My 200,000 mile refresh.
#16
Nordschleife Master
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jandackson (12-01-2023)
#17
Instructor
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Porschetech3 (11-28-2023),
TexSquirrel (11-28-2023)
#18
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OK, so building up my list of things to do to the engine.
I feel I must change out the primary chain tensioner (crank to IMS), and as I can't do that without splitting the case, it puts me in a quandry.
Is it possible to disassemble and replace while leaving the pistons in the sleeves? they are mated to the bores over 200k, so I would prefer not to remove if possible.
I have great compression (tested a year ago, but all in the 170s) So I would prefer not to do liners and pistons if possible.
Otherwise, maybe I will just keep dropping the pan and inspecting the tensioner pad every other oil change.
I feel I must change out the primary chain tensioner (crank to IMS), and as I can't do that without splitting the case, it puts me in a quandry.
Is it possible to disassemble and replace while leaving the pistons in the sleeves? they are mated to the bores over 200k, so I would prefer not to remove if possible.
I have great compression (tested a year ago, but all in the 170s) So I would prefer not to do liners and pistons if possible.
Otherwise, maybe I will just keep dropping the pan and inspecting the tensioner pad every other oil change.
#20
Racer
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uaos great product but nothing necessarily wrong with genuine porsche aos. Can be changed in under 2 hours. don't need to touch exp tank, manifold, alternator or engine mounts. if DIY guy i can explain how u do it and will save u $. pm me
#21
Rennlist Member
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996-CAB (11-28-2023),
binaryaudax (11-28-2023),
bmchan (11-29-2023),
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#22
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OK, so building up my list of things to do to the engine.
I feel I must change out the primary chain tensioner (crank to IMS), and as I can't do that without splitting the case, it puts me in a quandry.
Is it possible to disassemble and replace while leaving the pistons in the sleeves? they are mated to the bores over 200k, so I would prefer not to remove if possible.
I have great compression (tested a year ago, but all in the 170s) So I would prefer not to do liners and pistons if possible.
Otherwise, maybe I will just keep dropping the pan and inspecting the tensioner pad every other oil change.
I feel I must change out the primary chain tensioner (crank to IMS), and as I can't do that without splitting the case, it puts me in a quandry.
Is it possible to disassemble and replace while leaving the pistons in the sleeves? they are mated to the bores over 200k, so I would prefer not to remove if possible.
I have great compression (tested a year ago, but all in the 170s) So I would prefer not to do liners and pistons if possible.
Otherwise, maybe I will just keep dropping the pan and inspecting the tensioner pad every other oil change.
But, no, you can't split the case and leave the pistons in place.
You will need to pull and reinstall them.
#23
RL Community Team
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Not to mention the lifetime transmission fluid.
![hiha](https://rennlist.com/forums/graemlins/roflmao.gif)
I'm a former european mechanic.
It took me several hours to replace my AOS with the UAOS.
If you're very experienced like PorscheTech3, you can maybe do it in 2 hours, but a DIYer, or even an experienced mechanic it will take longer.
When my UAOS diaphragm failed recently, it took me 5 minutes to replace it.
Unless you have several years experience working a a water cooled Porsche indy, or a dealer several years ago, I really doubt 2 (or 4) hours is possible.
I'd love to watch a video proving me wrong though.
Last edited by TexSquirrel; 11-28-2023 at 07:48 PM.
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binaryaudax (11-28-2023)
#24
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![](https://cimg6.ibsrv.net/gimg/rennlist.com-vbulletin/843x1124/bent_rod_aos_damage_cylinder_d765ae7ace9fc3bca0b7c6b9320c88fe5ffeb8cd.jpg)
#6 cylinder scored on pin side of cylinder
![](https://cimg0.ibsrv.net/gimg/rennlist.com-vbulletin/236x315/bent_rod_aos_damage_52c2c5de576838a01a264eff7441724d5cd9b12e.jpg)
#6 rod slightly bent only about 20 thousandths
I'm not saying that EVERY AOS failure will cause a bent rod or cracked cylinder, but I am saying that thousands of bent rods and cracked cylinders have been caused by AOS failures, it is just a crappy part, and is inefficient to boot...This example was just found last week..
BTW :: The new owner now has a UAOS System to be installed on his new engine..the way it should have came from the factory...
Last edited by Porschetech3; 11-28-2023 at 09:17 PM.
#25
Racer
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Haha, quality IMSB, waterpump, Lokasil, and sunvisors.
Not to mention the lifetime transmission fluid.![hiha](https://rennlist.com/forums/graemlins/roflmao.gif)
I'm a former european mechanic.
It took me several hours to replace my AOS with the UAOS.
If you're very experienced like PorscheTech3, you can maybe do it in 2 hours, but a DIYer, or even an experienced mechanic it will take longer.
