Rod out-of-round ??'s
Rod out-of-round ??'s I tore my motor down last week because of a rod knock that developed over the summer. It is a 98 ls1 with 96k on it. I found #4,5,+6 had badly worn rod bearings, with #6 being the worst by far. The crank was a little scuffed but not bad. It is at the machine shop right now. Anyway I was checking all the rods for out-of-round and to no surprise #6 had about .002 difference around. The odd thing is the side-to-side measurement was larger than the up-and-down one. I would think with the bearing being toast and the rod hammering up and down on the crank the rod bore would elongate up and down, not the other way around. An engine builder buddy of mine says he has never seen a rod wear that way. Has anyone else seen this before? I am not too worried since I am replacing it anyway, I am just curious what would cause this.
Another odd thing... after a light honing of the cylinder walls (about .0005-.0010") #4 seemed to have a nickel size depression about half way down the wall that the hone barely touched. When I mic'd it it was about .0005 larger then the wall around it. It doesn't looked cracked or deformed at all. Once again I'm not too worried but it was just an odd thing to see.
Another odd thing... after a light honing of the cylinder walls (about .0005-.0010") #4 seemed to have a nickel size depression about half way down the wall that the hone barely touched. When I mic'd it it was about .0005 larger then the wall around it. It doesn't looked cracked or deformed at all. Once again I'm not too worried but it was just an odd thing to see.
I tore my motor down last week because of a rod knock that developed over the summer. It is a 98 ls1 with 96k on it. I found #4,5,+6 had badly worn rod bearings, with #6 being the worst by far. The crank was a little scuffed but not bad. It is at the machine shop right now. Anyway I was checking all the rods for out-of-round and to no surprise #6 had about .002 difference around. The odd thing is the side-to-side measurement was larger than the up-and-down one. I would think with the bearing being toast and the rod hammering up and down on the crank the rod bore would elongate up and down, not the other way around. An engine builder buddy of mine says he has never seen a rod wear that way. Has anyone else seen this before? I am not too worried since I am replacing it anyway, I am just curious what would cause this.
Another odd thing... after a light honing of the cylinder walls (about .0005-.0010") #4 seemed to have a nickel size depression about half way down the wall that the hone barely touched. When I mic'd it it was about .0005 larger then the wall around it. It doesn't looked cracked or deformed at all. Once again I'm not too worried but it was just an odd thing to see.
Another odd thing... after a light honing of the cylinder walls (about .0005-.0010") #4 seemed to have a nickel size depression about half way down the wall that the hone barely touched. When I mic'd it it was about .0005 larger then the wall around it. It doesn't looked cracked or deformed at all. Once again I'm not too worried but it was just an odd thing to see.
How are you measuring roundness/cylindricity of the rod? These tolerances are very tight usually around 0.004~0.008mm. Also for your reference 0.0254mm=0.001".
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
If it got really hot from a spun bearing anything can happen when the rod cools back down. If it's really bad just get another rod from the junk yard like you were planning to or use some better rods.
I am using the dial indicator on a rod honing machine. The tolerance I found was .0003" found here: http://efialchemy.com/db/ls1/ls1.html
Also the bearing did not spin, and the rod shows no signs of heat.
Also the bearing did not spin, and the rod shows no signs of heat.
I am using the dial indicator on a rod honing machine. The tolerance I found was .0003" found here: http://efialchemy.com/db/ls1/ls1.html
Also the bearing did not spin, and the rod shows no signs of heat.
Also the bearing did not spin, and the rod shows no signs of heat.
I work in an automotive engine precision measurement lab and I have measured rods that have spun bearings and an out of round conidition of 0.050mm is huge.
Just make sure you are measuring them right. A rough and crude way would be to use some type of bore measurement device and measure the diameters in crosshatches and subtract the max and min diameters/divide by two.
Last edited by zx9rgreen; Jan 2, 2009 at 07:58 AM.
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FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
After some beating the OEM rods are easily out that far sometimes. I don't know what happened to these but they are good now after being resized. The average aftermarket H-Beam doesn't seem to move that much but often the I-Beams are weird on the big ends? I have seen Carrillos that were not out more than .0002 or even less after 500 miles of NASCAR abuse so it all depends on what is happeneing to them I guess.
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Verdad Gallardo After some beating the OEM rods are easily out that far sometimes. I don't know what happened to these but they are good now after being resized. The average aftermarket H-Beam doesn't seem to move that much but often the I-Beams are weird on the big ends? I have seen Carrillos that were not out more than .0002 or even less after 500 miles of NASCAR abuse so it all depends on what is happeneing to them I guess.
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
On anything bad yes you have to do that. I throw some away and just get a new one sometimes if they are extremely fubar as most of these are easy to get weight matched at the big and small ends anyway if you are a WD. The Sunnen setup measures up and down and right to left twist and you can bend the rod back straight with basically a pry bar. Usually this is from hydro-lock or parts geting in chamber like dropped valves or pistons coming apart etc. These are the ones I usually just trash nowadays since it's so cheap to get new ones on most of these deals.
thats was "Jucin" The outlaw (HP) shop car, I don't know how much at the time it was talked about, at the time, but a gtp friend was kinda working there. But it was a just a 347, stock rods, crank, and the non fancy dimond 3.905/6.098 11500 pistons, it went like 9.41 @ low 140s on a 300-325, and they hit it with almost 400 and it went on the bumper and hurt it a little. I htink the bent rods pics are still up here. That car is now local, it needed alot of work, still has the powercoated block. 
Last edited by studderin; Jan 3, 2009 at 02:08 AM.
