blueovalz Posted April 11, 2007 Share Posted April 11, 2007 I'm in the process of assembling a 383 (Ford stroker, but don't hang up yet), and have noticed something unsettling about the rod bearings. First, some background; the rods I'm using are 6.250" long rods (I believe they are a Chevy rod), and the crank rod journals are 2.10". These rods are perfectly round on the big end at 2.227" in diameter. The issue is that with the bearing shells installed, I get an oblong hole that is ~2.107 wide and ~2.102 tall. So I removed the shells and measured the thickness of the shell at the ends and in the middle of the shells and get: About .058" -.059" on the ends of the shells, and about .061" - .062" in the middle of the shells. Are these bearings trash, or is this common? This is the first time I've really come across this (or noticed this), and it was just out of a whim that I checked the bearing clearance 90º to each other on a new parts re-build (yeah, I know, you always check regardless who does the work). Quote Link to comment Share on other sites More sharing options...
blueovalz Posted April 12, 2007 Author Share Posted April 12, 2007 I think I found a suitable answer to my concern today. An old race engine builder told me that it is not uncommon to see wider clearances at the sides of the rod for increased oil for the bearings and have the top/bottom clearance to be normal due to the push/pull done at this portion of the bearing.. He said it allows the oil a chance to pass from the crank to the rod and on around it. He as seen several cases of .025" and one time had a customer request .040" ellipticity (I think that's the correct word) for a really high RPM motor. I couldn't believe what I was hearing and had to ask him to repeat that. He seemed to know what he was talking about and I trust him, so.... Oh, here's the rods. Quote Link to comment Share on other sites More sharing options...
Pwbull09 Posted April 12, 2007 Share Posted April 12, 2007 Sadly i always thought pistons where sexyer outside the motor.j/k Good to know its normal incase i come accross that down the line. Quote Link to comment Share on other sites More sharing options...
BillZ260 Posted April 12, 2007 Share Posted April 12, 2007 Sadly i always thought pistons where sexyer outside the motor.j/k Good to know its normal incase i come accross that down the line. Funny, I was just thinking it's a shame to hide such a nice piece of metal way down in that block. Buleovalz - makes sence but I don't remember having much if any ellipticity in my build but it was pretty much stock. Interesting. Quote Link to comment Share on other sites More sharing options...
pparaska Posted April 15, 2007 Share Posted April 15, 2007 That's not uncommon. You can even order bearings with different "ellipicity" or whatever if you ask for the right versions. One reason for this ellipicity is so that the edges of the bearing shells don't scrape the oil off the journal at high loading. That nice round hole that the rods have now becomes elliptical in the other direction (parallel to the beam) when the centrifugal forces start pulling on the rod, and the wider clearance across the parting line is there to be taken up as the rod deforms, so that the bearing inner surface is somewhat round in that state. If it started out round, it would pinch in at the parting line under load and the edge of the bearing shell would scrape the oil off of the journal. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted April 15, 2007 Author Share Posted April 15, 2007 Great discription. Thanks Pete. I suppose I will continue building up the bottom end and get this thing in the car the Summer (or Fall...Winter?) Quote Link to comment Share on other sites More sharing options...
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