differences between 360 and 390 (external)

[1fine69]

Hello All. Just got my first big block, though it's my third F100. My question is, the VIN says 360, though the guy I got it from says it is a 390. Is there any way I can tell, externally? Thanks!

[bobbyinpd]

you can't, you have to measure the stroke. There are instructions on here on how to do it. Welcome to the group BTW!

[kaptnkaos]

Nope... externally they are identical with no distinguishing marks

The only way to be sure what you have is to measure the stroke.
Both have the same bore only the stroke is different.
Somewhere on the forum I read how to take the measurement, but I can't remember exactly. but here are the basics
You get the cylinder on the bottom, put a stick (wooden dowel) in the hole and mark it with the pencil...
Then you bring the cylinder to TDC and mark the stick again...
Then you measure the distance between the marks, that will give you the length of the stroke.
You can shoot 390nut a PM and he can give exact details how to do it.

KaptnKA S

[DuckRyder]

Is there any way I can tell, externally?

No there are not, however it is pretty easy to tell.

Get your self a long wooden dowel.

Turn the engine to top dead center #1 cylinder.

Remove #1 and #4 plugs.

Insert dowel into number one cylinder (as close to straight up in the bore as possible, don't break it off) and mark a fixed point on the dowel, remove dowel.

Insert dowel in number #4 cylinder, mark the same fixed point. (same cautions apply) remove dowel.

measure the distance between the marks.

~3.50 = 352 or 360
~3.78 = 390 (or 427 but probably not)
~3.98 = 410 or 428

Don't get your hopes up, I would say the vast majority of FE's in these trucks are 360's. Most of them get sold as 390's due to either seller dishonesty or ignorance.

Edit, yes you can take the measurement on the same cylinder if you make sure it is a top dead and bottom dead center. I do not reccommend leaving the dowel in the cylinder while turning as more than one person has broken the dowel off in the cylinder that way. If you use the same cylinder it does not matter which one. When number one is TDC number 4 should be BDC and vice versa though.

[kaptnkaos]

Thanks for coming to the rescue DuckRyder.
I forgot about using #6 too...
{Edit:} It has been pointed out that this is supposed to be #4

that's the way that 390nut said to do it as well.
I'd been taught to use #1 for both measurements... the principle is the same.

Which part did you say "No there are not, however its is pretty easy to tell." to???
If I got my facts wrong let me know...

KaptnKA S

[DuckRyder]

Which part did you say "No there are not, however its is pretty easy to tell." to???

I edited it to make it clearer, there were no replies when I started typing, I type slowly and am easily distracted...

If I got my facts wrong let me know...

No you have em right, and you're right, the point is to determine the length of stroke, you can do that any number of ways.

As an additional note, you usually will not get an exact measurement because its difficult to get the dowel standing up in the cylinder perfectly, usually it is pretty close though.

[sideoilerfe]

The 360/390 blocks are identical, even the casting numbers. Duckryder and kaptnkaos are correct. Measure the stroke. It won't be precise but you'll get close enough to tell.

I've seen alot of trucks for sale and the seller says that they're 390s but the first thing I do is look at the vin. A=240 B=300 G=302 Y=360 (except 66 and 67 then Y was 352) H= 390.

If I see a "Y", I ask, "Is this the original engine?" if his reply is "Yes" then I call him on it.

[SteveC]

i dont know if its #6 it think its #4 but this could be wrong as well anymore i run on less than 5 hours of sleep with class and work and all.

Anywho i copied and pasted this from the "did you know?" thingy

The 360 and 390 blocks are identical externally. The only way of differentiating between the two, since there are no external markings to tell you what you've got, is to measure the stroke. Simply rotate the crankshaft around until the #1 cylinder is at TDC (top dead center) as indicated at the timing mark. Remove the spark plug and insert a wooden dowel into the cylinder until you hit the top of the piston and make a mark on the dowel. (Use the valve cover lip as a constant reference source.) Then remove the spark plug from the #4 cylinder (when #1 is TDC, #4 is BDC) and make another mark on the dowel. Then measure the difference. A 360 has a 3.50" stroke and a 390 has a 3.78" stroke.

[DuckRyder]

i dont know if its #6 it think its #4 but this could be wrong as well anymore i run on less than 5 hours of sleep with class and work and all.

You know what, I think you might be right, 1 and 6 are the valve adjustment cylinders on a low lift cam.

Stand, by and let me double check...

[DuckRyder]

It is #1 and #4, which is a good thing because #6 ain't easy to get to.

What I get for going on memory I get different procedures mixed up.

[sideoilerfe]

...#6 ain't easy to get to.

What???

Yes it is.

[DuckRyder]

...#6 ain't easy to get to.

What???

Yes it is.

Are we gonna do this again?

No it ain't,

not with power brakes, and with CJ valves and a big cam all you'll be measuring with a dowel on #6 with #1 at TDC is how far it is from the backside of the valve to your measuring point....

[DBossMan]

You can distinguish between a 360 and 390 if you have an automatic trans and you are willing to pull the cover plate that gives you access to the bolts that connect the flex plate to the torque converter.

The 360 has a big half moon shaped cutout on the crankshaft flange.

The 390 does not.

Tim

[SteveC]

whats in the way of #6 making it hard to get to??? in my opinion #4 is the hardest to get to espiscally if you have a brake booster, and have to learn on the fender around the hood hinge

edit never mind... like i said being sleep deprived makes me think strange thoughts

[DuckRyder]

Just in case we all have 1 fine69 completely confused, we should probably recap:

Ford cylinders are numbers 1-4 from front to rear on the passenger side and 5-8 front to rear on the driver side.

So number one is the cylinder closest to the front of the truck on the passenger side, and #4 is the cylinder closest to the rear on the passenger side.

Get your self a long wooden dowel.

Turn the engine to top dead center #1 cylinder.

Remove #1 and #4 plugs.

Insert dowel into number one cylinder (as close to straight up in the bore as possible, don't break it off) and mark a fixed point on the dowel, remove dowel.

Insert dowel in number #4 cylinder, mark the same fixed point. (same cautions apply) remove dowel.

measure the distance between the marks.

~3.50 = 352 or 360
~3.78 = 390 (or 427 but probably not)
~3.98 = 410 or 428

Don't get your hopes up, I would say the vast majority of FE's in these trucks are 360's. Most of them get sold as 390's due to either seller dishonesty or ignorance.

Edit, yes you can take the measurement on the same cylinder if you make sure it is a top dead and bottom dead center. I do not recommend leaving the dowel in the cylinder while turning as more than one person has broken the dowel off in the cylinder that way. If you use the same cylinder it does not matter which one. When number one is TDC number 4 should be BDC and vice versa though.

Sorry for all the confusion.