Install aluminum head warm? Warning - obsessive.

Discussion in '80-Series Tech' started by IdahoDoug, Nov 17, 2005.

  1. IdahoDoug

    IdahoDoug

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    OK, with too much time on my hands staring at an empty block I'm almost ready to put the head on. I was wondering if there's any advantage to putting the aluminum head on warm since the block is stone cold.

    My theory is that the head has a greater thermal expansion than the iron block. So, if I bolt the head on in a slightly enlarged state then I could reduce the long term expansion stress of these two mated metals a tad.

    Nothing crazy here, I'll simply leave the head in the house at 65 degrees while the block is in the garage and probably at 40 degrees. Or, if there's someone here with serious metallurgical knowledge that says 'heat it in the oven'??

    My theory is that the greatest expansion difference occurs when the engine is hot, so if I can slightly relieve that it would be good. On the downside, if I do this and then when the engine is stone cold there's tension because I did this, it may not be a good idea. In other words, the engine sits all night under tension and is only under slightly less stress than normal when the engine's operating it may not be a good tradeoff.

    Overall, I suspect the engineers expect the parts to be bolted together at the same temperature so this is likely best.

    Any obsessive/compulsive thoughts?

    DougM
     
  2. kbellve

    kbellve

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    The head bolts have expansion built in...they are designed to stretch and rebound. They have a working range.
     
  3. Big_Moose

    Big_Moose

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    Doug,

    I would think that the differences in temperature in regards to thermal expansion / contraction would be nil - especially with only a 20+ degree differential. The head gasket would also act as an thermal insolator during the assembly stages, which would allow for the head / block thermals (internal temperature) to become equal by the time you have the engine buttoned up.

    I would just install the head, new head bolts - torqued to specs, and then if really worried - allow the engine to sit for a few hours allowing all metals to become "inner core" temps to become equal. Then complete a test run & let us know about the extra umph from the shaved head

    Joe
     
  4. Cube Dweller

    Cube Dweller Moderator

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    Just for giggles I did some math. Assume linear expansion, height of head is 7", with a difference in temp of 25 deg. The difference in deck height is 0.002 in. Totally insignificant, .002/7.0 = .000336. I'd bet a few :beer: 's your torque wrench has far greater inaccuracies. Bolt it up.
     
  5. IdahoDoug

    IdahoDoug

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    Actually, the expansion that troubles a head gasket is elongation of the head vs the block, so think in those terms. It puts shear stress on the gasket repeatedly, so my thinking was if anyone knew the temp at which cast iron and aluminum are at 50% of their expansion in the ranges of 20 degrees to 450 degrees it would be useful. Up and down expansion is handled by the bolts but that does not stress the gasket.

    DougM
     
  6. IdahoDoug

    IdahoDoug

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    I'm off to get the head - will check back before starting.
     
  7. Cube Dweller

    Cube Dweller Moderator

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    Maybe I'm missing something, but if you're trying to find the pt of 50% elongation over a temp. range, wouldn't it just be the mid. pt. of the temp range, since the expansion is linear, ie (450-20)/2 = 215 def F? I now understand your goal of trying minimize the dif. in shear across the gasket, but the differences in expansion will always occur as the temp of the engine is cycled. :confused:

    But it brings to mind an interesting point...as the block and head expand at diffent rates, where does the shear occur? Is the gasket slipping at the interface between the head or block or does the gasket stay fixed, expand and contract w/ the parts and shear elastically along the gasket itself? Seems like on heads I've pulled the gasket is typically well adhered to both mating surfaces.

    Hmmmm.
     
  8. IdahoDoug

    IdahoDoug

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    Cube,

    Exactly the kind of thinking I'm looking for. I think everything stays stuck, just that the expansion causes the gasket to undergo shear stress (surface against head stretched a lot, surface against block is not stretched as much). So, if there's a max stretch and a minimum stretch of the gasket, what temps should the block and head be to be mounted at the mid point? I'm also not sure the expansion is linear - doubt it.


