when i try to crank my 1987 MB 560 sl it make a metal to metal loud sound that may be coming from area of starter and it keeps that up as long as i have the key turned and it does not turn motor over

Sounds like flex plate bolts broke.it is bolted to crankshaft and tork converter.

Check your starter, as far as it shutting back off, check idol control valve

Does the starter motor just make a whining noise when you try start it? It might not be throwing in which case it needs replacing. If you hear it throw (kind of clunk) and then lock up without spinning you might have broken a tooth off of the fly wheel.