Pitted cam followers

Tom F2 · 09:03 AM

My 77 Turbo motor had twelve bad cam followers. I put around 6,000 miles on this car after I bought it last year. Last winter, I took out the motor to change the exhaust, and I found a few things that made me uncomfortable with how the engine had been overhauled, and I took it apart. The engine had new Webcam SC camshafts, but the receipts that came with the car don't show new rockers, so I assume that the shop re-used the original rockers. I assume that they looked better than this when they assembled the motor. I also found that valve spring height was set at 30 mm, or less! I suspect that the valve springs may have been bottoming out, but I didn't check. (Didn't notice it until I was disassembling the heads on the bench.) Here's the rub surface of the cam follower on two of the rockers. They're not all this bad, but all of them show this kind of pitting to some degree. The cam lobes all look fine. Can anyone tell me what caused this?

camgrinder · 11-27-2005, 09:21 AM

Can you post a picture or the camshaft?

30mm installed height? how many shims did the put under the spring seat?

What kind of oil were you using?

Tom F2 · 11-27-2005, 01:30 PM

Quote:

Originally posted by camgrinder
Can you post a picture or the camshaft?

30mm installed height? how many shims did the put under the spring seat?

What kind of oil were you using?

I can't post a picture of the camshaft, because it's in the engine now. I can tell you that it shows minimal wear - there is a palpable (barely, just enough to feel with a fingernail) circumferential ridge at the edge of the zone where the cam follower rubs and there are visible, but not palpable, grooves in the zone.

I can't remember how many shims I found, but there were lots, maybe 10 ??, in each valve spring pocket. I did not measure every valve spring height, I just measured a few when I noticed how many shims came out, and then observed that they all had a lot of shims. Do you know whether I was bottoming the springs at 30 mm installed height? I was able to compress an outer spring to less than 19 mm and found that there was still room for a 0.003" feeler gauge in all but one of the coil gaps.

I was running Mobil 1 15W50.

camgrinder · 11-27-2005, 02:32 PM

Looking at the rocker face, I know your lobes are toast. If you install new rocker arms this problem will happen again, and sooner than 6000 miles.
If the cams were previously welded (not billets) they can be reground and used with new or rebuilt rocker arms. I would also use non-synthetic oil with welded cams.

Tom F2 · 06:39 PM

Quote:

Originally posted by camgrinder
Looking at the rocker face, I know your lobes are toast. If you install new rocker arms this problem will happen again, and sooner than 6000 miles.
If the cams were previously welded (not billets) they can be reground and used with new or rebuilt rocker arms. I would also use non-synthetic oil with welded cams.

Thank you. You have probably saved me a major hassle.

I have held up installing the rockers because I don't feel that I understand this problem, yet. So, I will remove the camshafts tomorrow, and post photos of a few lobes.

Is there is a material incompatibility between welded cam lobes and the standard cam follower facing? Do the rockers need to be welded, too, in order to be compatible?

camgrinder · 11-27-2005, 07:55 PM

I'm not a big fan of welding 911 cams. The only time I do weld is to save a rare RSR or 906 type camshaft.
I have seen welded cams last a long time, and some not so long.
If I had to run a set, I would run the engine on Kendall or Valvoline Racing for at least the first 1000 miles. I would pull a rocker or two at a preset interval for inspection.
I had one customer who had a set of fully welded RSR cams . He ended up replacing rockers every two seasons. His engine was raced only and not street driven.

Tom F2 · 11-28-2005, 03:09 AM

Here are a few photos of the no. 5 intake lobe, which is where the worse of the two rockers that I showed came from. I don't have time to take out the camshaft before work. If these photos aren't clear enough, then I'll post more when I pull the camshafts tonight.

It's a dilemma as far as the oil is concerned. I understand that the synthetic is better for the turbo. So, it's worse for the cams? Maybe that means that I should not be using welded cams in this motor. It looks like some kind of camshaft change is inevitable.

Photo order is top of lobe, opening ramp, closing ramp.

camgrinder · 11-28-2005, 07:17 AM

That lobe looks fair to me. Its tough to be sure from the photos though. I agree with your idea the original installer put used rockers in the engine.
You might try a set of new rocker arms with some good non synthetic oil. Inspect them at 500 and 1000 miles. Then switch over to synthetic oil. The idea is to give the rockers and cams a chance to break in before you run the synthetic oils again.

911pcars · 11-28-2005, 02:24 PM

Could be a case of hard cam lobe vs. softer rocker arm tip (worn through case-hardening?) + camgrinder's assessment of synthetic oil.

