Cracked rod misalignment
09-18-2008, 01:33 PM
#1
Teching In
Thread Starter
iTrader: (12)
Join Date: Mar 2006
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Cracked rod misalignment I just finished an install of a set of rod bolts. I'm familiar with the cracked rod design and we carefully did one bolt at a time, however, on one particular rod it appears that the cap is misaligning.
It's looks like it's going together perfectly when the rod bolt first goes tight to iron, but the second you put torque on the bolt, you suddenly see the seam and can feel the step with a fingernail. The offset is only a thou or two (less than a normal sheet of paper) and is even on both sides but it has me worried about the bearing halves being misaligned.
I've tried doing the bolts in alternate orders, I finally took the cap all the way off and the fractures surfaces still look nice and jagged... I've tried assemblying these things 6 ways from Sunday and still can't get it right.
In the spirit of full disclosure I should mention that we accidentally attempted to install the bolts with the ferrules still in place but all those are now removed and I would assume that would tend to make the holes more centered instead of less (it actually becomes a minor interference fit).
Unfortunately if the seam was like this before I didn't catch it. Anyone run into this before or have suggestions?
It's looks like it's going together perfectly when the rod bolt first goes tight to iron, but the second you put torque on the bolt, you suddenly see the seam and can feel the step with a fingernail. The offset is only a thou or two (less than a normal sheet of paper) and is even on both sides but it has me worried about the bearing halves being misaligned.
I've tried doing the bolts in alternate orders, I finally took the cap all the way off and the fractures surfaces still look nice and jagged... I've tried assemblying these things 6 ways from Sunday and still can't get it right.
In the spirit of full disclosure I should mention that we accidentally attempted to install the bolts with the ferrules still in place but all those are now removed and I would assume that would tend to make the holes more centered instead of less (it actually becomes a minor interference fit).
Unfortunately if the seam was like this before I didn't catch it. Anyone run into this before or have suggestions?
09-18-2008, 01:34 PM
#2
Teching In
Thread Starter
iTrader: (12)
Join Date: Mar 2006
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
I might try to check the bearing for round using a set of bore Ts and a mic but it's going to be hard to do in the block because I don't have a ring compressor and I just finished torquing the heads down so I'm loathe to take one back off. Maybe I'd be able to feel the same step in the bearing surface that's on the outside and that would be enough. The bearing itself looks flawless and the motor turns over easily enough...
09-19-2008, 01:47 PM
#4
Teching In
Thread Starter
iTrader: (12)
Join Date: Mar 2006
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Man, you can hear the crickets in here...
I talked to an engine builder and got a few tips: First was to use some layout fluid (I forgot I had some Dykem stashed at work) to verify the seam. Next to take of the cap, spin the crank out of the way and measure the bearing for round. It's possible this was just weird from the factory.
I talked to an engine builder and got a few tips: First was to use some layout fluid (I forgot I had some Dykem stashed at work) to verify the seam. Next to take of the cap, spin the crank out of the way and measure the bearing for round. It's possible this was just weird from the factory.
09-20-2008, 04:15 PM
#6
TECH Fanatic
iTrader: (10)
Join Date: Aug 2004
Location: Rochester,Ny
Posts: 1,433
Likes: 0
Received 0 Likes
on
0 Posts
wow i might try to give a response,even if its not all that helpfull.When i did my rod bolts i did the same thing,one bolt at a time.And there was one that didnt seem to line up like it should have,it was just a tiny bit you could just barley feel with a fingernail..and it was the same deal,if it was like that before i didnt catch it either.I messed with it a couple times and it was always the same,so i left it and the car has been running great ever since.Not a single problem.I hope this helps.Its probably fine,i mean it would be rather hard for the fracture to not self-fit back together.
09-20-2008, 04:25 PM
#7
I had the same problem with a set of LS2 rods I was going to put in my latest motor. With the stock bolts, they where fine when torqued, but when I put the ARP bolts in them, 2 of them were .0015-.002 off on the bore gauge at the machine shop. They must be a tighter tolerance bolt. I decided against using them like that and opted for a set of Scat rods with ARP bolt for $275 and just put the stock bolts back in the rods and sold them and the ARP bolts separately.
