Bushings for piston pin holes to have more piston choices.
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Thread: Bushings for piston pin holes to have more piston choices.

  1. #1
    Junior Member Rpmfly1's Avatar
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    Bushings for piston pin holes to have more piston choices.

    I mentioned in a thread a while back about putting bushings in piston pin holes and using these in 2 and 4 stroke on and off road racing.

    I found a thread where it explains the process. We used this for racing and never had a failure on over 20 motorcycle engines.

    motoshop-norway: How to install the big bore kit on a Kawasaki bn125 engine with original 125 con rod

    This gentleman used a similar process to keep from having to install a rod by splitting the case and crank.

    This would bring the Raptor 250 pistons into use and the 74mm piston I plan on using is a Wiseco 40078M07400 high compression.

    We even found a supplier in the late 60's and evidently it is still being done.

    https://www.google.com/search?q=krys...M-rxoYS27OXqM:

    Big Bore Cylinder Kit by John | Photobucket
    Last edited by Rpmfly1; 02-25-2018 at 07:29 AM. Reason: more material.
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  2. #2
    Senior Member vanillagorilla1's Avatar
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    ive thought about this. probably works fine. If you pull it off let me know. Ive also heard about people reaming out the connecting rods. All of my builds have used new rods and bearings so it wouldnt be a big deal to do that before crank assembly. Im also wondering about compression ratios on these custom motors. I know the pistons have compression ratings, but isn't that for its given purpose? when you mix it with a different crank and head I wonder how accurate the rating still is.
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    Junior Member Rpmfly1's Avatar
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    vanillagorilla1, you can adjust the compression several ways. Thicker head gaskets, shim the jug, cc the head and increase the volume and turn
    the piston dome on a lathe. They say that the compression on the Raptor is 13.0 to 1 with that HiComp piston. I have a bookmarked cc and CI displacement program that tells you the cylinder volume,chamber volume, bore and stroke, and compression ratio that you can figure out what cc the chamber should be. Actually the last listed was a new one I just found that has it!

    Here is one: http://performancetrends.com/Calcula...splacement.php

    Here it is! https://speedmaster79.com/tools/engi...ression-ratio/

    The only thing missing is the head gasket displacement and those calculators are not free.

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    Last edited by Rpmfly1; 02-25-2018 at 05:59 PM.

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