Thread: 390 with 1U crank--> 410 , eh...pistons??

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Can anybody tell me, if there's a piston(height) difference between a 410 and a std. 390?

I'm at the start (just disassembled) of rebuilding my (to be 060 overbored) 390.

Now I read about using a 428 crank, in order to get to the 410 (like Ford did themselves with the mercury blocks), but there isn't anything about the pistons. I have a 1U casting lying here right now...

Did they (or do they still) use the same pistons in both 390 and 410? Do I get problems with compressionheight-differences or not?

thanx,
Tom

A 390 has a 10.17" deck height. A 410 has a 3.98" stroke. Both have 6.489" rods. Take the 10.17 inch deck height, subtract the rod length and one half the stroke. The remaining number will be the necessary compression height to achieve 0 deck. It is 1.691" Most pistons are going to be set no more than .025" down in the bore, so we subtract .025" from 1.691" to get 1.666" The piston you want will have a compression height between 1.666" and 1.691" I believe most pistons you are going to find will be around 1.675"

wich means i'll probably get away with regular oversize pistons...and if not a thicker headgasket would easily solve the problem if nescessary...

But you have to remember the piston wrist pin location is different for the longer 3.98 stroke. Some 390 slugs will push above deck height. It appears the low compression 360 truck pistons were indeed stock 410 pistons. The same slugs were used in some 390 truck applications. Car and truck pistons were al little different through the years compression wise. What kind of pistons do you have and what's the 390 out of ????
G.

that list actually does help a lot!
The block is a c5ae-a casting (a '65...nothing more) the pistons are hypereutectic flattops with eyebrows...

Denny good to see ya bud!!!!

Tommie those 390 slugs will stick out .080 above the deck. You can mill them and run a zero deck height. BUT it would be best to check valve clearnace for any interference especially if a performance cam is used. Then you would need to machine the reliefs back into them assuring no contact valve to piston. It might be cheaper than buying new pistons if you have a good machine shop around you. Again in mind your location and shipping costs involved....G.

okay, so I have the wrong set of pistons for the intended use...
Shit happens, but I'm not into the idea of milling those down to get zero deck height (the "bang" happens on top, that meat is there for a purpose, I don't like the idea...)

And after that, checking for valve clearance, wich sure enough will be a problem...

I'm not saying it's going to cheap, but...

The only difference between a 410 and a 390 is the larger crankshaftstroke of 3,98"...this has been a ford-factory idea for stroking up the 390...

Sure enough they didn't actually do all the work on their pistons, just to get the right compressionheight and clearances? Wich again means there is a (like stock) piston available for my intended use!

I'm not looking for special, custom made or forged pistons.... I'm looking for a set that fits...where all the above mentioned issues of clearance and compression are already solved (this was already solved in '66, so the right answer should be lying on a shelf right now!)

My hesitation in doing this myself (eh, I mean the shop) is this: the boring and checking of the oversize job is going to cost me 500...the balancing is going to cost another 1000 (remeber; talking Netherlands now ! ad up 20% for dollarprice...), and this is just that, I never mentioned hottanking, deckstraightness-check, connectingrods check and rods upper bearingjob...

My guess is, that buying a new set of pistons, is actually going to be cheaper than letting them do all that work on getting the ones I have, fit right!

anyone know what pistons, that solved the problem in '66, where used in the 410? and where to get them now?

thanx!

ow! and thanx for all the input up untill now...sure glad I brought this up!

The way I remember is the 410 had it's own specific piston. That said they were also used in all the low compression 360/390 truck engines. Thr 410 slugs lowered the truck 360/390 compression enough at the time. So you need to decide how much you want to spend. Is this a performance build or a stock type rebuild? I'm pretty sure Slivolite and Federal Mogul sell them in cast. And I know Ross or Diamond can make them forged but $$$$. I'm not sure if they are available in KB hyper applications. Let me poke around a bit and see what else is out there. BRB....G.

Okay, several hours further into the Sunday...

