I have a 97 4runner 4cyl with a 3rz-fe engine. I have heard from many people that this engine burns a lot of valve. A mechanic recently told me that the valve becomes tight over time on cylinder number 4. So the valve becomes burned over time. Has anyone heard about this..? If so how often should I check the valve adjustment.
Every 60,000 miles/4 years, or if you notice a change in valvetrain noise.
If the valve tightens up, the noise will decrease...right?
Ed
Excessive clearance leads to valvetrain noises; insufficient clearance is damaging because it's silent.
The closing of the valve pushes the metal into the cylinder head, decreasing the clearance and resulting in a burnt valve. That's why it's important to periodically check the valve clearances.
In theory, yes, but I think that the engine will take on a different sound if only one or two valves is hitting the head harder than the other ones.
I think Toyota engines started out quiet. So when a quiet engine becomes quiet, the valves are too tight! ;)
Not sure what you are trying to say...
Valves burn because of insufficient clearance in the operating mechanism. This is because they do not close firmly against the valve seat. If they are not firmly seated, they cannot transfer heat to seat and hot gases can escape past the edge of the valves. This causes the valves to get very hot. They can get so hot that portions of the valve literally melt and thus the valves are burned. I unfortunately have had way to much experience with burned valves. A little valve tick (caused because of excessive clearance in the operating mechanism) is to be preferred to too little clearance. Of course if you have decent hydraulic lifters, valve tick shouldn't be a problem....oh wait, most Toyota engines don't use hydraulic lifters (well except the new 3.5L V6 does). Interestingly, after years of building most of their engines with hydraulic lifters, the new Ford 3.5L V6 doesn't use them. Arrrgh - Ford is learning the from Toyota I guess.
Ed
I do wish Toyota would switch over to hydraulic lifters on everything.
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