Installing an IMS Retrofit Upgrade


How to install an LN ENGINEERING / FLAT6 INNOVATIONS Intermediate Shaft (IMS) Retrofit Upgrade

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The M96 Porsche engine foundĀ  in the Boxster / uses what is called an Intermediate Shaft to transfer rotation from the crankshaft to the camshaft sprockets. This Intermediate Shaft is critical to maintaining the camshaft timing, which in turn sets the valve timing. With these engines being what is called an interference engine, this timing is very important. If it is off, it will not only run poorly, but cause catastrophic engine failure as the valves opening at the wrong time will make contact with the top of the pistons.

This Intermediate Shaft spans the length of the engine, beneath the crankshaft. At the front (pulley side) of the engine, the shaft rides in a bushing fit area in the case. When the engine is running, this allows the shaft to center itself and turn on a small amount of oil film. At the rear of the engine (transmission side), the shaft has a sprocket which is turned by the crankshaft. This sprocket contains a ball bearing, which is supported by a rod / bolt which exits the engine behind the flywheel / flexplate.

Porsche originally used what is called the dual row bearing setup, which was not replaceable without the engine being dismantled. Porsche later used a single row setup, which is replaceable with the transmission removed from the engine. The bearing is pressed into the sprocket until the outer race contacts the shoulder in the sprocket, which doesn’t allow the bearing to go any deeper. An internal snap ring holds the bearing in place, and also provides the anti-thrust mechanism.

This rod / bolt has a head which acts as a shoulder for the inner race, and continues through the cover, where a nut holds it to the IMS cover. The IMS cover supports the inner race of the bearing, by contacting the inner diameter of the inner race, holding the bearing and therefore the shaft and sprocket in place.

With all of this information in mind, what makes this upgrade better than a stock replacement assembly? Without repeating the details listed on the vendors pages, there are a few major differences. The composition of the bearing itself is by far the largest improvement. This ceramic bearing has a much better service life, and should theoretically last the life of the engine. The material composition and size of the rod / bolt (which holds everything together) is superior to stock.

As one can see, any bearing or bolt failure on this assembly can cause catastrophic results. For those having the single row, the retrofit is a rather straightforward upgrade during a clutch change. As a side note, this is also a good time to inspect / replace the crankshaft seal (RMS) if needed. The installation of this assembly takes approximately an hour with the proper tools. A bearing puller that pulls from the inner race is required, and most people will have to buy one, as it is not a common garage tool. I found a very nice, heavy duty one at NAPA for around $85 (PN# BK 7002476).

I have seen cheaper ones, but this can be used for future projects also. The IMS upgrade also arrives with an installation tool. This tool serves two purposes: It provides a flat surface to use a soft mallet to tap the bearing in place without damaging the bearing, and it holds the rod / bolt in place, not allowing it to fall into the shaft (where only a magnet can remove it).

With all of that said, let’s begin installation. The oil should be drained at this point, as the oil level is normally above the point that we are opening. Assuming that the flywheel is off of the vehicle, one should be looking at the back of the engine. Loosen (but don’t remove) the chain tensioners. This relaxes the chain on the sprockets. Loosen and remove the nut on the center rod / bolt, and remove the three bolts around the cover. Using small crowbars, pry evenly on the small recesses cut in each of the three flanges on the cover. The cover is held in with a ring gasket, so it will come out tight. Once that is out, tap the bolt slightly while holding on to it, to break it loose from the inner race of the bearing, without letting it fall into the shaft. With a pair of Snap Ring Pliers, remove the snap ring that holds the bearing in place. Any automotive parts store should have these pliers for approximately $10.

Using the bearing puller, put the bearing out. Using emery paper or a small file, ensure that the surfaces that the crowbar contacted are clean and smooth. Clean all the other surfaces and inspect for damages. Installation is the reverse of removal except that the puller is not needed. Using the installation tool and a soft mallet, tap the bearing into place, until it bottoms out on the shoulder in the sprocket.

Remove the nut from the tool, which will allow the tool to be taken off, exposing the now installed bearing. Many times, the sprocket will become misaligned with the center of opening. Porsche sells a tool to correct this, but with the tensioners loosened, it should be able to be pried over without much effort.

This retrofit comes with Loctite threadlocker and gasket maker. Use the threadlocker on the threads of every bolt, and the gasket maker on the underside of each bolt head. This will help ensure that oil cannot leak past the threads of bolt heads. The torque value of ~10 ft/lbs was given for all the bolts, to insure that they were all even, but not over-torqued.

The threads for the cover must be inspected before beginning installation also. The threads on mine were in horrible shape, to the point that re-tapping them was not possible. At this point there is two options: use a Heli-Coil or other method of thread replacement, or drill and tap for larger bolts. I did the later. This must be done with extreme caution, as to keep debris out of the engine. The stock bolts are M6, and the replacement bolts shown are M8. This gave me a piece of mind that these would not strip out again, leaving me in dangerous territory.