My starter went out and when i replaced it it keeps hitting the fly wheel. a friend said he thinks the that ignition is not letting it disengage?

Check and test for a failed bendix gear in starter --flywheel damage or motor seized

There is no way the ring gear will hit the starter pinion unless the fly wheel bolts on the crank shaft or loose allowing the flywheel to run out of true. If you have had clutch/ rear seal work done lately the fly wheel will only fit in one position and if that was ignored at some time then the fly wheel will run out and touch the starter pinion.. I would also check the adjustment on the starter pinion as it has to be set by the lever pivot to a correct distance or it will touch the teeth of the ring gear

It sounds like the "bendix drive" is gone in your starter. This is the assembly that engages and disengages the starter to the engine. The only way to fix the problem is to replace the starter. Hope this helps.

the metal on metal noise is the starter hitting the fly wheel. it just need to be adjusted there are shims to add

There is a spring which may be weakened or broken that retracts the gear. Only a service will fix.

there is a starter relay that may be sticking, keeping the starter engaged. And also not letting it start.

Its a solenoid...it engages the bendix and truck starts...bendix should retract because power to it gets shut off by ignition switch going to "run".

Only way bendix would stay engaged or get a signal to keep turning ???
Bad contacts in ignition switch...maybe ??
Start relay in under hood power distribution panel has hot or welded contacts ?

I've gotta think about this one...hope this gives some help...

that means that the starter is not the right one and the fly wheel is hitting it or the starter is not fully disengaging or it is loose and again is being hit by the fly wheel.

sounds like the starter is not disengaging the fly wheel quickly like it should when you turn the key the starter cog connects upto a fly wheel that has teeth all around it when the teeth of starter cog connect between teen on wheel it spins it to crank your car then goes back to starter if you hold your key on after starting the noise you hear is the starter cog(teeth ) still engaged in wheel if this is the sound it needs to be serviced not neccassarily replaced

You may need to shim the starter and I would have the starter tested.It is not uncommon to purchase a faulty elecrical part of any type from a part store.