Bad cam
 

Hi
Need som advice about my cam.
My left cam is bad on one lobe.
Look at the picture.
The rocker arm is fine.
Can i wait to fix it?
I am planing to wait to winter to fix this.
The work shop is closed for holiday.

http://forums.pelicanparts.com/uploa...1183746608.jpg

Can you keep the valve adjusted? I had damage just like that and I could not keep a correct valve clearance. It got worse quickly and started making a huge valve clack. The damn spray bar was clogged in my case.

I have not install the rocker yet.
I think that i get correct valve clerance.
The problem is only on one side.
Thanks for the advice I should check the spray.

I've seen worse come out of engines that seemed to run well. I suspect that you might be able to run it this way for a while, but when replacing the cam later, you should also replace that rocker and have the rest polished.

I have to agree, mine had been this way for years, and it was multiple lobes. My damage was more like wormwood, and deeper. Of course I guess it wasn't terminal as John at DC cams repaired them.

I had a cam like that in my SC which ran well with it. I had DRC redo them. I think unless you put over 20k miles on this thing before winter, you don't have a whole lot to worry about.

George

Hello to all. I am a new user in this forum, so let me give a little background. I am a tech specialising in air-cooled 911 engine rebuilds and development. Between us we have done well over 100 rebuilds both for street and competition. It is fun work!

On the topic of worn cams/rocker arms/rocker shafts: Uncharacteristically, 7 out of the last 10 engines we did exhibited the wear Tom Langborg experienced. While I can not speak to the situation in Sweden, our research has led us to believe that recent changes in motor oil composition are the cause. Specifically, the EPA mandated a reduction in zinc and phosphate additives.
To learn more about this, check out Joe Gibbs racing oil or Comp Cams site.
It appears that primarily valve trains incorporating sliding surfaces are affected.

Upon recommendation, we are now using Lucas stabiliser with no ill effects, but it is too early for long-term results.
Is it safe to keep running pitted cams/rockers? I should think so. At worst the valve train will be noisier than a high-mileage or hard-used one already is.

I'll second what gottarideduc has observed. I've seen more damaged cams in the last year or so than any time in the past. Could it be coincidence? Perhaps... ...but in absence of any other explanation i'm beginning to think it might be the ZDDP reduction.

I've got confirmation from 2 other mech.'s that they've noticed an increase as well. Any other builders seeing this?

It (the change in motor oil spec) has made me nervous enough to put a container of GM's EOS (Engine Oil Supplement) into my car. When I picked it up, the GM parts guy knew all about it and figured it was a good idea...apparently they have some internal to GM documents about EOS's need and use....

Dennis

I'm going to talk to my mechanic about this tomorrow. Seeing as how I had bad cams and it was largely the reason for my rebuild, I don't want to spend all that $$$ again just a few years from now.

This problem has been going on for a few years now since the EPA mandated the reduction in ZDDP to extend cat life.

There is a lot of information here found by doing a search for "ZDDP".

The "World of Oils" is now totally different from just a few years ago and its prudent for anyone to find out what engine lubricants to use, depending on usage.

Talk to the most knowledgable people who have been rebuilding engine for many years and get some recommendations about what oils to use in your 911 (as well as other cars). Don't simply rely on Porsche's oil recommendations as their job is selling parts and not looking out for YOUR best financial interests any longer.

I suspect this might also be behind PAG's withdrawal of some other parts like the 996 X51 oil-sump update...

Steve, you must see a few engines *wink*... noted any increase in cam lobe wear?

LOL,..I have seen a "few" engines in my time and have noted higher rates of camshaft/rocker arm wear in the last 3 years. All of these have been street engines running unknown oils but with extended drain intervals. Our race engines use high-grade oils containing sufficient ZDDP to prevent such things.

Having done a LOT of reading on this subject over the past several months, I do know that the ZDDP additives get used up during normal service. Extended drain intervals of 6K miles or more is not in anyone's best interest if engine longevity is a high priority.

ZDDP does get used up and decomposes into various zinc and phosphorus compounds that actually increase the range of pressures at which the anti-wear films form, until these byproducts themselves break down.

A good article about the formation of ZDDP films and decomposition of ZDDP, among other things, can be downloaded here:

http://www.apmaths.uwo.ca/~mmuser/Papers/TL05.pdf