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Subaru Idler Pulley

Saturday, January 29th, 2011

About 200 miles ago (at 127k) I had some engine trouble with my '99 Legacy Outback. It was a normal Sunday with a trip to Wegmans. We took my car because it's easier to get the groceries in and out with the hatch-back. The trip there was uneventful and we made it all the whole way home and into the garage. I backed in a little too far to open the hatch, so I got back in the car and started it up to move forward a bit. The engine made a terribly loud rubbing/friction noise.

After lunch I took another look and it made the same noise. I was hoping it was an external part like the alternator, power steering pump or air conditioning compressor. These components are all run off a couple belts on the front of the engine, and are not necessary for the engine to run, so I took the belts off and started the engine praying that the noise was gone. It wasn't. After a couple tests the engine actually gave up on life and refused to start. I could still hear the noise while the engine was cranking, so I could tell it was an internal problem and totally out of my league. It also didn't help that it was 12° outside.

After much discussion with my dad and consultation with the factory service manual I have we thought it was something related to the timing belt, like an idler pulley that routes the belt. If you're not familiar, the timing belt keeps the valves synchronized with the pistons. This made me very nervous because this is an interference engine and if that belt jumps even as few as 3 teeth, pistons will collide with valves causing major internal damage. While I was wasting time trying to fix it myself I did see a single ball-bearing on my garage floor right below the engine. I was hoping that was just a coincidence and not part of a bearing that let go.

timing belt schematic

timing belt schematic 2

I had the car towed to the closest Subaru dealer, Van Bortel Subaru in Victor. It kills me to have a car towed and even worse to a dealer, but Subaru's are little strange and I'd rather have people who know exactly what they're doing fixing my car. That and their labor rates were only a little more than other shops in the area.

As it turns out, it was an idler pulley. When the engine was running and making the noise, the bearing was failing but still intact, but at some point it let go and caused the belt to jump a bit, hence the engine not starting after a few tries. The bearing basically exploded sending shrapnel around that part of the engine causing a little damage to a few parts. At the end of the day it needed a new timing belt, a couple cam shaft sprockets, the failed idler cog, the hydraulic tensioner mount and a few oil seals. Over $1000, sigh.

idler cog and bearing separated

This is the idler cog that failed; the bearing complete separated.

hydrolic tensioner

I'm not exactly sure why they changed this hydraulic tensioner. Perhaps the bearing on the pulley was on its way out. I also recently found out that there was a problem with these things in a certain year range not keeping proper tension and causing belts to jump.

camshaft sprocket

camshaft sprocket 2

These two sprockets are made of plastic and got damaged more than some of the metal parts. I'm sure this would have shredded the belt over time. From what pictures I've seen they look like the right (passenger) side intake and exhaust cam shaft sprockets.

I found a video on youtube that showed this exact part the engine and talked about these pulleys. I thought it was very interesting:

The guy at the dealership said he had only seen this scenario a couple times in many years and said the other idlers looked ok, so they only changed the one. I had asked about possibly changing all of them since they were already in there, but they said they didn't think it was necessary and since they were charging over $100 each, I decided to stick with just the new one. I'm hoping this gamble pays off and doesn't bite me in the ass.

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