these cams = POO

[Tim Hancock]

Here are some pictures of my latest find on my newly aquired '79 SC 3.0. I dropped the engine to fix a bad cobbed up exhaust head stud and to fix some leaks. It looks like I need to come up with some cams and rockers.



I have read some of the previous posts on cams but I would like some opinions on my situation.

My engine is a stock 1979 3.0
With:
-CIS
-stock heat exchangers
-stock 1 in 1 muffler
-gutted cat

I intend on leaving all the above as is (someday I may backdate the exhaust).

Should I get the stock cams reground stock, or get them reground to the 20/21 grind? I assume that there would be no cost difference. I realize that any performance gains would be minimal with the 20/21 and CIS (or would I actually experience a loss with the CIS and stk exhaust?).

Who has the best pricing for cam and rocker repair?

I do not know whether this corrosion damage will clean-up or will require welding therefor I will need a shop that can do both.

[Groesbeck Hurricane]

Tim,

I hate to say this, and I might be an idiot, but I do not see the major problem in your photos. Are the cam lobes rough? Is the lobe shown ground down somewhat via contact with the rocker? The oil in your "non-oil contact areas" could be seaping from the rocker shaft. This could easily be fixed with the motor in it's current location and state by removing the rocker shafts, cleaning, and re-installing with RSR washers if the shafts are in good shape. You will also be removing the rockers so you can get a better look at the cams without removing them from the entire assembly.

But wait, in the bottom photo I do not see the head stud. Is it there? This could be the cause of the oil leak and would need addressing now.

[Tim Hancock]

Sorry for the pictures not being easiest to decypher. Look at the top photo around the lower middle of the picture and you will see a highly pitted lobe. In the bottom photo (lower left) you will see a decent lobe surface and slightly to the left you can make out a pitted surface just below the rocker arm (this is hard to make out in the picture.

All of the head stud nuts are present and accounted for, but I will probably replace the lowers with steel per Wayne's book.

[afterburn 549]

well as you know there are only a couple of choices. sc sport or 964 grind.....from what i think i know the sc puts more unde the pedel

[ChrisBennet]

I would make sure that the spray bar is squirting oil on that lobe or your next cam might be "self machined" as well.
-Chris

[afterburn 549]

Good pt Criss, and also make sure the spray bar is not in upside dwn.
exra thought- instead of using the little aluminum plugs at the end of the galley where the spray bar is inserted tap the hole for a pipe plug...(4)....makes life a lot simpler for next time

[Tim Hancock]

For what it is worth, I have seen this kind of damage often in aircraft engines (Lycomings in particular). The camshaft is not immersed in oil when at rest (it is mounted high in the crankcase above the oil level). When the engine sits for long periods of time, the oil runs off and condensation occurs on the hard surface of the cams. This eventually causes rust pits. When the engine runs again these the sharp edges of the pits along with the rust, cause galling on the surface of the cam and followers. After enough of these cycles, the hardened surface is gone and the lobes wear down rapidly.

Luckily my 911 cams appear to have not begun to wear down any appreciable amount yet. My guess is that alot of these cams probably have this type of corrosion damage due to the fact that in 25yrs many have had idle times where they sat for extended periods.

So,

SC sport grind, 964 grind, stock grind ?

What is best for a stock 79 3.0 SC?

[ChrisBennet]

Originally posted by Tim Hancock
For what it is worth, I have seen this kind of damage often in aircraft engines (Lycomings in particular). The camshaft is not immersed in oil when at rest (it is mounted high in the crankcase above the oil level). When the engine sits for long periods of time, the oil runs off and condensation occurs on the hard surface of the cams.

I've head of this problem in conjunction with Mobil 1. As I recall, the fellow left his airplane in a hanger over the winter and discovered his cams were pitted during a spring checkup or something. He asked his mechanic and the mechanic told him that he'd seen this happen on planes during storage that were using (Aircraft) Mobil 1. This was many years ago.

You would think that if Mobil 1 had this problem in cars you would have hear about it in the Porsche community.
-Chris

EDIT: I found my notes; it was Brian Buxton who had this problem.

[Tim Hancock]

Chris, I have never heard of Mobil 1 being approved for aircraft use. It could be used in Experimental (homebuilt) aircraft, but as far as I know it is not legal in certificated aircraft. Oh well, I guess it doesnt matter.

It is a known fact though that the aforementioned corrosion pitting problem does occur in aircraft engines that sit long enough in non temperature controlled enviroments.

It is highly recommended that aircraft engines, unless properly pickled,
be run at least once a month and allowed to hit at least 180 deg oil temp to cook off any condensation in the crankcase.

OK, I will stop preaching about aircraft engines on this 911 engine site.

[304065]

It is highly recommended that aircraft engines, unless properly pickled,
be run at least once a month and allowed to hit at least 180 deg oil temp to cook off any condensation in the crankcase.

OK, I will stop preaching about aircraft engines on this 911 engine site.

Tim, do you figure the oil picks up another fifty or so degrees vs. the gauge? I use a cover over my oil cooler until the early summer to keep it around 212F.

Nothing wrong in my opinion with mixing the disciplines here-- a 911 motor and an 0-320 have a lot in common!

[ChrisBennet]

Originally posted by Tim Hancock
Chris, I have never heard of Mobil 1 being approved for aircraft use. It could be used in Experimental (homebuilt) aircraft, but as far as I know it is not legal in certificated aircraft. Oh well, I guess it doesnt matter.

It is a known fact though that the aforementioned corrosion pitting problem does occur in aircraft engines that sit long enough in non temperature controlled enviroments.

It is highly recommended that aircraft engines, unless properly pickled,
be run at least once a month and allowed to hit at least 180 deg oil temp to cook off any condensation in the crankcase.

OK, I will stop preaching about aircraft engines on this 911 engine site.

I checked my notes. Here are some corrections:
- It wasn't Mobil 1, it was "Aeroshell 15W-50 semisynthetic".
- It wasn't Brian Buxton. He just forwarded it from the someone else, so it wasn't Brian's plane (if has one), it was someone from the 928 Rennlist. It was back in 1998 if that helps.

I can't even say my memory isn't what it used to be - it's always been bad.
-Chris

[Tim Hancock]

I don't know why the 180 deg minimum target temp is reccomended as opposed to 212 deg. I think the point is that just starting an engine up on 20 deg winter day and running for 5 minutes will not bring the engine case temperature up enough to evaporate the accumulated condensation.

By the way, I keep a roll of black 200 mph tape in the plane to block off
the fins of my oil cooler for days when it is below 40 deg. Gotta get that oil tmep into the green somehow!

[jgparker]

If I remember right, Aero Mobil 1 was pulled from the market a number of years ago due to sludging issues. The problems with Aero Mobil 1 did not apply to regular Mobil 1. This was covered in a Bruce Anderson article in Excellence about 5 years ago. I'll see If I can find it tonight.

[304065]

Hmm, the ol' STC'd duct tape! I've got a roll of that myself!

[Henry Schmidt]

Originally posted by ChrisBennet
I would make sure that the spray bar is squirting oil on that lobe or your next cam might be "self machined" as well.
-Chris

Good call Chris
I doubt that this problem was caused by engine oil type.
I have seen this type of damage primarily from clogged spray bars. Generally this clogging is caused by poor maintenance or in engines assembled with silicone sealant. The seam of silicone squeezes into oil passages and get stuck in any small hole it finds. If the engine was assembled with silicone seal this could become a reoccurring problem.
As for the cams. I like 20/21 cams and you will notice a difference in performance. Elgin or Webcam can repair and grind these cams.
Good luck