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Idler Belt Pulley Replacement

Pelican Technical Article:

Idler Belt Pulley Replacement


1 hr






24mm wrench

Applicable Models:

Porsche 986 Boxster (1997-04)
Porsche 986 Boxster S (2000-04)
Porsche 987 Boxster (2005-12)
Porsche 987 Boxster S (2005-12)
Porsche 987 Cayman (2007-12)
Porsche 987 Cayman S (2006-12)

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
101 Performance Projects for Your Porsche Boxster

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.

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).

This photo shows the front of the engine and the three pulleys discussed in the text.
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.

Comments and Suggestions:
herbhenry2222 Comments: I have what sounds like a belt squeal. When the squeal is loud the oil pressure light comes on, punching the accelerator turns it off. Changing the belt didn't help. WD-40 on the bearings didn't indicate anything. Curiously, when I switch off the motor and the belt stops turning, the squeal continues for almost a second. Please help.
June 27, 2017
  Followup from the Pelican Staff: probably not belt related if the oil light is coming on. Check oil level, condition and pressure. - Nick at Pelican Parts  
W Comments: Hello, thanks for this guide.

Is it recommended to replace the tensioner at the same time as the pulleys?
June 18, 2016
  Followup from the Pelican Staff: It's not required but is a good idea. Saves a possible failure down the road.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
seta Comments: 98 boxster - i ordered the mubea replacements for the upper and lower idler pulleys. do they come with the necessary washers and spacers? if not, i'm missing the washer on the lower pulley. what is the part number for this?
January 4, 2016
  Followup from the Pelican Staff: I am not sure what they come with. I’m not the best with part numbers.

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
Sammy Comments: I striped the bolt in back so now how do I change it? 313-400-8121 Sammy
November 20, 2015
  Followup from the Pelican Staff: Which bolt? You can either use vise-grips to remove it. or Drill it out. - Nick at Pelican Parts  
ftp19601960 Comments: A few comments on 986: 1 to get longer alternator bolt out I jacked up engine front a little. 2 No need to buy new pulleys. They all the same and use the same bearing 15x35x15.9, such as 5202 size double row, angular contact. Bearings cost much less.
April 29, 2015
  Followup from the Pelican Staff: Good idea on the jacking up the engine, might be a little hard on the front mount though. As for replacing the bearings, I'm not sure I would trust a pulley that has had bearings pressed in and out more than once I have actually seen these pulleys break. Better to buy a new roller to be safe. - Casey at Pelican Parts  
zaskar14 Comments: To remove the tensioner pulley, when you say "backwards in orientation" do you turn the bolt clockwise to loosen?
February 26, 2015
  Followup from the Pelican Staff: You will hold the bolt with the 15 mm wrench behind the pulley, and you will loosen the 24 mm nut by turning it counter clockwise. Backwards in orientation means that the bolt goes through the pulley from the rear when compared to the other pulleys which have the bolts going through the front. - Casey at Pelican Parts  
Dr Suess Comments: I would like to suggest a technique for helping with the removal of the pulley. When I tried this the first time, the bolt on the back was starting to flop around even with the 15mm wrench on the back, this made the loosening of the pulley very difficult due to the fact that it is applied with Loctite. In order to stabilize the bolt I used both the 15mm wrench and a large screwdriver wedged behind the bolt & wrench in order to stabilize the bolt in position. This made both loosening the old pulley and replacing the new pulley much easier.
February 28, 2014
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it.
- Nick at Pelican Parts
d_roas Comments: Just loosen the other bolt and swivel the alternator up a bit, no need to bend anything!
November 7, 2013
  Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it.
- Nick at Pelican Parts
Paka Comments: What are the part numbers for the different pulleys?
July 13, 2013
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
Mike Comments: I wonder if Wayne has actually done this in the car. When I replaced the top idler pulley, the long bolt does not simply "pull out". It runs into the back of the sheet metal that surrounds the shifter cables as they pass through the rear bulkhead. You can pull the bolt forward until the head hits the sheet metal, but you can't extract it. When I did this, I bent the sheet metal forward about 1/2" to get clearance. An alternative might have been to remove the alternator. But it CAN'T just be pulled out.
February 15, 2013
  Followup from the Pelican Staff: A little creative thinking bending the sheet metal forward for bolt removal. Thanks for the tip. You might check your engine and transmission mounts. When failing they change a lot of clearances for the engine and transmission.

- Denny at Pelican Parts
Rocket Man Comments: 1. Is there a technique to tell if the spring loaded arm of the tensioner pully is going bad on Boxster?
2. Is a belt tensioner tool ever needed for Boxsters/996?
September 20, 2012
  Followup from the Pelican Staff: The only way the spring tensioner can fail is for the spring to break. In that case all belt tension would be lost.

- Denny at Pelican Parts

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Page last updated: Mon 1/22/2018 02:13:50 AM