Timing Chain

Hi, I have a 1995 toyota t-100,2 wheel drive,4cylinder. (2.7 3 RZ FE). My mechanic tells me that commen problem is that the timing chain becomes loose and wears a hole in the cover,allowing antifreeze to contaminate the oil. I have 175,000 miles and wish to avoid this happening. First is this a recognized problem with these motors? Second is there a way of anticipating this happening? (Noise,ect?) Thanks george