Tuesday, November 26, 2013

Cherokee Cylinder Head Failure/Replacement

The universe has an interesting way of self regulation. This is manifests itself whenever I seem to be coming out ahead in my automotive endeavors. Case in point, I get an E36 M3 for a song and I get rewarded with cylinder head failure in my '97 Cherokee.

What started as a nearly undetectable misfire morphed into a coolant drinking, combustion-stifling dropped valve and cracked head after dragging the E36 back from Raleigh. As it turned out, the misfire was due to an intermittently sticking valve at low loads. As soon as the load was high enough to overcome the loss of compression through the valve, all cylinders ignited properly. However, if you drive in that misfire load range for a long, long time you may start to notice some other problems pop up. The valve itself was good enough to go on the wall of offerings to the Gods of Speed. There was some galling so bad on the side of the valve stem that it looked like it was made from aluminum.

Initial thoughts of rebuilding the head were squashed when I remembered that these things don't have press in valve guides, therefore, it's a bit more expensive to fix the stuck valve. In addition to that, 4.0 heads tend to crack going over speedbumps so magnafluxing was a must. These small bullshit tasks that I didn't feel like doing in the first place were adding up quickly so I just went up to Parks and ordered me a reman cylinder head...for $305.00. You can barely take a head off and put it back on for that money, even if there's nothing wrong with it.

All in all, a cylinder head job on a Cherokee is as basic as it gets in terms of repair of major engine functional groups. The main lesson I learned from this kerfuffle: check the prices of new cylinder heads before robotically taking yours to the machine shop for a reaming.

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