ID flathead

I'm going to look at what is supposed to be a '53 Merc motor. It's all together. How can I tell if it is a 53 Merc or something else...Ford 50 or who knows with out tearing it down? Numbers, markings? Thanks

 

It is just about impossible to tell externally. Only way to know for sure is to measure the stroke.
Pull a head or the oil pan and measure the stroke. Only way to know for sure.
If the seller won't allow you to do that, assume it is Ford(3 3/4" stroke) Merc is (4")

 

stick one of those 1/2 measuring tapes down in the spark plug hole. let it go all the way to the bottom mark it, then let it come all the way up and mark it. measure the diff.

 

Can't do that on a flathead 'cause the plug locates over the exhaust valve.

As Carter stated, it's impossible to know for sure without measuring the stroke. I've torn down several "Mercs" that had Merc heads, intake, B&B clutch, etc, only to have a Ford crank. Pay low, or have the heads removed to see any obvious damage/cracks, and to easily measure the stroke.

 

Thanks guys. Thought I had it bought if I wanted it and now the guy says he may put it in a truck he has. I will pull heads if I get the chance to buy.