1zzfe Valve Adjustments
Posted 16 November 2004 - 09:31 PM
Posted 16 November 2004 - 11:01 PM
Posted 17 November 2004 - 05:35 AM
Posted 17 November 2004 - 07:03 AM
Posted 23 November 2004 - 01:53 PM
The cams and valve buckets are hardened, too, but it is just possible for these to wear at very high mileages. So you most likely would end up with increased valve clearances and thus noise at higher mileages. (Increased clearances are more noisy than harmful to the engine, up to a point. Decreased clearances are dangerous because they will cause the valve to overheat and eventually burn out.) However, the vast majority of Toyota engines will go to the junkyard far in the future never having needed a valve adjustment.
It's still important to check them every 60 k, though, especially if you've had any problems with overheating or oiling. It's also a good idea to replace that valve cover gasket every so often anyway.
It's kinda funny how many car people are stumped by adjusting valves -- anyone who works on motorcycles is intimately familiar with several types of valve adjustments.
I checked my Corolla at 80,000 miles and the clearances were still perfect. I recently sold a 1988 Corolla with 210,000 miles and its valve clearances were also perfect!
Posted 23 November 2004 - 07:47 PM
Posted 24 November 2004 - 09:03 AM
A valve gets much of its cooling from contact with the valve seat. When the clearances are too small, it does not spend enough time in contact with the valve seat. The valve gets too hot, and after a while, the edge of the valve gets soft. The hot gases from the combustion chamber can even erode little canyons in the edge of the valve. This is a burned valve.
I've seen this happen on neglected motorcycles. The owner didn't want to spend the money to have the valve clearances checked because he thought he would be able to hear tapping if the valves needed adjusting.
When the valve clearances are too large, you'll hear the tapping noises, but the noises are generally not harmful unless the excess clearance is extreme -- the noise will drive you nuts long before any damage will occur.
So in the case of the V6 engines you're talking about (where there's a history of burned valves), you should DEFINITELY check the valve clearances. Shrinking valve clearances DO NOT make noise, and they can sneak up on you! The ONLY way to tell if you have this problem is to get in there and measure.