What Would Cause Crankshaft Damage Like This?

[mikedsilva]

I'm pulling this 3.0SC motor down.. it had sat for a few years but full of oil.

When splitting the case, I found what appears to be the surface of the main journals delaminated? The corresponding bearings didn't look too bad...

Have a look at this video.. then see the pictures of the bearings that I pulled out after I removed the crankshaft.
Only the main journals have this delamination... all the rod journals were perfect as were the rod bearings.



Have you ever seen bearings with that sort of damage before? What could cause that? The oil didn't appear to have any water contamination.

Someone suggested that if the ground strap was missing, then when starting it might have drawn the current through the engine and earthed through the bearings? Is that possible??

[Tom_in_NH]

Very interesting. It certainly looks like material was electrically transferred, like a weld.

[brighton911]

How odd that is. Re the missing ground strap, good theory as the damage sure looks to be electrical but I don't think absent strap would do that. If the starter got all it's return from the engine ground wires (on my 3.2 a cluster of brown wires at the intake manifold), I think you would see those same wires in a cooked state. And the ground path still would not be via the crankshaft bearing. I am assuming your engine ground wires are OK so now I am out of ideas. Hopefully someone can shed some light on this strange one.

[mikedsilva]

OK, really hoping someone can shed some light on the damage to the surfaces of the crankshaft in the video. Basically, it looks like little pieces of surface have delaminated....

[stownsen914]

Was any welding done on the car, or (eek) on the engine? I could see it if someone made a bad grounding choice while welding.

[917_Langheck]

But do you know what the condition of the engine was prior to being shelved? Could it be it was damaged before only to be now revealed?

[stownsen914]

Or for that matter, a poor grounding choice while jumping the battery, or starting the engine outside the chassis. Would be tough to do, but might be possible.

[mikedsilva]

Originally Posted by 917_Langheck

But do you know what the condition of the engine was prior to being shelved? Could it be it was damaged before only to be now revealed?

This I don't know. The engine was apparently sitting for several years.. went to try to start, blew tonnes of smoke etc..

The muffler that was fitted to it, had some real ghetto welds done to the tips.. they were gigantic.

[brighton911]

Good point on the welding issue being a possible cause. I have had alternator diodes literally blown up from an exhaust shop doing work (non Porsche).

[RobFrost]

Based on the info given, I'd say somebody welded the exhaust and they clipped the Earth onto a driveshaft or suspension. To complete the circuit the current had to get to the gears and to do that it had to get into the crankshaft.

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[PeteKz]

Strange. Although the marks on the bearing shells look like significant current ablated them, I tend to think that there are plenty of other paths to ground from the engine or transmission. I am thinking of how someone may have welded on the exhaust system with the ground clamp on the body somewhere, that would have caused sufficient current flow through the crank and mains that would have done that. I’m not seeing a good way for that to happen.

[stanglife]

Vote for moisture contamination or bearing material contamination.

[gled49]

I started seeing this crank damage on SC engines in the 80’s. When I was at Garretson’s, and saw this, Bruce Anderson, sent the folks he knew at Porsche this info, with no real results, except to suggest it was a crank treatment failure. Nitrating failure. He said that their Nitrating was like our Tuftriting. Maybe someone else can chime in. I only saw this on SC engines, and we thought it was probably a bad batch of cranks, lucky you.

[dannobee]

I was holding off responding hoping someone with Porsche specific experience could pinpoint the exact cause and correction.

I personally saw cranks with damage from faulty hardening years ago. Usually from chroming the bearing surfaces, but once in awhile nitriding failures. Gled's time frame roughly coincides with mine, although at the time my failures were seen in nascar engines.

The damage on this crank could very well be arc damage during the hardening process if I were to make a guess. Or some kind of contamination during the process. With the failures that I saw, the cranks looked normal when originally installed, but after running, the damage would occur sometime during use. I would assume this to be the case in this example as well.

Although nitriding has been around for a hundred years, it was only perfected in the last 20-30 years or so. Before then, some parts of the treatment might be hardened to a depth of 0.080" or deeper, while a little ways away the treatment might only be 0.0005" deep.

Remember, some of these cranks are now pushing 50 years old. There was a lot that we didn't even know that we didn't know.

[gled49]

At the time we weren’t grinding cranks, we just wanted standard cranks so we replaced them.

[RobFrost]

Originally Posted by PeteKz

I tend to think that there are plenty of other paths to ground from the engine or transmission.

If earth is a driveshaft or suspension then current can only get back to Earth through the gears because those things are all insulated from the body by rubber bushings.

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[PeteKz]

There are brown ground wires in the wiring harness, and between the distributor and CDI box, which in turn ground to the engine case, which in turn ground to the tranny case. And to the throttle rod and clutch cable. The rear suspension arm is grounded through the torsion bars to the body too. The axle is grounded to the suspension arm through the wheel bearing. I'm probably missing a few.

Only one way to find out...

[Dpmulvan]

Originally Posted by RobFrost

Based on the info given, I'd say somebody welded the exhaust and they clipped the Earth onto a driveshaft or suspension. To complete the circuit the current had to get to the gears and to do that it had to get into the crankshaft.

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Technically it’s called a workpiece clamp and it’s not a ground to earth. You can weld electrode negative or electrode positive depending on machine and process. Placing the clamp too far away from the weld or poor contact may cause crappy welds but it’s not going to melt or arc off your crank. Electronics is a different story.

[RobFrost]

Originally Posted by PeteKz

Only one way to find out...

Multimeter from the driveshaft to the exhaust.

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[mikedsilva]

Didn't want to start a new thread, but thought I'd ask as here as it's pertaining to this same engine case (was on the backburner, now on the front burner!)

Here is a pic of one of the backs of the main bearings. I've not come across marks like this before. I assumed it was due to the above issues with potential current going through the case when something was welded.


Well, now I am rebuilding the engine and using a different crankshaft.
The case has been cleaned up internally and I refit a new set of Glyco main bearings, to meaure bearing clearances, use some plastigauge to get a visualy, and finally, to fit with oil and make sure crankshaft rotates freely, which it does.

When I pulled the case apart, and removed the crank and bearings, I noticed that the backs of teh NEW bearings now have very feint imprints on them, similar to the OLD bearings..





Here's is a pic of the tunnels showing their current condition.


Any input appreciated.