How To MCculloch MC100 parts help

[Tom Day]

take stock measurement for crank diameter , connecting rod i.d. in bore and bearing size.
add crank dia and total bearing dia together.
the difference between those two and the i.d. number of big end of rod is the acceptable amount of clearance in set up.
in most parts you will find them a little undersize on the crank surface and bearing surface.
the rod will be slightly oversize .
to much wear in all the parts will make for a loose engine.
may be fast but won't last long.

brian santee is working on different project.
he may have figured out slightly bigger bearing source.
maybe he'l post his findings if he reads the thread,




WE need those Bearings! Please keep us posted!

[doug tenney]

I don't know how many sets Steve O has, but it seems like that's a solution... for a little while.

In order to see what your clearance is "supposed" to be, go to http://www.jtekt-na.com/engineering-tool...g-library/
and download the Needle Roller Bearing Catalog. Then look at pages B-8-14 through B-8-18. The equation is on B-8-16, and Table B8-17 says to multiply the normal clearance by 7 if the application is a two-cycle engine crank pin!

I nominate Brian Santee to work through the math and tell us what is says! I gotta go mow the lawn.

Dave Bonbright and the US Motor Power (US820) people had to face the needle bearing obsolescence problem head-on in the last few years. I seem to recall that they ponied up for a dedicated run of custom needles after an unsuccessful (for the kart application) stint with caged needles.

Torrington invented needle bearings (derived from sewing needles), was bought by Timken and then sold to JTEKT, who owns Koyo. I believe the current source of US820 needles is Koyo.

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Brandon, if you're still looking at your thread, I routinely trust Scott K's and Steve O's information implicitly.

However, the attached PDF [scarfed from the MacBob (RIP) website] might be useful.