Honing for oversize piston
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  1. #1
    Senior Member elime's Avatar
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    Honing for oversize piston

    A quick over view of what is involved.

    .0025" cylinder wall to piston clearance.

    Last edited by elime; 08-21-2015 at 01:21 PM.
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    Senior Member joeband's Avatar
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    are you working on darrell's tw225 parts bike again?
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    Senior Member macbig2k1's Avatar
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    Sorry, that I have to write this.

    But this big sh*t!
    You'll need the exact piston diameter and the exact inner diameter of the cylinder, and than you'll know the piston clearance.
    Without special machines you could get a bigger piston clearance in the middle and a smaller on the top/bottom. And the exact round bore could be round like a egg after this.

    No one should do this at home with some cheap tools.
    This is a job for professional companies, with professional machines and tools.

    If someone don't has a company in his neighborhood, he should send it to them.

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  5. #4
    Senior Member elime's Avatar
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    Quote Originally Posted by macbig2k1 View Post
    Sorry, that I have to write this.

    But this big sh*t!
    You'll need the exact piston diameter and the exact inner diameter of the cylinder, and than you'll know the piston clearance.
    Without special machines you could get a bigger piston clearance in the middle and a smaller on the top/bottom. And the exact round bore could be round like a egg after this.

    No one should do this at home with some cheap tools.
    This is a job for professional companies, with professional machines and tools.

    If someone don't has a company in his neighborhood, he should send it to them.
    Actually I had exactly the opposite problem you describe -- it was bigger at the top and bottom and smaller in the middle -- like an hour glass. I got around this by dressing the stones on the end, removing a small amount of material, then the cylinder "trued up" and the walls became parallel. Well, with very careful measuring it was all within .0005" of perfect. With my small cylinder hone (up to 70mm) I didn't have this problem at all but I had to use the large cylinder hone because it is a 71 mm piston.

    As for the out of roundness (egg shape) it was less than .001". Both the taper and out of roundness may not be perfect but are well within tolerance.

    I was very meticulous and did many measurements and I have confidence I did a respectable, decent job. I will be the one using it so I will suffer the consequences if it doesn't work out as planned.

    I have to add I value your opinion and thank you for sharing it with me. Tony
    Last edited by elime; 08-21-2015 at 05:48 PM.
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    Senior Member elime's Avatar
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    Dang it Sebastian, you have me on defense and doubting myself so I had to do some measuring. I took some pictures to make my case.

    Here is a picture of the piston with the micrometer on it. The diameter at the bottom of the skirt is 2.7928" and I tried to show that in the picture.

    P2120017.JPG

    To measure the cylinder I used an inside micrometer and then measured it with an outside micrometer.

    P2120018.JPG

    Then I measured the inside micrometer and it measured 2.7952".

    P2120020.JPG


    2.7952" minus 2.7928" equals .0024" Wiseco calls for a minimum of .0020". I think a little bigger is good, especially on an air cooled engine.

    OK, I was emphatic it was .0025" and this time it came out a little smaller. If I measure again it will be maybe a little bigger. These are such small amounts it is easy to get slight variations. But now I feel better. Tony
    Last edited by elime; 08-21-2015 at 06:52 PM.
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    Super Moderator littletommy's Avatar
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    I don't think he was saying it can't be done, just that for most folks, it's better to have it done, unless you have the knowledge and tools.
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    Senior Member Fred's Avatar
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    While I agree that precision work is best, and usually, done by dedicated precision machinery let me remind all that some pretty darn accurate work is possible by the dedicated and patient artisan. Witness the back-street gunsmiths of Peshawar and Kabul who turn out accurate firearms using the most basic of tools.
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    Last edited by Fred; 08-21-2015 at 07:26 PM.
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    Senior Member elime's Avatar
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    Quote Originally Posted by littletommy View Post
    I don't think he was saying it can't be done, just that for most folks, it's better to have it done, unless you have the knowledge and tools.
    I am not trying to fight or argue. I am just double checking my work and sharing it with anyone interested.
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    Senior Member Fred's Avatar
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    However despite elime's diligence his technique does not allow for precisely maintaining axial alignment. Never the less I am very comfortable using one of elime's earlier honed cylinders in Betty Boop which has perhaps only 500 miles on oversize piston and honed cylinder. I would only trust Tony to do this by hand, would never attempt it myself.
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  11. #10
    Senior Member elime's Avatar
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    Quote Originally Posted by Fred View Post
    However despite elime's diligence his technique does not allow for precisely maintaining axial alignment. Never the less I am very comfortable using one of elime's earlier honed cylinders in Betty Boop which has perhaps only 500 miles on oversize piston and honed cylinder. I would only trust Tony to do this by hand, would never attempt it myself.
    Thank you Fred.
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