When my UAOS diaphragm failed recently, it took me 5 minutes to replace it.
Unless you have several years experience working a a water cooled Porsche indy, or a dealer several years ago, I really doubt 2 (or 4) hours is possible.
I'd love to watch a video proving me wrong though.
Not to mention the lifetime transmission fluid.
![hiha](https://rennlist.com/forums/graemlins/roflmao.gif)
I'm a former european mechanic.
It took me several hours to replace my AOS with the UAOS.
If you're very experienced like PorscheTech3, you can maybe do it in 2 hours, but a DIYer, or even an experienced mechanic it will take longer.
When my UAOS diaphragm failed recently, it took me 5 minutes to replace it.
Unless you have several years experience working a a water cooled Porsche indy, or a dealer several years ago, I really doubt 2 (or 4) hours is possible.
I'd love to watch a video proving me wrong though.
uaos no question easier to replace.
I'm a european mechanic in my head. I'm 29 but have been working on cars since I was ~12.
"who's the better wrench?" - Top gun hk vs tex
Edit - because you doubted me - these are from my OP where I eventually did my own aos.
you need to remove coolant hose that goes to bleeder valve to give left arm room like so:
![](https://cimg1.ibsrv.net/gimg/rennlist.com-vbulletin/960x1280/842892e5_2d29_4533_8769_17b85c9f3945_bf4a22ab108d1f82170852cf6a2abae6943efaa3.jpeg)
Right arm fed between plenums - this is where you look just above alternator and below manifold while your arm is back there. No view unless solenoid is unclipped and moved from atop the alternator.
![](https://cimg0.ibsrv.net/gimg/rennlist.com-vbulletin/960x1280/ff02b670_c4db_4a49_8e12_70245264b0e7_592b64c8d9a706dda31c6c4e955a53610e81f36a.jpeg)
Last edited by hkovalcik; 11-29-2023 at 11:25 PM.
#26
Racer
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delete - yes uaos is great product but rod bend doesn't happen unless owner keeps driving the car. pooled oil in cylinders from failed aos is reason for rod bend and owner should replace aos/tow car immediately. there is a thread where people argue whether or not u can bend a rod just by starting the car with oil pooled in cylinders but general consensus was "unlikely"
Last edited by hkovalcik; 11-30-2023 at 01:00 AM.
#27
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I'd second the if it ain't broke, don't fix it suggestion.
Maybe have it dynoed to see if it lost anything, but unless it burns oil or lost 50hp, I'd leave that car alone and keep driving it. Better spend 25 grand five years down the road than tomorrow.
Maybe have it dynoed to see if it lost anything, but unless it burns oil or lost 50hp, I'd leave that car alone and keep driving it. Better spend 25 grand five years down the road than tomorrow.
#28
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Yep. Nothing better than being on the road or track in your 20+ year old 996 with old brittle parts that are known to fail as they age. Same can be said for the joys of being down 50 hp. Who in their right mind wouldn't embrace the joys of waiting for AAA on the side of the road.
![Smilie](https://rennlist.com/forums/images/smilies/smile.gif)
#29
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delete - yes uaos is great product but rod bend doesn't happen unless owner keeps driving the car. pooled oil in cylinders from failed aos is reason for rod bend and owner should replace aos/tow car immediately. there is a thread where people argue whether or not u can bend a rod just by starting the car with oil pooled in cylinders but general consensus was "unlikely"
Yes, just turning over engine with starter, with enough oil in cylinder, can cause damage that might not be apparent immediately but thousands of miles later will show up all to well.... Can't compress oil, so something (rods, cyl, piston, flattened/hammered rod bearing, etc,) has got to give....
jmo
Last edited by allcool; 11-30-2023 at 11:29 AM.
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Porschetech3 (12-01-2023)
#30
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Is it possible to disassemble and replace while leaving the pistons in the sleeves? they are mated to the bores over 200k, so I would prefer not to remove if possible.
I have great compression (tested a year ago, but all in the 170s) So I would prefer not to do liners and pistons if possible.
I have great compression (tested a year ago, but all in the 170s) So I would prefer not to do liners and pistons if possible.
At 200k miles, your bores are way out of round/taper all the 996 experts say. The rings have now seated into OOR bores. Its not uncommon for out of round cylinders to seal and run well, as rings have worn/seated into their location. The problem comes from trying to seat new rings in old oor/tapered bores. The majority of these re-ring attempts result in wiping out the rings in a few thousand miles...
IMO, do a detailed cam dev check and a detailed leak down test and a new compression check. Also try and do a detailed inspection of all chains for broken/missing cracked rollers/pieces that can jam up the pumps. Use this new information to decide what you'll do...
Last edited by allcool; 11-30-2023 at 11:54 AM.