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Thread: annealing copper head gaskets

  1. #21
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    Good Grief, BoschZEV,

    Copper sulphate is blue.
    I've used 50 lb bags of it.
    Ready for the Ishihara test?

    By the way, ever wonder why it is such a common practice to paint copper head gaskets?

    ....Cotten
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  2. #22
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    Jul 2012
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    CuS is blue
    Cu4S04(OH)6, hydrated copper sulfate, is green

    The formation of the latter is the primary cause of green copper roofs. But, no matter the chemical formula, I think we've beaten it enough to make it black-and-blue by now.

    Quote Originally Posted by T. Cotten View Post
    By the way, ever wonder why it is such a common practice to paint copper head gaskets?
    I didn't know it was common to do this. But, having never painted one myself, superstition is my guess for why someone might paint theirs.

  3. #23
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    Uh Oh!!! Sounds like a little pissin match is in the works!!!!! Lets re-focus on the issue at hand.

    Lets look at what works and what doesn't: GWW (on this forum) rode his '30 chief with sidecar on the cannonball last summer. He ran solid copper head gaskets with cast iron heads on his rig and did not have one single issue with them. This speaks volumes about that set up, as that chief earned it's keep, dragging a sidecar and passenger cross country which is easily twice the work of any other similar sized bike that made the trip! In contrast, the VL's and other flat heads were dropping like flies with (I assume composite) head gasket blow outs. When they came to Denver, I was wishing I had solid copper VL head gaskets to sell, could have solved a lot of problems. Now granted, I suspect that many of those failures could have been caused by other issues besides just the gasket material, but the point here is a properly set up flat head with solid copper head gaskets can make a virtually bullet proof seal. In addition, Gary had the heads off a few times to deal with valve issues (another topic!) and still never had any sealing issues on the head gaskets.

    So, I don't really care what color copper sulfate or sulfide is, my engine isn't in the chicken coop! I'll be running solid copper head gaskets on my 31 chief and not worrying about head gasket seals!

    GWW, can you chime in and share your tips on how you set the heads up?

    Gene

  4. #24
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    Gene!

    That supports my contention: copper gaskets work for cast-iron heads, and composites are best for aluminum.

    American machines,... anyway.

    ....Cotten
    Last edited by T. Cotten; 04-08-2015 at 05:13 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  5. #25
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    Quote Originally Posted by gharper View Post
    but the point here is a properly set up flat head with solid copper head gaskets can make a virtually bullet proof seal.
    That's definitely the case. Another significant advantage of solid copper that we haven't discussed as yet is that its thermal conductivity is much higher than that of any composite gasket. Nearly 2/3 of the energy of combustion is wasted in the form of heat, all of which is generated at the top of the cylinder and only a fraction of which goes out the exhaust pipe. The rest of the heat has to be conducted to the head, through it to the fins, and finally into the air stream. Aluminum is 2-3x better than cast iron iron at conducting heat which is one of the most important factors why it is a better material to use for a head. However, even with an Al head the heat first has to get to it before it can be conducted away and a composite head gasket is a significant heat barrier. In contrast to the poor thermal conductivity of a composite, no metal is better thermal conductor than solid copper.

    In addition to its much better ability to conduct the heat of combustion from the cylinder walls to the head, there is the additional factor of thermal expansion. The hotter the top of the cylinder gets, the more it expands. As a result, with a composite head gasket each time the engine is used its expansion and contraction is larger with a composite gasket than with a solid copper one, putting differential stresses on the gasket and making it more likely to fail.

    Your example of the reliability of your friend's sidecar rig makes a good point. Although the differential effect is not as large, the thermal expansion issue also is there with a cast iron head. This is why in all ways I can think of (other than partially disassembled storage in a leaky chicken coop) solid copper is best for both Al and cast iron.

  6. #26
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    So BoschZEV,

    Don't you suspect that the aluminum heads conduct heat to the air better than cast iron?
    Wouldn't a copper gasket conduct heat downward, whereas a composite would keep the cylinder more even?

    ....Cotten
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  7. #27
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    filibuster, whatever happens, don't ask which oil is best In your old bike. :-p

  8. #28
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    Heat is going to move from hot areas to less hot areas. Aluminum heads not only stay cooler themselves (because of better air cooling), but help to keep the cylinder cooler because heat from the cylinder moves into the head. (As long as the head is cooler.)

    I'm staying out of the gasket issue.

  9. #29
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    Quote Originally Posted by fciron View Post
    filibuster, whatever happens, don't ask which oil is best In your old bike. :-p
    ^^^ that's great! ^^^
    Pisten Bulley is Harry Roberts in Vermont.

  10. #30
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    Quote Originally Posted by T. Cotten View Post
    Wouldn't a copper gasket conduct heat downward, whereas a composite would keep the cylinder more even?
    fciron already has explained why your understanding of this is wrong. A closely related example is the use of copper utensils by professional cooks. They use copper precisely because the high heat conductivity all but eliminates the possibility of hot spots when cooking. If you've ever tried to reheat a meal in the ceramic pot originally used to bake it in the oven (where it had been exposed to heat from all sides for uniform cooking), especially if you did it on an electric stove, you almost certainly had to scrub rings of burned food from the bottom of the pot because the heating was less even than in a metal pot. Ceramics have low thermal conditivity (as do composite gaskets) so the food immediately above each cooking element got too hot and burned.

    OK, science has explained how and why to anneal copper head gaskets, why copper doesn't "make horrible impressions into the aluminum," why it doesn't cause corrosion of the aluminum (except in damp chicken coops), why heat always flows from hot to cold, and why copper keeps temperatures more uniform. Science explains why to use copper for head gaskets (although it can't explain why anyone would want to paint them). I think we're done here.

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