: Brittle camshaft cover bolts



dachew
01-23-06, 10:50 AM
A funny thing happened this past weekend as I was changing out leaky camshaft cover gaskets on my 99í. Iím always extremely careful when working around aluminum engine parts because I have met the Helicoil process and am not eager to repeat the experience. However, as I was applying torque to the camshaft cover bolts, two of the heads snapped off. Remember the camshaft cover bolt torque value is 8nm or 71 inch lbs which is less than 10 foot pounds. This is not a lot of stress for a bolt. The bolts had not even begun to tighten either. I was able to use a small screwdriver to back out the bolt ends without removing the cover. Apparently, the bolts had simply fatigued from a long life and had become extremely brittle. I made a quick trip to the local AutoZone and picked up 8 new hex head, 20 mm cap screws (This would be a good time to take a moment and condemn all Germans for the one that came up with the idea of building this engine with Torx bolts.) They fit perfectly, look bright and shiny and new, and they torqued down perfectly.
I think there may be a couple of issues this experience brings to light. First, the OE bolts holding the camshaft cover down, at least in my case, are garbage. I will think hard about replacing all of these torx bolts in the future as I work on various bits of the engine Ė I like cheap insurance. Second, I believe that, if the garbage bolts are not the cause of the ubiquitous leaky Catera valve cover gaskets, then a likely suspect might be the coil cassette. If youíve replaced your sparkplugs and put more than 8nm of torque on those two bolts, you may flex the plastic camshaft cover away from the mating surface of the head.
As an aside, if youíre going to replace a camshaft cover gasket, you might as well clean out the intake plenum and throttle body. I couldnít believe the amount of goop that built up in there in only two years.