man_who_knows_nothing

hiu i have a 92 sc 400 my check engine light went on the dealer said it was the o2 sensors after the cat. they want $700 i found some on a web site oxygensensors.com for like $50 they are universial will tyhis be harder to install. how difficult is it to install one? next my valves are knocking i tried to get some info on this aswell. the dealer wamts $700 for this one to. how difficult would it be to fix this myself. o and one more thing do those cleaner things you add to your fuel actully work at all?

i have a 92 lexus my o2 sencors have gone bad they will come on now and then but for the most part there bad. they are the ones behing the cadiletic converters. i got the dealer to give me a quote it was over $600 dollars. are there any cheaper ones i can get? and my rocker head is ticking its something with the valve timing. again the dealer want like $600 so i think im going to try to do it myself. where can i get the infomation for the ajustments needed? thank you i hope that someone can help me