Valve Question 3.4 L V6

So I was talking to a friend of mine who is a machinist yesterday. He told that recently he had seen two sets of heads from 3.4 L Toyotas with burned exhaust valves. He assumed it was because people were not getting them adjusted on time.

Today I called a couple of dealerships to see what the service schedule is, and how much they would charge to do the work. My truck has 72K on it. I almost never have work done at a dealership, but I thought I would ask anyway. I was asked if they were making noise. I said no, but if the valves were tight they wouldn't make noise anyway, and that's when you have burned valves, not when they are loose. The mechanic said that the valves will get loose, not tight as the shims wear. So if it isn't making noise, don't worry about it.

I don't really know how shim and bucket valves work. Is that true? do the valves on this engine get looser or tighter as the shim wears? If it is true, I won't worry about getting them adjusted. If it isn't true, I just found a place NOT to take my truck.

 

The mechanic is right when he says wear to the shims will cause the valve clearance to loosen.

However, if the valves and seats are wearing, the valves will retreat into the heads. This will cause the top stem of the valve to move up and reduce the valve clearance.

I have personally seen a 2.4 tacoma with a burned valve because of this, but that engine is known to have a problem with valve wear.

My mechanic has told me my 4.0 should be checked at 100k or so (toyota says 60k but recommends only an audible check for noise). He also says that most he has seen tighten up on the v6 engines, have already been rebuilt including a valve grind.

Ask them what it would cost to check them, should be much less in labor than actually adjusting. Then if they are out of spec, you can decide what to do.