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Old 10-07-2018, 01:04 PM   #1
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AOS Failure: what breaks first?

Hey y'all:
So, I had what looks to be complete AOS failure at the track on Friday.
My first session was delayed 90 minutes because someone in a new Ford GT oiled-down the track. They cleaned it up the best they could in 90 minutes, but we're talking about nearly 3 miles.... right on the line. So we knew all of our sessions would be shortened.
Long-story shortened: lap #2 I got into the oil-line and took my first on-track spin. I kept it on the asphalt, so I got going again. I noticed almost immediately a big blue / white cloud behind me, but I've seen the "Boxster Smoke Bomb" a number of times, so I thought it'd burn-out, as usual, and be fine. Seconds later it was clear this was not that simple, so I found a place to get off-line, pull off track and shut the motor off. I was of course frustrated.... and hopeful I hadn't done any damage. 30 seconds later I noticed all the other cars were stopping on the track! I was hopeful that whatever incident prompted that would distract from my own embarassment of being IN THE DIRT, haha! Moments later, I heard whistling, then saw someone waving at me from the flag station across the track. I took my helmet off so I could hear him say "Get Out of the CAR! You're on FIRE!" YUP. Little flames shooting out the exhaust (remember: motor was off).

They put me on the flatbed and took me back to the pits. Once there, I tried to turn the motor over; it turned for a split second, then stopped. HARD.

So, I towed it home and forgot about it (as much as I could) until today.
First things first:
The exhaust was full of oil. Every pipe-joint is dripping, as is the header-flange. I suspect the fire was simply the fuel that was still being dumped into the motor in cylinders that weren't firing, due to so much oil.
The little "vent / drain" that sits on the bottom of the air filter housing (that I remove to get to the middle spark plug on the left side) was also full of oil, suggesting it was WAY up in the intake as well.
When I pulled the middle plug on the right side, that cylinder was completely full of oil; ran out into my armpit as I removed the plug.
None of the plugs look like they have any physical damage to them, from anything hitting them. And once they were all out, the motor turns freely with the starter motor. I can hear what to ME sounds like normal valvetrain noises, nothing more. It was clearly hydraulic-locked on that cylinder.

SO: it seems I MIGHT have dodged a bullet. TWO questions, for those of y'all who know:
1) What else should I check before buttoning it back up? I mean, should I drop the pan and look for bent rods? or?
2) I'll replace the AOS, but I'll be honest: any PCV system that includes such an easy path for the oil to dump into the intake, such as we have with this AOS system, seems like a design-failure. For decades, we've been dumping PCV into catch-cans which then vent to atmosphere, or to header-pipes, and drain back to the sump. Why don't we simply do that with these motors? What am I missing? Is there a better design on the market already? What are y'all racers doing?


Thanks again for all of the knowledge base here. 'preciate your time for me!

Last edited by maytag; 10-08-2018 at 06:13 AM.
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Old 10-08-2018, 08:46 AM   #2
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Rent a bore scope & inspect all the cylinders, then pull off the sump plate & look underneath with the scope.
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Old 10-08-2018, 09:05 AM   #3
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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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Old 10-08-2018, 09:14 AM   #4
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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.

Last edited by 911monty; 10-08-2018 at 01:23 PM.
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Old 10-08-2018, 05:01 PM   #5
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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
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Old 10-08-2018, 05:24 PM   #6
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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.
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Old 10-08-2018, 06:45 PM   #7
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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!
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Old 10-08-2018, 07:40 PM   #8
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Originally Posted by maytag View Post
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.
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Old 10-08-2018, 07:55 PM   #9
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Thanks guys.
Gilles, I had the same thought to run a compression test. I'll probably do that after I check cam position.

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Old 10-08-2018, 09:41 PM   #10
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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?
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Old 10-09-2018, 05:03 AM   #11
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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.
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Old 10-09-2018, 09:21 AM   #12
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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

Last edited by 911monty; 10-09-2018 at 10:09 AM.
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Old 10-09-2018, 05:32 PM   #13
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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!
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Old 10-09-2018, 07:49 PM   #14
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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!
You'll find the scavenge pumps the same place as the cam plugs. The pumps are driven off the exhaust cams. Bank 1 pump is toward the rear and bank 2 is toward the front. They are held on by 4 bolts, replace the bolts with the o-rings.
As far as identifying by manometer, not likely. But what happens if one fails is the head fills with oil and reduces the vapor space allowing oil to be pulled from the head into the vent pipe and into the AOS sump. There are swirl vanes in the sump of the AOS which will centrifuge out small amounts of oil in vapor, but will become overwhelmed by liquid oil from lack of retention time..

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Old 10-09-2018, 08:18 PM   #15
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Perfect.
Thanks again, Monty!

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Old 10-13-2018, 11:12 AM   #16
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Hello Maytag, did you have a chance to check your engine?
Hopefully everything is ok and was only an eye opener..
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Old 10-31-2018, 06:12 PM   #17
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Hey all..... update.

