MkII AOS DIY

Ok, I just finished this completely and here's my write up. Hopefully it will save the next guy some time. The bottom line is I had to unbolt the AOS first so I could put a socket on the front most intake manifold bolt (not mentioned in other AOS write ups I saw). And you need to get the two AOS bolts from the bottom. Most difficult and critical parts in BOLD. Parts I used AOS 99610702651 Gasket 99711024700 x 3 Spring clamps 99951265009 x 3. Note this is a 997 part but they are identical to your stock spring clamps. For 996s, they've changed these to the worm-screw type, which I dislike. Just be very careful removing the spring clamps as they tend to slip and fly around. You will never find them if they do. Worse, they may fall into the intake holes or AOS engine hole if you don't cover those well. AOS removal on a ’03 Carrera Coupe manual transmission 1. Disconnect MAF and remove the airbox, serpentine belt, throttle body, and front intake plenum 2. Push the left rubber sleeve all the way to the left, then wiggle the plenum out 3. Remove the alternator (maybe optional but I removed it to get more room) 4. Remove the vacuum line to the intake plenum and the one to the rear resonator actuator 5. Remove the vacuum elbow and changeover valve on the left intake manifold 6. Disconnect the brake booster vacuum line from the intake manifold 7. Remove the O2 sensor wires from their guiding rails or clips 8. Lower the engine (jack at its strongest point) till it’s resting on the rear subframe cross member and leave the jack there to support it 9. Disconnect the lower AOS vent hose using BOTH HANDS from the bottom 10. Move the vent line out of the way so it’s not blocking the rear AOS 5mm allen head bolt 11. Remove the rear AOS 5mm allen head bolt using a mini-ratchet + 5mm hex bit Craftsman 7 pc. Reversible/Ratcheting Screwdriver Bit Wrench Set - Ratcheting Screwdriver And Bit Set - Amazon.com Craftsman 7 pc. Reversible/Ratcheting Screwdriver Bit Wrench Set - Ratcheting Screwdriver And Bit Set - Amazon.com 12. Remove the front AOS 5mm allen head bolt (a mini-ratchet with a handle that bends downward) 13. Loosen and move the hose clamp on the hose (away from the AOS) that connects to the very bottom of the AOS 14. Unseat the AOS and push it a little toward the front of the car so you can put a socket on the front most intake manifold bolt (otherwise it’s blocking that bolt) 15. Remove the the front most intake runner bolt, then the remaining 5 intake manifold bolts 16. Seperate the rear plenum and remove it 17. Siphon the coolant from coolant reservoir 18. Disconnect the vertical coolant hose between the alternator and the power steering pump (so you can remove the intake manifold from the car) 19. Remove the left intake manifold 20. Disconnect the upper AOS vent hose 21. Remove the 2 coolant lines from the AOS 22. Remove AOS from the engine compartment AOS reinstall Reverse of the above. After you connect the coolant lines to the AOS and the vertical coolant hose between the alternator and the power steering pump, you can choose to refill the coolant at this point and do a pressure test (before refilling coolant) to 18 PSIG and see if there’s a any leak at the AOS and the coolant line when things are still apart If you use new o-rings on the AOS vent hoses, apply some o-ring grease on them. That will prevent the dry o-rings from being crushed when inserting into the AOS. Do the same to the orange o-ring at the bottom of the AOS. Torque the intake manifold bolts to 7.5 ftlb To put the rear AOS allen head bolt in place, you need to manipulate the bolt with BOTH HANDS and be careful not to drop the bolt on the cavities of the engine. It can be very difficult to retrieve the bolt. Image courtesy of Atlanta Porsche Parts. AOS.jpg

Very good writeup. That last intake bolt all the way in the back is all guess work. I had to do that completely by feel. Same goes for the AOS rear bolt. Dropped that and spent 2 days trying to find it. Also, the intake bolts had thread locker on them, so I used some in the re-install and cleaning them up. Loctite Blue (not red). Since you will be working directly over the open intake runners, two things: lift straight up and out the back, hopefully the intake o-rings will stay on the manifold, then immediately cover the intake runners with a shop towel so you don't drop something down one of the intakes! Replace the intake o-rings with new, and get a new throttle body o-ring as well. Also be prepared to break most if not all of the vacuum plastic tubing and learning how they are routed.

