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Discussion Starter #1 (Edited)
This is a follow-up howto to my post on changing the serpentine belt. After a few days with the new belt, the low-rpm squeal/chirp returned, so I figured it was time to change the tensioner out. There have been some posts on various Toyota/Lexus forums regarding premature tensioner failures, so it made sense to refresh that part.

What I didn't realize going into this project was how much of a PITA is was to extract the tensioner.

Tools you want/need:

  • All the tools needed to remove the serpentine belt
  • At least a few socket extensions (2x 6", 1x 3", etc)
  • 12mm and 14mm deep sockets (6pt)
  • 14mm box wrench
  • 3mm allen wrench
  • 8mm socket
  • 7mm socket (or an SAE around the same size)
Parts:

  • Belt tensioner (Toyota 16620-31040)
  • Optional R07 10mm O-Ring (to refresh oil dipstick tube o-ring)
  • Zip-ties
Removal procedure:

Get the car into the air, and remove the rear undertray and the passenger rear wheel & liner.

Either remove the serpentine belt, or at the very least, release tension on the belt and insert the 5mm allen key into the tensioner so that the belt can be slipped off the A/C compressor pulley and the alternator pulley.

Remove the rear seat lower cushion (held on by super grippy velcro) and place out of the way. Push up on the rear headrests and remove them. Remove the 2x 8mm locking nuts from the top of the rear seat back, and the 2x 7mm bolts at the bottom. Lift the rear seat back cushion out and place out of the way.

Using the 3mm allen wrench, remove the 10x screws and washers holding the rear access panel on, and place it out of the way. This hole gives great visibility to the alternator, A/C compressor, and ultimately is probably the easiest/only way to extract the tensioner while the engine is installed.

With the belt off the 2 pulleys mentioned, extract the 4 bolts holding the A/C compressor on. Do not disconnect any hoses or pipes. Clip any zip-ties holding wires to the hoses, and disconnect the A/C compressor electrical connectors (one near the front, and one near the rear). Rotate the compressor and extract it through the hole. The hoses should be flexible enough, but try not to kink them unnecessarily.

With the compressor out of the way, remove the lower alternator bracket. This is a great opportunity to refresh the o-ring at the bottom of the upper oil dipstick tube if yours looks as gunky as mine did. Remove the dipstick. Remove the upper 10mm (or 12mm, I forget) bolt holding the tube on and pull the tube upwards. Slip the o-ring off and replace. Work the tube back onto the lower portion and replace the bolt.

Using the 14mm box wrench, remove the front lower alternator bolt. This is pretty hard to do from the access hole, but it's not impossible. With the lower bolt out, move to the wheel liner, and assemble the 14mm deep socket, 2x 6" extensions, and the 3" extension. You can't actually remove the upper alternator bolt since the upper coolant hose is directly in the way, but you can sort of mush the hose enough to get the socket on and loosen the bolt. With the upper bolt loosened, the alternator should now be able to swing upward a little bit, and that's all that's needed to remove the tensioner.

Remove the 4 visible bolts in the tensioner using extensions and a ratchet outside of the access hole. This gives you plenty of room to apply torque and not scrape your knuckles. For the last bolt that's underneath the lower alternator mount, you'll want to put a stubby 14mm socket on it and try to apply torque from inside the hole to the left, near the front of the engine. There's not a lot of room, but there's really no other way to get to this bolt. Once loose, remove the tensioner and bolt together.

Install procedure:

Before installing the new tensioner, place it in a vise and apply tension so that you can place a 5mm allen key into the retaining hole.

Clean up the threads of the 5 bolts that hold the tensioner in place. Work some copper anti-seize into the threads and loosely fasten them. Using the extensions and ratchet, torque the 4 lower bolts on. Slip the ratchet and stubby 14mm inside the hole and torque the upper bolt as best you can.

Remount the lower alternator and place the lower bolt in and torque. Remount the lower alternator bracket. Tighten the upper alternator bolt from the wheel well, and place the belt over the pulley.

Work the A/C compressor back through the hole, making sure the hoses are routed correctly and not kinked, and none of the electrical connections are trapped in front. Tighten the 4 bolts that hold the compressor in place, and reconnect the 2 electrical connectors. Place the belt over the compressor pulley.

From underneath the car, verify that the belt is routed correctly and apply tension to the tensioner, pull the 5mm allen key out, and release. Check again that the belt is seated properly on every pulley. At this point you can fire the car up and make sure everything is working as expected.

Button up the rear access panel, the rear seat back, and the rear seat bottom. Close up the undertray and the wheel well, and remount the wheel.

Check out the album here.

Unfortunately, even after replacing my belt and tensioner I'm still getting a low-rpm chirp after the engine is warm, so I'm thinking the idler pulleys need to be replaced. Maybe yet another howto in the near future. See below from a Toyota forum (looks like you're not the only one seeing codes from slipping belts @esseye)
 

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Oh man, wonder if that means mine will show up again. Knock on wood, let's hope mine was only the tensioner.

Wonder if our idlers are in the same place - not exactly sure how the SC layout changes the belt setup, if at all other than the SC and its idler.
 

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Discussion Starter #3
From the service notes, it looks like the #2 idler pulleys are in the same location on both the NA and S. The S of course has a few more higher up to drive the supercharger.
 

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Has anyone figured out the part number interchangeability on the pulleys? Lotus does not have stock, and wants me to buy the entire upper assy for 2k.... for 4 pulleys (one of which is the squeal culprit).
 
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