390 crank ID
 

So I need some help identifying this crank that is in my truck. The builder told me it was a 390 but after tearing it down to the block and crank I'm not so sure. How/where is any part numbers on the crank that will help me identify it? The builder told me to look for a 2T or a 2U stamped in the crank. Not sure I can trust him cause the stroke is 3.50 and the bore is 4.05 so I'm pretty sure it's a 360 and he just tried to take my money. Any help would be greatly appreciated.

also if I do have a 390 crank will 360 rods work with the 390 crank?

thanks

Tim

2U or 2UA is 390, the "T" is a 360 crank.
The 360 rods are too long to use on a 390 crank.

2T = 1965/67 352 & 1968/76 360 / 2U = 1966/72 390.

1968/76 F100/350 360/390: The bore is the same (4.05"), the stroke is different. 360: 3.50" / 390 = 3.78."

Thanks guys. So I have a 390 crank cause I found the 2U stamp but the stroke is still only 3.50. How can that be? I'm confused

Measure again, a 2U or 2UA crank is going to have 3.784" stroke.
How are you measuring the stroke?

Well my micrometer batteries died so I turned the crank until the piston was all the way at the bottom of the stroke and them had to use a tape measure. It was 3 1/2" to the top of the hole. I did that on all the holes so I don't think I did it wrong but I might have. Going to get new batteries tomorrow and make sure but

Are you measuring this directly in the bore with the head off or are you measuring through the spark plug hole?

In the bore with the head off. The engine is out of the truck and on the engine stand.

Micrometer batteries...

What kind of BS is that? /jk Sounds like blinker fluid or left handed crescent wrench!

With the heads off, a straightedge and a tape measure should be sufficient. The only tricky part is getting the engine to TDC and BDC (stroke = TDC-BDC). The harmonic damper should have a mark for TDC for Cylinder #1 and BDC is 180º away from that. Stroke = BDC - TDC.

A regular tape measure is not accurate enough for this stuff. It is made for carpenters and has built in tolerances for saw blade kerf. A micrometer or ruler is what is needed. And not a school ruler but a machinists ruler.

The 390 has a stroke of 3.784 whereas the 360 has a stroke of 3.500, a difference of 0.284 which is just a tad larger than 0.25 or 1/4" Thus, even a crude school ruler can be used to discern the difference between a 360 and a 390. There is no in-between. It's either one or the other IF it is a FE engine.

I guarantee its an FE engine. This ain't my first rodeo with FE ' s. Just don't understand the stroke measurement that I am coming up with. Either way the crank is a 390 so I know you can't intermix rods so it is what it is. I now realize I got screwed on the build and will have to start over. Thanks for yalls help.