Pelican Technical Article: Idler Belt Pulley Replacement Wayne R. Dempsey
Time: 1 hr
Tab: $150
Talent:
Tools:
24mm wrench
Applicable Models:
986 Boxster (1997-04) 987 Boxster (2005-08)
Parts Required:
Three tensioner pulleys
Hot Tip:
The top and bottom pulleys are different, despite them looking the same
Performance Gain:
Quiet running engine
Complementary Modification:
Replace drive belt
This article is one in a series that have been released in conjunction with Wayne's new book, 101 Performance Projects for Your Porsche Boxster. The book contains 312 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 950+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Boxster owner's collection. The book is currently available and in stock now. See The Official Book Website for more details.
Check out some other sample projects from the book:
The Boxster uses a complex belt path to drive all of the accessories of the engine off of a single belt. Even when I change the belt in my Boxster, the path is so difficult to remember off the top of my head, that I have to refer to my own diagram in Photo 3 of Project 5 (belt replacement). The bottom line is that the three belt pullies that are located on the crankshaft pulley side of the motor get a lot of wear and tear over their life. It's not uncommon for one or more of them to fail and begin to start squeaking.
When you get a high pitched squeaking noise from your engine compartment, it's typically very difficult to diagnose where it's coming from. I typically like to open the engine access lid and run the engine while I'm carefully listening for the origin of the squeak. Be very careful of your hands and any items that might get stuck or caught in the engine if you're running it with the rear panel off. I often use a can of WD-40 with the spray nozzle extender attached to try to isolate which pulley or piece of equipment is making the noise. With the engine running, I typically soak the bearing shaft of each belt pulley, listening carefully for changes in the squeaking noise. Check every one, including the water pump, power steering pump, alternator, and the air conditioning compressor. Often, the noise will go away when the lubricant finds its way to the bearing. This works about 50% of the time to isolate the noise.
Another way to check the pulleys is to remove the drive belt and actually turn them with your hand. Sometimes you can feel significant resistance or hear a grinding noise as you turn each shaft by hand. Again, check each one, including the shafts of all of the accessories. All three of the idler pulleys should feel about the same. The accessories (alternator, water pump, etc) will each feel different, so it's difficult to tell if there's anything wrong with the bearing unless you spin these on multiple cars every day.
Sometimes a squeaking noise may be caused by a belt that may be deteriorating. As belts age they sometimes get worn out and smooth, and that may cause them to slip which can result in a squeaking noise. If you suspect the belt may be the problem, then I recommend you replace it first. Or, you can try out some of the spray-on belt dressing that is available at your local auto parts store. The belt dressing is a temporary fix that makes the belt a little stickier and less prone to slipping.
Fortunately, the tensioners are very easy to replace. Simply remove the back panel behind the seats (as detailed in Pelican Technical Article: Drive Belt Replacement). Then remove the drive belt from the engine. Removal of the two idler pulleys is as simple as unbolting them and replacing them with a new one. Be careful not to drop the large washer that is on the front of the two idlers, and the spacers in back either. Although they look almost identical, the top and bottom idler pulleys have two different part numbers so be careful not to mix them up if you are replacing them both at the same time. Reinstallation is a snap, simply install the bolts and tighten to 34 ft-lb (46 Nm) for the upper bolt if it's an M10x145 (8.8) bolt or 48 ft-lb (65 Nm) if it's an M10x145 (10.9). The lower pulley is tightened to 17 ft-lb (23 Nm). The bolts that are used on the pulleys originally had self-locking compound on them when they were new, so if you are reusing them again, then simply add a little bit of blue Loctite 242 to the threads prior to installing them.
The tensioner pulley is a little bit different. It is attached to a spring-loaded arm via a single bolt that is backwards in orientation from the other two idler pulleys. You need to get a 15mm wrench on the head of the bolt behind the pulley and then loosen the pulley with a 24mm wrench on the front. Be careful not to drop the spacer located behind the pulley when you pull it off. Reinstall the new pulley in the same manner, using a small bead of blue Loctite 242. Tighten the assembly to 44 ft-lb (60 Nm).
Figure 1
This photo shows the front of the engine and the three pulleys discussed in the text. The yellow arrow points to the top idler pulley, the green arrow points to the lower idler pulley. Although they look the same visually, there are two different part numbers for these two rollers. The purple arrow shows the tensioner pulley which is attached to a arm which is spring loaded by the pulley tensioner mechanism (blue arrow). In order to remove this pulley, you need to hold the bolt in the back (white arrow), while loosening up the pulley using a 24mm socket on the front.
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