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Old 09-03-2019, 10:17 AM #1
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Serp belt system drama

Sharing info and looking for thoughts. Last Saturday the truck started making a chirping noise on cold startup, which deteriorated into a full-time squeal. Spraying water on the serpentine belt killed the noise temporarily while the belt was wet, ruling out lack of tension. Switching AC on and off had no effect on the noise.

The belt and 3 idler pulleys are ~1 month old, replaced early August while troubleshooting a noise which turned out to be unrelated. Belt and idlers are Toyota parts except for the tensioner which is a Delco part (bad decision on my part) installed during the timing chain replacement in July 2018. The belt is the Tacoma part# which is made by Bando and costs ~1/2 of the 4Runner part.

Round 1:
I removed the belt and checked all pulleys for wobble and abnormal rotation. Found one of the month-old upper #2 idler pulleys (passenger side near power steering pump) was shot. Detectable wobble while hot and bolted to the engine with the belt off, and abnormal resistance to rotation when it cooled. Replaced this with the year-old Dayco pulley I removed last month, no wobble and smooth rotation, reinstalled the Toyota belt, noise still present.

Round 2:
Thinking the belt was damaged from the bad pulley, I removed it and put the previous Gates belt which I kept as a spare back on. Noise got worse. Part # suggests it is shorter than the Toyota belt: K7P2119 for the Gates vs. K7P2120 for the Toyota/Bando belt. RockAuto and Advance Auto websites both say this Gates part is the right one.

Round 3:
Whipped out my mechanic's stethoscope and probed each pulley bolt and driven component as I should have done first. Found the noise coming from the tensioner pulley, it was grinding like a rock crusher. No wobble with the belt off. I found a Gates pulley at NAPA which can serve as either the #1 lower idler (near AC compressor) or tensioner pulley via a sleeve insert. Installed this and the Toyota/Bando belt, and no further noise.

So...the Delco tensioner has been on the truck since July 2018 with ~30K miles of use with the shorter Gates K7P2119 belt. I then install new Toyota idlers and correct-length belt, and the tensioner pulley bearing fails in 4 weeks and ~2K miles of use. And then there's the new Toyota idler developing a bearing failure, with the correct belt on. Any thoughts? Belt routing was verified exactly per the shop manual diagram every time. I'm thinking either crappy Delco pulley bearings (it has 2 separate bearings pressed in), or the tensioner spring is too tight from the factory? If it trashes the NAPA/Gates pulley bearing (single bearing), the whole tensioner gets replaced with a Toyota part.

Note: Replacement of the 3 idler pulleys and belt last month was unnecessary. Exhaust bracket bolted from the bellhousing to the cat flange rusted in half and the two pieces were rubbing together when hot, chirping noise was transmitting everywhere and hard to locate.

Last edited by waypoint; 09-03-2019 at 10:19 AM.
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Old 11-25-2019, 02:56 PM #2
PJ2zero9 PJ2zero9 is offline
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Quote:
Originally Posted by waypoint View Post
Sharing info and looking for thoughts. Last Saturday the truck started making a chirping noise on cold startup, which deteriorated into a full-time squeal. Spraying water on the serpentine belt killed the noise temporarily while the belt was wet, ruling out lack of tension. Switching AC on and off had no effect on the noise.

The belt and 3 idler pulleys are ~1 month old, replaced early August while troubleshooting a noise which turned out to be unrelated. Belt and idlers are Toyota parts except for the tensioner which is a Delco part (bad decision on my part) installed during the timing chain replacement in July 2018. The belt is the Tacoma part# which is made by Bando and costs ~1/2 of the 4Runner part.

Round 1:
I removed the belt and checked all pulleys for wobble and abnormal rotation. Found one of the month-old upper #2 idler pulleys (passenger side near power steering pump) was shot. Detectable wobble while hot and bolted to the engine with the belt off, and abnormal resistance to rotation when it cooled. Replaced this with the year-old Dayco pulley I removed last month, no wobble and smooth rotation, reinstalled the Toyota belt, noise still present.

Round 2:
Thinking the belt was damaged from the bad pulley, I removed it and put the previous Gates belt which I kept as a spare back on. Noise got worse. Part # suggests it is shorter than the Toyota belt: K7P2119 for the Gates vs. K7P2120 for the Toyota/Bando belt. RockAuto and Advance Auto websites both say this Gates part is the right one.

Round 3:
Whipped out my mechanic's stethoscope and probed each pulley bolt and driven component as I should have done first. Found the noise coming from the tensioner pulley, it was grinding like a rock crusher. No wobble with the belt off. I found a Gates pulley at NAPA which can serve as either the #1 lower idler (near AC compressor) or tensioner pulley via a sleeve insert. Installed this and the Toyota/Bando belt, and no further noise.

So...the Delco tensioner has been on the truck since July 2018 with ~30K miles of use with the shorter Gates K7P2119 belt. I then install new Toyota idlers and correct-length belt, and the tensioner pulley bearing fails in 4 weeks and ~2K miles of use. And then there's the new Toyota idler developing a bearing failure, with the correct belt on. Any thoughts? Belt routing was verified exactly per the shop manual diagram every time. I'm thinking either crappy Delco pulley bearings (it has 2 separate bearings pressed in), or the tensioner spring is too tight from the factory? If it trashes the NAPA/Gates pulley bearing (single bearing), the whole tensioner gets replaced with a Toyota part.

Note: Replacement of the 3 idler pulleys and belt last month was unnecessary. Exhaust bracket bolted from the bellhousing to the cat flange rusted in half and the two pieces were rubbing together when hot, chirping noise was transmitting everywhere and hard to locate.
Ahhh that sucks that it wasn't even the serpentine belt or pulleys to start with. I've done similar things like that to find out what I was doing wasn't even close in relation to the actual problem. I think you just got a bad part, but you can check how much tension you have on the belt by seeing how much you can push/ pull the belt. It's recommended to have at least 1/2" to 1" of give from centerline.
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