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Interference Engine...or Not?

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Does anyone know WITH CERTAINTY which LS 400 years have which type engines? I've read that Gates' info is not 100% accurate and people are debating this in other Lexus forums as well.

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gen I is going to die if the timing belt brakes. gen II and III will not.

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gen I is going to die if the timing belt brakes. gen II and III will not.

English please. ;)

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gen I or generation I (one) is LS400 years 90-94

gen II (two) is LS400 years 95-97

gen III (three) is LS400 years 98-00

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Exactly what does interferance mean in rgard to the engine? Clue me in please.

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it means that camshafts and crankshafts are not gonna turn in a proper time and all the valves and pistons will be FUBAR and engine body will be useless as well

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Okay, that's what I suspected. It was previously my understanding that the 1990 gen 1 engines would not destruct if the timing belt broke. Is that non-interference?

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Did you check out the link I provided? It says it is a non-interfence and it shows what that means. Someone responded that it is an interference engine. I don't know where he gets his information. So, best check with someone who knows for sure.

In any event, if it is due for a timing belt and you plan to keep the car for a while, why not get it done and not worry about getting stranded or worse?

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What concerns me about the Gates site is that it lists all Volvo engines as interference. The early SOHC engines are definitely NOT interference engines, and this is well known among those that fix them. I have seen lots with busted belts, and no damage. So this inaccuracy makes me question the other comments Gates makes.

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I've always been told by Lexus people and mechanics that the first generation LS has an interferance engine and the subsequent models do not.

I'd be weary, its possible that Gates simply marked it incorrectly, I've been told by multiple people that it IS an interfearance engine. If I had one I'd operate on that hunch just to be safe.

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Do the gen 1's have variable valve timing? If they do, they WOULD be interference engines.

Yep, the gen 1 LS400's are interference engines. Change your timing belt now or your engine later. My timing belt was changed 8K ago by previous owner. It actually looks like all Lexus/Toyota V8's are interference engines. It looks like the IS is the only V6 interference engine as suspected. Please don't waste one of these Toyota V8 powerplants because you didn't change your timing belt. These engines can virtually go forever with the proper maintainence. It's documented. These V8's are so underpowered it's nuts. I bet you could build the old school 4.0l V8 to 400HP and it would be just as reliable (or close to) as stock through it's lifespan?

Here it is> http://www.skillcentre.com/lexus.html

LEXUS

Engine Interference Recommended Interval

2.5L NO 60,000 Miles

3.0L V6 NO (52)

3.0L Inline 6 (1992-97) NO (26)

3.0L Inline 6 VVT-i (1998-01) YES (26)

4.0L YES (26)

4.3L YES (26)

4.7L YES 90,000 Miles

Notes:

VVT-i (Variable Valve Timing with Intelligence).

(26) On 1995 & prior models, replace at 60,000 mile intervals. On 1996 & later models replace every 90,000 miles or 72 months under normal service, or every 60,000 miles in severe service.

(52) On 1990-95 models replace every 60,000 miles. On 1996-98 models except E5300 replace every 90,000 miles or 72 months under normal service, or every 60,000 miles in severe service. On 1996 & later ES300 replace every 90,000 miles or 72 months. On 1999 & later RX3OO replace every 90,000 miles if vehicle operates under severe conditions such as low speed driving for extended ranges, door-to-door deliveries, taxi or law enforcement situations.

Sum more> http://www.autoref.com/lexus01.html

I believe Variable Valve Timing is used to achieve maximum power (HP) with higher compression engines. That's why we can get all of this crazy power out of these small V6's and even 4 cylinders (Honda S2000) these days. Honda calls it V-Tech and Nissan calls it VVT. Look at the inline 6 in the Supra. Have you seen or read about the inline 6 in the Nissan Skyline (Europe only)? You can build the stock twin turbo inline 6's to about 500HP with simple bolt on mods. Computer technology (precise fuel management) with fuel injection play the biggest role in the amount of HP we get out of our cars with efficient gas mileage. Jeez, we're getting 22-27 MPG on the highway with these fairly large V8's. That wouldn't of been heard of in the 60's - 70's. These engines have more power to boot... Technology marches on...

