jschunke

Valves Interfering Or Not?

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Does anyone know if the first generation ls400 engine

valves were non-interfering?

In other words if the timing belf breaks is there a

chance that the valve will hit the piston and bend?

Thanks

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Second the non-interference....

No damage if timing belt breaks.

Gen I engines are the only ones like that - I believe. Gen II, III, IV will cause damage :(

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My Lexus Service man told ME that the engine in my 1993 LS400 IS an 'interference' engine. [and that was AFTER I asked him to have the timing belt changed!!]

Is what 'he' said the last word on this? No... but 'his' opinion DOES hold some weight - I think.

Speaking of which...

Have ANY of you EVER heard of an LS400 timing belt breaking or failing?? And I don't mean because the water pump broke and caused the belt to fail. I mean the belt - all by itself - failed or broke or whatever.

Craig!! :)

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There are as many oppinions on this subject as there are

lexus owners! I was under the impression that the first gen

4.0 liter was the only non-interference engine. But it

seems that I may have been deceived, along with many

other Lexus owners.

This is a most important aspect of a belt driven engine, and

personally I would not have touted my 93 LS as much as I

have done so if it is in fact an interference engine.

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A local Lexus mechanic told me my 2nd Gen LS 400 was non-interference. It seems that getting the facts about this question is harder than proving that Santa Claus doesn't exist! :rolleyes:

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Ok...

Just talked to very reputable import shop that specilaizes in Acura / Lexus.

95's and up are INTERFERENCE engines...will cause damage if timing belt breaks!!

90-94 are NON-INTERFERENCE engines... will NOT Damage engine if T-belt breaks.

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Joe,

Thanks for the additional clarification :D

Can we post this PERMAMENTLY somewhere? IT seems like a FAQ to the LS Forum....

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No offense 99 but I'm not convinced either. B)

Primarily because your reputable Lexus expert shouldn't know more than MY reputable Lexus expert. :P

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I hear you guys - no offense taken :lol:

I'm pretty sure the local lexus service rep told me the same thing - but everyone double check!!

To be continued......

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like i posted before, let's all chip in on some gas $, i'll run my gen 1 LS until the timing belt breaks and we'll all have a definite answer. i figure the nobel prize money would cover a new car after that :lol:

Not a bad idea except that won't tell me anything about MY LS! :angry:

:P

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From what I gather its next to impossible to develop a true "free spin"

engine with 4 valves per cylinder. That's because the valves are close

to the edge of the cylinder.

Maybe the first gen. is less likely to have interference than others, but

there is always a chance (however slight it may be) for a clash with the

piston if a valve is fully open and the engine continues to spin.

The only real test is to remove the timing belt (or when one beaks), fully open

a valve and spin the motor. Any volunteers? :o

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I thought all 97 and older are non-interference? Gen 1 and 2 engines are almost the same, with except latter has higher compression, semi-dual exhaust manifold, hot-wire air metering,...

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My 92 is a non-interference engine. That has been established. Engines either are or they are not. The camshaft installation procedure listed in the shop manual depends on the engine being non-interference.

When the change occured to interference I do not know, but the first years of the 4.0 litre engine are N-I.

It is possible make even 4 valve engines N-I by using valve reliefs in the pistons deep enough to avoid contact at TDC at full valve lift, and that is what Lexus did.

If anyone had stripped a timing belt, and the engine was interference, we would have heard about it for sure. On the Volvo 16 valve 8 of the valves will hit, and the valves bend, the guides crack, and the engine is essentially unrepairable. Those who have had that happen squawk quite a bit, and I am sure Lexus folks would too.

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The transition from non-interference to interference may have

occured in gen II (95 ). It's only conjecture, but the compression

ratio was increased from 10.0:1 to 10.4:1, perhaps by eliminating

the indentations in the pistons which made room for the intake

valves.

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Youre idea does have some logic to it...my 95 LS400 has 106,000 miles, bought it w/104k.

The seller, who bought it at 88,000 miles, told me t-belt was changed by the previous owner. Dealer has no record of it, only record for 60k and 75k serv and some oil chngs, there are no stickers. Its poss. that it was done at private shop. Should I take the chance? Is it possible to inspect it from the outside?

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