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Location: nevada
Have a question going back over 50 years- I had a Rupp kart with a Mac 6 engine. I bought the engine used at a kart shop. The owner said that sometimes these engines fail and the rod's small end needle bearings would try to come out the exhaust port. He showed me the improved piston that didn't have a wrist pin hole on the exhaust side. I didn't think much about this until mine did the same thing he described several months later. My question is- Why would it do this?
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Location: Richland Center, Wi.
Wrong length wrist pin or neglecting to ever do a rebuild. At some point the piston and bearing need to be replaced, or a loose wrist pin shifting . The side to exh was never an open bearing. It was a closed bearing different than the intake side. I have never had a small end failure and I've done this a long time. While on the subject of bearing the big end rod bearing are getting really hard to get so you mic those and if in spec you reuse them. Don't just throw them out. those haven't been made in 30 years.
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Steve- in a former company I had we bought pins for knock out dies (I use to make rivets) we could buy these pins 3" long in .001 size increments from .020 up to .250. All you would have to do is cut them close to length with a Dremel cut off disc and then kiss them on a grinder to length. If you want the source for the pins I will dig it up. E-mail me at work since I only visit the site on days that end in a "y".
Jim
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USMP minimum order was 20,000 sets I had heard to get them made