The bolt on the crankshaft is a 27mm or you could use a 1 1/16". I personally would consider having the chain changed at that mileage as a preventative repair. Also replace the tensioner assembly. I would not consider a chain replacement "light engine work", so you might let a qualified tech do this repair.
Just my opinion.
14 year MB tech
7 year shop foreman @ independent MB/Volvo shop