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Old 03-20-2024, 08:56 AM   #1
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Single-row IMS/IMS bearing in 2.5L M96?

Hello all! First post here!

I have a 1998 Boxster that apparently has a Porsche factory replacement engine installed (it has an "AT" code after the "M96/20" in the engine S/N). The engine has an "X" year model code, so the block should be from 1999.

Porsche has no record of the engine replacement, and I'm trying to determine if it is a drop-out from another warranty-replacement car.

Here's the really odd thing: The IMS is the later type that only accommodates the single-row IMS bearing.

Would Porsche have manufactured this "AT" coded 2.5L M96 with a single-row bearing? Or must someone have rebuilt it with a new, single bearing IMS and IMS bearing?

Many thanks for any guidance that you may offer!

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Old 03-20-2024, 09:10 AM   #2
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The engine is definitely a factory reman due to the "AT" designation:

Engine serial numbers have 8 digits.

1st digit - No of Cylinders

2nd digit - Engine Version

3rd digit - Model Year

4th-8th digit - Serial Number

On a MY2005 Boxster the original engine would have the number 615*****.

Depending upon the year of reman, it could carry the oversized non serviceable bearing; the only real way to know for sure is to pull the flywheel and look at it, if it has the large 22MM center bolt nut, it is the oversized bearing.
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Old 03-20-2024, 09:51 AM   #3
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Originally Posted by JFP in PA View Post
Depending upon the year of reman, it could carry the oversized non serviceable bearing; the only real way to know for sure is to pull the flywheel and look at it, if it has the large 22MM center bolt nut, it is the oversized bearing.
Thanks, JFP! In this case the existing IMS bearing is serviceable/replaceable with the LN Engineering P/N 106-08.2.2 retrofit kit. Thus the mystery!

I'm trying to determine whether Porsche built this "AT" engine originally with the later (M/Y 2001-2004) style of IMS complex or perhaps the engine has been rebuilt a second time with these parts.
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Old 03-20-2024, 10:22 AM   #4
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Originally Posted by 986FTW View Post

I'm trying to determine whether Porsche built this "AT" engine originally with the later (M/Y 2001-2004) style of IMS complex or perhaps the engine has been rebuilt a second time with these parts.
The answer lies in decoding the engine numbers as I described above...............if it was remaned a second time, the numbers would still tell you its configuration and age, and if the factory rebuild took place 2005 or later, your assumption about the IMS bearing is incorrect....
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Last edited by JFP in PA; 03-20-2024 at 10:26 AM.
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Old 03-20-2024, 11:19 AM   #5
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Yes, JFP. One would think this and that's why it's a mystery. For reference:

Engine S/N: M96/20AT65X65242
Installed LN Engineering IMS P/N: 106-08.2.2

So it's a factory manufactured replacement 1999 M/Y engine, but it has an LN Engineering retrofit kit normally used for a 2000/2001-2005 M96 engine.

Question is how? Could it possibly have come from Porsche with the updated (M/Y '00/'01-'05) intermediate shaft, or has someone rebuilt it with the later-model IMS subsequently?

Last edited by 986FTW; 03-20-2024 at 11:28 AM. Reason: correcting P/N for IMS retrofit kit
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Old 03-20-2024, 11:39 AM   #6
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As Porsche never uses LN bearings, someone else has been inside this one...............
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Old 03-20-2024, 12:11 PM   #7
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Yes, I know that the the LN Engineering retrofit kit isn't factory.

The issue is that the IMS itself (which accepts the LN Engineering P/N 106-08.2.2 retrofit) is a later-model shaft. Could it be from the factory on this 1999 M/Y block, or must someone have rebuilt this engine with an updated intermediate shaft?
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Old 03-20-2024, 12:36 PM   #8
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The factory ALWAYS went back to what was originally in the engine, with the sole exception of going to the last design oversized IMS on anything remaned after 2004.
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Old 03-20-2024, 03:32 PM   #9
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Thanks, JFP! That's helpful information!
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Old 03-20-2024, 06:14 PM   #10
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Have you tried the LN site? I bought a used engine with an LN bearing in it, using the car serial number I was able to find when and where the LN bearing was installed.
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Old 03-21-2024, 06:15 AM   #11
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Have you tried the LN site? I bought a used engine with an LN bearing in it, using the car serial number I was able to find when and where the LN bearing was installed.
Thanks, elgyqc! In this case, I'm aware of the LN retrofit installer's identity. My quest is to determine why the engine has the later-model IMS complex (including crankshaft!). I've now determined that the engine was completely rebuilt by an unknown shop using later-model parts in place of the originals.

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