Trending Topics
09-22-2008, 04:11 PM
#8
Teching In
Thread Starter
iTrader: (12)
Join Date: Mar 2006
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Checking bearing concentricity:
So here's what went down: As mentioned, cracked rods are only supposed to go together one way and once you clamp then down the seam all but disappears.
That was not the case for one rod in my engine after I torqued (and measured bolt stretch) a set of ARP pros.
With some careful maneuvering you get access to the big end of the rod with crank in the motor and heads on. By the way I marked cap and bearings DR and PASS for driver side/passenger side. In some of the pics where you only see “PASS” it looks like a pass/fail thing: it's not.
I tried using some layout fluid prior to torquing it to see if the seam was actually shifting as I clamped it. Fluid comes out blue and is designed to scrape off revealing bare metal if there’s any shear force.
Torquing it down requires some creativity. Can’t scratch anything…
T bore gauges are kind tough to use so I measured it three times each way to get consistency.
Here’s the part where it gets really weird… Measuring across the seam high to low both ways revealed a 0.008” misalignment rod to cap which is obviously not good (bearing to crank clearance should be ~0.002-0.0025”). However when I do the same measurement with the bearing in place it’s ~0.001 THE OTHER WAY, meaning if the cap was shifted left, the bearing seam is a smidge shifted to the right. This is exactly counter intuitive of the problem at the bearing surface I was expected and it’s only on one side of the bearing, the other is flawless.
The Dykem didn’t show anything unusual in terms of seam slippage. You’d should see pronounced points of blue showing shiny underneath that aren’t there (what’s seen in the pic is just from the camera flash).
Rods are not interchangeable between all ls1s so be sure you know what you have if you ever try to mix and match.
At the end of the day all the bearing surfaces looked perfect so I decided to run it. I just talked this through with my engine builder friend Ollie who gave me one last recommendation: He suggested I take a file and just smooth off any potential lip on the bearing surface to be sure it can't snag. It'll basically be a chamfer that runs 0.100" on the bearing surface at a angle to the seam so I'm only going a couple thou deep. Beyond that, he agree with my determination.
The motor will see the full normal break in period before I start pushing things and I’m adding a few gauges so I should be better able to keep tabs on things already.
-Joel
So here's what went down: As mentioned, cracked rods are only supposed to go together one way and once you clamp then down the seam all but disappears.
That was not the case for one rod in my engine after I torqued (and measured bolt stretch) a set of ARP pros.
With some careful maneuvering you get access to the big end of the rod with crank in the motor and heads on. By the way I marked cap and bearings DR and PASS for driver side/passenger side. In some of the pics where you only see “PASS” it looks like a pass/fail thing: it's not.
I tried using some layout fluid prior to torquing it to see if the seam was actually shifting as I clamped it. Fluid comes out blue and is designed to scrape off revealing bare metal if there’s any shear force.
Torquing it down requires some creativity. Can’t scratch anything…
T bore gauges are kind tough to use so I measured it three times each way to get consistency.
Here’s the part where it gets really weird… Measuring across the seam high to low both ways revealed a 0.008” misalignment rod to cap which is obviously not good (bearing to crank clearance should be ~0.002-0.0025”). However when I do the same measurement with the bearing in place it’s ~0.001 THE OTHER WAY, meaning if the cap was shifted left, the bearing seam is a smidge shifted to the right. This is exactly counter intuitive of the problem at the bearing surface I was expected and it’s only on one side of the bearing, the other is flawless.
The Dykem didn’t show anything unusual in terms of seam slippage. You’d should see pronounced points of blue showing shiny underneath that aren’t there (what’s seen in the pic is just from the camera flash).
Rods are not interchangeable between all ls1s so be sure you know what you have if you ever try to mix and match.
At the end of the day all the bearing surfaces looked perfect so I decided to run it. I just talked this through with my engine builder friend Ollie who gave me one last recommendation: He suggested I take a file and just smooth off any potential lip on the bearing surface to be sure it can't snag. It'll basically be a chamfer that runs 0.100" on the bearing surface at a angle to the seam so I'm only going a couple thou deep. Beyond that, he agree with my determination.
The motor will see the full normal break in period before I start pushing things and I’m adding a few gauges so I should be better able to keep tabs on things already.
