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Warning: Found out my injector cups were off by 0.002 inches
I was pulling injectors on a 2008 Cummins ISX in Atlanta last Tuesday and decided to mic the cups before slapping new ones in. Turns out two of them were out of round by 0.002", which is basically nothing but the manual says it'll kill the seal. Anyone else ever find stuff that's technically within spec but still causes issues down the road?
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gracej994d ago
...so I had a buddy who was chasing a ghost misfire on a Duramax for three weeks and it turned out the injector hold down bolts had a hair of thread locker built up on the bottom, just enough to throw the torque spec off. He was pulling pistons and testing harnesses and all kinds of crazy stuff and it was literally 0.0005" of dried loctite making the injector sit crooked. These engines are finicky things, you really gotta sweat the small stuff even when the manual says you're fine. That 0.002" might show up as a cold start miss next winter or a weird idle shake you can never quite figure out.
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milesbarnes4d ago
Oh man that is a crazy story, that's the kind of thing that makes you want to throw a wrench across the garage. But ngl I gotta call something out here real quick. Most injector hold down bolts on a Duramax (especially the LLY and LBZ) are torque-to-yield bolts, so if they were re-used with dried loctite on the bottom that could definitely mess up the clamping force. But 0.0005" of thread locker isn't going to change the torque spec by a measurable amount, it would be more like the bolt bottoming out on the dried loctite in the hole if it was on the threads themselves. Tbh I think your buddy might have actually been dealing with a different root cause, like a cracked injector cup or a bad copper washer that just happened to get fixed when he pulled everything apart and put it back together. Those older Duramax injector cups are notorious for hairline cracks that only show up once the engine is hot and under pressure.
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