earossi

Galling is serious. In discussing the findings on the cam with Steve, he noted that he was seeing a lot of similar cam lobe damage and he attributed it to the change in oil formulations that have reduced the amount of zinc addititive in today's oils. There are lots of discussions on this forum about that. The parts that see the damage are rubbing parts under high loading.......such as cam lobes dragging across the rockers. Attached are several photos I took of the damage to the single lobe.

As far as power is concerned, the larger valves and cams are worth 2 to 5 horsepower, according to Steve. For me it was not an incremental investment since I had to replace or pair the cams and I was going to replace the intake valves as part of my rebuild. The cams probably cost me couple hundred more than repairing my stock cams. The bigger cost was in getting the ECU remapped at about $1000.

All that being said, I think that the biggest bang for my buck was installing the close ratio gearbox which has totally transformed the car in the lower gears.

So, I am willing to give back the several horsepower in return for a smoother running engine that does not stall.

nine9six

OMG, Ernie!
That galling is significant! Did Steve point out that the galling is relegated to one area of the cam lobe, as opposed to across the entire surface where the rocker rides; thus more evenly spreading the stress load?
I guess one could also blame the lack of oil additives, but the root cause seems quite apparent.

Appearance might say Porsche engineering stack up of tolerances could have used a second look! Surfaces/bores do not appear to be adequately perpendicular to relative surfaces. Prolly not a good thing when it comes to the equal distribution of load on cam/rocker surfaces.

Did this galling create an issue in the engine, or is this how things looked when you decided to have the cams installed and larger intakes machined? Just curious...

Can they grind, plate/hard chrome, grind; the galled area back to spec, or is a new cam needed?

P.S. Thanks for the pictures!

earossi

When I tore down the engine, there was no "visual" damage except to a ring land on one of the pistons.

I agree with you that there were multiple issues going on in my motor leading up to the cam failure. Again, in talking to Steve, he has noted that he sees a lot of rocker arms where the rotating axis of the rocker is NOT parallel to the rocker arm. Consequently, out of spec rockers produce localized stresses as they ride up on the cams. Steve has a fixture that locates the centerline of the rocker and then he allows the rocker to rotate on that axis until it contacts an optically flat measuring surface.....and you can easily see that many rockers are slightly cocked.

Had I had good lubrication, the out of spec rockers might have done OK. But, the combination of oil with low ZDDP and some out of spec rockers apparently was the recipe for the failure I experienced.

Keep in mind that the engine had 107k miles on it when I tore it down.

I was concerned about engine main and rod bearing damage due to debris from the cam failure......but those bearings looked and measure out to be perfect. I think they could have made a 200k mile run. That tells me that prior owners did a good job of keeping the oil in the engine clean.

Regarding your question about repairing cam lobes.....yes, it is common to repair them if they are not too far gone. I suffered a cam failure on my first 911 in 1966. When I took the car into my indy for replacement of the cam.....he could not help me. He claimed that cams were not even available in the States at that time......and that the cost to have one shipped from Germany would be over $1000 (in 1967 dollars!) and would take 4 to 6 weeks to get it.

Since I was living in S. Calif in those days and had been a hot rodder, I took the cam which had three damaged lobes, and drove down to Iskenderian Cams in Orange County. They took my damaged cam......made templates of the lobes from the lobes that were not damaged......then they welded up the damaged lobes with Stellite and then ground the lobes against the patterns. Cost me $100! We put the cam back into the car, and those cams performed for the next 60k miles I owned the car!

Finally, Steve W refurbished all my rockers so that they are now square to the cams.

nine9six

I hear ya Ernie,
But I'm not a big fan of welding on a cam...Stress and warping are the two biggest factors.

Localized heat on a cam lobe, twists and tweaks the poop out of the length of the rest of the cam. Metal needs to be stellite inlayed/welded, normalized, stress relieved, machined, and ground.

I like, grind out galling; hard chrome surface above spec; grind cam lobe back to spec.

earossi

Interesting discussion. I'm on shakey ground discussing the welding process. But, I had proof positive that welded out stellite worked on a cam for my first 911. There was no dimensional tolerance change on the repaired cam that prevented it from running for about 60k known miles. For all I know the car is still running on the repaired cams. And, when I took the damaged cam to Iskiederian (back in the early 70's), they advised that such repairs were common and reliable.

