I have a little dilema. I'm sure I have a 390 but a few things don't add up.

Short story long: I'm in the process of restoring my truck, so I've basically torn it all apart, including the "390" that was in it, as it was supposed to ahve been rebuilt but I don't trust their work. The block is standard bore, but the stroke was only 3.5. Damnit. It's a 360, but has pistons skirted like a 390, and every single compression ring was busted. We have several FE's sitting around here so I decided to take a shot at another one that's been sitting on an engine cart for god knows how long, but the engine looks like a really clean engine.

As I start tearing into engine number 2, two things become apparent: this thing has never been tore down, and it must have been a really low mile example. It still had the stock rod and main bearings std (one of which is stamped Clev 11 68 with a ford logo) that were still in really good shape. So far so good, but the engine was locked up.

I pulled the heads off and the boat anchor masquerading as an intake (I have a performer to go back on it from the other engine) and what do I see? Rust. Lots of it. By the looks of it, one of the pistons had water sitting in it for a long time, and the other was fairly bad, which sucks because this is a standard bore block as well, with virtually no ring groove.

Now on to the problem. Since the engine was locked up, I found the piston that was furthest down the hole, and it measured 3 7/8 or 3.875. Judging by the pistons that were at the top, these things come up practically flush with the deck.

So now, confused since that isn't the 3.784 that I should have come up with, or a very lucky 3.984 (We do have a couple 410's around here, both in trucks).

So I put that aside and pulled the pistons out, they are stamped 390 2v. Ok, so maybe the pistons don't come up as far as they appear to. I pulled out the crank, hoping to shed some light on the situation, but no. There aren't any casting numbers on this stupid crank ANYWHERE. There is a 24, and a 3 and that's it. None of the 2U or IU or anything of the sort.


So now on to my actual question: Being that one piston was at the top of the deck, it would make sense for the one I measured to be at the bottom, right?

These pistons come practically flush with the deck, unlike on my newly discovered 360, which were a good bit down the bore. Where did the difference in measurement come from?

Also, I noticed the Rods make the rods that came out of the 360 look like toothpicks. These C7AE-B Rods sure are beefy.

The flex plate didn't have any counterweights on it that I understand is standard for a 410 crank, is it possible that I just have a 390 with a crank that isn't stamped and I'm mis-judging the deck clearence, and that's why I didn't get 3.784?

Is there any other way to identify the crank?

The only other info I have is that this engine came out of a car, and if the rod bearing number was a date, that was 11/68

Sorry for the long post.

 

The 410/428 1U and 428 CJ 1UB cranks have a unique balance pad on the 4th counterweight.

428 Cobra Jet Crankshaft Identification

Note the 428 SCJ 1UA crank does not have the same balance pad. But if the crank is a 1U or 1UB it'll have the balance pad as noted. If you can take a few pics and post them it would help.

 

In 1968, a 390 2v was an option in cars. 9.5 CR, "Regular Fuel".

Those same pistons, or pistons with those same specs in later motors I suppose, are used in the 360. The 360 piston end up down the hole due to the combination of shorter stroke, longer rod, and shorter compression height (compared to a 352). You can see all those numbers here:

FE Series Engine Specification Chart

The 360 rod is the same length, if not in fact the same part, as the 352 rod. 352 car pistons have a higher compression height, thus the 10+ CR's in some 352s.

390 pistons would be into the head with a 428 crank. Note the compression height on 410 pistons in the above link.

In cars, the 410 was 10.5 CR. Ford used the same trick in PU 390s as they did in the 360--they used the 410 piston on top of the 390 crank and rod to lower the piston in the hole and lower the compression, a standard practice for truck engines subject to hours of WOT with heavy loads.

 

Awesome, thanks for the information guys. At least I have an standard 390 crank in excellent condition with some beefy rods. Now I just need to decide which block I want to use

The 390 cylinder walls aren't worn at all, no ring groove or anything, on a std bore. it's just too bad two of them got rusty, or I'd just slap some new rings in and let 'er rip. I still haven[t given them a good honing, but I'll probably end up having to bore it, in which case it won't matter which block I use I guess... Maybe save the other block for a survival 445 stroker later on down the road.

One last question: Are the cam specs the same on the 390 and the 360? The one that came out of the truck looks brand new. Or should I get a better stockish grind from crane or comp or something?

The only thing keeping me from throwing a big cam in it in the first place is I don't want to change the valve train, or put in a stall converter.

 

That's interesting, because the pistons out of my 360 look identical to the ones that were in the 390, to the eye ball, they are just in better shape.

I don't have any problems buying new pistons, but if they are the same as the ones in the 360, could I just swap the rod and use those pistons with new rings? They dont say 390 on them, but the skirt and pin height look the same, with STD stamped on the top, so they may not be originals. If they are the same that saves me some money.

 

Cleaned up, inspected, and mic'd for size and fit in the bore, plus new rings, run 'em.