3RZ timing chain... is it the issue or not?

Greetings all. I have a 97 taco 4x4 w/ the 3RZ 2.7L motor. The truck has about 164,000 miles on it and it has not had an easy life. The previous owner beat the crap out of it but since I bought it 5 years ago, I have nursed it back to life and replaced basically everything… shocks, exhaust, alternator, brakes, water pump, frame undercoating, the head (the whole head, not just the gasket), and the list goes on. All things considered, it’s in pretty good shape for being an almost 20-year-old beater.


A few weeks ago I noticed the faintest whirring/rattling noise coming from the front end of the motor particularly when it is cold for about the first 3 minutes after start-up.


The sound is one of those that I feel like may have been there forever and I just never noticed it before but never the less, it still bothers me enough to ask questions and do some wrenching. The timing chain, to the best of my knowledge, is original. After 164k I know it will have some wear but I figure it should be good for another 150k, or until a crank bearing takes a crap, whichever comes first. I have never had a chain fail therefore I don’t know exactly what one sounds like when it is on its way out.


I pulled the power steering and A/C belts to eliminate any noise the pump or compressor may be making. Noise persists.



I pulled the valve cover to have a look at the chain, guides, and tensioner. I didn’t see any wear marks on the chain to indicate that it might be dragging on the timing cover.


The chain was tight with the tensioner in. It didn’t have slack in it when I tried to wiggle it with my fingers.


The guides seemed to be in one piece as well. The guide closest to the tensioner had some lateral slack in it but only with the tensioner removed. It had about ¼” of free play in it so I could wiggle it back and forth towards the cab and back toward the bumper. According to the shop manual it is only bolted at the bottom so I don’t think this is an issue. Am I wrong?


I pulled the tensioner out to see how much more “push” it had to offer. It had about 10 “clicks” (I counted twice) of movement in it when I removed it from the head so it is not fully extended, only about half way by my evaluation.


What’s the consensus on this? Is there a way to gauge chain wear without tearing the motor down to measure length between links? Is there a definitive noise this thing would make if it is in fact the chain? Should I just say to hell with it and drive the damn thing till it gets louder?


I took the attached pics to give everyone some scale of what I am talking about. They are not great but it’s the best I could do with one hand on the iPhone and the other on the flashlight.


Thanks in advance for any advice.

 

I'm not sure of the amount of slack you should have (FSM shows checking numbers of removed chain) but in this engine the chain tensioner works on the oil pressure. If engine is not running the spring holds tensioner against the chain so the engine can start with correct timing. As soon as the engine starts the oil pressure pushes tensioner piston against the chain so no matter how much slack you have (within reasonable limits) there shouldn't be any noise from the chain (unless the hydraulic tensioner doesn't work).

There is another timing chain in this engine, and it is deeper inside running the balance shaft. But it also has it's tensioner, so there should be no noise from it. Of it works of course.

 

Since the noise is faint, I would not worry about it as long as the engine is running smoothly while producing good power and reasonable fuel economy. If it gets louder in a short period of time, I would take it to a trustworthy mechanic for a confirmation before replacing parts.

By the way, good job restoring it to reliable daily runner after the previous abuse. These things will run forever with just regular maintenance.