help identifying this piston

[DanielRobert]

I need help.... not mental help , but piston help. I have  flat top pistons that came with a 440 block I have. Stamped 3671223 and then an os after that. Nothing thats stamped for an overbore on them.
Inside the piston its got that same number on one skirt and the number C4969 on the other skirt. Can anyone tell me what these are? They do not slide into my 71 440 block that has a standard bore but will slide in(tight) to the 440 motor that I got the pistons with. I believe that block is bored but my Harbor Freight digital micrometer says something different each time i measure the bore.

Please help!!

thanks, Dan

[70 sublime]

Does that say the letters OS

Or

The numbers zero five 05

[DanielRobert]

it really looks like an OS to me and the same with the inside number....did they ever make a .050 piston?

[Kern Dog]

That is an OS.
No aftermarket piston company used a part number like that or machined the piston that way. These could be factory replacement pistons from many years ago. Tracking down the number through a Google search may turn up something, maybe it will not. The internet is only as good as the information others have shared.
Good luck. 

[John_Kunkel]

I believe that block is bored but my Harbor Freight digital micrometer says something different each time i measure the bore.

HF makes an inside digital mic? Exactly what measuring tool are you using?

All of your questions (piston/bore size) can be answered by using the correct precision measuring instruments.

[DanielRobert]

Using a telescoping gauge tool then mic'ing it with the lousy HF digital gauge . I know it's a cheapo tool but I fell for the whole accurate to .0001 deal. One thing I do know is the piston won't fit into my standard bore 440 and will slide into the 440 which I have no clue(yet) how far over bored it might be. And the standard bore 440 has clean bores opposed to the unknown 440 that has over spray in the bores. I'll figure it out but need to know if this piston would work in the over bored block. The piston end ring gap isn't giving me any clues either.
Thanks guys

[BSB67]

You should be able to make a relative good estimate using a ring to measure end gaps in both blocks to determine the bore dia. difference between the two blocks.

And measure the compression distance to get an idea of compression ratio

[69rtse4spd]

Any markings on the front pad of the 440. Need inside telescoping mikes, then outside mikes to get a true I.D. reading.

[DanielRobert]

Which begs the question....how much bigger is the bore than the piston? Example; a .030 bore would be 4.350 so the piston would measure what? How much smaller are they than the bore? That'd determine a lot. The ring  end gap on the piston in the bored 440 is a whopping .047(feeler gauges used) but the same ring in the unbored 440 is at .016     The piston was used in the bored block to square up the ring but wont fit in the unbored block.  Doesnt make any sense. Seems like someone was trying to use stock rings on a bigger piston. I'll get the proper tools to measure everything but need to know what size the piston is in any given overbore.  .005 smaller? .010 smaller?

[Challenger340]

Which begs the question....how much bigger is the bore than the piston? Example; a .030 bore would be 4.350 so the piston would measure what? How much smaller are they than the bore? That'd determine a lot. The ring  end gap on the piston in the bored 440 is a whopping .047(feeler gauges used) but the same ring in the unbored 440 is at .016     The piston was used in the bored block to square up the ring but wont fit in the unbored block.  Doesnt make any sense. Seems like someone was trying to use stock rings on a bigger piston. I'll get the proper tools to measure everything but need to know what size the piston is in any given overbore.  .005 smaller? .010 smaller?

Usually the recommended "clearance" is built into the Piston for a particular OverBore size ?

For example:
A .030" CAST Piston for a .030" Over Bore(4.350") will measure somewhere around 4.3475" to 4.385" with a recommended running "clearance" of .0015" to .003" ?  
But that's why it's also so important to measure all 8 Pistons in a set and verify their sizes ? because although "usually" SETS of 8 are fairly consistent within .0005" from smallest to largest.... not uncommon to find one or two over .001" bigger than the rest which needs extra clearance Honed in it's Cylinder to prevent being too tight and scuffing.
and as expected,
the amount of "Clearance" built into Pistons is also dependent upon the Piston Material and Construction design ?
CAST, Cast Hypereutectic, 4032 Alloy Forgings, 2618 Alloy Forgings, Cam & Barrell design, Slipper Skirt, and on and on....
with
Recommended "adjustment" to that BASE Piston to Wall clearance recommendation that's built into the Piston, by ADDING .001" to .003" clearance to be performed by the Machinist during Honing according to the application ? Ie: Nitrous or Boost ? Compression Ratio ? Expected rpm's ? Fuel ? Skirt length ?

Not uncommon to find 2618 Alloy Forgings that measure 4.3450" intended for a 4.350" Bore with a recommended .005" Clearance, but because the Guy is running at 7,000 rpm with 12:1 C.R. ? we end up "fitting" them @.0065" to .0070" in the Bores we Hone to 4.3515" or 4.3520".
Of course hence why we also use .005" over "File-Fit" Rings to SET the ring end gaps on the Extra Clearance dimension Engines ? Ring Sets marked 4.350"+.005"

Clear as mud right ?

[c00nhunterjoe]

Which begs the question....how much bigger is the bore than the piston? Example; a .030 bore would be 4.350 so the piston would measure what? How much smaller are they than the bore? That'd determine a lot. The ring  end gap on the piston in the bored 440 is a whopping .047(feeler gauges used) but the same ring in the unbored 440 is at .016     The piston was used in the bored block to square up the ring but wont fit in the unbored block.  Doesnt make any sense. Seems like someone was trying to use stock rings on a bigger piston. I'll get the proper tools to measure everything but need to know what size the piston is in any given overbore.  .005 smaller? .010 smaller?

