INSTALLING ANY BEARING INTO AN ENGINE WHOSE BEARING HAS FAILED AND IN WHICH DEBRIS STILL RESIDES IS A WASTE OF TIME AND MONEY. THERE ARE STORIES OF 'WITHIN DAYS' FAILURES IN SUCH ENGINE INSTALLATIONS. THE ENGINE PRE-INSTALLATION QUALIFICATION PROCEDURES SUGGESTED BY LN SHOULD BE USED AS A GUIDE.
An IMS bearing is like any other rotating part, it wears and eventually fails. Some sooner, some later. Same as with any rotating part in any machine. We have seen original bearings go more than 250k miles and some not even 10k. Porsche says the first generation double row bearing fails less than .5% of the time over a 10 year 100k mile life. The second generation single row ('00-'04) between 5% and 10%. Even 10% is only 1% per car year.
Replacing a Bearing
An IMS bearing is most economically replaced when the transmission is removed for a clutch job. Replacement of the RMS (Rear Main Seal) with the improved "Cayanne" seal is also a good idea at this point.
The replacement of the bearing in the first two IMS design cars with another ball bearing IMS bearing requires some special tools (generations are generally dual bearing '97-'99, single bearing '00-04, improved single row bearing '05-'08 but there are replacement engines and especially in the first year of these groupings there were two generations used).
If you have a late 987 model ('06-'08) it will have the third generation IMS design which is a much more complex/expensive design to update. This could also be true of a replacement engine in any model year car, especially a recent replacement. And is probably true of late '05 cars as well. True for all Caymans until '09 models. The only way to be sure what version of the IMS you have is to remove the transmission and look at the IMS bolt/nut/cover. In the third generation design, the only replacement options I know of are from LN and are expensive.
It is much more expensive to update a Tiptronic engine's IMS bearing than a stick shift engine because the engine and transmission need to be removed from the car before the transmission can be separated from the engine to gain access to the rear of the engine and the IMS and RMS. On a stick shift car, only the transmission needs to be removed, saving perhaps 6-8 hours of labor.
The IMS bearing is also used in 996s and early Caymans.
Can the RMS/IMS be done by an owner?
Yes if the tool kit is purchased or rented, the instructions are followed very carefully and if nothing goes wrong. Many have done replacements successfully, occasionally you hear of someone who didn't follow the instructions, didn't lock the camshafts and got into big trouble. By far the majority have opted to have an experienced Porsche mechanic do the job. I've heard quotes of $1,600 to $3,200 for a clutch replacement, RMS replacement and LN IMS replacement.
I've often said that I want my heart operation done by someone doing their one thousandth, not the first one. The guts of the engine are similar. Both cost money. Sometimes it is best to pay for expertise.
Is there a way to detect that the IMS is failing before the problem takes down the engine?
Maybe!
A mechanic or owner can measure the camshaft variation between banks and tell there is wobble in the valve driving chain that goes over the sprocket on the IMS shaft if the owner is lucky enough to order that service at the time between start of failure and engine destruction. This variation can be from multiple causes so it is not definitive as to the IMS bearing itself failing. An owner could use the durametric software to read the camshafts deviations.
An owner can detect metallic particles caught in the oil filter if they are lucky (and look during in the failure interval) and determine by their being attracted by a magnet and from their type if they are from the IMS. Of course not all particles you might find are specific to the IMS bearing.
The problem with both the camshaft deviation measurement and oil filter or magnetic drain plug inspection is that the IMS bearing can easily fail in the intervals between inspections. Who of us are going to do these inspections every 500 miles? And even that frequently might not be enough to catch the problem between beginning and catastrophe.
Cautions
Consider your budget, the reputation of the parts/kit supplier, the reputation of the installer. How long will you keep the car, what is it worth on the open market. How much do you love it. How much else are you spending in its maintenance. Why are you replacing this part when others have been known to also fail.
There have been a multitude of online experts whose theories sound good but whose testing is limited in quantity or duration. Replacement of an IMS is sufficiently costly in terms of time or labor and the use of a relatively untested part sufficiently risky that you should consider the cost/risk trade-off carefully.
Also consider carefully if you are capable of doing the replacement yourself or if it is best to pay an expert.
If you decide to do-it-yourself, buy or make all the tools and read (and reread) and then follow the instructions carefully. Most of the problems reported didn't. Some of the online instructions are just plain wrong.
Another problem is with IMSs that have failed and the engine is not cleaned of any residual debris. The new IMS can fail quickly if this isn't done (and done right) as can any other oil lubricated part of the engine.