I need to know how to identify a 351M or a 400.

I have read that you can put the balancer pointer at TDC so that puts the #1 piston at TDC (front passenger piston towards radiator) and that put the #4 piston at BDC.

You then remove the #4 spark plug and put a clothes hanger and try to get a measurement of either 3.5" (351) or 4" (400) by touching the piston...

IS THAT CORRECT?

Is there any other way to distinguish, like externally, It is in a 78 Ford Ranger 4wd...

Also, let's say he has a 351M, alls he would have to do is get a new crank and pistons for a 400 but he could reuse the stock rods from the 351M?

 

when #1 is at TDC #4 should be at BDC. the important thing is that you know how the cylinders are numbered?

 

If the engine has the original carb, and the tag is still on it, and/or if the dizzy is original there is a Ford engineering number on the base. Either the tag on the carb or the number on the dizzy will define (by being decoded) whether it's a 351M or a 400. Otherwise, there's not much hope visually.

 

Well how are they numbered?

Back of engine
4 8
3 7
2 6
1 5
Front of engine
??????

 

correct. passanger side front to back is 1234 and driver front to back is 5678

 

Cool, thanks...where is a code decoder if the tag is on the distributor and/or carb?