391 Cranks
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Post Fiend
Joined: Feb 2001
Posts: 6,624
Likes: 8
From: Missouri
391 Cranks
According to autozone they sell reman 391 cranks with the 1 3/4" snouts for $199 with matched michigan 77 bearings to go with. They also sell 390 cranks with matching bearings for $159. Has anybody used these cranks? I doubt they have been balanced and I don't know what their undersizing limits are but this is by far the best price I have seen. I just pulled the heads off of my supposed "390" and found out it is a 360. I guess the guy that sold me the truck didn't know much about the motor he put in there. Have to replace the pistons and crank anyway now I'm just a set of rods away. Anybody have a recommendation on where to get rods? PAW sells them but I would have to see if they will se ARP bolts instead of their bolts.
Senior User
Joined: Jul 2001
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391 Cranks
Let us know what you find out. I'm converting my 360 to a 390 (actually, it'll be 406 cid with the overbore) this fall and need new crank, rods and pistons, too. That does sound like a good price on the crank.
ksd
69 F100 Explorer lwb 2wd FE 360 C6 3.25:1. WANTED: straight/clean styleside long box w/aux fuel tank for 67-69 F series.
ksd
69 F100 Explorer lwb 2wd FE 360 C6 3.25:1. WANTED: straight/clean styleside long box w/aux fuel tank for 67-69 F series.
Fleet Mechanic
Joined: Jul 1999
Posts: 1,360
Likes: 1
From: Iowa
391 Cranks
Have you had your block sonic checked yet? Most FE blocks won't handle an .080 overbore. And some of those that do tend to run hot.
Jason Kendrick
1970 F100 Custom 390/C6
1978 F150 Ranger Lariat Supercab 460/C6
Jason Kendrick
1970 F100 Custom 390/C6
1978 F150 Ranger Lariat Supercab 460/C6
Senior User
Joined: Jul 2001
Posts: 109
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391 Cranks
No, but it'll be done as part of the process. 406 is the plan, but if the block won't take .080 over then I'll settle for what I can get. The engine is still in my truck right now, so I won't know until it's in the shop how big I can go. My builder has had a lot of success making 390's into 406's, though, so I trust him.
ksd
69 F100 Explorer lwb 2wd FE 360 C6 3.25:1. WANTED: straight/clean styleside long box w/aux fuel tank for 67-69 F series.
ksd
69 F100 Explorer lwb 2wd FE 360 C6 3.25:1. WANTED: straight/clean styleside long box w/aux fuel tank for 67-69 F series.
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Post Fiend
Joined: Feb 2001
Posts: 6,624
Likes: 8
From: Missouri
391 Cranks
Look for a 74-76 truck block with a mirror image of 105 stamped into them where the 352 is on your block. These blocks have better chances of going to a 4.13 bore than other 390 blocks.
Cargo Master
Joined: Aug 2000
Posts: 2,931
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From: SW Michigan
391 Cranks
Rat, I have never used an autozone crank but the price seems quite good and Michigan (Cevite) 77 bearings are a good brand. Don't worry about undersizes, the ford crank has large journal diameters and even a 030/030 crank will be fine. Some of the tractor pulling guys use a cast ford crank with the rod journals cut .300 and have no trouble. The 391 FT forging would be great but the snout is too big, and the balance would be wrong. If you want the forging it can be made to work but would require extra machine work. Doesn't autozone offer reman rods as well ? If your pitons have the tapered skirts you can use what you have. I reringed a 390 in my 71 with double moly hastings rings. Get a 'bundle of grapes' hone and glaze break your cylinder walls before using the new rings, and is this not the perfect oppourtunity to do your oiling fixes while the engine is apart ? DF
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Post Fiend
Joined: Feb 2001
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From: Missouri
391 Cranks
DF, I have a 360 right now. I thought it was a 390 but when I pulled the heads this weekend I measured a 3.5" stroke. Still have the 105 block and plan on going 60 over. Are you saying that I can run a 390 crank & rods with 360 pistons? I don't want to but it would be good info because if I remember right the 360 pistons have the tapered skirt and the 390's don't. The block is already .030 over. To get that crank at that price from autozone I need a 390 crank to trade in. Looks like I'll be making a trip to the pull-a-part to get a crank. Also autozone doesn't sell 390 rods, go figure. A local machinist said that he will sell me the rods for 8 bucks a piece, install my ARP bolts and magnaflux & balace them for $96. Since I don't think 400-450HP requires a $forged crank$ I will be getting the cast.