Since last we spoke, life has been going on. So very little progress on the car until the last couple of days.
In a bout of frustration that I couldn't use my garage for a honey-do project that I really didn't want to be doing, I put the plugs back in and fired the motor up. It started to smoke badly, immediately, so I shut it off and rolled it out of the garage, then closed the door so I didn't fill the garage with smoke. My thought at that point was that there was probably plenty of oil that needed to burn off.

So I fired it up again in the driveway. it fires immediately, but idles rough. When you rev it, it smooths out. But SMOKE. I mean, LOTS of smoke. THICK, HEAVY, SCARY smoke. It was so bad that I finally shut it off. Once the smoke dissipated, I found to my dismay very heavy LIQUID OIL coating an 8' diameter on my garage door. And puddles under the exhaust tips.

::sigh::

So tonight I had an hour, so I did a compression check. I'm a little frustrated with myself over that. The first cylinder I checked (left front) had 200psi. !! That seemed VERY high to me. I checked it three times, then went to the next cylinder which gave me 210. The rear cylinder on that left side read 200. HUH.
so I went to the right side; 150, 155, 152. HUH.
So I went back to the left side: 153, 150, 152.

yeah. so... there's that. I don't know what could possibly have changed, but I assume it's in my method. or my tool. I don't see how it could be something in the motor. I'm open to suggestions?

So then I pulled the oil filter. I cut it apart and pulled out every foreign body I could find in it. See the photo, below. None of it is ferrous. there are two pieces that worry me in the slightest: the two closest to the pencil tip. The one is shiny metal, the other is hard plastic. Everything else seems to be gasket / sealant material (the red stuff is probably the stuff I used on the IMS this summer)

Here's something else that's... well.... odd. When I was underneath looking up, I noticed that there appears to be a plug missing over the end of intake cam, left-side, front. I don't recall pulling that cover for anything. ever. and the metal around where it looks like it should seat is shiny, like there was a cover in place recently. This is directly above the scavenge-pump on that left side. The green plugs on the rear of that bank are new, because I replaced them when I did the IMS. They are both canted; sitting proud of the head at the top, but flush at the bottom. Now, it is possible that I didn't seat them correctly when I installed them recently, and if they were the only oddity I'd assume that was the case. but I have to look at the aggregate of all of this. I can't imagine what would cause those cams to "walk" forward / aft, but I haven't been into this motor to see what sort of thrust surfaces or bearings exist to locate the cams fore/aft. I really can't imagine BOTH cams doing this.... so I'm inclined to dismiss it... but it's nagging at me.

Unless there are other, better ideas here (I'd welcome them!) my next steps will be to peek into each bore with a scope. I don't expect to learn anything. I'll probably do the compression test again, to satisfy my frustration over tonight's test. (I may borrow a tool from someone, and try that). Then I figured I'd pop all the cam plugs and check cam timing. I'll pop the covers on the scavenge-pumps while I'm at it. Assuming I don't find anything, then I'll replace the AOS, and probably remove & clean the intake and exhaust, so I can rule-out "puddles" of oil remaining in it. Then fire it back up.... and cross my fingers.

Any other thoughts or ideas y'all may have here?



Last edited by maytag; 10-31-2018 at 06:19 PM.
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Old 11-01-2018, 03:37 AM   #18
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Re: Camplugs - sounds like the crankcase built up pressure and popped what it could out ... I'd just put them back in ..

Re: tremendous oil smoke & running rough - sounds like you just need to let it run - I mean mostly at idle for a while - just in case .. and then
1) spray Seafoam Spray intake cleaner down the throttle body (while it's running.. don't overload it)
2) run a couple tanks with Seafoam motor treatment in the fuel

https://seafoamsales.com/auto/
(or use your favorite alternative to this)
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Old 11-01-2018, 04:28 AM   #19
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those cam plugs typically pop out if too much sealant or carelessly applied sealant is used on the cam covers. It clogs either an oil or vacuum passage (can't remember) and those tend to pop out. Not sure if you've had your cam covers off but look into this.

If you've had an AOS failure, your intake is full of oil. I would pull off the throttle body and cross over tube and get as much out as you can with paper towels. Really get into the plenums.

Given the compression ratio of the motor, I think you'd see more like 180 or so, so one cyl at 200 is odd. 150ish for the rest is fine since the reading is dependent on the seal of the gauge to the cylinder, the strength of the battery, etc.
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Old 11-01-2018, 06:18 AM   #20
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My thought at that point was that there was probably plenty of oil that needed to burn off. So I fired it up again in the driveway. it fires immediately, but idles rough. When you rev it, it smooths out.

so I went to the right side; 150, 155, 152.
So I went back to the left side: 153, 150, 152.
Hello Maytag,

IMHO these are great news..! (way better than the original prognostic)

Your engine has pretty good and even compression (w/less than 10% difference between cylinders), I would remove the intake plenums to clean them properly and perhaps cranking it a bit more with the plugs removed to remove as much oil residue as possible, then reinstall the plugs and run it until the smoke goes away.

Did you check the vacuum to see the AOS condition? I have an extra (used) AOS in good condition removed from my 987S that you can have it if you want, shipping it should be a few bucks..

Again, these seem to be optimistic news, good luck!
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