iamdub
Full Access Member
Went through this a year ago on my brother's '05 Sierra. Classic Castech failure. It had been a slow leak over a long period of time, likely since before he bought the truck, so the whole inside was sludged up. The leak was slow enough that the liquid burned off and never made a milkshake on the oil filler cap. What prompted investigating was he suddenly lost oil pressure after the average pressure readings had been gradually decreasing over a couple of weeks. While accelerating in a turn, a large chunk of sludge broke free and was sucked up to the pickup tube, blocking it off. Just mentioning this as a warning in case things look much worse once you pop off them heads.
Pulled the motor to scrub it out by hand and replace all the usuals- timing set, oil pump, lifters etc. and the top end parts that were damaged from the lack of oil- rockers, pushrods, etc. We never found a set of non-Castech 706 heads and, after this experience, just didn't feel we could trust another set of them. We did find a local deal on some low-mile 799s from a 2010 Silverado. They work fine, but the compression was dropped slightly. I don't think he could tell cuz it ran so much better afterward regardless. If it were me, I would've gotten thinner gaskets to maintain or slightly increase the compression. The cost of the gaskets would probably be the same or cheaper than OEM gaskets and head shaving (even if just a cleaning pass).
I've never had to replace the dowels and I've never needed to find TDC to torque the rockers. I just put the rocker anywhere on the cam's base circle. You have more than a 150° range on the base circle.
