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Thread: Hardened seats coming loose

  1. #1
    Join Date
    Oct 2010
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    8

    Default Hardened seats coming loose

    I have the heads off of my’49 and the seats are need of replacement. I have also read the multiple posts of these dropping out yet I see that Carl Olsen’s shop and V-twin’s shop both install seats. How do they get by with it- or do they?

  2. #2
    Join Date
    Jul 2002
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    North Hills, CA and Pine Grove, CA
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    5,140

    Default

    Replacing Panhead seats is easy. Trying to get them to stay in place is something else altogether.
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  3. #3
    Join Date
    Jul 2010
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    Ohio
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    There is no need for hardened seats, a myth started when lead was removed from fuel. Aluminum bronze works very well and will expand as the heads expands. Panheads have a bad reputation for dropping seats, but in my opinion its only because the wrong material is being used, a hardened seat will not grow in heat and will probably come loose.
    Bob Rice #6738
    He that conquereth his own soul is greater than he who taketh a city.

  4. #4
    Join Date
    Jun 2001
    Location
    Central Illinois, USA
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    3,468

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    Daverz!

    If you had some OEM replacement seats, they can be safely installed within the original cast-in seats.

    Unfortunately, all modern offerings, whether hardened steels or bronze alloys are spec'd to be installed at a drastic interference within the aluminum casting, with the original seat cut away.
    Plumber's-port heads do not have the structural support, and can crack disastrously upon installation.

    A reason for this extreme interference for steels is that the seat will shrink permanently if it reaches a critical temperature, due to advanced timing or a vacuum leak. Apparently there is some similarity with the bronzes, but I have never cooked one to measure its thermal expansion.
    I did find that a six thou interference on a steel seat drops to less than one at running temperatures, and that is without any shrinkage from a temperature spike.

    Not only must the seat be held by the casting, it must remain tight enough to transfer its heat to the head.
    Later Pan castings have much more "meat" to work with.

    Have you investigated oversize valves?

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

  5. #5
    Join Date
    Oct 2010
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    8

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    Thanks Cotton, That is the most extensive explanation I have heard, good information and point well taken. Do you have a source for oversize valves?

  6. #6
    Join Date
    Jun 2001
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    Central Illinois, USA
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    Daverz!

    I haven't 'sourced' anything like that for years, as I have been distracted.

    There were OEM oversized valves, and various aftermarket productions over the decades.
    A talented headmeister would probably trim down large ones so some of your seat's life was saved.

    Finding "talent" is why most of us either do it for ourselves and take the blame, or it don't get done.

    ....Cotten
    Last edited by T. Cotten; 02-08-2018 at 03:32 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  7. #7

    Default

    on my head that had the seats replaced,the heads I came up with at the time were all cracked.My machinist cut the entire seat area out of the head so as not to have weld contamination.It was put in a kiln welding device at a major manufacturing plant.Then he welded thru a hole in the kiln & slow cooled[govt job 3rd shift!]The head was machined for .0075" interference..Then heated in a kiln & then pressed in.I was scared to run it at first...20 years later,most pulling a rig I think it worked fine!

  8. #8

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    I done some shopping around on ebay. Found 1/8 inch oversise valves. V Twin repops. lowered the valve stem height around 100 thousandths.

  9. #9
    Join Date
    Jan 2002
    Location
    South Dakota
    Posts
    199

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    The trick to replacing any valve seat is using a material that has a matched coeficient of heat expansion to the head it is going in, a round concentric hole with the proper press fit.
    Carl

  10. #10
    Join Date
    Jun 2001
    Location
    Central Illinois, USA
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    Quote Originally Posted by Carl Olsen View Post
    The trick to replacing any valve seat is using a material that has a matched coeficient of heat expansion to the head it is going in, a round concentric hole with the proper press fit.
    Carl
    That would be the Great Trick indeed, Carl!

    Do you know of a seat replacement or material that has a thermal expansion coefficient anywhere near cast aluminum?

    I left that zodiac long ago in fear and frustration, so thanks in advance!

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

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