Issues You May Face When Rebuilding GM Gen IV Engines - Engine Builder Magazine
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Issues You May Face When Rebuilding GM Gen IV Engines

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There are a couple of problems with the Gen IV motors that may affect how you rebuild the AFM motors, especially the ones with aluminum blocks.

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• Lifter noise after a two-hour shutdown can be an issue with the engines that have AFM. If the ticking lasts more than 10 seconds after startup and it’s diagnosed as lifter noise, GM is replacing the lifters with the latest “Delphi II” lifters (p/n 12639516).  We recommend using all new “Delphi II” “De-Ac” lifters in these engines to avoid the possibility of a warranty 30,000 or 40,000 miles later, because you have to remove the heads in order to replace the lifters, and that gets really expensive!

• Some of the aluminum engines with AFM have experienced oil consumption, too. GM says that the oil spray that is discharged from the AFM pressure relief valve in the crankcase may result in carbon deposits in the ring grooves that stick the rings and cause oil consumption. They have modified the rocker cover to change the calibration for the PCV for some applications, but the real fix is the installation of a shield (p/n 12639759) over the AFM relief valve to deflect the oil down into the pan instead of allowing it to hit the crank that throws it up on the cylinder walls. Rebuilders should include this shield with the LC9, L76, L96, LS4, LFA and LZ1 along with a picture and instructions so the installer knows where it goes and why it must be installed before putting the pan on the engine.

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• The cam phaser hasn’t created any problems for GM, but it probably should be replaced when the engine is rebuilt for a couple of reasons. The cam gear is a part of the phaser, so if the gear is worn, the phaser will have to be replaced. There are some internal parts that wear, too, and there’s no easy way to get the phaser apart to inspect them. So, the only real alternative is to try to clean it and pressure test it to see if it’s okay – or replace it every time to make sure it will go the distance without a comeback.  By the way, there are two different phasers.  The one for the LFA and LZ1 Hybrids is a p/n 12602699, and the one for all the rest of the VVT applications is p/n 12606358.

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Tech Tip originally appeared in Engine Builder magazine’s "Rebuilding GM’s Gen IV Engines" by Doug Anderson, March 2012. The complete article can be downloaded HERE.

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