MHO,
Sherwood

Tom F2 · 11-28-2005, 05:50 PM

I called Web-Cam. They said that I have to use new Porsche (not aftermarket) rockers with their cams. I am skeptical, because I have understood that material compatibility is a big thing with cams and cam followers. For example, I have read that a cast iron camshaft in a Chevy needs a lifter with a steel face, and a steel camshaft needs a chilled (cast) iron lifter. I think that the graphite in the cast iron acts as a lubricant, which helps with scuffing wear and galling. I believe that the Web-Cam hard weld is a completely different (harder) material from the original cast iron that Porsche uses for the camshafts, so the rocker, which is compatible with the original cam, would not be compatible with the hard weld. I'm thinking that I'll have the exact same problem, only I'll have spent the $$ for new rockers. Any ideas?

Has anyone ever put in a pair of stock (Porsche) SC/Carrera cams and adapted the forward end of the left camshaft to drive the turbo oil pump directly? This would eliminate the drive pulley for the air injection and make it possible to mount the oil pump directly to the cam housing, like Porsche did in the original 930/50 motor. The sheet metal and the oil line from the turbo sump would have to be adapted, but this could elimnate the camshaft problem.

camgrinder · 11-28-2005, 06:14 PM

I have installed left side oil pump drives on SC or 964 cams.
I think street cars should only run cast iron cams, either original cams or aftermarket chill cast billets. Race cars can run welded cams if they have to. Street cars idle at low speeds for greater amounts and usually have longer intervals between oil changes.

WERK I · WERK I's Garage

To cloud things a bit more, Tom F2, I'm using WebCams SC Grind (welded) in my 930. I used dino straight 30W for the first 20 minutes and then used 10-30w dino for the next 1000 miles. Since then I have been using Castrol Syntech Full syn 20-50W in the engine with no problems. No pitting observed on rockers or lobes.

btw, used new fatory rockers during the rebuild.

camgrinder · 11-28-2005, 06:50 PM

Dave, your method is the best way to go with welded cams.
For Tom to do this now would require the cams be reground so they are fresh, and he has to install new rocker arms.

911pcars · 11-28-2005, 10:28 PM

The last thought was to use only new rocker arms with new hard-welded cams (e.g. from WebCam or equivalent). Okay, let's take some new factory rockers and put about 10k miles on them. Now, let's compare them to new rockers.

My question:
Besides a companion pattern caused by rubbing with a particular cam lobe, what prevents this almost-new rocker from being used with a hard-welded cam? Is the surface hardness so thin that a new surface can't be reground to replicate that found on a new rocker?

Can a hardened surface be applied to a rocker arm that's compatible with a hard-welded cam? At $65 and change per rocker and shaft (new), that could buy a lot of heat treatment. 65 x 12 = almost $800. That's about the same price as a set of cams. Hate to throw things away needlessly. Any options here?

Sherwood

camgrinder · 11-28-2005, 10:48 PM

I regrind the rocker face all the time. The surface hardness is very deep. To me there is no need to weld 911 cams since I stock billets for most all 911's except the center oiling cams.

Tom F2 · 11-29-2005, 02:44 AM

Quote:

Originally posted by camgrinder
I have installed left side oil pump drives on SC or 964 cams.
I think street cars should only run cast iron cams, either original cams or aftermarket chill cast billets. Race cars can run welded cams if they have to. Street cars idle at low speeds for greater amounts and usually have longer intervals between oil changes.

John, this matches what I have heard about steel camshafts in other contexts. So, it sounds like one option would be to get a pair of cast iron camshafts from you, and have you regrind a nice set of used rockers that I happen to have. Another option would be to find a nice used SC/Carrera camshaft with rockers, and get the front of the left cam set up for the oil pump. What could I expect the first option to cost, and what would be the cost for the adaptation of the oil pump drive on the second option?

Thank you for your input on this, it's been a great help.

Tom F2 · 02:55 AM

Quote:

Originally posted by 911pcars
The last thought was to use only new rocker arms with new hard-welded cams (e.g. from WebCam or equivalent). Okay, let's take some new factory rockers and put about 10k miles on them. Now, let's compare them to new rockers.

My question:
Besides a companion pattern caused by rubbing with a particular cam lobe, what prevents this almost-new rocker from being used with a hard-welded cam? Is the surface hardness so thin that a new surface can't be reground to replicate that found on a new rocker?

Can a hardened surface be applied to a rocker arm that's compatible with a hard-welded cam? At $65 and change per rocker and shaft (new), that could buy a lot of heat treatment. 65 x 12 = almost $800. That's about the same price as a set of cams. Hate to throw things away needlessly. Any options here?

Sherwood

Sherwood, I think that the problem with the hard welded cam is the same as the problem that we've seen with the unbushed chain tensioner pulley levers - the steel to steel interface results in pitting and galling, even with good lubrication. One of the materials has to have some "self lubricating" properties, i.e., brass or bronze (I don't know which) for the tensioner levers, and some kind of cast iron in the camshafts, at least for street use. So, in my opinionm, no amount of replacement or regrinding the rockers is going to fix the problem with welded cams.
Tom

David · David's Garage

If you buy new Porsche rockers I'd recommend knocking the sharp edge off the face. The edges are so sharp when new that you can cut yourself on them.