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Thread: 1940 chief cracked cylinder

  1. #1

    Default 1940 chief cracked cylinder

    I purchased a 1940 chief ,the motor is 1944 when disassembling the heads to check the condition of the motor I noticed a small crack in the front cylinder that is close to the intake valve and leading out to the edge of the cylinder, I am new to this is this something that can be repaired ,or do I have a big problem. Thanks jerry

  2. #2
    Join Date
    Feb 2011
    Posts
    255

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    i have seen this alot even on the early 20s indians , crack plugs are what i have the machinist used several in one area , they are tapered with a thread .i do not suggest welding .

  3. #3
    Join Date
    Apr 2015
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    116

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    Hi,
    Repairing a crack, as hairynob24 has suggested, is possible but with a valve seat crack going right to the cylinder bore, it might be an issue. Things to consider are; installing a hardened valve seat and installing a cylinder sleeve. If both are to be done, the order (which one to do first) could be a consideration. Personally, I would track down an uncracked cylinder. If a suitable replacement cannot be found, then a repair has to be attempted.

  4. #4
    Join Date
    Aug 2009
    Location
    rural eastern South Dakota
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    934

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    Quote Originally Posted by Yellow53Chief View Post
    Hi,
    Repairing a crack, as hairynob24 has suggested, is possible but with a valve seat crack going right to the cylinder bore, it might be an issue. Things to consider are; installing a hardened valve seat and installing a cylinder sleeve. If both are to be done, the order (which one to do first) could be a consideration. Personally, I would track down an uncracked cylinder. If a suitable replacement cannot be found, then a repair has to be attempted.
    My 47 Chief was +.030 with a front cylinder cracked into the intake port. The crack in the adjacent cylinder wall was visibly 3/8" tall, and visible into the valve seat. I ran this cylinder for a very long time, 10 years with a 27 tooth sprocket, and several of those years with 23 tooth and sidecar. Bored them to +.050 and started riding conservatively, no more long-hauls to Davenport. Finally installed fresh cylinders 4 years ago. .. You can run that cracked cylinder, unless it obviously swells and leaks, which would be evidenced with backfiring (mine backfired under reduced throttle consistently), but don't worry, be happy!

    Hard-seating the intake would invite more cracking (IMO), because of the reduced amount of material thickness between port and cylinder. Sleeves also would be problematic as heat transfer in the cracked area is insufficient due to limited surface contact.

    If my cracked cylinder hadn't had the seat ground so many times I'd still be running it.

  5. #5
    Join Date
    Aug 2009
    Location
    rural eastern South Dakota
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    If this were a stroked sport scout with a 1/2" long crack, that would be an approaching red flag. I've witnessed that. No catastrophic failure, but the backfiring came back through the carb a few times too many for our comfort level.

  6. #6
    Join Date
    Jan 2008
    Posts
    178

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    My 1940 Indian 4 has 3 cracked exhaust valve seats. The cracks extend about 1/2" down the cylinder bores. They have been like that for many thousands of miles with no adverse effects and no loss of performance. Tom Wilcock

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