I'm not certain if Isky Cams is still around, but back in the early 70's, they were pretty much the king of cams for hot rodder.

EMBPilot

any updates here?

nine9six

Granted, my experience comes from the repair ships main feed pump shaft bearing journals, which turn at 100k rpm, but the theory is the same.

Perhaps automotive cam lobes are simply ground journals of the parent material and not hard-faced; and its the rocker face that is hard chromed or stellite inlayed. Dissimilar materials...

However, the above supposition makes no sense to me...With the cam being the considerably more expensive component, compared to a single rocker. If something were to gall, I'd much rather it be the single rocker face, than a cam lobe; considering the costs of repair involved.

Does this make any sense?

earossi

Well, it's been awhile since I updated this topic. So, let me correct that now.

To date, I've had the car in the hands of three "seasoned" recommended techs. Though there have been multiple checks and redundant testing, there has been no absolute diagnosis of the staling issue. Conclusions are that mechanically, the engine is fine and that the cause more than likely is related to electrical issues.

So, since the last update, I've done or had done a number of things. Continuity checks were run on the engine harness wiring and connectors. All connectors were cleaned with electrical contact cleaner. All sensors were replaced (speed sensor, temp sensor, TPS and MAF).

The engine was just smoke tested (for the third time) and found to have some extremely minor leakage around a few of the Variram actuators...but not enough to constitute a vacuum leak.

I then had the engine dropped to chase a few oil leaks, which turned out to be a failed and leaking oil pressure sender. While out, I had the cam timing checked, which turned out to be slightly different than my build sheet settings, but well within spec for the Web Cams.....(Web Cam specs are for 1.8mm in the overlap position. The settings just validated were 1.85 and 1.86mm left to right banks).

So, I've made a decision to change out the LWF for an OEM dual mass flywheel in hopes that the greater inertial moment of the heavier dual mass will allow the engine a little more response stability to allow the ISV to catch the deceleration that has been the precursor for stalling on my engine.

For now, I've elected to retain the Web Cams.

The car should be up and running in a couple of days. Stay posted.

earossi

Interesting discussion. My guess is that galling of a cam lobe is easily repairable, whereas galling to a rocker arm results in scrapping the rocker since any weld repair attempt to the rocker would produce distortion in the part.

Zeus993

The close ratio gearbox - was that through California Motorsports?

Tx

earossi

I sourced the MotorSports gearbox from an independent owner. A wonderful gearbox!

nine9six

Precisely the opposite idea, for the same reason...

A cam costs more than a single rocker. A cam being significantly longer than a rocker, is more suseptible to warpage/distortion when welded. Small distortions close to the welded heat affected zone, are compounded the further away from the weld area, thus affecting other lobe and bearing journals further away from the welded area...Perhaps there are ways to isolate the heat affected zone, as produced by weld repairs?

Im not saying you cant weld up a cam, as it is a viable repair to galled cam lobes; Im just suggesting a grind, hard chrome plate, grind to spec repair; would be a kinder, gentler, less intrusive, less costly repair method.

Apples and oranges, I know; but Ducati 4 valve, desmo superbike rockers are repaired in the manner I just described.

If Steve Weiner regrinds rocker parallellism error from rocker face, to cam lobe, the same methodolgy can be applied.

Cant wait to hear how your latest changes affect the stalling issue!

My best,
Paul

earossi

Paul,

Not meaning to be contrary, but one does chrome plating to place a very thin uniform barrier coating on a softer substrate. The problem with galling is that the galling mechanism produces a rough surface of non uniform depth. The area requiring repair is usually much thicker than the chrome plating process is capable of producing. So any repair first requires a buildup of the damaged substrate before considering something such as a chrome plate overlay.

Since a cam is a large mass, heat related distortion is minimalist and any distortions can be corrected when the repaired areas are finish machined. Not so for a machined part with a rather fragile structure represented by a small mass rocker that is a rather complicated in design.

