Is the timing Gears and a 1990 custom I6 have plastic gears or metal gears? and should they be replaced at anytime?
Thanks

 

Well, I don't know what it is made of, but I can tell you that on 6 cyl, they should normally be changed every 90K, or at least, that is how it is on my Eagle, I looked for timing gear sets (gear to gear timing) for your truck, but I couldn't find anything, or timing chains either.

 

It's my understanding that the gears are non-metal and have suffered some failures. Not aware of any standing mileage or age recommendations for replacement.

 

I have a 1987 F150 with the 6 cylinder. The timing gears made it 111,000 miles and then sheared off 8 teeth.... Good news though... I changed the gears and the water pump while I was there.... she fired right back up.... and I drove back home...