restoring rocker arms.

tctnd · 06-16-2014, 08:15 PM

Looks like spalling, not wear. As nothing is actually absolutely rigid the surface compresses and deflects slightly with each cycle. The surface is much harder than the substrate (and may actually be work hardening over time) and much less tolerant of flexing. Eventually microscopic cracks form and the hard surface begins to flake off. You can see the same sort of damage on older railroad tracks.
regards,
Phil

RedCoupe · 06-16-2014, 08:45 PM

I agree with tctnd. The hardened surface of the cam is starting to come off. It takes quite a while before the spalling progresses further, but at some point the hardened surface is gone and the lobe wears like crazy and you have a flat lobe! I know this through experience!

The Watson · 06-17-2014, 03:34 AM

Thanks guys. That is the answer I was hoping for since it limits the issue to the cam rather than both the cam and rocker.

RedCoupe · 06-17-2014, 05:27 AM

I think that high ZDDP oil can have a role in preventing cam spalling like this. I wonder if the valve springs are stock Porsche? It's this sliding action that is tough on cams, particularly with "modern" oils and high pressure valve springs. Had to tear a GM v6 apart this past weekend to fix a daily driver problem, and I was amazed at how perfect the roller lifter cam looked, even after 150k of abuse from other family members.

Steve@Rennsport · 06-17-2014, 08:30 AM

Do you know which oil this engine has been using?

The Watson · 06-17-2014, 08:40 AM

No history in this car unfortunately. It was supposedly rebuilt two owners ago, and it then sat for 20+ years without being run.

Steve@Rennsport · 06-17-2014, 10:35 AM

Quote:

Originally Posted by The Watson

No history in this car unfortunately. It was supposedly rebuilt two owners ago, and it then sat for 20+ years without being run.

Thank you. I've seen plenty of cams looking just like yours and most are caused by using oils containing insufficient ZDDP. Your rockers look pretty normal in the picture, but I'd need to see them for myself to determine whether they are damaged or not.

I would strongly recommend reconditioning the rockers while the cams are getting repaired.

Lapkritis · Lapkritis's Garage

20+ years is a long time for moisture to do some work in the engine... if you crack it open instead of starting it up right away then you would find rust on surfaces where oil flowed away with gravity. The start up knocks it away and you're left with surface pitting that is large or even microscopic.