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Thread: New exhaust seats in a 1925 JD front cylinder

  1. #1
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    Jan 2006
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    Default New exhaust seats in a 1925 JD front cylinder

    Has anybody ever done this with any luck? I have a good 1925 JDCB cylinder that is nice except it needs more of a seat. I have heard of cutting and installing a seat but I have also heard of them coming out. Wilson Plank used to on Indians braze the new seat in and had great luck with it.

    I want to hear some responses on opinions of this.

    Jerry

  2. #2
    Join Date
    Jun 2001
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    Central Illinois, USA
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    The problem, Jerry,..

    Is modern seats.

    Everybody swears by, and sells only hardened steel seats.
    They shrink at flatty temps, requiring enormous interference.

    If only there was a producer of traditional cast-iron seats, the thermal expansion coefficient would be the same, and they could go in at a coupla thou without fear of cracking the casting.

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

  3. #3
    Join Date
    Apr 2010
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    Jerry,Head Hog,when alive did a spray weld overlay & then cut them.I told the Knuck guy from my area that you know, bought the system from eastwood? & did some panheads

  4. #4
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    Does anybody make oversize valves, Jerry?

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

  5. #5
    Join Date
    Nov 2009
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    Cotten, If steel seats are a problem due to the expansion ratio differences, why not simply make your own seat out of cast iron and fit them with the smaller interference? I've also heard of a machining process that cuts the hole at a slight undercut angle and the seat edge is cut to match. Once installed with heat on the cylinder, the seat is locked in place.

    Jerry, I've talked with Wilson about the process. He did this in a kiln basically, and at the same time brazed in a sleeve, returning the bore and valve seats to standard. He told me he also discovered at the same time that the intake nipples must be brazed in as well because the high temperatures cooked out what ever sealant the factory used and they always leaked after that. Jim Wall worked with me to do this process on a set of early Chief cylinders as spares for the Cannonball. It is really a furnace brazing process, using a silver solder impregnated paste which is applied to all surfaces and the parts are fitted with a few thousandths clearance. The entire assembly is put in a kiln and SLOWLY brought up to a temp just above the melting point of the silver, held for 15 minutes, then SLOWLY cooled off. Slowly means 12 hours each way at least! The end result is a new sleeve, or seat that is thermally bonded to the base metal and will not move! The advantage of the process is that the entire cylinder is heated and cooled evenly so stresses are lessened. Also, after this process, I sent the cylinders to be cryogenically stress relieved. This is a few day process to cool the cylinders in a nitrogen filled container and held there for 24 hours, then slowly warmed, then heated to 300* F. That's another topic...

  6. #6
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    Quote Originally Posted by gharper View Post
    .. why not simply make your own seat out of cast iron and fit them with the smaller interference? ... ..
    I did, Gene!

    And my K. O. Lee outfit has a 'clincher' to roll the casting over a relief on the seat.

    But I stopped taking in motorwork twenty years ago.

    If hard steel seats are heated to silver-solder temps, they are effectively pre-shrunk anyway (and not as hard).

    ....Cotten
    Last edited by T. Cotten; 07-01-2019 at 11:06 AM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

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