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Cargo Master
Joined: Jul 2000
Posts: 2,281
Likes: 18
From: Northern California
391 Cranks
That's a VERY fair price for the rods, I needed 2 extras and paid $25 each (could have bought a set for $100).
Ford mixed pistons up on the FE, some got lower sitting pistons for the truck to reduce compression. You really have to measure them to know for sure. You mentioned 30 over already, so they are likely 360 car type pistons with 8.5 or so compression.
I'd ask what the core charge is on the crank first. I paid just over $300 for a 428 crank with no core. The time and effort to find and pull a 390 crank might be too much for a small core charge.
Ford mixed pistons up on the FE, some got lower sitting pistons for the truck to reduce compression. You really have to measure them to know for sure. You mentioned 30 over already, so they are likely 360 car type pistons with 8.5 or so compression.
I'd ask what the core charge is on the crank first. I paid just over $300 for a 428 crank with no core. The time and effort to find and pull a 390 crank might be too much for a small core charge.
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Post Fiend
Joined: Feb 2001
Posts: 6,624
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From: Missouri
391 Cranks
[font size="1" color="#FF0000"]LAST EDITED ON 06-Aug-01 AT 09:48 AM (EST)[/font][p]I just found out the core charge is 25 bucks fr the cast crank and 60 bucks for the steel one. Not worth going to the junkyard over. L2291F60's will change that. Thanks for the info.
Posting Guru
Joined: Jul 2001
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391 Cranks
Don't want to step on anybodys toes here but you guys know that the 391 crank is not the same as a 390. The 391 is slightly longer in the stroke and if that is not taken into consideration you can have some major problems.
Cargo Master
Joined: Aug 2000
Posts: 2,931
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From: SW Michigan
391 Cranks
Flash, the 391 and 390 crank have the same stroke, if there is any differance, I have been unable to measure it. Rat, yes I am saying you can use 360 truck pistons (360s didn't come in cars) with a 390 crank and rods. I miked my 360 truck pistons and my 390 car pistons and the 360 piston is .005 taller. Because the FE pistons are usually at least .010 down the bore, sometimes much more, this will do nothing bad but will help quench. The L2291Fs will do fine however, and forged pistons are stonger anyway- my 421 (410 crank, 060 over 390 block) has the L2291Fs with the tops milled about .100 for the long crank. DF
Posting Guru
Joined: Jul 2001
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391 Cranks
Wrong my dinosaur friend. They are different. The 390 is 3.78 and the 391 is 3.79. Not much but enough that if deck height is critical- it ain't gonna work. Also, the main journals are not the same size. All of which can be workable but why mix it when the correct parts are available?
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Post Fiend
Joined: Feb 2001
Posts: 6,624
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From: Missouri
391 Cranks
[font size="1" color="#FF0000"]LAST EDITED ON 06-Aug-01 AT 10:02 PM (EST)[/font][p]According to Steve Christ's book the 390 crank is a 3.784" stroke and a 391 is a 3.79" stroke. A .006" increase in the stroke or a .003" decrease in clearance should not hurt anything and should help the quench like DF said. Racers use them as 390 cranks with L2291F pistons all the time and have no problems. So I guess you are both right.
Posting Guru
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391 Cranks
Let's see, the 390 is according to Ford, on the main bearing dia.2.7484-2.7492. The 391 is 2.7472-2.7480. Don't think those are the same numbers. Close and it might all work together but why try to put a 391 crank in a 390 when the parts are readily available?