390 Internal or external balanced
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Mountain Pass
Joined: Jun 2006
Posts: 147
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From: Forestport, NY Adirondack
390 Internal or external balanced
I just pulled an early 70's 360 from my panel truck. I am replacing it with a rebuilt 390. Problem is... i rebuilt the 390 2 years ago and have forgot wich bottom pulley to use. The 360 had a harmonic balanced pulley. The pulley I have for the 390(I think it goes to it) does not have the balance weight on it. I think 390 to be around 1976 or so. The one on the right is 360 and the one on the left is what I think goes to the 390.
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
Both the 360 and 390 are internally balanced. The only externally balanced FE's are the 410 (Mercury only) and the 428. Those use an external balance on the flywheel. The 428 SCJ uses an external balancer at the front too.
The harmonic balancer you want to use is the one on the right. That's the same one my '73 390 has. The one on the left looks to be passenger car maybe.
The harmonic balancer you want to use is the one on the right. That's the same one my '73 390 has. The one on the left looks to be passenger car maybe.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Does that particular balancer type have the rubber sandwich between the steel outer weight and the cast part?
I cheaped out at the end of my F100 engine rebuild years ago and reinstalled a junkbox damper, and that caused me a fair amount of grief. The timing marks were way, way off for one thing. Jus' sayin', if this is the case a rebuilt engine, really deserves a fresh balancer.
I cheaped out at the end of my F100 engine rebuild years ago and reinstalled a junkbox damper, and that caused me a fair amount of grief. The timing marks were way, way off for one thing. Jus' sayin', if this is the case a rebuilt engine, really deserves a fresh balancer.
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Mountain Pass
Joined: Jun 2006
Posts: 147
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From: Forestport, NY Adirondack
Thanks for the info. I am pretty sure the 390 came from a later 70's truck. According to the previous owner. The 360 I found in a junk yard for a 100 bucks with the t-18 tranny. I know nothing about it, just it smokes more than my aunt Ethel. As for rubber in between, I don't see rubber. Looks to be bolted solid.
Hotshot
Joined: Jul 2005
Posts: 13,834
Likes: 25
From: Middle Tn.
Both the 360 and 390 are internally balanced. The only externally balanced FE's are the 410 (Mercury only) and the 428. Those use an external balance on the flywheel. The 428 SCJ uses an external balancer at the front too.
The harmonic balancer you want to use is the one on the right. That's the same one my '73 390 has. The one on the left looks to be passenger car maybe.
The harmonic balancer you want to use is the one on the right. That's the same one my '73 390 has. The one on the left looks to be passenger car maybe.
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Mountain Pass
Joined: Jun 2006
Posts: 147
Likes: 0
From: Forestport, NY Adirondack
Now you got me wondering if the 360 is a 360. Maybe I should pull the pan and make sure it's not a something else. It makes me wonder since someone took the time to pull this engine and it smokes pretty bad. Maybe it's not a runofthemill 360.
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FTE Leadership Emeritus
Joined: Jul 2002
Posts: 42,561
Likes: 421
From: Long Island USA
Check everything 
I once took a rebuilt 360 out of my highboy that my brother rebuilt. He swears it was the original factory motor that he rebuilt.
"Knowing" that a 390 and a 360 are both internally balanced, I reused that flywheel to build a 390, and after I got it all together and in the truck, I started it up to find I had a REALLY BAD vibration.
Turned out, the flywheel had the big ugly weight on it for an FT. By this time, the 360 crank I had was gone to the crank grinder's for a core, so I never went back and found out exactly WTF was going on.
But somehow, that 360 that my brother redid turned out to have an externally balanced flywheel. Again, it was factory - he bought the truck brand-new and KNEW it was what it was.
How the heck a 361FT crank wound up in that truck, who knows. But it was real.
Moral of this story: CHECK EVERYTHING. Never assume.
I once took a rebuilt 360 out of my highboy that my brother rebuilt. He swears it was the original factory motor that he rebuilt.
"Knowing" that a 390 and a 360 are both internally balanced, I reused that flywheel to build a 390, and after I got it all together and in the truck, I started it up to find I had a REALLY BAD vibration.
Turned out, the flywheel had the big ugly weight on it for an FT. By this time, the 360 crank I had was gone to the crank grinder's for a core, so I never went back and found out exactly WTF was going on.
But somehow, that 360 that my brother redid turned out to have an externally balanced flywheel. Again, it was factory - he bought the truck brand-new and KNEW it was what it was.
How the heck a 361FT crank wound up in that truck, who knows. But it was real.
Moral of this story: CHECK EVERYTHING. Never assume.
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Lead Driver
Joined: Aug 2003
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From: Boulder Creek, Ca
Not an authority, perhaps by posting the crank pulleys' casting #'s a more knowledgeable member than I am can narrow it down, when all is done the pulleys; crank, as well as accessories, should be a match set?
Cargo Master
Joined: Jun 2014
Posts: 2,212
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From: Central Florida
Here's a good primer on FE crankshafts from DIY Ford: Ultimate Ford FE Engine Crankshaft Guide
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