Old Arias Forged Piston-to-bore Clearances?

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nm9stheham

nm9stheham

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Hey all,

I am taking a long shot that someone in this knowledgeable crowd might have some old Arias piston experience. I have a set of old Arias forged pistons that are probably 15-20 years old, that I am planning on putting in a block for street use (not a Mopar, but Opel 1.9L). I have had them over a dozen years. I'll take a wild stab that these were custom machined off of castings for Chevy 305 pistons... the piston diameter is 3.680".

My machinist and I are debating the clearance to run... my only experience in using forged pistons in this particular engine was with the old TRW and Hepolite's and I would run them at .0035 to .004" with no issues rallying. He is thinking more like .006", which I don't like for just running around on the street.

Under the crown they say 'Arias' and 'Alcoa' and '40' in cast letters. The material coloration is bright aluminum, rather than any sort of light grey like the old TRW's were, so IDK on the actual material. And, there are no steel strips in the skirts to manage expansion like in the old TRW's. So any ideas on the piston-to-bore clearance would be appreciated.

Thanks!
 
I have some NOS Cleveland Arias pistons. I was just gonna set um up at the old TRW spec of like .004-.0045. and be done with it. They'll be fine.
 
MOPAROFFICIAL said:
Somewhere .0045-.006 is where I'd run them.
You could run the TRWs up to .008 and be fine.
Click to expand...

And I HAVE! I've run some old TRWs at .010 before because the block I had was .060 and needed boring again. I honed it and had at it. It ran damn good.
 
Thanks guys.... and if it makes any difference.. the casting blank style is like a so-called 'round forging' type, as shown in the current CP-Carillo piston catalog. (Who bought Arias a couple of years ago.)
 
The clearance should really be built into the piston, not the bore.

The piston size is nominal. The bore size is actual.

If you have a piston for a 4 inch bore, that is nominal. The bore should finish at 4.000 plus whatever extra you think you might need.

The clearance would then be what the piston diameter is.

For example in the above situation, the piston may measure 3.996 and at a 4.000 finish you'd have .004 clearance.

That's why piston size is nominal..as In Name Only. The bore size is actual because that is how displacement is calculated.

Unless you measure your pistons and they measure actual bore size. But I doubt they will.
 
Roger... the shop has the pistons so will set the bore for clearance from whatever they actually are. I found them to be 3.680" (1" from the skirt bottom IIRC).
 
.020" over 3.660 = 3.680"
I gotta say I just threw a good set of calipers on them and verified if they were .020 over or what. So my number is not to .0005" accuracy.

FSM lists:
Standard bore at 3.659-3.660"
Standard piston clearance, nominal at .0014" (bottom of skirt)
 
Aria's pistons are 2618 aluminum. I ran my Ford dirt motors with Aria's at .004-.005.
 
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