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Isx compressor knock, much better now.

Discussion in 'Trucks [ Eighteen Wheelers ]' started by unapez, Aug 28, 2017.

  1. Aug 28, 2017 #1
    unapez

    unapez Bobtail Member

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    Jan 18, 2017
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    Hello all, I am sure that many with the cummins single stage compressors have (or will) experience an issue with knocking. Mine knocked like crazy until today, when working to compress air. And a bit less when unloaded. I considered replacing it, or just the head... but wanted to try a few things first.

    First off, it appeared that the head on my compressor had been replaced at some point. I used an engine stethoscope and found no knocking in the bottom of the compressor, so no bad bearings. So I figured the head was full of carbon.

    It's a 2006 isx engine with egr. I removed the air inlet tube from the intake manifold that leads to the compressor, and while the engine was running, slowly poured about 1/3 can of seafoam in the tube. I let that circulate through, and hooked it back up to the intake and like magic, almost no knocking! Ran it for a day and then drained my air tanks well, it seems much better.

    I hope this helps someone.
     
    unapez, Aug 28, 2017
    unapez, Aug 28, 2017
    #1
    QUALITYTRUCK Thanks this.
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  3. Aug 28, 2017 #2
    GrapeApe

    GrapeApe Road Train Member

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    Jan 7, 2013
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    The root cause of this most of the time is cam timing, they were set poorly from the factory. Now just imagine what your intake manifold and head look like inside. I'd schedule some downtime soon to pull the intake and EGR valve to clean them out. Re-time the cams to spec and you'll notice that the compressor will be quiet and it wont make so much soot. Not much you can do with the head other than vacuum it out with a shop vac. Do not try to knock off the carbon inside the head, just vacuum up the loose stuff by the manifold gasket. You will not get it cleaned out and will only cause problems digging around in there.

    We had an 07 CM870 that we bought new, the compressor was noisy day 1. The dealer said it was normal for those engines, I would not take the truck unless they checked it. They agreed to check it and it was off. They timed it correctly and the compressor was quiet. We recently sold that truck with over 700,000 miles and it has never had an EGR or compressor issue. I've seen the same issue many times, if the compressor is knocking, check cam timing.
     
    GrapeApe, Aug 28, 2017
    GrapeApe, Aug 28, 2017
    #2
    KB3MMX, QUALITYTRUCK and Heavyd Thank this.
  4. Aug 28, 2017 #3
    unapez

    unapez Bobtail Member

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    Jan 18, 2017
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    I plan on checking the overhead cam timing soon. The compressor is timed to the crank correctly, I verified it by removing the oil fill tube, barring the engine to the "insert pin" position and using a borescope to look at the mark on the compressor gear. It sits perfectly at 3 o'clock.

    Btw, I don't have a LOT of soot coming from the engine exhaust, but some. I purchased the truck used, and it appears very little preventative maintenance was done. I have done a lot since I bought it, and It's getting to where it's a real nice truck overall. I haul grain locally, hauling 80k and it pulls as expected. Just a few rattles and leaks I've been working out along the way. A rattle only gets worse until something breaks, so I fix anything with a noise.
     
    unapez, Aug 28, 2017
    unapez, Aug 28, 2017
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    KB3MMX Thanks this.
  5. Aug 28, 2017 #4
    GrapeApe

    GrapeApe Road Train Member

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    I'm not talking about compressor timing, the injector cam is the one that is usually off. You need the wedges, to check timing and a stout puller to get the gear of to adjust it. Those 2 things are quite pricey, so it's not worth it to buy the tools for 1 job. As much as I hate to say it, this is 1 job that an honest dealer can do cheaper unless you have access to the tools. I'd clean out the intake and EGR valve yourself. That'll only cost you some gaskets and your time. There is also a little tube off the manifold going up to the exhaust gas pressure sensor, clean that out too. It wouldn't hurt to change that sensor if the tube is plugging up. They're not that much and you can never clean them good.

    I'm not saying that your cam timing is off, but you should check it. 9 out of 10 times, if you can hear a compressor knocking that gets quieter when it unloads, the timing if off. If it is, correct timing and cleaning all that soot build up out, you will notice a few MPG points and a smoother running engine.
     
    GrapeApe, Aug 28, 2017
    GrapeApe, Aug 28, 2017
    #4
    DDlighttruck Thanks this.
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