I got a knock about mid thorttle at low rpms eveything is fine the motor is smoking so I think the rings are bad but at about mid thorttle I got a knock sounds like around bellhousing or bottom end dont really hear it when I just rev it up but when cuising down the highway about 60 then all of a sudden it will start knocking and doesnt stop untill I slow down, any clues on this?

 

This is almost always cause by the vacuum advance holding the timing to far advanced. Pull the hose off the vacuum unit and if it stops doing it, try changing the unit or if it an adjustable one back down the advance. The spring gets weak and allows the unit to over advance the timing.

 

Is the truck a manual or auto trans??

 

Why would that matter?

 

With the engine on, pull on spark plug wire on the distributor at one time, rev the engine to half throttle, listen for engine knock, and put spark plug wire back on distributor. Do this with every spark plug wire on the distributor and note which cylinder or spark plug wires removes or eliminates the knock. Post your results.

 

How is he suppose to do this a 60 mph going down the highway, which is when the engine knocks? This is not a mechanical engine problem, but an ignition problem causing a high speed knock, or in reality a to far advanced ignition timing.

 

Would this advance ignition timing creating a knock during acceleration and would a timing advance problem should not knock during deceleration. I was thinking the problem was internal, but the timing should be fairly easy to check.

 

The truck has a 4 speed in it and its 2wd. the motor has race heads dont know the specs for them and the block is bored 60 over no stroker though. It has points and the vacum advance is hooked to the timed port of the carb. everything else is stock that I know of the knock has did it ever since I had but it just a steady knock at a certain rpm if I rev past it it seems to go away and it doesnt seem to matter if it has a load or not. just as long as it is in gear I dont know if it is because a little load from eveything moving or what also the motor shakes pretty good at idle but smoothes out if it revs up a little thought it was a miss but every things seem to be firing. runs good driving lots of power no miss just that knock. Sorry this was alot I know

 

Go bad and read 78fordranger's original post. Doesn't do it except at highway speed, hence not a mechanical engine problem.

 

I was thinking of a flexplate problem(crack, loose bolt), but good point about the steady speed.
Besides I wanted to know!

Could it be the mechanical advance sticking after advancing, then in addition to vacuum advance causing the knock??

 

Possible, but I had this problem with my 460 and it was the advance unit.

 

Yup, does sound like a flex plate. Have you checked the timing.

 

Had a broken flexplate (428CJ in a Torino Cobra no less) and they make noise whenever there is a light load, until they get super bad. Never sounded like a knock either.

 

It could be the notorious FE wristpin knock.

 

At 60 mph cruise only, I think not.