I have my 97 2wd f150 4.2. My grandpa had a new engine put in as replacement by the ford dealership and am thinking maybe they put a different year 4.2 because I’m trying to get an idler pulley but the gates one from oreillys literally fits over the current pulley so there’s no way it’s the right part. Maybe I’m wrong?

Anyways, does anyone know if the idler pulley size changes whatsoever throughout the years of 97-03?? It’s smooth not grooved btw.

 

There could have been a change depending on equipage for the year, AC etc..
A tensioner pully usually does not have groves as there is no point to having them if the belt runs on it's back side over the pully..
A different size pully may affect the belt length.

 

and something i've seen alot of is manufacturers using "common parts" meaning instead of having the OEM 3.4" smooth pulley.....might have a 3.375" grooved pulley instead. JUST because it will work!. Why make 2 pulleys when 1 CAN substitute for the other! change brand. Personally I would go DAYCO (they invented the serpentine belt ...NOT AL GORE..)

 

Went to my neighborhood pep boys instead and they took the Time actually search a little rather than the oreillys I went to and found the correct one which was identical in size. Did get the typical brand but we’ll hope for the best

 

Check out rockauto for parts.

Cheaper than the dealership, and the correct part.... AND... can usually get OE parts.

I sound like a commercial for them, but am not affiliated with them. Other than being a satisfied customer.

You get a free fridge magnet every order. I have a couple. I am sure I have lost some too.