    DougM
     
  9. CreeperSleeper

    CreeperSleeper SILVER Star

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    I think that this is positive and creative thinking, but given the 20 million iron block/alum heads that were installed with them both cold and how that has worked 99.9% of the time, I really think that it wouldn't be worth the headache trying to figure out something that should (in therory) work better. I would really hate to see you pull that head off again... JMO
     
  10. IdahoDoug

    IdahoDoug

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    I hear ya, just that most heads are not installed in cold garages with both parts at 40 degrees. Hmmm.....

    DougM
     
  11. firetruck41

    firetruck41

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    I'm an idiot, but I think the expansion/contraction will be out the door the first time you run the engine and let it cool over night, the 20 deg is nothing compared to the operating temp vs. sitting out side over night. I'm interested to read what others say. I assume the FSM says nothing about heating it? If that's the case I still don't think the 40F vs 70F (temp in factory?) makes much difference when compared to overall operating and environmental temp range.
     
  12. Nomis

    Nomis

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    I'll let you borrow my space heater to warm up the garage - just swing down here to Tampa when you get a chance - while you're here, you can use my garage as it's currently a nice 72* :flipoff2:
     
  13. CreeperSleeper

    CreeperSleeper SILVER Star

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    Good point. If it were me, I would put out the work lamps and space heaters now and crank them up. That will give everything a day to warm. You will be doing the work in shorts and t-shirt drinking Corona with lime!
     
  14. landtank

    landtank SILVER Star

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    Take the head to bed and sleep with it tonight, and then install at first light.
     
  15. Scamper

    Scamper

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    I can't imagine that Toyota worries about the temp differentials if they exist at all. I would imagine they have everything at pretty much the same temp when they assemble.

    But if you're going to worry about the differential coeffecients of expansion for iron vs aluminum, then you should also take into accout the expansion and contraction of the gasket itself (which, if I'm not mistaken is steel with some coating). IMO not worth that much firing of the neurons.
     
  16. cruiserdan

    cruiserdan SupportingVendor Emeritus Moderator

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    WAIT, STOP!>>>>>>>>>>>>>>>>>>>>>:eek:


    The head should be installed at operating temperature........

    :flipoff2:
     
  17. Gumby

    Gumby Supamod Staff Member s-Moderator

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    Be careful of getting anything stuck in the wrong port. Intake is for intake. Exhaust is for exhaust.
     
  18. Beowulf

    Beowulf

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    Should they shower together before going to bed? ... after waking up but before the union? ... or complete the union then shower seperately?

    Decisions, decisions.

    :D

    -B-
     
  19. IdahoDoug

    IdahoDoug

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    Gumby,

    For some, everything's an intake...

    Well, it's 3 freakin' thirty and I just walked in the door to find you guys have been horsing around and didn't solve this conundrum in my absence. So, I'll be slapping it in at whatever temp the portable heater gets things.

    Of course the trip to get the head had to have a whack job component. When I dropped the head off Monday I bought some excellent cider from a place we only get to when we're in Spokane. The next day the stuff was undrinkable. So, I opted to return it and get some fresh stuff. Add fermenting cider to a warm 80, shake and you know what happened. Yep, literally 100 yards from the place's driveway one of them exploded. From the back seat, it drenched the windshield and you don't wanna know what the back seat looked like. As I was pulling off, I could see cider flowing under the front seat, so I parked it on an angle in the ditch and opened both right doors to watch most of a gallon flow off the rockers. Soaked every towel, etc. Drove in their place and asked for rags, water, etc and spent an hour wiping and soaking things.

    Does anybody else enjoy these little foibles of life or is it just freakin ME that gets 'em just when I don't have time???

    Head looks great.

    DougM
     
  20. CreeperSleeper

    CreeperSleeper SILVER Star

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    My friend, I'm at a loss for words.
     
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