Probably been asked a million times before, but got to find out...

Trying to determine if I have the 360 or 390:

At a bore diameter of 4.05 the only difference between the 360 and 390 is the stroke. 360 = 3.5" stroke, 390 = 3.78" stroke.

So I decide to check my stroke to find out if i bought a 360 or 390. I pull the plug, drop a rod down, slowly turn the engine around till i get the tdc and bdc and came up with

3.98" stroke.

Thats the crank used in the 410 and 428 if i remember correctly. Is it even possible to drop that crank into the 390?

 

Yes. Its also called the Merc 410.

If your really crazy you can score a 4.25 storke crank, and that should put you around 430. It may not rev to high, but it will pull like a diesel

 

Huh. Guess it does make sense. So im running a whoppin 414cid with the .020 over bore.

Cool.

 

Just a fyi 360/390/410 block is exactly the same, just different rotating assemblies.

Nice find! It's always a good day when you discover you have 20-50 more cubes than you thought you might have. Don't see too many .020 over 410 pistons, sure it's not .030 over?

 

Wow, congratulations! Did you actually check the bore, or did you check the stroke with the heads still on it?

 

might want to make sure you have the hatchet by the balancer.

best of luck,
dp

 

I bought it from thew original owner. His memory has slipped alot, but he had the actual receipts from the rebuild in '94. Must have bought the crank someplace else because it didn't show up on the receipt. A set of .020 rings and pistons did tho.

DEEPROOTS:might want to make sure you have the hatchet by the balancer

uh-hatchet? an external lobe or something?

 

Krewat:
Did you actually check the bore, or did you check the stroke with the heads still on it?

I did a heads on measurement with a dowel from bottom to TDC, and when the number came back bigger I checked it again. same-same.


DeepRoots:
might want to make sure you have the hatchet by the balancer

No clue what the hatchet is. External crank balance?

 

crap, I couldn't find a photo.
It's an external balancer on the front of the engine. It's visible with no disassembly. If it doesn't have it, either:
1. It isn't a 410
2. It isn't balanced properly, and will not run well
3. The crank was internally balanced (VERY unlikely)

 

So it would sit behind the dampner, im guessing. I will take a look at it and get back to reply.

Is the 410 the only FE crank with the external hatchet, or was there a crank from the FT series that would fit?

 

The 410 uses the 428s 3.98" crank. So they are both externally balanced. The FT cranks are externally balanced, forged steel and have a larger diameter snout. They can be made to work by having this snout turned down to FE size. You would also have to have the correct flywheel, harmonic balancer/pulley, and timing cover. They do not however come in the 3.98" size.

 

Uh, the counterweight is only for 428 SUPER Cobra Jets. 410's and all other 428's use regular 390 style balancers with no counterweights. External balancing for 410's and 428's is done via a 28oz counterweight attached to the flywheel or flexplate. 360 and 390 and 427 engines use a neutral flywheel or flexplate.

 

ok, so where does that leave me? It could be a 410 crank internally, and there is no easy way of finding out by looking for a counterweight?

Ya I'm confused, but that dont take much...

 

Do you have an auto or manual? In other words, a flywheel or a flexplate?

 

Its the 'ol stock 4sp (in need of synchro's)