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4.0 Rod Bearing Size

Old 10-10-2016, 12:05 PM
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Default 4.0 Rod Bearing Size

Hey I've been over in the New Pistons thread, but had to start a new one to get help on a different question.

My Rod Bearings are different.

Top: Standard
Bottom: .001

The top bearings are all worn more. right at the top and middle of each bearing.

Considering the wear on the Standard Tops, I'm worndering which bearings to buy.

Should I express order a set of .001 undersize real quick? Or standard?
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Old 10-10-2016, 07:22 PM
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Nevermind. Called my machine guy, he gave me proper guidance.
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Old 10-10-2016, 08:24 PM
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Yeah, the top shell always wears more from the pressure of combustion. All the bottom shell does is contain the rod from centrifugal force. Think about it. At idle, the pistons change direction every .04 seconds.

Last edited by dave1123; 10-10-2016 at 08:29 PM.
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Old 10-12-2016, 11:27 PM
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I like the math there Dave. That's a good way to look at it. When the piston goes boom its gonna slam that top bearing. Never really thought about Rod Bearings in detail like that.
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Old 10-13-2016, 04:29 AM
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If you're really interested, think about the inertia stress on pistons at, say, 3000 rpm! You begin to wonder how any engine stays together for long. We've had over 100 years to design something better and we haven't done it. Well, we have if you consider turbines. They are fuel hogs.
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