L134 crankshaft pulley bolt socket size?

Pretty sure I've used a 1-7/16" with success, but it was just a "little" big 

just a heads up I got from an older, very experienced flat fender mechanic: beware of using a big breaker bar. Crank damage possible. But the nut zooms right off with an impact wrench and proper socket. Worked great for me.

To try to turn a stuck engine, I pull out the starter & use a pry-bar on the flywheel's starter ring. If the engine is out, I have a six foot piece of 6" angle iron that I bolt to the flywheel using the pressure plate bolts. With it, the leverage is such that you can easily break said bolts right off, so be gentle. Heck, in any case be gentle. Most folks find that a 4 foot piece of 4" angle iron is enough. I have this one for diesel engines & have never made one to use on gas engines, as I am too lazy.

Lots of time, penetrating oil, & patience is the key here. Oh & be sure that the penetrating oil gets into the cylinder & does not just flow onto the valves. The piston is offset from the spark plugs, so some kind of funnel/tube is needed to get the penetrating oil into the cylinder. I almost always pull the head so I can see where my problem is, this also alleviates the offset issue. The Marvel Mystery Oil you are using is fine, as is the Aerokriol. I have used both of them with good results.

Note: WD-40 is NOT a penetrating oil, it is a water disperscent.

Also be aware that stuck valves can stop the camshaft from turning which stops the crankshaft from turning. You could pull the valve covers & pry up on the valves to see if this is your issue, or to be clear, one of your issues. Again be gentle as the valves are easily damaged this way.

IHTH, Cpt Logger.

If it's stuck then the rings are stuck to the pistons and cylinder wall. If you force it to turn you'll probably do damage. Rings will break, score the cylinders and break ring lands off the pistons.

Pull the head off and look inside, clean the cylinders, cut the ridge if there is one, knock the pistons out, remove the rings and clean the grooves. If you're lucky, you can lightly hone the cylinders and put it back together with the minimum amount of parts.

More work I know, but if you make a hurting engine run, you're most likely going to do more damage and end up with an engine that costs more to fix. Unless a rod or piston breaks, then maybe you've ruined the whole thing.