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Thread: Piston Ring Locator

  1. #11
    Supporting Member Toolmaker51's Avatar
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    Toolmaker51's Tools
    Quote Originally Posted by Rikk View Post
    My first homemade tool post!

    So I whipped up this little tool from a used piston to make it easier. The length between the top and bottom of the tool is within .003" all the way around, so much more accurate.
    As I get in other engine types for rebuild, I will make the same tool for each.

    Attachment 33082
    Very good idea. I believe you could solve the .003 OOS issue easily.
    The process of manufacturing washers [punching ID, stamping OD] does not insure flat parts. Next, surface of cast piston is likely not dead perpendicular to skirt, especially in 3 locations. Finally, small relative area of cap screw could 'dent' each washer into different cup shapes.

    Use 3 smaller, narrower [there fore stiffer] contacts held the same way. 3/16" keystock, dowel pins, etc. 3 points of contact is always stable, yet no assurance each is on same plane.
    Just like surveyor's tripod, adjustable legs AND leveling jackscrews.
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

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    Rikk (01-15-2020)

  3. #12
    Supporting Member olderdan's Avatar
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    olderdan's Tools
    Quote Originally Posted by Toolmaker51 View Post
    Very good idea. I believe you could solve the .003 OOS issue easily.
    The process of manufacturing washers [punching ID, stamping OD] does not insure flat parts. Next, surface of cast piston is likely not dead perpendicular to skirt, especially in 3 locations. Finally, small relative area of cap screw could 'dent' each washer into different cup shapes.

    Use 3 smaller, narrower [there fore stiffer] contacts held the same way. 3/16" keystock, dowel pins, etc. 3 points of contact is always stable, yet no assurance each is on same plane.
    Just like surveyor's tripod, adjustable legs AND leveling jackscrews.
    Agreed anything can be refined but a.003 thou error is acceptable for this application and is better than using a sloppy unringed piston to square a ring in a bore, you will be relying on touch with a feeler gauge for the final measurement. Most of my work is one offs otherwise I would copy this idea.

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    Toolmaker51 (01-15-2020)

  5. #13
    Rikk's Avatar
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    Rikk's Tools
    Quote Originally Posted by olderdan View Post
    Agreed anything can be refined but a.003 thou error is acceptable for this application and is better than using a sloppy unringed piston to square a ring in a bore, you will be relying on touch with a feeler gauge for the final measurement. Most of my work is one offs otherwise I would copy this idea.
    True, in this application I have an .008-.016 tolerance, so a few thou tilt won't change things much. Normally file for .008, recheck then hone the corners and check again. Generally end up with .009-.010 in the end.

    The bores in these things are surprisingly resilient. First thing to go is the overhead rockers/cam. Always because of dirty oil plugging the oil system. People think these things will run forever without changing the oil.

  6. #14
    Supporting Member tonyfoale's Avatar
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    tonyfoale's Tools
    Quote Originally Posted by Rikk View Post
    62? Just a pup in racing years. As long as you can crouch and lean, you can still ride.

    I originally did some laps on my friends bike in a parking lot and loved it. He knows I've ridden my entire life and told me if I got my racing license he would let me campaign his bike for a day. So I did and loved it. When time and life permit, I would love to build a bike to run now and again.
    Unfortunately, I am not 62 anymore.
    Be careful if you try racing again, it is highly additive and takes over.

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    Rikk (01-15-2020), Toolmaker51 (01-15-2020)

  8. #15
    Supporting Member Toolmaker51's Avatar
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    Toolmaker51's Tools
    I'm not familiar with small industrial type motors, and my visualizations tend to minimize deviations. .003 on a small bore is not very consequential; it will alter measurable gap as bore increases. So the easier technique might felt tip a particular point to index the gap each time. Then angled or not, moving to file, replacing to check would create least possible variation.
    Sincerely,
    Toolmaker51
    ...we'll learn more by wandering than searching...

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    Rikk (01-15-2020)

  10. #16
    Supporting Member tonyfoale's Avatar
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    tonyfoale's Tools
    Quote Originally Posted by olderdan View Post
    Agreed anything can be refined but a.003 thou error is acceptable for this application and is better than using a sloppy unringed piston to square a ring in a bore, you will be relying on touch with a feeler gauge for the final measurement. Most of my work is one offs otherwise I would copy this idea.
    I am amazed that there seems concern over a 0.003" error. As Alan says that is acceptable. It is a very simple calculation that over a bore diameter range of 50 to 100 mm that error represents an off square error range of 0.086 to 0.043 degrees, which is totally inconsequential. The difference in the ring gap would not be measurable with garage feeler gauges.


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  11. The Following User Says Thank You to tonyfoale For This Useful Post:

    Rikk (01-15-2020)

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