Arias Forged Piston Clearance ??
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Thread: Arias Forged Piston Clearance ??

  1. #1
    Opel Rallier since 1977
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    Arias Forged Piston Clearance ??

    Hey all,

    I am taking a long shot that someone might have some good info on this question. 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. I have had them over a dozen years.

    My machinist and I are debating the clearance to run... my only experience 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.

    These have no real markings.... the are flat tops, 2 eyebrows, and a raised .052" high flat dome. Under the crown they say 'Arias' and 'Alcoa' and '40' in cast letters. The material coloration is bright aluminum, rather than any sort of grey like the old TRW's were, so IDK the actual material. There are no steel strips in the skirts to control expansion. So any ideas on the piston-to-bore clearance would be appreciated.

    Thanks!

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    Member guyopel's Avatar
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    .004 if piston has oil groves in the skirt and .006 if it has the smooth skirt with floating pins.
    HTH
    Guyopel
    I have not failed - I've merely found 10,000 ways that won't work."
    ---Thomas Edison
    It's amazing what God lets man get away with when lightning is so cheap. Mark Twain

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    Opel Rallier since 1977
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    Tnx Guy. Is that from some rule of thumb, or some Arias knowledge, or where? These have grooves across the skirts, not the usual fine ones for production type pistons, but individual ones, maybe .040" wide and spaced about 1/4" apart. And floating pins.

    What is left of the Arias site is not much use anymore.... CP-Carillo bought them 3 years ago. I shoulda taken pix before taking to the shop.

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    Member guyopel's Avatar
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    I have used 3 sets of Arias piston, of that early style.
    The new design pistons now available are an improvement and I like the thinner ring designs and that has skirt and piston top coatings.
    Guyopel
    I have not failed - I've merely found 10,000 ways that won't work."
    ---Thomas Edison
    It's amazing what God lets man get away with when lightning is so cheap. Mark Twain

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    Opel Rallier since 1977
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    Ah OK, that is good. Yes these are definitely older pistons.... I have had them for more than a dezon years and got them off of eBay from what may have been an estate. So do you think these are the .004" or the .006" variety? Thanks very much.

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    Hey Manta Rallier, You can try to contact the SCTA-BNI.org (organizers of Speed Week at Bonneville). The whole Arias family were members of the Gear Grinders Club and Nick 3 (I think) is still a member. I'd ask him the next time I see him, but I'm guessing that August might be some time off your schedule! You can also try an email to [email protected] Howard is the current Gear Grinder secretary so he could forward your questions to Nick. HTH -- Doug (former Gear Grinder Secretary)

    The GG are a member club of the SCTA & BNI. Southern California Timing Association/Bonneville Nationals Inc
    Manta Rallier likes this.

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    Opel Rallier since 1977
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    Well that is going to the top! Thanks!

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    I used a lot of Arias piston and Carrillo rod combos in the latter half of the 70s, mostly 95mm bores in 1.9 blocks for rally or road racing motors.

    The rods were great, never a failure, and never even measurable deformation requiring re-sizing.

    Most of the pistons worked fine, but I did have one set that lasted only 5 minutes before expanding to the point of destroying themselves on the cylinder walls. Arias replaced the pistons, evidently they used the wrong piston blanks that had a bad expansion profile, something from their drag racing side.

    So, can't help you with the clearance required, my 70 yr old memory isn't that good, but I think they mostly were designed for smaller clearances.

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    Opel Rallier since 1977
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    I found what looked from the pix to be the identical Arias piston slugs, but cast a little larger and machined for a Porsche 928 engine. The Arias spec sheet showed .003" clearance.... BUT that 928 engine is an aluminum block V8. So for putting that piston in the lower expansion rate cast iron block, I decided it better to be in the .005-.006" range. I don't like too much clearance for the street, but I also know how these bores can distort when the head and bellhousing are attached, and I'm not using torque plate in the block when boring/honing, so better safe than sorry.

    See post #70 in tis link for the piston sheet if you are curious: https://rennlist.com/forums/928-foru...r-walls-5.html

    Thanks again for all the input!

    BTW, BruceB, have you ever posted over on RallyAnarchy?
    Last edited by Manta Rallier; 1 Minute Ago at 12:53 PM.

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