cylinder head nuts

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    The chrome nuts on the head of my Series 81 are nicked from wrenches, the chrome yellowing, and pitted. What is preferred. Having the old ones rechromed, or just getting new ones. Resto Supply seems ot have the proper ones to fit.

    Jack Davis



    Use stainless steel nuts and polish them if you wish.

    I don’t believe that they are supposed to be chrome anyway.



    Thanks Peter. Good tip.



    I bought black nuts from ARP which were the correct wrench size, plus they had a washer formed on one side. Worked great.


    I neglected to say that the nuts in question are acorn nuts. I see in a post by Greg Long awhile back on another thread that PA introduced acorn nuts on its 1928 models.



    Be sure the acorn nuts don’t bottom out, or you will blow head gaskets.


    Make sure that they were introduced on the Series 81 and not just the senior cars.

    Per Ed’s comment, if absolutely necessary, an extra washer or two will take up some gap.


    Finally thought to look in the 1928 PA Parts Catalog No. 207 for the Series 81. In several pages with line drawings of various views of the engine it is evident that acorn nuts are securing the head, and page 7 specifically lists part #117913 “nut,” and part #118129 “washer.” The illustrations appear to show a rather low crown rounded head virtually identical with the stainless steel Standard Acorn Nut in Resto. Supply catalog page 43. It is definitely not what the Resto. catalog shows as a “Pierce Head.” Does that settle it?



    Jack, you are correct, an acorn nut was used on the Series 81 engine head. A GOOD washer under the nut is imperative, because the head is aluminum, and the old, pure aluminum is quite soft, and a typical 7/16″ washer will cup and still allow the aluminum around the stud to crush.

    I use a grade-8 .100″ thick machine washer. It does not stick out from under the nut, and is very hard, and does not distort from the pressure of torquing the head nuts.

    There are a few very important items to look at when installing a cylinder head on any flat-head engine.

    The area around the engine block ‘deck’ where the stud is threaded into the block, sometimes gets a raised ridge around the stud. And if the cylinder head is freshly milled, the bore in the head for each stud, will have a crisp, hard corner. The head gaskets fit tight on the head studs..

    The result is that often, I know of at least 4 cars that the head did not seat down against the gasket itself, instead it rested against the raised lip around the stud, and the gasket in that area did not get crushed and seal between the head and the deck of the block.

    So: take a drill or better a counter-sink and chamfer the hole around each of the stud-holes in the head. This chamfer can be only 1/16″ inch wide, but it will allow the head to seat all the way down agains the gasket and the cylinder-deck of the block.

    Next, you must torque the head several times over a period of time, I think I covered this in a previous message?

    If not, let me know and I’ll write it again here.

    Greg Long



    Thanks so much for your counsel, especially at such a difficult time for you. I lost my Great Dane “Hannibal” 21 years ago and I miss him still.

    I am of two minds about the head. I have not removed it thus far. It seems very secure and the engine ran well for the very brief time I ran it a few weeks ago. I started out making my own gaskets where needed, but found there were some I could not fashion, so I did get the Series 81 gasket set. That means I have the copper head gasket and manifold gaskets. Should I go ahead and install them even though what is currently in place seems OK? I have been reluctant to mess with the head, being very much a “newby” at this.

    And I have never used a torque wrench, which I’ll need if I do remove the head. Can you recommend one? It looks to me like the click or clutch type might be the best for my limited needs.

    I’ll look for your earlier message on repeat torquing on head bolts.

    Jack Davis



    My Dear Departed Mechanical Engineer Father used to tell me: IF IT IS NOT BROKEN, DON’T FIX IT!

    In those days, every time I tried to FIX something that was not broken, I broke it.

    In this regard, a Wiser Man, I never knew.




    I have always subscribed to that same school of thought, especially in realms where I am a babe in the woods.

    Still, if all I do is replace the higher arched acorn nuts currently on my engine with stainless in the proper shape, I’ll need to know what torque measurement they should be cinched down to. And I gather the process is alternating nuts, and only torquing to a limited degree and then retorquing again several times over a period of days to reach the proper setting?




    Torque to 50-psi max, run until at driving / operating temperature, re-torque when cold, repeat in two weeks, repeat in two weeks.



    Jack, if not removing the head, you can replace nuts one-at-a-time. You should torque all nuts first, then replace (with anti-seize lube) and torque each one as you go. The hot/cold re-torquing steps are only required for a new gasket. Yours is already fully compressed. If you remove all nuts at one time, the gasket may not reseal and require replacement.


    Jack, I would not mess with the head, until you need to, which might be never.

    The head gaskets rarely fail except when the engine is seriously overheated.

    Greg Long


    Thanks to all for this useful advice. You’ve no doubt saved me a lot of trouble.




    We are trying to keep you from going cylinder head NUTS!

    And you would go NUTS if you ever over-torque those cylinder head fasteners and crack that aluminum cylinder head.




    Speaking of torquing , I have the water jacket back on now and am wondering what lbs torque I should tighten those nuts to. The jacket is brass and clearly a replacement back in the 1970s or thereabouts, so not likely to crack, but I don’t want to risk stripping the threads in the lip of the block.

    I do have bad dreams about cracking the head. I have the starboard side of the engine pretty well cleaned and painted [see photo], but the head remains stubbornly stained and resistant to CLR and pretty much everything else but emery cloth, and I don’t want to use much of that or it will appear too polished.



    The water jacket bolts don’t need to be torqued, per se, but sufficiently tight so that the jacket does not leak around the perimeter or at the holes.

    The way to test is to fill the cylinder bock with water and see if / where it leaks.

    Then tighten the bolt associated with the leak a touch and see if it stops.

    Then, move on down the line.

    I not only used the cork gasket, but used Permatex Ultra Black on each side of the gasket to make it adhere.

    I also used a touch, to a minor glob, of the Permatex on each of the bolt threads to seal them a bit more.

    Maybe even a touch on the inboard ID of each crush washer.

    Any “free floating” Permatex pieces in the cooling system will get captured in your fancy, new fangled, ladies’ hosiery toe, cooling system filter.

    Have fun.




    Thanks for the tip. I’ll follow your advise to the letter. I used Ultra Black Permatex on both sides of the gasket, and a dab in each of the bolt holes. Should be secure, but testing will tell.

    By the way, my wife gave me the hairy eyeball when I asked her for one of her old pantyhose. My explanation that it was for the radiator was met with thundering skepticism, as was my exclamation that “this is what the guys in the Pierce-Arrow Society told me to do.”” She is a bit concerned about all of you.


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