ShaneC

for the 90K service i plan to do the Timing belt and water pump on my own at a friends shop(only if i need to). a friend of mine brought up for the GS400 the timing belt can run up to 150K (of course it can vary depending on driver) and if timing belt snaps, it will not affect and damage other parts of the car. is this true?

PetesLS400

It may last to even 200K miles, who really knows, why gamble?

Lexus recommends at 90K miles for a reason, why argue with that?

gserep1

if the belt snaps while driving, it WILL cause valve damage. Why take the chance? I changed mine on time and feel confident when I drive long distances at high speeds.

Chpsk8

I think the question he is asking is if the GS400 has an interference or nointerference motor.

Interference means that you'll grenade the motor if the timing belt snaps. Noninterference means you coast to a stop and call a tow truck and go replace the belt.

No words of wisdom from me beyond "search for interference motor" threads. Thats the answer.

Oh, and if you are going to tear into it to replace the timing belt, you might as well replae the waterpump wihle you're in there.

gserep1

By saying that the valves will bend if the belt snaps while driving implies that the 1UZ-FE engine is an INTERFERENCE engine. The compression ratio is 10.5:1 which means that the piston has to be very close to the heads when it is at top dead center. The valves HAVE to be closed that time. If valves are down and the piston is up, there will be damage.

Hope that is clear enough. Wouldn't want you to have to rebuild your engine.

ShaneC

wow. i learned some new terms interference and nointerference motor.
i guess i will start preparing to change the timing belt and waterpump. i really didn't want to do it myself if i didn't have to cause it's waaayyyyyyyyyyy too much work. at the same time i dont want to spend $1000+ at a dealership. that could go towards bodykit find... i guess better safe then sorry.

Thanks Guys!!

Billh2

Actually, that's not 100% accurate. There is a time when the piston is at TDC (Top Dead Center) at the end of the exhaust stroke, when the exhaust valves are just closing and the intake valves are starting to open called the overlap cycle. Both valves are slightly open. The piston is chasing the exhaust valve closed and the intake is starting to open. (On race engines, this is the area that causes the most problems with piston to valve clearnace, it's mainly affected by lobe center) On non-interference engines, the engineers have designed valve clearance notches in the piston that will clear the valves if they happen to stop at maximum lift. (during normal running, the valves are nowhere near the pistons at maximum lift) this is a non-issue on engines with low compression ratio, but our engines, at 10.5:1 they can't machine the valve notches deep enough to clear in the event of a drive belt failure.

RTIS250

iTrader: (9)

i would definately change the belt and pump.. you might want to change the idlers and crank seal while you are in there as well. it makes no sense to chance it.... the engine is, in fact, an interference engine, and if the belt brakes while the car is running, it will cause engine damage. when changing the belt, you might also want to consult a manual, as, if you dont have the crank and cams on the right marks, if a cam spins (they are under tention), you will also cause engine damage.