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What If The Timing Belt Breaks?


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What happens if the timing belt or tensioner/idler Breaks?

Info from about.com:

the timing belt breaks on a non-interference design, there is enough clearance between the pistons and valves to prevent damaging contact. An interference design does not have sufficient clearance between those parts and engine damage would result from a broken timing belt.

Is the IS200 a non interference engine and is it ok for the timing belt to break? what exactly happens?

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from posts on here it is meant to be an non interference design - but looking at info for the cambelt replacement it gives warnings about valve/piston contact so not so sure but I would be surprised if its interference.

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  • 4 weeks later...
from posts on here it is meant to be an non interference design - but looking at info for the cambelt replacement it gives warnings about valve/piston contact so not so sure but I would be surprised if its interference.

Does anyone know the difinitive answer to this?, my IS is 5 years and 10 months old (50k) and it has to be done by 6 years or 100k which means its due very soon.

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taken from lexus.eu technical manual pages:

" always turn the crankshaft clockwise. if the timing belt is disengaged, having the crankshaft pulley at the wrong angle can cause the piston head and valve head to come into contact with each other."

for me that good enough to say interference head!

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Agree with Rob and Aido.

It would be hard to get a 10:1 compression ratio with a non-interference design IMHO because if the size of the combustion chamber. The engine is "square" with the bore and stroke being 75mm there is therefore only about 7.5mm clearance between the piston and the head at TDC.

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from posts on here it is meant to be an non interference design - but looking at info for the cambelt replacement it gives warnings about valve/piston contact so not so sure but I would be surprised if its interference.

Does anyone know the difinitive answer to this?, my IS is 5 years and 10 months old (50k) and it has to be done by 6 years or 100k which means its due very soon.

It has to be done at 6 years or 60k. It used to be 10 years or 100k but Lexus changed it and personally i think it's better to get it done at 60k. But there have been plenty of people on here that have left it until 100k and had no problems.

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from posts on here it is meant to be an non interference design - but looking at info for the cambelt replacement it gives warnings about valve/piston contact so not so sure but I would be surprised if its interference.

Does anyone know the difinitive answer to this?, my IS is 5 years and 10 months old (50k) and it has to be done by 6 years or 100k which means its due very soon.

It has to be done at 6 years or 60k. It used to be 10 years or 100k but Lexus changed it and personally i think it's better to get it done at 60k. But there have been plenty of people on here that have left it until 100k and had no problems.

Sounds like its not worth the hassle to take the chance. It will get done next month! Cheers guys.

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Agree with Rob and Aido.

It would be hard to get a 10:1 compression ratio with a non-interference design IMHO because if the size of the combustion chamber. The engine is "square" with the bore and stroke being 75mm there is therefore only about 7.5mm clearance between the piston and the head at TDC.

Most Toyota engines are non interference. Even ones with 10.5:1 compression. There are cut outs in the piston heads that give the required clearance. Not sure about the IS200 engine, a workshop manual should confirm this within the engine description.

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If it actually is non-interference, why all the panic and 'peace of mind' cam-belt changes? If it breaks, you break down and have to be towed to a garage where they will replace the belt and reset the timing. And that's it - no other damage. So why would Lexus suddenly recommend a very expensive 6 year change point, if the only problem would be a breakdown?

But I'm far from convinced - gut feeling, and fluff34567's quote from the tech pages, suggests it's an interference design. Yemgi - could you quote the section that suggests otherwise?

I believe the cut-outs are because the valve timings mean the valves are open as the piston approaches the very top of it's stroke, as opposed to being cut-outs to avoid valves that are stuck right down because of serious timing problems. Having an exhaust valve open as long as possible helps with exhaust gas scavenging from the chamber, and having an intake valve open as early as possible means being able to start loading the next charge of fuel-air as soon as the piston starts to drop on the intake cycle.

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Wether there is interference or not, it never is good for an engine to experience a belt break. I don't think it is overpriced, I had mine changed by Lexus for 600€ while Peugeot charged me 800€ for my 405 :wacko:

£400 every 5 years is not much IMO.

here is the page of the manual that shows the piston heads.

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Most Toyota engines are non interference. Even ones with 10.5:1 compression. There are cut outs in the piston heads that give the required clearance. Not sure about the IS200 engine, a workshop manual should confirm this within the engine description.
I believe the cut-outs are because the valve timings mean the valves are open as the piston approaches the very top of it's stroke, as opposed to being cut-outs to avoid valves that are stuck right down because of serious timing problems. Having an exhaust valve open as long as possible helps with exhaust gas scavenging from the chamber, and having an intake valve open as early as possible means being able to start loading the next charge of fuel-air as soon as the piston starts to drop on the intake cycle.

@ Colin - The only pistons I have seen without "cut outs" on the crown are on 2 strokes and long stroke bike engines so maybe, maybe not. Like Mike said they don't necessarily provide enough clearance when the belt goes.

The only way to test either theory is let a belt break at revs and see what happens, anyone want to try?

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Wether there is interference or not, it never is good for an engine to experience a belt break. I don't think it is overpriced, I had mine changed by Lexus for 600€ while Peugeot charged me 800€ for my 405 :wacko:

£400 every 5 years is not much IMO.

here is the page of the manual that shows the piston heads.

How much?????? :o :o

You can buy the parts to do the cambelt for around £80-£100 and then it's 3and a half hours labour.

You should be able to get it changed for between £200-300

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How many times have you heard of a poor mug breaking down, going to a garage, being told the engine is shot due to a broken Cam Belt.

I don't trust garages at all. Especially when they show you a bent a valve (the same one they've had for years).

This is why it is £400 - people think that it would cost £000's if they don't do it and it's like an insurance policy. The garages are on a bender and I reckon every mechanic will tell you "interference" or not, there is a risk and you should do it!

Personally, I would say pay the £400 (at £100 p/h for the 3.5 hour job plus the belt it's worthwhile) and have it properly guaranteed.

The fact that Lexus have changed the schedule to 60k means it can and does break!

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you've all got me worried.

mine is at 91k, 8yrs old, and it hasent been changed.

ill book myself into a garage.

There are lots of people who didnt have it changed until 100k without any problems but wouldnt really want to do too much more.

It's not an expensive job so it's best to get it done just in case :)

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I had mine done....X reg 6yrs old and only 45k at the time, when the old belt was taken off it had a small nick along the edge running about 2 inches and moving inwards, i supplied all parts, belts/tensioner and a new water pump and fitted for about 400 all inc.

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