Index Home About Blog
From: Dave Baker
Subject: Re: Question on interference engine failure, does this sound right?
Date: Fri, 3 Feb 2006 03:00:06 -0000
Message-ID: <43e2c812$0$27800$>

Eric B. <never@noway.not> wrote in message
> > I don't see why the shop wouldn't pull the head to see if you just
> > have a couple bent valves. Even a boroscope might be able to determine
> > if there's any piston damage.
> > 
> > No matter what you decide to do, make sure the hydraulic timing belt
> > tensioner is also replaced. These may fail after they are compressed
> > once and this may have been the reason the replacement belt failed.
> > 
> > Larry
> Well the shop gave me the option of whether I wanted the head pulled or
> not. I was told that the job would take several hours, and that the
> engine probably would need to be replaced anyway.

I disagree. It's very unlikely that there's much else wrong other than the
bent valves. Pistons might be marked up a bit on the crowns but that won't
hurt them. You don't generally get much piston damage from valve contact
unless the head of the valve comes off and bounces around down there for a
while. There's a slim chance a couple of valve guides might be cracked but
that's no big deal.
Dave Baker

From: Dave Baker
Subject: Re: Question on interference engine failure, does this sound right?
Date: Fri, 3 Feb 2006 11:27:38 -0000
Message-ID: <43e33f05$0$27804$>

Don <> wrote in message
> On Thu, 02 Feb 2006 12:15:17 -0600, Steve <no@spam.thanks> wrote:
> >Eric B. wrote:
> >
> >
> >> To make a long story short, the best theory as to what happened is .
> >> . .. balancer belt (2 years old, about 20K miles or so) got loose
> >> somehow and managed to get caught under timing belt (also 2 years
> >> old, about 20K miles or so) causing the timing belt to slip.
> >
> >Brand new belts can break. That's why interference engines aren't worth
> >owning, IMO. Junk design from the get-go.
> >
> >>
> >> But here's the wierd thing .
> Not wierd at all.
> > . . the service manager informs me that 2 of my
> >> cylinders compression test at 150 (I'm guessing that's about normal?)
> >> and the other 2 cylinders have NO COMPRESSION AT ALL (no reading on
> >> the pressure
> >> guage)
> NON-OPERATIVE VALVES!!  The timing belt broke, the camshaft is NO

AIUI from the OP's post the belt just slipped rather than breaking although
by how many teeth is unknown. However it's all a bit odd. If it slipped
enough to cause some valves to hit (usually exhaust ones if a belt slips and
cam timing gets retarded) then all cylinders should have been affected

It's also not sensible to run a compression test on an engine if the cam
timing is known to be out and risk more internal damage than was there to
start with. It may be worth fitting a new belt correctly timed and then
checking compressions if the labour charge isn't excessive before assuming
that anything is in fact bent.

Also as you say, a quick look under the rocker cover can often identify
badly bent valves as can checking the valve clearances if the engine has
solid lifters rather than hydraulic. A leakdown test with compressed air is
of more value than a compression test in such cases and safer as it doesn't
require the engine to be cranked over.
Dave Baker

Index Home About Blog