AOS Failure: what breaks first?

[BYprodriver]

Rent a bore scope & inspect all the cylinders, then pull off the sump plate & look underneath with the scope.

[maytag]

Originally Posted by BYprodriver

Rent a bore scope & inspect all the cylinders, then pull off the sump plate & look underneath with the scope.

Good idea! So, what am I looking for? I mean, what are the weak spots on this motor? Am I looking for broken wrist pins? Bent rods? Broken ring lands? All or any of the above?

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[911monty]

Based on some of the severe AOS failures i'd suggest removing the green plastic cam plugs and check for timing and rotation.

Apparently you want more. There are a several weak links in the cam drive system that can fail, but let's look at what happened to you. A previously healthy AOS fails after spin, not unlikely as oil accumulates in head from centrifugal force and overwhelms AOS, but this happens to a running engine. You say you restarted and a continuous smoke cloud ensues. How hard was the engine stop? A weak link in this scenario is the tang that drives the oil scavenge pump. If oil is not being pumped from the head the AOS also fails. Continuous smoke cloud. I'd certainly look here.

[maytag]

Originally Posted by 911monty

Based on some of the severe AOS failures i'd suggest removing the green plastic cam plugs and check for timing and rotation.

Apparently you want more. There are a several weak links in the cam drive system that can fail, but let's look at what happened to you. A previously healthy AOS fails after spin, not unlikely as oil accumulates in head from centrifugal force and overwhelms AOS, but this happens to a running engine. You say you restarted and a continuous smoke cloud ensues. How hard was the engine stop? A weak link in this scenario is the tang that drives the oil scavenge pump. If oil is not being pumped from the head the AOS also fails. Continuous smoke cloud. I'd certainly look here.

Thanks Monty; always helpful posts! I'll check the cams for sure.

See video, below. You'll see them come up on me as I recover from the spin. Then you'll see how the cloud goes. Does this look like I should consider the oil scavenge pump?
I shut the motor down after I pulled off track. Once back in the paddock (after a flatbed tow) I hit the starter; the motor turned about half revolution (-ish, haha) and then locked-up.

https://youtu.be/tCfB0xFVJhg

[911monty]

I guess I should have said pumps, there are two one on each head, but for the cost of 2 o-rings I'd absolutely remove and check. Just make sure to mark for proper orientation before removal, they will go on either side but oil passages won't be lined up.

[Gilles]

maytag, sorry about your engine!

Just a crazy suggestion.. this is what I would have done at my garage since it's basic and helps you with a starting point

After removing the plugs, try to rotate the crank (hopefully) for a couple of 360's. If it goes, then with a compression gage you can see if the cylinders are close to each other's and move on.

Good luck!

[BYprodriver]

Originally Posted by maytag

Good idea! So, what am I looking for? I mean, what are the weak spots on this motor? Am I looking for broken wrist pins? Bent rods? Broken ring lands? All or any of the above?

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Don't know what to tell you, just anything that looks different or shouldn't be there.

[Gilles]

Originally Posted by BYprodriver

Don't know what to tell you, just anything that looks different or shouldn't be there.

BY, how difficult would be to measure distance between the top of the piston and the plug? Could this help to ensure that you don't have a slightly bent rod?

[maytag]

Originally Posted by Gilles

BY, how difficult would be to measure distance between the top of the piston and the plug? Could this help to ensure that you don't have a slightly bent rod?

Thanks Gilles. A piston-stop is easy enough to build and use to check piston height, but a simple compression test will tell most of that story.

Thanks, everyone, for your responses here. I wasn't looking to start down a road of paranoia-induced "what-if" scenarios, haha. I just didn't want to start breathing a sigh of relief that I'd dodged a bullet, simply because the motor turns without making weird noises, without first checking to see if there are other COMMON breakage-points that I should be looking at.

