I have just finished changing motors in my pick up from a 390 to a 390 from a 66 Ltd this engine was a 2v so I put the 4v of other motor onto this one seemed to run alright however when I actually road tested it the distributor gear got eaten and motor started backfiring out the carb severely as it went out of time I had thought maybe there were diffrent dist gears but was told here there isn't . Would the intakes differ how high the distributor sits and cause this? or if the cam was changed out is there a diffrent dissy gear that would mesh proper , or are shims required , or? I don't know what cam is in this motor the oil pump is new but was installed on the previous motor without incedent. Oh yah I also replaced dist and the same thing happened as quickly ran good up till then though ? thanks for your help
ktownford
1968 F250 4x4 390

 

well its more than likely your intake u put on is not exactly like the old won, it either sits to high or low and that would result in eating up the gears on the dizzy.

 

I have heard that comp cams do not have a proper meshed gear for the FE dizzy and eats them up. Its possible that it has one of those in it if it has had any work done to it. The intake question you had is also a possibility. I have read here that some say to put the dizzy in before torquing the intake bolts down so that it gets in its groove right and does not cause any binding.

 

FE's dont locate the dist. by the intake. They pilot the block. It would take a major offset of intake to really make a difference. The big rubber seal is the only contact the intake has with the dist.

You do need to check gear height. Install the dist. and see if you can move the shaft up and down a bit. If it is binding on the block, this would cause undo wear(making it hard to turn, thus wearing the gear). I am running a block in my '69 that the spotface on the bottom of the dist. hole is ground up from this problem. I cleaned it up and made sure my distributor is not hitting it. NO problems all summer.

Larry

 

I had this problem on my 68 F100 with the same motor you have. Check the cam thrust plate. Mine was broken, and was allowing the cam to walk back and forth, and chewed up the gears on both the cam and the distributor. You will also want to check the cam bearings. I decided to forego all of that, being I had just bought the truck for $500 and could afford to drop a motor in it.