Thanks Joe. Great tips you have right there! I followed most of those but I skipped the thread locker. I just don't want to fight with thread locker next time if I have to do it again. I'll check the bolts from time to time to make sure they are tight. Is yours also MkII? Most of the write ups were on MkI where the AOS is NOT blocking the front most intake manifold bolt so it's easier. The whole issue with MkII is part of the AOS is like an inch on top of that intake manifold bolts making socket impossible. You can use a box wrench but then you won't be able to remove the bolt (blocked by the AOS. The extra support u-channel bracket that's below the big round part which was not present in MkI AOS).

Quotes source post: 11930200

Ahsai- how did you fix the vaccum Lines ? Just rejoin with rubber vacuum hose ?

Quotes source post: 11931382

I bought 2 meters of the stock vacuum line (p/n 00004320501) from Sunset to cut them myself to replace the old lines. I like the stock look and the skinny stock lines. http://www.ecstuning.com/Porsche-200...501/ES1353321/ They last fine even after 11 yrs and I didn't have to replace them. However, the Elbows and other rubber connectors are hardened so may as well replace them. My vacuum reservoir has a small leak at the bottom of it. The whole vacuum system is like $150 from Sunset - vacuum reservoir, 2 changeover valves, 2 "Y" connectors, 4 elbows, and about 50" of vacuum lines.

I replaced the AOS on my 96 C2 2002 a couple of years ago. I don't know if there are slightly different routings of some hoses on a 2002 and a 2003, but on my car it was very, very hard to replace the AOS when lowering the engine only to the subframe cross member. Some hoses where blocking a lot of space around some of the bolts so they where insanely hard to remove and reinstall. I have replaced the AOS once more, and then I removed the subframe cross member and lowered the engine a lot more than the first time. I think it was worth the extra effort of removing some of the cables and hoses (like when you remove the engine completely) from the engine to get it down. Robert

The one additional, and very important, step I will mention is to label and photograph as much as you can. I didn't do this and when the time came to hook up some of the vacuum lines it was a mess. I managed to get the car to the dealer afterwards and had them clean up my mess. So the actual task is fairly straightforward but all of the little bits you need to finish up to complete the job are a nightmare if you don't have them clearly identified. But hey at least now I know for the next time!

Just curious, how long did it take you to do it?

Although I've only worked on BMW AOS's as haven't needed to change out my 996 one yet, I'm really surprised as this AOS seems like a self contained unit, that no one has bothered to just remotely located it and run additional tubing to a more accessible location. I know AOS's don't go out that much but I could see the relocation making sense for track junkies. Or even better yet, just using a more robust AOS from another car and adapting the tubing and such.

Alpine, Great idea. There was a recent thread discussing the relocate+upgrade idea for the AOS using BMW/generic parts. One Rennlister in that thread has a fix for the issue. http://986forum.com/forums/performan...p-version.html . The AOS is one of those nasty issues that undermines the reputation of the M96 because of the oil smoke and access issue. We need to share a better solution.

Quotes source posts: 11931632, 11932115, 11932189

Yes, mine is the same with lots of wires and hoses blocking access to the rear AOS bolt and it would seem impossible at first hence my write up. It's VERY time consuming to trial and error without knowing in advance WHERE and HOW to remove the two most difficult bolts (the rear AOS bolt and the front most intake manifold bolt). It turns out the MOST difficult and critical is the rear 5mm allen head AOS bolt (the one closer to the rear of the car). Once the two AOS bolts are removed, you can lift up the AOS and then you can get a clear shot at the front most intake manifold bolt. To remove that AOS allen head bolt, you need to remove the lower vent line on the AOS first because it's blocking the bolt. To remove the lower vent line, you need to lower the engine first and use both hands to disconnect the lower vent line. I thought about removing the cross member but I don't want to get a new alignment (may or may not be needed. Need to research more) plus I don't want to risk bending any lines such as a/c, hydraulic lines, coolant pipes, etc. I can see how easy the whole process would have been if I have another inch of room to work with. The vacuum lines are actually very easy once you know the complete layout. I have a write up here https://rennlist.com/forums/996-foru...omponents.html I replaced everything in the photo (except the rear plenum) for $150 or so. Took me half a day to remove and half a day to put it back in but that's including new AOS, new vacuum system (valves, hoses, vacuum reservoir), new alternator, new starter cable, new o-rings on the AOS vent hoses, new oil filler tube, new coolant hose, etc. Also including all the time trial-and error on the impossibles and 45 min fishing the rear AOS bolt that fell into one of the cavities on the top of the engine. It's important to use BOTH hands to insert that bolt. If you follow the steps above, I expect one can do the AOS in 4hrs or less. The trick is to not waste time and energy on the impossibles If I were to do it again, I'm pretty confident I can do it in a few hrs.

