The only way I can see a valve job helping is if the timing chain is stretched and they replace that at the same time. A sloppy chain will retard valve timing resulting in increased torque at low rpm and decreased torque at high rpm. The ability to pull a load will be reduced. One way to check for a stretched chain is to watch the rotor in the distributor, (if you still have one), to see how far you can turn the crankshaft before it starts to turn. I don't know what normal looks like because I just pull the cover off and look at the chain. Another way to measure the wear is to remove the fuel pump block-off plate on the right front of the engine and use a stiff piece of wire to pull the chain in and out. Older carbureted engines had a mechanical fuel pump bolted there that could be removed. Newer engines that were never available with a mechanical fuel pump won't have that plate.
Before I would commit to a valve job, I would insist on seeing the results of a cylinder leakage test. This involves bringing each piston, one at a time, to top dead center, then forcing compressed air in through the spark plug hole. A gauge on the tester will indicate the precent of air leaking out. If the engine is cold, ten percent is not uncommon. You can listen at four places for the results of the leakage. Hissing at the tail pipe indicates a leaking exhaust valve, at the intake system means a leaking intake valve, at the oil fill cap or dipstick tube is due to leakage past the piston rings, and air bubbles in the radiator indicates a leaking head gasket or cracked head.
Tuesday, June 8th, 2010 AT 6:34 AM