-Joel
09-26-2008, 11:18 PM
#9
Even when you tested to see if it was out of alignment, did you put back in the stock bolts to see if the misalignment was still there? I know you said it fit fine until torqueing, so I wonder if it's the case of the ARP bolts not quite fitting the LS1 cracked rod (which has been documented). I know the ARPs work fine, but without re-honing the rod to size, problems like you're describing are not uncommon.
You should be good, though.
You should be good, though.
10-03-2008, 04:43 PM
#10
Teching In
Thread Starter
iTrader: (12)
Join Date: Mar 2006
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Didn't try the stock bolts as they mostly had ferrules jammed on the ends of them.
It was weird that bearing surfaces aligned so much better than the outside of the cap did so I'm really wondering if this could have been a factory defect that my friend didn't catch during diassembly.
By definition you can't resize cracked rods and a hone would just open things up so I didn't go there either. The ARPs are slightly longer than stock or the Katechs (I had all three sitting side by side, Katech's from my blown motor) but I'm a mechanical engineer and I can't think how it would make a difference at the seam.
FWIW I think the misaglignment wasn't necessarily related to torque because after closer inspection the issue is still present prior to full clamping, it just looks a lot more obvious after the fact.
The car is now up but I need to troubleshoot an alternator that's supposed to be self exciting but isn't before it sees any real drive time.
It was weird that bearing surfaces aligned so much better than the outside of the cap did so I'm really wondering if this could have been a factory defect that my friend didn't catch during diassembly.
By definition you can't resize cracked rods and a hone would just open things up so I didn't go there either. The ARPs are slightly longer than stock or the Katechs (I had all three sitting side by side, Katech's from my blown motor) but I'm a mechanical engineer and I can't think how it would make a difference at the seam.
FWIW I think the misaglignment wasn't necessarily related to torque because after closer inspection the issue is still present prior to full clamping, it just looks a lot more obvious after the fact.
The car is now up but I need to troubleshoot an alternator that's supposed to be self exciting but isn't before it sees any real drive time.
10-03-2008, 06:04 PM
#11
On The Tree
iTrader: (8)
Join Date: Nov 2007
Location: TN
Posts: 193
Likes: 0
Received 0 Likes
on
0 Posts
Didn't try the stock bolts as they mostly had ferrules jammed on the ends of them.
It was weird that bearing surfaces aligned so much better than the outside of the cap did so I'm really wondering if this could have been a factory defect that my friend didn't catch during diassembly.
By definition you can't resize cracked rods and a hone would just open things up so I didn't go there either. The ARPs are slightly longer than stock or the Katechs (I had all three sitting side by side, Katech's from my blown motor) but I'm a mechanical engineer and I can't think how it would make a difference at the seam.
FWIW I think the misaglignment wasn't necessarily related to torque because after closer inspection the issue is still present prior to full clamping, it just looks a lot more obvious after the fact.
The car is now up but I need to troubleshoot an alternator that's supposed to be self exciting but isn't before it sees any real drive time.
It was weird that bearing surfaces aligned so much better than the outside of the cap did so I'm really wondering if this could have been a factory defect that my friend didn't catch during diassembly.
By definition you can't resize cracked rods and a hone would just open things up so I didn't go there either. The ARPs are slightly longer than stock or the Katechs (I had all three sitting side by side, Katech's from my blown motor) but I'm a mechanical engineer and I can't think how it would make a difference at the seam.
FWIW I think the misaglignment wasn't necessarily related to torque because after closer inspection the issue is still present prior to full clamping, it just looks a lot more obvious after the fact.
The car is now up but I need to troubleshoot an alternator that's supposed to be self exciting but isn't before it sees any real drive time.
And for the alternator, how excited is it supposed to get?
01-22-2009, 10:42 AM
#12
Teching In
Thread Starter
iTrader: (12)
Join Date: Mar 2006
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Just thought I'd bump this and mention that I've put more than a 1,000 miles on the car now without incident. I'm getting prepped for a dyno tune.
Part of my problem was that I had a hard time measuring the resolution I needed using t-bore spreaders and micrometers. I know my clearances are close to right but not necessarily perfect.
Part of my problem was that I had a hard time measuring the resolution I needed using t-bore spreaders and micrometers. I know my clearances are close to right but not necessarily perfect.