I checked the stroke and deckheight issues with the new crank and an old piston this morning...result?

Well, I seem to have some 2mm too much piston. (hey!, the excact height as stated by FFR428, in metric numbers that is...)

I also checked for the stock 410 merc pistons, but they'll give me no more than 8.2:1 comp.ratio....(the ones i can find, cast and hypereutectic)

And I wanted to put on some better breathing cj heads, wich lowers the compression even more since those chambers are some 4cc's larger...(as to the stock 390 heads)

Now I do have a friend, who might be able to machine those new flattops I bought!

Since 2mm doesn't look like they're really gonna mis that fat, I'm actually considdering this option....still, it probably wasn't put there for good looks, now was it?

But here's the actual question; how deep should the valve-clearance be deepended out?

Let's see if I get this right...:
stock deckhight clearance on a 410 is stated as .015" (ford performance) wich is approx. 0.4mm...(steve christ and george reid even have a clearance of .005", but I go for the worst here)
I take of 2mm (because it's at least this much too far up) and the extra 0.4mm!

This gets me to 2.4mm wich the valveclearance has to be deepended out, right?

Finishing thought on this...:
Take the piston down to zero deckheight and deepen out the valveclearance, 'till it reaches stock clearance...
Now I should have a better compression and still keep clear of the valves, right?

Ow!
Heat-expantion of the piston! how do I convert that into numbers?


Well, any help would be appreciated!
Have a nice sunday,
Tom

Just something else I noticed.....why are you boring the block .060? That will pretty much max out the block! If you have no other choice due to scoring or taper I understand but if it's just for cubes you might want to rethink that decision. ???

G.

G...
it's a "performance" rebuild...
but still keeping it on the street/strip level, not too wild (or insane)...

it's just that I have the one block and some new/rebuild parts here, like the bigger crank, the cj heads, a weiand intake, and a demon street carb, mallory ignition...

it's the pistons that are holding me up right now!
;-(

it's a block that has been rebuild in the early eighties...it's already at 030... just oversize rings will put more strain on those...

Ok I see.....off hand on V/P clearance as I remember IN- .070-.090 and EX .100-.120 as recommended. I need to confirm those though....not enough coffee yet. But that's a nice selection of parts you have. As far as the 410 slugs you found you sure on that CR??? Stock 410's from 66-67 were 10.5:1 from the factory??? Also thickness of the head gasket your using? You can run steel shim headgaskets (.018) to help but that 8.2:1 does not seem right.

G.

well...about the compression...
here's one:
http://cgi.ebay.com/ebaymotors/FORD-...spagenameZWDVW

And in the pic you see a list of available pistons from that particular company...

But I found a cr calculater later this day on the internet.
http://www.campbellenterprises.com/R...o%20calculator

Filled in the details, and depending on the total cc's going in the eyebrows, I get a calculated cr somewhere between 10.29 and 12.41 to 1...the first being quite okay, the last hugely over the top...

(details are ;72cc head, 3.98 stroke, 4.08 bore, deckheight .005, gasket .041, just the dish cc's I'm not sure of). Wich tells me a zero deckheight will render the engine useless for tapgas! (that's why I went for the stock .005 deckheight, so that's what I'll be trying to achieve, either with new or machined pistons)

I asked some sites to make me a price on a set and shipment, so maybe I know more by tomorrow...

On the overbore subject, I'm going to have the engine checked out by the shop this week...
Maybe I don't even need a new bore and can stick with the size I have (it looks very clean!like it never ran more than 1000miles after the last job...)you can still see the honework from that time (looking for the right word here, it's that diagonal cross filed/honed/whatever surface you see, when looking at the cylinderwalls)

And that leaves me with the possibility of searching for a good set of fine pistons, instead of destroying the ones I have...

Thanx for the compliment on the other stuff I bought, still a newbie actually, it's a first for me, this t-bird project!
That's why I leave the tricky bits for the professionals...just hope to reckognize something as tricky, when I stumble upon it!
greetz,
tom