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03-03-2021, 07:54 PM | #1 |
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Rod bolt won't torque to spec
Has anyone experienced an ARP bolt not able to torque down to specification? The shop was trying to explain this issue during a rod bearing job. Max torque achieved was 20 N-m. I asked if the threads were stripped and they are not. Not sure what the deal is. I'm heading to the shop tomorrow to get some eyes on this. Any recommendations as for how to handle this?
As if this weren't enough, the adjacent rod journal is out of round (min: 50.6mm max:52.0mm). Motor did not spin any bearings but the two in question were well worn into the copper (2008 model year). What's the max tolerance for out of round journals and how does this happen? I guess there's no visual scratches. Shop thinks I need to pull the motor and find a new one. |
03-03-2021, 08:12 PM | #2 | |
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03-03-2021, 08:34 PM | #3 | |
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As I understand it, the rod bolts should be torqued to 50ft lbs, but they only achieved 14.75ft lbs (20nm). That sounds like something yielded, but it's hard to imagine one of those bolts yielding so far below their intended design? The crank rod journal variance seems WAY too high? 1.4mm (.0551") difference between min and max? I'm not buying that. Either the measurements were incorrect or the reporting of the measurements is a mistake. I would also very carefully inspect the internal threads of the connecting rod and ask them to remeasure the crank journal, so you can see the numbers yourself. What does their torque wrench look like? Is the shop supplying the bearings and bolts, and what brand are they?
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03-03-2021, 08:53 PM | #4 | ||
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03-03-2021, 09:57 PM | #8 |
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It's stripped. Answer new rod is needed. Sucks to say.
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03-03-2021, 09:57 PM | #9 | |
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If the rod is truly stripped, then this is a new one for me. Go figure...I save the motor from rod bearing failure but it still needs to be replaced for a stripped rod and out of round crank... |
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03-03-2021, 10:01 PM | #10 |
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03-03-2021, 10:47 PM | #11 |
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How are they able to measure the big end bore for roundness without a full tear down? Or are they measuring the crank? Regardless, there is no way in hell that a rod or crank is that out of round without puking parts all over the ground.
And as for not tightening... if they managed to strip the rod, that would be a surprise. They are made of very stout stuff. As are the bolts. This smells fishy. Keep us posted.
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03-03-2021, 11:24 PM | #12 | |
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The old OEM bolts were used to measure clearances, and I'm wondering if they could be over tightened. Could the "torque+130 degrees" procedure for new OEM bolts yield an over tightened bolt if it was already stretched? |
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03-03-2021, 11:27 PM | #13 |
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When problem solving it's really difficult to force yourself to stay out of the "solution" space while you are trying to determine "What is" and "What is not". Try to understand the actual facts first.
Some of what I can think of to look for and ask about: Is your oil pan covered and safe from debris? Was this the first cylinder they attempted? Or the 3rd, or 8th, or...? I would inspect the internal threads of the connecting rod. Is there residual anti-seize on the threads? Are the threads pulled out or torn? Will the rod easily accept, by hand, an undamaged bolt (even an original bolt)? If the untorqueable rod and cap are still assembled, look to see if you can see the parting line between the rod and cap and if the numbers are lined up and the same, it should be nearly impossible to see the parting line. Once it's apart, do the mating faces of the rod and its own rod cap have any smearing? (If the cap was put on backwards, or a cap from another cylinder was used, then the freshly cracked faces will likely show evidence of misalignment and skidding or smearing, shiny spots.) Does the face of the rod cap, where the bolt head touches, show any uneven scuffing, or is it uniform? See pictures for reference of what the mating faces and parting line should look like. Inspect the bolt. Does it have residual anti-seize on it? Lay the threads on top of the threads of another bolt and see if they mesh correctly. Does the bolt easily, by hand, thread into a known good rod? Inspect the rod bearings, especially the set from the untorqueable cylinder. Do they look any worse than the other rod bearings? Ask to see the torque wrench. What is the appearance of the torque wrench? Does the torque wrench have a calibration sticker on it, if so, is it up to date? Here's why I suck at problem solving, I can't help jumping into the "solution" space. If, if, if, the threads in the rod are pulled out, what would explain that? What are the forces required to pull out connecting rod threads? (Bert at BE can probably answer that?) Would using the BMW torque to yield procedure on the BE bolt cause threads to rip out? (Bert would probably know?) Could a faulty torque wrench cause that? As far as the crank variant of 1.4mm, that needs to be verified (ain't no way). I could very well be wrong, and have been MANY MANY times, but the idea that ripped threads in the connecting rod and the crank being out of round by that much, being explained as a pre-existing condition...not buying that at all. Just my opinion.
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03-04-2021, 08:58 AM | #14 |
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The only reason that I can imagine why the shop believes that the crank rod journal isn't round, is if they didn't actually measure the crank, but instead applied either multiple pieces of plasti-gauge across the bearing, or one long piece lengthwise to the bearing and then made an interpretation of that data?
Bearing shells are not uniform thickness by design, and the plasti-gauge would show approximately a .0005" (.0127mm) variance. The mechanic would then have had to screw up some decimal points to report the variance that they did though, but at least that would be believable.
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03-04-2021, 09:23 AM | #15 | |
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Rod bolt won't torque to spec
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03-04-2021, 09:28 AM | #16 | |
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03-04-2021, 09:44 AM | #17 | |
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Sure, you can get away with using plasti-gauge, I've built plenty of american motors with the stuff, but with the tolerances in these bearings/engines, I probably wouldn't go that route. If these guys are using plasti-gauge and going that route, that's a non-starter for me. -Duke |
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03-04-2021, 12:52 PM | #18 |
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...and my understanding is that BE pre measures all of their shells and builds their kits according to a target clearance that their research has determined.
So, if your crank is within the tolerances of what BE expects it to be, then the bearings should create the intended gap that BE was aiming for. I don't know if it's a fact, but I've heard that some shops don't measure the crank rod journals, but give the journals a visual inspection and then proceed.
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03-04-2021, 01:13 PM | #19 |
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this case stinks to high heaven... good luck OP
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03-04-2021, 01:31 PM | #20 |
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Plenty bearings come out that look like it would have blown, yet none of these issues arise. This crank is very hard and doesn't scratch easily. Few people have been lucky to spin bearings and walked off without replacing the crank as journals looked fine. They shut the car off soon as they caught a noise. One fool slapped new bearings on a scoured crank and his engine lives on for longer than we expected. This shop must have done the damage to the rod during repair. |
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03-04-2021, 01:47 PM | #21 | |
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I'm not giving any credibility to the rod journal measurement since it doesn't seem like there's a reliable way to do this with the crank in the motor. It seems pretty evident that the engine needs to be pulled. At that point it's either a rebuild or a replacement. The shop was not about to admit guilt and I respect that. Theories as to the rod threads being buggered as a pre-existing condition were weak at best. The best theory put forth was excessive heat due to oil starvation from lack of regular oil changes. I'm not sure how much heat would be needed to compromise the threads however. The #7 bearing was the most severely worn and that rod was fine. Pics of the original bearings are attached. There's very fine pitting that was hard to notice close up. This was the evidence for the poor maintenance upkeep. |
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03-04-2021, 02:22 PM | #22 | |
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Maintenance and upkeep has very little to do with how your bearings look. I would get another opinion from a professional before allowing the shop off the hook. Keep us up to date. Cheers,
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