I recently bought an '86 f150 4x2 with a 351w and a c6 trans. when i looked at the truck the guy said there was something wrong with the flex plate which was making an awful sound. he said it originally had a 300 6 and they put the 351w in it to make a little hot rod. well my dad said they probably put the torque converter on wrong and it was binding up and making the noise. so we took it off the flexplate and put it back on correctly and torqued the bolts to the correct specs. put it all back together and it is still making the noise. well my dad and i noticed that the flex plate was dished in the center and my dad said it should be flat for a 351w so now we think they reused the original 300 6 flexplate instead of getting the proper one. could this cause it to make this noise, is this even possible, are the two different? i dont know what to do, i dont think it's a rod because he said it ran good in the other truck it was in until they put it in this one so i doubt it magically broke a rod when they swapped it but you never know.

thanks in advace
Justin

P.S. I paid $425 for a rust free truck in Kentucky. Tell me thats not a deal.

 

Thread moved to "221, 260, 289, 302, 351w V8" Forum

 

It sounds like that would be your problem. The 300-6 flexplate looks right, will bolt up and has the right number of teeth (164) but has no imbalance weight since the 300-6 is internally balanced. The 351W requires a 28oz. imbalance, so you will get a potentially engine-killing vibration in addition to the interference problem you are experiencing. You need a 164-tooth C6 flexplate from a 351W or a pre-'81 302. (In '81 the 302 went to a 50oz. imbalance, so even though it will fit, that one won't work either.)
Also, make sure your replacement flexplate comes from an engine with a C6, the AOD flexplate is also different.

 

thanks alot i'm gonna tear it down tonight.