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  1. #1

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    Ultra 310 Cylinder Head

    Don't know the history of this head, but obviously the spark plug hole has been repaired with a threaded insert. The spark plug cannot be installed all the way, and ends up about 1/4-inch higher than the other plugs. The dome is eroded.

    Is this head usable or will that spark plug prevent the motor from running right? Was the dome erosion caused by the plug not being all the way into the cylinder? It looks more like detonation damage than damage caused by a dropped valve or broken piston.



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  2. #2
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Can you pull the plug and post a picture of the hole from both sides and a picture of the plug?

    Sean

  3. #3

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    I got the head without plugs. To rule out a problem with the plug itself, I tried 2 different plugs in the hole with the same result.







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  4. #4

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    Here are better shots of the top and the plug.



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  5. #5

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    Took a closer look. The threaded insert appears to be the correct one and is installed properly. The apparent problem is that the motor was run with the spark plug not fully tightened down. This left some of the threads exposed to combustion, which fouled the threads. The threads are clean up to a point, and badly fouled below that. I'm trying to clean up the threads with a bore brush to see if I can get the plug all the way in. Otherwise, I'd have to replace the threaded insert, which might be a pain.

    If the motor was run with the plug not all the way in, would that cause detonation that would have resulted in dome damage? I'm thinking that the ignition timing in that cylinder would be slightly off with the plug backed out.

  6. #6
    Myself's Avatar
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    Try a thread chaser.....carefully.

  7. #7

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    Thought about a thread chaser or a tap, but I don't want to risk damaging the existing threads. I don't want to do anything that might preclude returning this head to the seller. If I can't clean it up with a bore brush, it's going back.

    Still trying to decide whether the metal erosion is going to cause a problem. It looks like the threaded insert and valve seats are protruding from what's left of the dome surface.

  8. #8
    My name is Sean and I am addicted to STXs smokeysevin's Avatar
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    Quote Originally Posted by grumpy_steven View Post
    Thought about a thread chaser or a tap, but I don't want to risk damaging the existing threads. I don't want to do anything that might preclude returning this head to the seller. If I can't clean it up with a bore brush, it's going back.

    Still trying to decide whether the metal erosion is going to cause a problem. It looks like the threaded insert and valve seats are protruding from what's left of the dome surface.
    What does the piston look like?

    Sean

  9. #9

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    I don't have any other parts from the motor. I only bought the head. It was described as "used" with no mention of the damage or repaired hole.

    The price was right. But I'd rather pay more for something that won't cause a problem in the future.

  10. #10
    dcuhpw's Avatar
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    Those I take valves look rough.

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