I've broken this engine (190k miles) down twice now in the last week and replaced the head gasket and still getting coolant in the oil. The head has been shaved and smooth and still dumping coolant in oil (about a quart every 5 min. approx.). This motor did have a noisy clanking sound for several years that I always assumed to be those pesky yota valves. Now I'm wondering, with all I've read here, could I have the prob with the timing chain wearing thru the tc cover? and if not, what else?

 

Sounds like the timing chain to me. Pull the valve cover off and look down the driver's side of the engine, you'll need a flashlight, and check if there's grooves worn into the side of the chain cover.

 

Yup, chain wore through the timing cover. The chain dampener on the driver's side was about two thirds worn away, which allowed the chain to cut into the cover. But the crack was so small (yet about 2 inches log), that light would not shine thru when shining a flashlite thru the water pump opening. Why do they make those things out of plastic? I'd rather do a head gasket again than a timing chain....GEEZ, What a Pain!

 

They make them out of plastic because the chain does make contact with the guide until the slack is taken up by oil pressure and as the tensioner eventually wears. Now, if they were made of some harder material.....say metal, for example... consider what will happen to the chain. It wouldn't last nearly as long. Keep it mind, it was also an early design. Now, you can get steel backed guides to prevent this.

Timing chain rattle is an early warning sign that the chain is making excessive contact with the guides, btw. Something to pay attention to, in the future. I've learned this the hard way with 6 bent valves and an engine rebuild. You got off a bit easier.