Quotes source posts: 11932335, 11932416

My old one was still good but I chose to replace it as PM. I've heard that you can fit the Porsche sport AOS ($1300+), which is like 50% bigger into our car but I would think it needs some modifications. The AOS is self-contained but one of its outlets is connected directly to an opening on the top of the engine case so if you need to relocate it, you will at least need an adapter plate to cover that opening where the existing AOS sits.

The complication with a remote AOS is arranging a drain-back for the condensed oil. If you read the link I gave above, that was discussed by the inventor of the improved system as he patiently critiqued my fumbling attempts to propose a generic alternative to the porsche AOS .

Yes, I had read the link and understood the issues. Probably overkill for a street car though. A working stock AOS does not seem to create problems for street cars as far as I remember on the forums.

Quotes source post: 11933035

I expect the even more complicated part is how to duplicate the spring diaphragm inside that regulates the crankcase pressure to ~5" H2O.

Thanks for the write up. Since my car has 125K on it I'm going to change this and the water pump over the winter. While in there what soft hoses should also be replaced that are listed in this diagram? 4, 12, 5, 13, 20? Am I correct to assume that 2, 10 & 11 come with a new AOS? Is 18 the piece that is easily broken?

Hi kpl, I found all my hoses still in good shape so I only replaced hose #20. In addition, I also replaced the following parts: - 19 (x2), 18, 15, 22 (x3 - one on #4 and two on #5). Yes, 18 is the piece that's easy to break but mine was still strong. I replaced it anyway hence also replacing 15, 19's and 20 at the same time. 15 is the Oetiker type (one-time use) from the dealer. You can use a NORMA 8-16mm worm-drive clamp to substitute. I reused the 14's (but you may want to replace these with NORMA 8-16mm worm-drive clamps as well) and the hose clamp at the very bottom of the AOS (not in the diagram). I took my chances reusing those clamps and so far they seem to be sealing fine. NORMA clamp https://www.belmetric.com/cr816-norm...th=15_145_1044 You can get these from eBay easily. Our MkII AOS doesn't have parts 2, 10 & 11. Please let us know how it goes as I'm curious if you also face the same challenges I mentioned in my 1st post. Doing the water pump the same time is good. You have overlap steps of removing the airbox, serpentine belt, lowering the engine and draining the coolant.

THANKS! are 4 & 5 hard plastic lines as opposed to rubber or metal?

Quotes source post: 11938796

That's correct. 4 is corrugated since it needs to bend during removal/install. It snakes through between the intake runners of the intake manifolds). 5 is smooth but both are hard plastic.

Started the process today. All of the work from the top went very quickly. I'm now stuck trying to figure out how my AOS is mounted from the bottom. I'm trying to disassemble everything while I wait on parts to arrive later this week. First strange point is that I don't appear to have 5mm hex bolts attaching the AOS...the front AOS bolt is a standard 10mm bolt (not hex), and I can't seem to find the rear bolt - not exactly sure what I'm trying to find, but I can't feel any 5mm bolts back there Is it typical to have the electrical lines running under the lower vent hose? Maybe the shop that replaced the AOS (by the PO) a few years ago didn't attach it with the correct fasteners? Thanks in advance!

I've never done the job before....but I do save some pictures when I see good ones....and sometimes that includes 911 pictures....here is one that I have, hope it helps! <img src=http://audipages.com/911/tn_AOS1.jpg>

Quotes source post: 13251959

It's possible the previous installer didn't even fit the rear bolt as that's the most difficult bolt in this job. Yes, somehow Porsche engineers found it totally appropriate to run electrical wires there to capture the AOS and block you in every way. The 10mm bolt may be nothing as long as the threads and length are correct. Just to clarify my terminology of front and rear. Can you feel if the rear bolt is there based on the pic below?

