Jump to content

  •  

Show
Photo

What If The Timing Belt Breaks?


  • Please log in to reply
20 replies to this topic

#1 sercombe

sercombe

    Member

  • Members
  • PipPip
  • 85 posts
  • Lexus: IS200 - Granite Sky

Posted 01 April 2007 - 04:41 PM

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?

Have something to contribute?

Sign in or register to start a topic...

#2 Rob

Rob

    Club Post Guru

  • Members
  • PipPipPipPipPipPipPip
  • 7,317 posts
  • Lexus: .
  • Location: Please Select
Contributor

Posted 01 April 2007 - 04:51 PM

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.

#3 Bazaar

Bazaar

    New Club Member

  • Members
  • Pip
  • 7 posts
  • Lexus: IS200
  • Location: Please Select

Posted 30 April 2007 - 11:53 AM

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.

#4 winnie

winnie

    Established Member

  • Members
  • PipPipPipPipPip
  • 611 posts

Posted 30 April 2007 - 12:05 PM

I would change it just for peace of mind.

#5 Rob

Rob

    Club Post Guru

  • Members
  • PipPipPipPipPipPipPip
  • 7,317 posts
  • Lexus: .
  • Location: Please Select
Contributor

Posted 30 April 2007 - 12:11 PM

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!

#6 aido

aido

    Sex, Drugs & Sausage Rolls

  • Members
  • PipPipPipPipPipPipPip
  • 12,314 posts
  • Lexus: Aristo V300
  • Location: Please Select

Posted 30 April 2007 - 04:46 PM

Yeah I was always lead to beleive it's an interference type design Rob :)

#7 MacRS200

MacRS200

    Club Post Guru

  • Members
  • PipPipPipPipPipPipPip
  • 4,585 posts
  • Lexus: Altezza RS200 Tip, IS200 Sport
  • Location: Please Select
Contributor

Posted 30 April 2007 - 06:05 PM

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.

#8 Rikos

Rikos

    Club Discount Negotiator

  • Members
  • PipPipPipPipPipPipPip
  • 3,919 posts
  • Lexus: IS200 Sport

Posted 01 May 2007 - 09:49 AM


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.

#9 Bazaar

Bazaar

    New Club Member

  • Members
  • Pip
  • 7 posts
  • Lexus: IS200
  • Location: Please Select

Posted 07 May 2007 - 09:34 AM



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.

#10 ColinBarber

ColinBarber

    Lexus Knowledge

  • Global Moderator
  • 8,732 posts
  • Location: Please Select
Contributor

Posted 07 May 2007 - 10:28 AM

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.

#11 yemgi

yemgi

    Club Post Guru

  • Members
  • PipPipPipPipPipPipPip
  • 1,572 posts
  • Name: Guilhem
  • Lexus: SC'd IS200 - IS-F
  • Year: 2008
  • Location: Sussex

Posted 07 May 2007 - 05:23 PM

from the workshop repair manuals I have, the design is non interference type

#12 Mike_B

Mike_B

    Established Member

  • Members
  • PipPipPipPipPip
  • 995 posts
  • Lexus: Alfa Romeo 159 Sportwagon

Posted 07 May 2007 - 07:21 PM

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.

#13 yemgi

yemgi

    Club Post Guru

  • Members
  • PipPipPipPipPipPipPip
  • 1,572 posts
  • Name: Guilhem
  • Lexus: SC'd IS200 - IS-F
  • Year: 2008
  • Location: Sussex

Posted 07 May 2007 - 08:58 PM

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.

#14 MacRS200

MacRS200

    Club Post Guru

  • Members
  • PipPipPipPipPipPipPip
  • 4,585 posts
  • Lexus: Altezza RS200 Tip, IS200 Sport
  • Location: Please Select
Contributor

Posted 07 May 2007 - 11:07 PM

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?

#15 Rikos

Rikos

    Club Discount Negotiator

  • Members
  • PipPipPipPipPipPipPip
  • 3,919 posts
  • Lexus: IS200 Sport

Posted 08 May 2007 - 09:48 AM

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

Have something to contribute?

Sign in or register to start a topic...


Not what you're looking for?

Register now, we have a huge community of enthusiasts to answer any questions you might have