From: matth@progress.COM (Matthew J. Harper)
Newsgroups: rec.autos,rec.autos.tech
Subject: Re: TOYOTA's timing belt
Keywords: Timing belt, 60000, crankshaft...
Date: 21 Aug 92 10:36:43 GMT
Organization: Progress Software Corp.

greeven@clipper.ingr.com (John Greeven) writes:

>I'm sorry to disagree with this rather scary reply.  In most engine designs
>with cam timming belts (instead of chains), the valves cannot hit the tops
>of the pistons under any normal circumstances.  Therefore, if the belt breaks
>the engine stops running and no component collisions can occur.  This type
>of collision is commonly possible in engines with timming chains, however.

  BZZZZZT!  

  "And here's Dan to describe your wonderful parting gift.  Thanks for
   playing 'Decribe That Auto Phenomenon'"!-) !-) !-)

  Just because the valves won't hit the pistons under 'normal' circumstances
doesn't mean it won't happen when the belt breaks.

  The reason they don't collide normally is because the belt keeps the two
in synch.  When the piston is up, the valves are out of the cylinder and
vice versa.  When the belt breaks this timing is screwed up and the piston
goes up and the valve comes down.  SMACK!  Could mean anything from
nothing happened (lucky...) to a full head job or engine job.

  This is not to say it will happen on all cars, mind you.  As the change over
from timing chains to belts happened, many car companyies did *not* change the
clearance on the valve/pistons at the same time.  This lead to many of the
kind of incidence we speak of in this thread.  Many cars today have had this
problem accounted for.  The ones I know of are Toyota, Honda and Subaru.  
(Subaru *never* had this problem though!-).  Nissan's were (and still are I
believe) notorious for this problem.  When it happens in the Nissan's it 
usually meant (means?) a minimum of a head job.

>Specifically, I own a 1988 1/2 Toyota Camry with a V6 2.5 liter engine.  It
>is not possible for this engine to have a valve to piston collision if the
>belt breaks.   I also owned a 1980 Mercury Zephyr which had a 4 cylinder
>engine with a rubber timming belt.  This belt gave way at about 70k miles
>and the engine merely stopped running - no valve collisions.

>Be aware that this may not be true for all engines with timming belts, but
>I suspect that it is true for most.

>Just my 2 cents worth.  BTW, IMHO it is very irritating to me when people get
>on the network and speak from authority when in fact they have limited
>knowledge about a particular subject.  I am especially disappointed when
>the questionable information might scare someone or cause them to spend money
>unnecessarily.

  What do you mean "spend money unnecessarily"?  A Rubber timing belt *will*
break sometime.  It's guaranteed.  Isn't it better to have it checked regularly
and replaced while the car is still drivable than to wait until it breaks
simply because no damage will occur if it does break?

>John Greeven
>greeven@clipper.ingr.com


  One quick note while I'm here:

  Is anyone else pissed off and fed up with the fast-work brake places that
have the adds on lately that pray on people fears?

  "Your dealer said he can get to your breaks next week.

   A lot can happen between now and next week.

   Bring it in to XXXX today.  We'll get the job done (before you get killed
   because you waited those extra 7 days during which time your pads will
   disintegrate and your brake shoes will fall out of the car taking you
   and your kids and the neighbors kids to a fiery death down some long
   forgotten imbankment that's so overgrown that you won't be found for weeks.)

  Anyway, you knwo what I mean, no?-)

-Matth


          Matthew J. Harper ! Progress Software Corp. ! {disclaimer.i}         
   God created heaven and earth to grow barley and hops. Now he homebrews !-)  
--
          Matthew J. Harper ! Progress Software Corp. ! {disclaimer.i}         
   God created heaven and earth to grow barley and hops. Now he homebrews !-)  
-- 

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