When I dealt with Isky Cams on my first weld repair of a Porsche cam, it was a bread and butter repair process for them. That was 40 years ago. I put over 60k mikes on that weld repaired cam and never experienced any further issues with the cam or related hardware.

earossi

Time for an update. The stalling issue is still there. Since last posting, I've done some more work; but, to no avail. So, allow me to update this thread which has been out there a while.

After a total engine rebuild, I have experienced an intermittent stalling issue. Once the engine is warm, any removal of load from the engine at an engine speed of around 2000 rpm, often results in the engine idle dropping to a stall. Does not happen every time, but I can easily duplicate it more than 50% of the time. Since it occurs on a warm engine, the issue could be thermally related. Or, it may be electrical. Unfortunately, many things were "touched" during the rebuild, making a solution difficult. In addition to engine mechanicals, the main engine wiring harness was replaced. The DME has been sent out several times; initially to have software mods made to accommodate the Web Cam RS hydraulic cams and RS inlet valves that were installed for the rebuild.

The car has been reviewed by three different recommended indies. They have not found the issue, though they all agree that the engine runs well except for the stalling issue. The motor currently has about 1000 miles on it since the rebuild.

I have replaced or substituted every engine sensor except for the throttle position sensor. That includes the speed sensor, MAF sensor, inlet air temperature sensor, and cylinder head temp sensor. All spark plug wires and distributor caps and rotors have been replaced. The distributor belt was replaced. I've replaced the ISV.

The DME was reprogrammed for the cams. In chasing the stalling issue, I pulled the DME and sent it off to the firm in Florida that specializes in DME repair. They pronounced the DME as OK. Sent it back a second time and they installed their software to replace the original performance software. Has not made a difference other than their software results in a slightly rougher idle.

Just got the car back from the shop after having them do a bit of work. Here are the findings: I had them recheck the cam timing, since this is an area that I "touched" during the rebuild and which I was less than confident of my work. The Web Cams call for an inlet valve lift of 1.8mm (no tolerance given) in the overlap position. On the check, one side of the motor measured out at 1.81mm and the opposite side measured out at 1.86mm. Not much difference. So, my work was not perfect, but should be OK. They did mention that the rocker arm on the #1 inlet valve was noticed to be "tight" on the shaft when replacing the hydraulic rocker with a manual rocker needed for the cam timing check. They were able to "clean up" the shaft to eliminate the tightness. They then pulled the remaining inlet rockers, and did not find another that was "tight". They didn't pull the exhaust valve rockers.

A leak down was done on the engine. 3-5% on all cylinders. A smoke test was done on the engine. Some slight leakage around the Variorum area, but not abnormal.

The car had a LFW prior to the rebuild that did NOT cause stalling. However, with the LWF in place, I could hear tranny gear rattle. So, to eliminate the rattling, and to provide some inertia to "help" the engine recover from a drifting idle, I installed a new dual mass. So, I replaced the 12# LWF with the 27# OEM flywheel. The dual mass has "improved" things a bit in that it does catch some of the rpm excursions in time to coast through a stall. Bottom line: the dual mass just masks the root cause.....does not cure it.

In rethinking electrical issues. I did NOT replace the DME cable harness; just, the engine electrical harness. Maybe I disturbed a connector when removing the DME? And, when I replaced the ISV, I elected to purchase a Bosch ISV specified for my engine. Carries the same P/N as the Porsche OEM part, but at less than half the cost of the Porsche part. Is it possible that the OEM part is superior in performance to the Bosch part?

My issue may be getting close to holding the record on this forum for duration without results. I welcome any input at this point.

nine9six

Ernie,
Not to be contrary, but much has changed in 40 yrs...and cam lobe galling is usually less than .025" deep...

FWIW, I am well aware of what galling is, and repair methodologies by use of hard chroming.

If properly applied, there is no set limit to the thickness of hard chrome, but as a general rule, chromium is most stable on ferrous alloys in the range of 0.0005 to about 0.025 in a single application. Chromium deposits over 0.025 per side can begin to become rough with build up at edges and pitting. Success with thick chromium deposits has a lot to do with the initial surface finish of the base metal.

When applicable, "after plate finish requirements", i.e., uniformity, mimimum thickness, surface micro finish and micro-crack acceptance level, dictate the best chromium procedure to follow. The initial set up, tooling and especially anoding procedures, are critical steps to achieving the most success.

HTH