Usually the recommended "clearance" is built into the Piston for a particular OverBore size ?

For example:
A .030" CAST Piston for a .030" Over Bore(4.350") will measure somewhere around 4.3475" to 4.385" with a recommended running "clearance" of .0015" to .003" ?  
But that's why it's also so important to measure all 8 Pistons in a set and verify their sizes ? because although "usually" SETS of 8 are fairly consistent within .0005" from smallest to largest.... not uncommon to find one or two over .001" bigger than the rest which needs extra clearance Honed in it's Cylinder to prevent being too tight and scuffing.
and as expected,
the amount of "Clearance" built into Pistons is also dependent upon the Piston Material and Construction design ?
CAST, Cast Hypereutectic, 4032 Alloy Forgings, 2618 Alloy Forgings, Cam & Barrell design, Slipper Skirt, and on and on....
with
Recommended "adjustment" to that BASE Piston to Wall clearance recommendation that's built into the Piston, by ADDING .001" to .003" clearance to be performed by the Machinist during Honing according to the application ? Ie: Nitrous or Boost ? Compression Ratio ? Expected rpm's ? Fuel ? Skirt length ?

Not uncommon to find 2618 Alloy Forgings that measure 4.3450" intended for a 4.350" Bore with a recommended .005" Clearance, but because the Guy is running at 7,000 rpm with 12:1 C.R. ? we end up "fitting" them @.0065" to .0070" in the Bores we Hone to 4.3515" or 4.3520".
Of course hence why we also use .005" over "File-Fit" Rings to SET the ring end gaps on the Extra Clearance dimension Engines ? Ring Sets marked 4.350"+.005"

Clear as mud right ?

Crystal, but you could have summed it up by saying its different from a street car to a race car and cast thru different alloy pistons.

[DanielRobert]

Which begs the question....how much bigger is the bore than the piston? Example; a .030 bore would be 4.350 so the piston would measure what? How much smaller are they than the bore? That'd determine a lot. The ring  end gap on the piston in the bored 440 is a whopping .047(feeler gauges used) but the same ring in the unbored 440 is at .016     The piston was used in the bored block to square up the ring but wont fit in the unbored block.  Doesnt make any sense. Seems like someone was trying to use stock rings on a bigger piston. I'll get the proper tools to measure everything but need to know what size the piston is in any given overbore.  .005 smaller? .010 smaller?

Usually the recommended "clearance" is built into the Piston for a particular OverBore size ?

For example:
A .030" CAST Piston for a .030" Over Bore(4.350") will measure somewhere around 4.3475" to 4.385" with a recommended running "clearance" of .0015" to .003" ?  
But that's why it's also so important to measure all 8 Pistons in a set and verify their sizes ? because although "usually" SETS of 8 are fairly consistent within .0005" from smallest to largest.... not uncommon to find one or two over .001" bigger than the rest which needs extra clearance Honed in it's Cylinder to prevent being too tight and scuffing.
and as expected,
the amount of "Clearance" built into Pistons is also dependent upon the Piston Material and Construction design ?
CAST, Cast Hypereutectic, 4032 Alloy Forgings, 2618 Alloy Forgings, Cam & Barrell design, Slipper Skirt, and on and on....
with
Recommended "adjustment" to that BASE Piston to Wall clearance recommendation that's built into the Piston, by ADDING .001" to .003" clearance to be performed by the Machinist during Honing according to the application ? Ie: Nitrous or Boost ? Compression Ratio ? Expected rpm's ? Fuel ? Skirt length ?

Not uncommon to find 2618 Alloy Forgings that measure 4.3450" intended for a 4.350" Bore with a recommended .005" Clearance, but because the Guy is running at 7,000 rpm with 12:1 C.R. ? we end up "fitting" them @.0065" to .0070" in the Bores we Hone to 4.3515" or 4.3520".
Of course hence why we also use .005" over "File-Fit" Rings to SET the ring end gaps on the Extra Clearance dimension Engines ? Ring Sets marked 4.350"+.005"

Clear as mud right ?

Well, not so bad...hard to get my head around this but I'm beginning to think that since I can't identify exactly  what my pistons are or what size they
re supposed to be, I 'm better off buying new ones. BAM! another $500.00 which I'm trying to avoid.

Thanks for the info

[John_Kunkel]

You're giving up too easily. Do you intend to use the pistons in the standard bore block or the block they came out of?

Measuring the piston skirts and compression height will tell you all you need to know about the pistons. If you're not confident of your measurements, take a piston to the local machine shop and have them measure it. They'll probably do it for free; even if they charge you, it'll be cheaper than a new set of pistons.

As an aside, if the pistons seem to be too tight in the block they came out of there's probably a carbon ridge at the top of the bore, clean it off. In very rare cases I've seen stock cast piston skirts bent out by the simple act of laying the piston/rod assembly on the piston top and allowing the rod to fall over on the inside of the skirt from its own weight....remember, stock clearance can be as little as .0005".

[DanielRobert]

yep, piston is a factory .020 oversized. Thus the OS after the part number.
Duh on my part , but these Mopars are new to me.