Changing Primary Timing Chain Tensioner
My 95 M3 developed an annoying rattle on deceleration of the engine, at around 1,500rpms. The noise is generally loud enough to be heard from the passenger compartment, and when listening from the engine bay it emanates from the front of the valve cover. The noise got louder as time passed and became more noticeable putting around parking lots at low rpms. After searching bimmerforums.com and posting about my problem, I found out that this was a common occurrence with the 95 M3 models (S50 engine). It also didn't seem to be a high mileage problem (mine occurred at around 31,000 miles). The VANOS is often thought to be the culprit (and many dealers and mechanics will insist that this is the problem) but in most cases with the above symptoms it's the primary timing chain tensioner going bad. BMW obviously realized this and sometime ago changed the design of the tensioner. Fixing this problem is just a matter of swapping the original tensioner for the new style tensioner. The hardest part of this fix was locating the large 32mm deep socket, which I ended up borrowing from a friend.
32mm deep socket
11 31 1 726 503 - Primary Timing Chain Tensioner - $98.00 (list), $70.50 (*)
07 11 9 963 418 - Sealing Ring (optional) - $0.41 (list), $0.26 (*)
* I purchased my parts from Pacific BMW (800) 909-7278
let engine cool so it's not hot to the touch.
Figure 1 shows the tensioner extended. Figure 2 shows the tensioner locked in place. If your tensioner does not look like figure 2, place the large end of the tensioner on a tabletop. Compress the notched end of the tensioner until it the retaining ring hits the outer sleeve. While keeping pressure on the tensioner, squeeze the open ends of the retaining ring together so it will fit within the outer sleeve. It should click into place and look like figure 2.
Locate the tensioner (figure 3), it's on the passenger side of the engine, towards the front and below the valve cover. Place a rag under the old tensioner to catch the oil that will drip out when you unscrew it. Use the 32mm socket and remove the old tensioner, but do it slowly because it's under pressure from the spring. Figure 4 shows the difference between the old (top) and new style (bottom).
Place the new sealing ring on the tensioner, or use the one from the old tensioner. When screwing in the new tensioner, it's important that you line up the notch (vertically) so that it fits into the tab of the chain rail inside the engine. If you're not sure, stick your finger inside the hole and you should be able to feel the tab. While keeping pressure on the tab, hand screw the tensioner into the engine block. tighten the tensioner with a torque wrench to 28 lb/ft.
Remove the rag from the engine bay and wipe up any spilled oil. I pulled the fuel pump fuse (#18) and cranked the engine a few times to get oil to the tensioner, but I don't think this is necessary. When you start the car, you may hear the chain rattle for a sec or two, then quiet down. Let the car idle for a couple of minutes and go for a test drive.
All in all a very easy fix, best thing is that the annoying rattle is all gone and the engine is smooth as butter at 1,000 to 1,500rpms.
Thanks to all from bimmerforums.com that helped me, especially bimmer95.
Taken from http://www.geocities.com/rick_poon/tensioner.htm