Do I have a 360 or 390?

[derrabls]

I got this truck and the guy said it had a rebuilt 390 in it. From the vin number check it came with a 360 from the factory. How can I tell which one I have? Since it has been rebuilt how do I find out how much it has been bored? Thanks.

[FORDification]

The 360 and 390 blocks are identical externally. The only way of differentiating between the two, since there are no external markings to tell you what you've got, is to measure the stroke. Simply rotate the crankshaft around until the #1 cylinder is at TDC (top dead center) as indicated at the timing mark. Remove the spark plug and insert a wooden dowel into the cylinder until you hit the top of the piston and make a mark on the dowel. (Use the valve cover lip as a constant reference source.) Then remove the spark plug from the #4 cylinder (when #1 is TDC, #4 is BDC) and make another mark on the dowel. Then measure the difference. A 360 has a 3.50" stroke and a 390 has a 3.78" stroke.

A 360 can easily be converted to a 390 by swapping in the 390 reciprocating assembly (crank, rods & pistons). The 352 has the same stroke as a 360, just a slightly smaller bore.

352 (4.00" bore / 3.50" stroke)
360 (4.05" bore / 3.50" stroke) - a 352 crank in a 332-390 block.
390 (4.05" bore / 3.78" stroke)

As for checking the bore, there really isn't a way to do this with the engine assembled. I'd check with the guy you got it from and see if he still has any of the paperwork on it, or can at least put you in contact with the shop who did the work....it's possible they have that info in their records. Whenever an engine is bored out you obviously have to replace the pistons with larger versions, which are usually stamped on top as to the oversize (.010, .030, etc.) You might get lucky and be able to remove a spark plug, rotate the engine around to get the piston as close to the spark plug hole as possible, and check for that stamping on top of the piston. However, if it's been a while since the rebuild, then the top of the piston will be carboned up a bit, so it's unlikely you'd be able to see anything useful.

[derrabls]

Once again you have came through with a quick response. That is a lot better than pulling a head or taking the oil pan off, thats what other people have recommended. Thanks a lot. As everybody else says...