There is some inside info you need to understand the "why" here. While in Baja last week my idler pulley came off my 1985 4Runner. The replacement pulley I acquired in Guerro Negro was different in many ways. It came from a Gen3 truck (1990-1994). It did fit without any modification.

This bearing is a repeat offender and does cause problems, eventually. Figured I would post this little bit of tech for everybody.

I was able to pound out both bearings, making the bearing replaceable in both styles of pulley when the bearing takes a crap (this has been debated). The older style pulley has a snap ring retainer, the new pulley does not. The part you would acquire from the dealer when the bearing takes a dump is totally different and the bearing will not be replaceable (I saw the part on Friday). It costs $170 IIRC. When I've replaced the 6204 bearing before it was only a few bucks. I would guess the same for the 6203. Note that there are frequently additional letters after this number, depending on brand. These numbers usually tell if the bearing is not sealed, sealed on one side, or sealed on both sides. You want a bearing sealed on both sides.

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I acquired the replacement pulley from a 1985 4Runner and decided to make a side by next comparison with the newer style pulley. The pulley that was on my truck was the same as the pulley I pulled from Matt's 1985. Should be no surprise as they were both the same model year (although there are some differences). The Baja donor was from a Gen3 truck (1990-1994).

Here is what I've learned.

Old Pulley: The bearings are different, bearing size 6204, ID is 20mm, OD 47mm. It was held in place with a snap ring. This pulley rode on another part that both backspaced the pulley from the motor and filled the gap between the spindle and the bearing (no idea what it's called). You can see the part in the pic. There was also a large washer with a lock washer, and a 19mm nut holding it on. The pulley was a cast part, weighed 12 oz without the bearing (almost twice the newer), and was 64mm in diameter at the belt surface.

Newer Pulley: The bearing size was 6203, ID is 17mm, OD 40mm. The pulley rode on the spindle without an internal spacer. This pulley had a fat washer/spacer front and rear with a 14mm nut and no lock washer. This pulley was a stamped part, weighed 6.5oz, and was 73.6mm diameter at the belt surface.

Pics up at: http://ratstew.home.comcast.net/pulley/