Failure of the timing belt on the SC430 is almost unheard of. I have never talked to anyone who has ever personally heard of one failing due to wear.
The usual mode of failure is an idler or tensioner failing or the water pump seizing and one of those components taking out the timing belt.
Replacing the water pump, tensioner and idler at 75K miles, and then all of them again plus the timing belt at 150K might make sense, but for the small cost of parts compared to labor it is sort of a no brainer to do them all at once..
Hi gang, like some of you with low miles on your cars, I just urned over 8000 miles on my 2005 TAP. When I originally purchased the car this past November, I took it to the local Lexus dealership for a general inspection. The advice I was given, by a very competent, seasoned service manager, was to treat the car as if it were new and just go along with the regularly scheduled service intervals and not to worry about the timing belt given the low miles. Time, he said, certainly plays a role in belt deterioration, but heat and friction are the major players. I, more than likely, will not wait for 90 - 100 thousand miles for replacement, but I don't feel the urgency right now.
I think you are talking about the serpentine belt?
Well you think wrong.
The water pump in the Lexus 4.3L engine is driven by the timing belt (not a serpentine belt like on many cars, including my 4.4L BMW engine).
This is why if you look at any Lexus parts supply house or ebay you will see many kits for sale which include a timing belt, idler pulley, tensioner and water pump.
Get a quote sometime to replace just your water pump and you will see that to change out your water pump you must remove the timing belt. It will be very close to the cost of replacing your timing belt because the normal timing belt service includes a new water pump and the other ancillary parts, and the timing belt itself can be had for between $25 and $50.
This is also why it is very important to renew your coolant every couple of years to keep the water pump happy (read well lubricated). If the water pump seizes it will cause the belt to break and your valves (timing uncontrolled) will get cozy with your piston heads (to the tune of $5K-$6K in repairs).
I agree 100% with SC43052. It looks as though the timing belts aren't the primary failure point (e.g., breakage or losing teeth), but rather the various bearings at the pulleys and particularly the water pump. Change them all and rest easy.