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Timing belt replacement experience & observations

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Recently replaced timing belt and components on my interference engine SC300 at 120,000 miles on the odometer. I will share the experience and observations as there are many discussions about timing belt replacement time frames. My Lexus is a Southern car never exposed to the harsh elements and extreme cold like Northern cars - which are variables negatively affecting composite made timing & serpentine belts and various other engine components life span. My experience and thoughts:

In my case, even before it was wise to replace the timing belt, there are other parts or components needing replacing as well. The timing belt itself was in excellent condition, but other components and seals had begun to deteriorate.

I have owned my SC for sixteen years. Up to now my repair expenses consist of a rear tail light bulb replacement. I do my own maintenance and oil/filter changes using Synthetic oil.


1) Replaced timing belt, idler, water pump, red coolant, coolant hoses, serpentine belt, tensioner & pulley, platinum spark plugs, plug wiring, master brake cylinder, synthetic brake fluid, thermostat, ceramic brake pads, valve cover gaskets, camshaft and crank seals, mobile 1 synthetic oil, etc

2) Purchased most components and parts from CARID and Toyolex's timing belt/water pump kit consisting of Aisin Factory complete OEM 13 piece timing belt kit and parts (Item # 16100-49838-AIS).

3) Ordered Lexus brake master cylinder and Lexus tensioner/pulley from Toyota directly (coordinating with Lexus) due to problems acquiring these two components after market. There are various two or three hole Master Brake Cylinder mounting versions for the SC300 dependent upon date of manufacture and if vehicle has traction control. VIN number determines which master brake cylinder is correct. Also eventually ordered some seals and spark plug wiring thru Toyota due to quality issues or seals damaged installing them. Most other parts were OEM thru CARID and Toyolex.

4) Of course there are other viable OEM or after market parts distributors - I chose these based upon my research. Several returns were efficiently handled by these companies. Note: Toyota may not accept a return if component or pieces indicate they were bolted up or installed whether incorrect item was Toyota's fault or not. In my case, Toyota parts people were very professional and helpful. I did pay a premium though to Toyota dealer for the Toyota tensioner & pulley (available only as one unit thru Toyota) and the master brake cylinder (available only thru Lexus).

5) Although brake pads worn very thin (120,000 miles), did not have to turn the rotors. Specifically installed Toyota ceramic brake pads to minimize chance of squealing. Others have reported problems using non OEM brake products causing noises. And the brakes are now smooth as butter!


A. Timing belt removed was visually in excellent shape - zero cracking or apparent wear on the teeth. Surprisingly supple and smooth looking. The OEM definitely a quality product.

B. Serpentine belt cracking. Based upon my experience, due to their looping it is normal for Serpentine belts to show inside cracks eventually and can safely be used for a long time afterward. Given their ease of replacement and relative low cost, they should be replaced per suggested schedule to prevent a breakdown on the road. A case of "do as I say, not what I did!" But still amazing that the serpentine belt lasted 120k miles and was still working!

C. Water pump showed it had been intermittently leaking for awhile. I had previously added small amounts of coolant past year thinking minor loss was due to heat evaporation during very hot summer highway trips.

D. Left cam seal was leaking slightly.

E. Front crank seal was also seeping.

F. Power steering unit and hose not leaking - so did not disturb.

G. The tensioner pulley was pitted.

H. Spark plugs did not show much wear, but the spark plug wires showing signs of insulation heat damage.


The Lexus SC300 manuals I have were invaluable. Although I worked as a gas station mechanic as a young man, this is a much more sophisticated engine than back in the day. If you have a mechanic you have trust and confidence in, most guys should have a professional do the timing belt/water pump replacement using the Aisin kit and any additional parts you can envision, e.g. spark plug wiring!. When obtaining a cost estimate to do the Timing belt replacement, request the cost of replacing all the parts in the kit and any potential other items. Any vehicle with over 100k miles will have additional issues once the engine is opened up.

To authentic gearheads, driving an SC is psychic income to the "feel good" senses! Artistically, it is a work-of-art on wheels. Mechanically, it is an engineering masterpiece! Driving one is hedonistic - especially when people stare admiringly or comment! So as it ages, check with your doctor if your heart is safe to have one!






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