Toyota Repair: 97 tacoma 2.4 liter 2rz noise, timing chains, valve adjustment

Question
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Followup To
Question -
My 97 Tacoma 2 wheel drive pickup has 120,000 miles, Oil changed every 3,000 miles. I hear a rapping sound under the front of the valve cover when i hit the throttle. When the engine is just started it's quiet, after it warms up i get the rapping like a timing chain. I have seen other 2.4 owners on newsgroups hearing the same noise. I was just wondering if timing chains or possibly tensioners fail at around this mileage on these models. Any help is greatly appreciated.
Answer -
There is really no particular mileage as to when there may be a timing chain problem but I believe they should last at least 200,000 miles in most cases, personally I have not encountered a failed timing chain component at this mileage,(120K) it's possible that there may be another problem but I wouldn't rule out the timing chain.
Thank You for getting back to me. Is it very difficult to do a valve adjustment on this model vehicle?  

Answer
Yes it is somewhat difficult because the valve clearance is adjusted with removeable shims and requires some special tools, these engines are somewhat noisy to begin with and this is a common complaint, I doubt if the valve adjustment will help but you can give it a try.