390 crank ID
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Laughing Gas
Joined: Jul 2012
Posts: 998
Likes: 3
From: North Pole
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
also if I do have a 390 crank will 360 rods work with the 390 crank?
thanks
Tim
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
Likes: 785
From: Simi Valley, CA
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.
The builder told me to look for a 2T or a 2U stamped in the crank.
1968/76 F100/350 360/390: The bore is the same (4.05"), the stroke is different. 360: 3.50" / 390 = 3.78."
Hotshot
Joined: Apr 2009
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From: Stanley, VA
How are you measuring the stroke?
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Laughing Gas
Joined: Jul 2012
Posts: 998
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From: North Pole
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
Hotshot
Joined: Apr 2009
Posts: 14,333
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From: Stanley, VA
Are you measuring this directly in the bore with the head off or are you measuring through the spark plug hole?
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Laughing Gas
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Cargo Master
Joined: Jun 2014
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From: Central Florida
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.
Elder User
Joined: Jan 2014
Posts: 898
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From: Chillicothe, IA
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.
Cargo Master
Joined: Jun 2014
Posts: 2,216
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From: Central Florida
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.
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Laughing Gas
Joined: Jul 2012
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From: North Pole
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.
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