Hudson head out of spec

Kdancy
Kdancy Senior Contributor
edited September 2014 in HUDSON
What is the measurement for stepdown head to be considered out of spec?

Comments

  • RL Chilton
    RL Chilton Administrator, Member
    If you mean as far as thickness, I've been told that less than 2.000", it's wall art, as it's too prone to warp at anything less than that.  
  • Ol racer
    Ol racer Senior Contributor
    FYI

    2" is the original thickness of Alum or Iron head and .060 - .080 milled is about max...
  • Kdancy
    Kdancy Senior Contributor
    Ok, so shoot for 1.94" as minimum?
  • Ol racer
    Ol racer Senior Contributor
    Ive milled the heads lot further for power, however for street use have the Shop take off just enough to ensure its flat probably .020 - .030, leaving 1.980 - 1.970 thickness.
  • RL Chilton
    RL Chilton Administrator, Member
    Yes, of course, Ol racer has it right.  .060 under 2" is what I was thinking, just not typing.  
  • Chris Smith
    Chris Smith Expert Adviser

    Would someone please explain how a head held down with 21 head bolts could warp even if its not two inches thick. Ol Racer, have you experienced any head gasket failures due to over milling?  

  • SuperDave
    SuperDave Senior Contributor
    Hudson knew they had a problem and changed to 1/2 head bolts. Jack Clifford said it should have been 3" thick! maybe a little overkill?..
  • Ol racer
    Ol racer Senior Contributor
    edited September 2014
    fyi
    The heads will warp especially when needed to remove for inspection while warm...In the past ive milled the heads around .100 max and never blew a gasket back then using 1/2"studs. I did flycut the Exh pockets for clearance when had a race cam.

  • Glowplug
    Glowplug Expert Adviser
    edited September 2014
    Chris...

    To partially answer your question, I offer the following: Hudson BIG SIX engines 48-56 all have a common problem; the thickness of the Siamese cylinder webs and how heat is dissipated in this area. Couple that with water circulation that is not optimized and the blowing of head gaskets is simply a matter of how much expansion and contraction the joint created between the top of those areas the head gasket and the head will accept before the gasket is forced to move ... in other words, blow. Head bolts in these areas are subjected to much more stress than those in the remainder of the engine due to the small metal mass to which the bolts are fastened. These bolts will stretch and after multiple heating and cooling cycles it is not uncommon to find the bolts have reduced torque values.

    There are several hypothetical ideas about what causes the instability of the head gasket... the chief culprit when the head is flat and the gasket installed properly and all the bolts are new of proper grade and correctly torqued is... inability to evenly cool the engine causing among many results the minute changes in torque which allows the head gasket to be subjected to edge pressure and the resulting loss of gasket.

    Serious flat head racers... do not use composition gaskets because of this very factor. Copper or steel head gaskets are used with high grade bolts selected and matched for linear size distortions when heated and cooled. The head gasket then is no longer a part of the equation and the task is now to balance the combustion chambers and circulate sufficient cooling to prevent pre-detonation.

    In other words... the thickness of a Hudson head is actually a factor of what average torque value the head bolts will consistantly achieve while not over coming that factor with too high a compression.
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