Quotes source post: 13251998

You can't even see the rear bolt in this pic

He didn't say which rear!!! Give me a break! ;-)

Quotes source post: 13252041

Here's the front bolt. Clearly not a 5mm hex. I can barely feel a similar bolt in the back, but it will be tough to remove.

And I thought changing my filler tube was a pain in the ***...

The electrical lines shown in PW's photo are under the AOS hose nipple on my car and what a PIA it is to release the hose clamp with those wires under there. My fingers are still numb. I am doing mine right now with the trans out and working from the flywheel end of the engine. I discovered late today that I can just reach that rear bolt from the back of the car, reaching past the coolant tank, so am going to give that a shot tomorrow. No way I can handle that bolt from under the car at the flywheel and keep what is left of my sanity. BTW - both bolts are 5mm socket head on my car.

Spruden, if you lower the engine to the max and your hands are not too big, you could reach that bolt from the side with just your fingers, right below the fuel rail. Or you can try what Rockhouse mentioned.

Oh boy, looks this is like a big 9-DIY on a 10 scale, assuming 10 is for the ISM bearing/Engine rebuild job... I just hope my AOS will last a while longer, if not I will have to take it to dealer or a good Porsche Indie and pay the price... At that time, it may make sense to also do the IMS/RMS upgrade. WOW, you guys are tough DIY'ers, good job!

Quotes source post: 13254630

It's not bad...just takes time. The two AOS bolts on your Mk I are different and they're a lot easier to remove so no fear.

My dealer quoted me $488 labour and $275 parts, which is $200 less than my Indy. It's going in on Tuesday.

Quotes source post: 13254630

I'm not an expert mechanic by any means but was able to do this job myself. It doesn't require any special skills but it is time intensive and requires patience as you will get frustrated. Unlike an IMS/RMS there's no special clearances or tools needed to do the job, it's just the removal of a lot of components and contorting your limbs to get to places you may not think you can reach. It's crazy that a part that is essentially a wear item requires so much work to get to it.

I agree - just finished mine today and it was excruciating, even with the transmission out. I did lower the engine and then was able to get a socket wrench with extension on the invisible rear bolt on the AOS. I never could get the clamp off the top coolant hose so I broke the nipple off and worked on it with the AOS in the garbage can. Reinstall of the new AOS was better but still not easy and I used a worm type clamp on that top coolant hose just in case I ever need to get near it again. If this thing leaks I may open a credit line at the dealer!

A job well done!

Thanks for the informative post Ahsai! And thanks for the answering some of my questions via PM. Much appreciated. Just wanted to add to this post regarding the Motorsport version of the 996 AOS. It is an expensive option, but if you are having oil ingestion issues on the track, it is an option. The 996 107 926 00 version installs in our Mk 2 cars very straight forwardly (is that a word?). I believe it is easier to re-install than a stock version due to the access to the front manifold screw. The taller motorsport version gives access to the front mani screw. This allows you to install the AOS completely before putting bank one mani back on. I replaced the front most mani screw with a socket head cap screw (my mani screws were flanged 10 mm hex screws). This allowed me to use a 1/4" drive long ball end 5mm allen driver to tighten the front screw. Still not "easy", but I suspect a lot easier than a hex socket given the room back there. The only change needed to run this AOS is a re-route of the bank two vent line (item 4 in the diagram earlier in this thread). It no longer will run under both manifolds then to the bottom of the AOS. It now connects to the top of the AOS pointing towards the passenger side of the car. I routed around the bank two mani, down the front of the motor, then back up to the connector. I protected the plastic corrugated plastic hose in a few spots with rubber to prevent chafing. I was already replacing hose #4 due to a leak caused by chafing on a bracket, so make sure to protect this hose. There is some good spots to zip tie it, and try to isolate it from moving/vibrating. Again thanks to Ahsai, and to Pelican Parts for a good overview and pictures. Pelican's DIY is for Mk 1, but it does give you good general info.

Quotes source post: 14399870

Thank you for taking the time to write up the tedious details. That is exactly what we need ! Now if we could reduce the price of the Motorsport AOS to less than $700..... The regular AOS is 10% of the price of the Motorsport version.URO - are you reading this ??? To help(?) with future bolt removal - replace with internal hex/Allen /socket head bolts? http://www.pelicanparts.com/catalog/...pg7.htm#item23