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For what its worth...I mentioned this in another thread. Our shop had a 1990 LS400 come in with a broken belt as a result of a seized water pump and the engine was fine. Our personal experience says they are non-interference motors (or extremely well thought of by the Valvetrain Gods :) ).

Chet

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Got a "confirmation" from a local Lexus dealer that my 97 is non-interference but he did stress that it won't matter if you're moving fast when it breaks.

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For what its worth...I mentioned this in another thread.  Our shop had a 1990 LS400 come in with a broken belt as a result of a seized water pump and the engine was fine.  Our personal experience says they are non-interference motors (or extremely well thought of by the Valvetrain Gods :)  ).

Chet

Maybe the pistons and the valves were not in the same space when the belt broke? Do you know for sure that they're non interference? It seems like they are according to the data I've seen.

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drove my 94 LS400 (115K) to lexus dealer for gerneral check-out, and got a confirmation from service dept that it's a non-interference engine. broken timing belt will NOT destroy engine internally and no bent volves.

but I've made up my mind to change TB anyway.... but not at dealer though! they want $1200 for the job including belt+water pump+pulleys+labor.

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Wow! This string of posts seems a bit odd with so many completely opposite opinions. I had a timing belt break, after the water pump seized, on my 1990 LS400 many years ago at 84,000 miles and absolutely no damage was done. The car just coasted to a harmless stop and I even had time to pull off the road and coast into a parking lot.

Some dealers and repair shops probably enjoy (and profit by) this confusion since needlessly replacing timing belts can "enhance" revenue. Only recently I decided to have the belt replaced a 2nd time at 180,000 simply to avoid the inconvenient of being stranded again. If I didn't use the LS400 for an occasional 400 - 800 mile round trip weekend trip, and after discussion with the owner of my local Lexus repair shop, I would have just driven the car until the belt broke again - just for the fun of seeing how long it would last.

We also have a 1998 V6 Camry which I verified aso has a non-interferance engine, which we never drive outside of town and which we will probably drive until the belt breaks or the water pump fails. That's why we program our favorite tow truck companies into our cell phones! The reason that I bring this up is that 1999 seems to be the first year that Toyota went on the interferance engine bandwagon.

My advice would be to be sensitive to the smell of antifreeze which might indicate that a water pump is failing and, if so, could lead to belt failure.

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Maybe the pistons and the valves were not in the same space when the belt broke? Do you know for sure that they're non interference? It seems like they are according to the data I've seen.

At any point in time, several valves are always going to be open and destined for collision with a piston so there is no getting lucky with an interference motor. When the belt breaks, the valves freeze in place but the pistons will continue to move. This is true even for an automatic transmission although it is much worse in a manual tranny. In any case, it doesn't take much of a hit from the piston to bend the valves and ruin the pistons if the motor is an interference motor. In a non-interference motor, the valves can't touch the pistons even if the valve is down and the piston is all the way up. So why build interference motors? - because the smaller the gap between the piston and the valve, the more compression and horsepower you can get out of the motor.

The interesting thing though is that the Lexus that the shop repaired also had a water pump seize around 80K exactly like 1990LS400 mentions in his post. Maybe this was more common than I thought. :blink:

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Good to hear that the 90-94 are non-interference engines. I have no idea when the belt was last changed on my car. I will probably have it changed soon though.

I agree about the Volvo engines. My uncle had a 1986 Volvo wagon, with 256K and the timing belt broke. He just simply installed a new belt and the car ran perfectly.

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UCLABB,

Thank you! Conjecture seems to be rampant on this topic all over these boards - you answered the question with a simple link. I just purchased a 97 LS 400 with 93k miles and was wondering, since the timing belt has not been replaced, what the damage would be if I drove it until it broke(not wanting to shell out the $$ to have it replced so soon after purchase and all :) )

Thanks again for the link!!

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gen1 (90~94) & gen2 (95~97) are all non-interference engine. gen3 (98+) are VVTi which is an interference type to get more horse power.

90~96 is recommended to change TB at 90K, but for 97 and up, lexus factory recommends 120K or 7-year whichever comes first.

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95 has a newer head design and can cause valves smashing into pistons if belt breaks. My source could be wrong but please make sure.

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