It sounds to me like the typical AOS failure "catastrophe" happens at relatively high RPM's, where the energy in the rotating / reciprocating assembly is enough to break lots of things when that piston comes to a sudden hydraulically-locked stop. I think I avoided this. I think what I'm seeing is that after I shut off the motor, the oil continued to run (because of gravity) into the cylinder whose intake valve was open. Then when I hit the starter again, there was enough oil in that cylinder that it made a short attempt to compress, then locked. But the starter shouldn't provide enough energy (force) to break anything internally (other than, perhaps, the starter, haha).

SO:
Yes, I'm going to peek inside the cylinders with a borescope.... because I bought one and want to use it, haha. I'm considering a deeper sump & baffle, so if I do that, I'll also poke around with the borescope on that side. And Yes, I'll probably do a compression check, because all the plugs are out and the motor just clicked 150k miles: I'd like to see what we're dealing with. But then I'm going to clean it all up, button it back up, get it good-n-hot to burn out as much of the oil as I can, and hope I'm not looking at replacing o2 sensors, or other.

As for the AOS: I'm not entirely convinced that it's bad. I'm running on the working theory that this is all related to the spin, and I simply overwhelmed the AOS. I'm going to purchase a manometer, so I can check it once it's back together. In the meantime: I'm going to go trace-out the pathway of the AOS vent & drain, and look for a place to intercept and add a catch-can of sorts, that can give me a warning if it starts getting accumulation, but won't immediately dump it into the motor. Again: what a STUPID design this AOS is. Tell me again how brilliant the Porsche engineers are?

Thanks again everyone.

[911monty]

What no paranoia induced "what if" scenarios.......Too bad it's the season for a good scare HAHA.. so here goes. In case you missed this hair raising tale in your search read the attached. My post #31 and several later asks to check what the OP amazingly discovers in his second thread. For your Halloween amusement I present

AOS - Question

CamShaft Timing


PS I do have a question for data. Did you get the clutch released in the spin or did the engine possibly spin backward? Thanks

[maytag]

Originally Posted by 911monty

What no paranoia induced "what if" scenarios.......Too bad it's the season for a good scare HAHA.. so here goes. In case you missed this hair raising tale in your search read the attached. My post #31 and several later asks to check what the OP amazingly discovers in his second thread. For your Halloween amusement I present

AOS - Question

CamShaft Timing


PS I do have a question for data. Did you get the clutch released in the spin or did the engine possibly spin backward? Thanks

aaaahhhhhh......
So, I can't even picture yet where these scavenge pumps are, and how they sit. I'll have to become more familiar. If one or both are bad, will I see that in a test of the AOS with a manometer?
And I'll definitely be checking the cam positions. Too easy to check to not do it....

Thanks Monty!

[BYprodriver]

Originally Posted by Gilles

BY, how difficult would be to measure distance between the top of the piston and the plug? Could this help to ensure that you don't have a slightly bent rod?

That will be hard to do. 1st I would remove all the spark plugs & just spin the engine over with the starter, should spin fast & easily. Look for any liquids coming out & identify. (oil, coolant,etc.)

[maytag]

Originally Posted by BYprodriver

That will be hard to do. 1st I would remove all the spark plugs & just spin the engine over with the starter, should spin fast & easily. Look for any liquids coming out & identify. (oil, coolant,etc.)

You'll note that your comment about spinning the motor with the starter is precisely the first thing I did, weeks ago. ;-) i guess we're thinking alike.

All the liquid I'm seeing come out of the motor is oil. I've seen no indication of coolant in the oil. Peering into the expansion tank, I see no indication of oil in the coolant.

The couple of specs found in the oil filter are probably not horrible, given the nearly 150k miles on the motor. ??

I'm really hopeful I've dodged the big bullet here. But the are enough things concerning me that I'm probably going to take it slow over the winter.

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[BYprodriver]

Originally Posted by maytag

Good idea! So, what am I looking for? I mean, what are the weak spots on this motor? Am I looking for broken wrist pins? Bent rods? Broken ring lands? All or any of the above?

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How did this workout ??