Ashley P

bearing wear

19 posts in this topic

My brothers dirt circle engine has a problem with #1 rod bearing. Chevy 383.  The bearing has worn down to a mixture of copper, pretty even wear on both halves.  The bearing shells have lost their "press fit", they have moved in the rod (the backs are shiny and the rod has almost lost it's "cross hatch" machine marks), don't see any heat damage, the throw has some wear.  The #1 MAIN bearing shows a little bit of damage from foreign matter.  All other bearings look next to new.

I suppose it's possible that a piece(s) of debris landed in the #1 main, did some damage, then moved to rod.  But the rod shows more than just debris damage, IMO.  Any opinions?

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No, sorry.  Will see about a pic.  I may have to draw it and mail a copy to you... ;)

And when I say the bearing moved in the rod, it has NOT spun, but like vibrated or something to polish the outer sides of the bearing and rod.

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We discussed that possibility.  He has not yet measured that. He said we wants a way to measure the "pinch" on the rod bearings as the rod is tightened.

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Measure the width of the top rod bearing.  If it's wider than the others by a few thousandths it detonated.  Number 1 is a long ways away.  I thought these things mostly ran 2 barrel carbs and dual plane intakes, now telling how that wieghs into things.

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Width of bearing...  Hmmm.  I was aware a detonated bearing would lose it's "press fit" like this bearing has, but didn't know the width tell-tale. Thanks for the tip.

We discussed detonation.  I detonated an engine for 1 WOT pass up to 90 mph, 11:1 on 93 octane.  Next day the head gaskets were leaking.  Replaced them.  Weeks later, massive oil smoke and low compression on #5 cylinder.  Broken TRW piston, all rod bearings fell out of the rods.  All were worn across the center of the beam side, detonation I supposed.

His bearing doesn't have that wear pattern, but it might have initially.  It's survived two races (estimated 25 minutes above 5000 rpm) since a mysterious noise was noticed.

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10580335_10153746860321259_871808511_n.j

12626046_10153746860246259_1622510427_n.

 

Looking at the backside you can tell how the outsides are "polished", the rod bore mimics that.  No word yet on width.

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I dunno.  The rest of the bearings are SO clean and nice...this single rod is nasty.  The main that feeds this rod (and only this rod) does show some damage from trash, but nothing serious.  I think that rod is the last bearing to get oil, so trash would have to miss all the other opportunities to only end up there.  Could it have been trash?  I guess it's possible, but looking to rule out anything else (or at least plan ahead to be able to rule things out for next time).

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So Mike, the bearing is .001" wider.  What do you think?   The effect of detonation or effect of whatever was destroying the bearing material?

Disney, the rest of the engine looks great.

Put that rod in another hole and run and see what happens?  lol

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Nope, not detonation.  At least not enough to cause this.  I guestimate it sucked the pan dry.  Just barely though.  Mains share load, so starving number one (the lightest load) a little won't kill it.  Starving a rod is instant death, since it carries all it's own load.

 

If the rod measures good run it.

JohnC likes this

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I didn't delete, John.

Dern skippy, mstrpgth!

Mike, sucking pan dry is a thought..  So, maybe somehow (under braking or something) it momentarily sucked air, starved #1 rod, but then had good oil for the next 2 races and thus lived to tell the tale??

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