Interference engines

A but of a build up, but I *do* have a question...

The timing belt on my '87 16V Scirocco stripped last Tuesday.

This is the second time I've had one strip out on a 16V Scirocco. And the
third time I've had a timing belt strip out. The first time was many years
ago on a Fiat X-1/9. The result was that the valves became works of modern
art (bent in interesting ways) with all the attendant repair work required.
I was told back then it was because the engine was an "interference" type.
The top of the piston fits so closely to the head that if the a valve is
open when the piston comes up they will "interfere" with each other and
something will get wonked.

Fine. I was also told that the 1.8L 16V's in the Scirocco's were
interference engines and that there were only two possible positions the
engine could be in where they would not mash things up.

When I lost the belt on the first Scirocco some years back I happened to be
at idle, at a stop light. Everyone said that that was what saved me because
it (somehow) increased the probability that the engine might be in one of
those two position when the belt went. The shop put in a new belt, timed
the engine, and it ran fine for another five or six years. In fact, it was
running fine until I took it off the road a few months back.

When I lost the belt Tuesday I was coming down an exit ramp, clutch on the
floor, engine at idle. The shop put in a new belt, timed the engine, and
it's running fine (so far, anyway).

My question is, was I misinformed that the 1.8L 16Vs are "interference"
engines, or have I just been really really lucky twice?

- Bill

my 2 cents, at low RPM the oil pressure is lower and the lifters aren't
pumped up as at higher RPM.


"Bill Leary" > wrote in message
...
>A but of a build up, but I *do* have a question...
>
> The timing belt on my '87 16V Scirocco stripped last Tuesday.
>
> This is the second time I've had one strip out on a 16V Scirocco. And the
> third time I've had a timing belt strip out. The first time was many
> years ago on a Fiat X-1/9. The result was that the valves became works of
> modern art (bent in interesting ways) with all the attendant repair work
> required. I was told back then it was because the engine was an
> "interference" type. The top of the piston fits so closely to the head
> that if the a valve is open when the piston comes up they will "interfere"
> with each other and something will get wonked.
>
> Fine. I was also told that the 1.8L 16V's in the Scirocco's were
> interference engines and that there were only two possible positions the
> engine could be in where they would not mash things up.
>
> When I lost the belt on the first Scirocco some years back I happened to
> be at idle, at a stop light. Everyone said that that was what saved me
> because it (somehow) increased the probability that the engine might be in
> one of those two position when the belt went. The shop put in a new belt,
> timed the engine, and it ran fine for another five or six years. In fact,
> it was running fine until I took it off the road a few months back.
>
> When I lost the belt Tuesday I was coming down an exit ramp, clutch on the
> floor, engine at idle. The shop put in a new belt, timed the engine, and
> it's running fine (so far, anyway).
>
> My question is, was I misinformed that the 1.8L 16Vs are "interference"
> engines, or have I just been really really lucky twice?
>
> - Bill
>

I call really lucky twice.

Don't forget at higher RPMs you are usually accelerating in gear. This gives
the rotating mass in the engine more momentum which allows it to continue
rotating after it dies. Also the force of being in gear will force the
pistons around for another HIT.

I have seen 1.8T motors survive broken timing belts while at idle & those
are most definatly interferance engines.

Craig



"Bill Leary" > wrote in message
...
>A but of a build up, but I *do* have a question...
>
> The timing belt on my '87 16V Scirocco stripped last Tuesday.
>
> This is the second time I've had one strip out on a 16V Scirocco. And the
> third time I've had a timing belt strip out. The first time was many
> years
> ago on a Fiat X-1/9. The result was that the valves became works of
> modern
> art (bent in interesting ways) with all the attendant repair work
> required.
> I was told back then it was because the engine was an "interference" type.
> The top of the piston fits so closely to the head that if the a valve is
> open when the piston comes up they will "interfere" with each other and
> something will get wonked.
>
> Fine. I was also told that the 1.8L 16V's in the Scirocco's were
> interference engines and that there were only two possible positions the
> engine could be in where they would not mash things up.
>
> When I lost the belt on the first Scirocco some years back I happened to
> be
> at idle, at a stop light. Everyone said that that was what saved me
> because
> it (somehow) increased the probability that the engine might be in one of
> those two position when the belt went. The shop put in a new belt, timed
> the engine, and it ran fine for another five or six years. In fact, it
> was
> running fine until I took it off the road a few months back.
>
> When I lost the belt Tuesday I was coming down an exit ramp, clutch on the
> floor, engine at idle. The shop put in a new belt, timed the engine, and
> it's running fine (so far, anyway).
>
> My question is, was I misinformed that the 1.8L 16Vs are "interference"
> engines, or have I just been really really lucky twice?
>
> - Bill
>

Twice lucky. ;-)
Change that belt every 40K miles and then it won't strip or break on you.
I have seen them break after a meer 44K miles. Owner's son was driving it
like a "Bat out of H#LL"............well you know. ;-)
Caused damage to the valves, but the pistons survived.
Also worked on a VR6 where the chains had jumped. That wasn't pretty
either!

I have seen 2 belts snap while the interference engines were at idle.
Owners were lucky like you.

Don't push your luck and change that belt more often and before it breaks!

JMHO
--
later,
(One out of many daves)


"Craig" > wrote in message
...
>I call really lucky twice.
>
> Don't forget at higher RPMs you are usually accelerating in gear. This
> gives the rotating mass in the engine more momentum which allows it to
> continue rotating after it dies. Also the force of being in gear will
> force the pistons around for another HIT.
>
> I have seen 1.8T motors survive broken timing belts while at idle & those
> are most definatly interferance engines.
>
> Craig
>
>
>
> "Bill Leary" > wrote in message
> ...
>>A but of a build up, but I *do* have a question...
>>
>> The timing belt on my '87 16V Scirocco stripped last Tuesday.
>>
>> This is the second time I've had one strip out on a 16V Scirocco. And
>> the
>> third time I've had a timing belt strip out. The first time was many
>> years
>> ago on a Fiat X-1/9. The result was that the valves became works of
>> modern
>> art (bent in interesting ways) with all the attendant repair work
>> required.
>> I was told back then it was because the engine was an "interference"
>> type.
>> The top of the piston fits so closely to the head that if the a valve is
>> open when the piston comes up they will "interfere" with each other and
>> something will get wonked.
>>
>> Fine. I was also told that the 1.8L 16V's in the Scirocco's were
>> interference engines and that there were only two possible positions the
>> engine could be in where they would not mash things up.
>>
>> When I lost the belt on the first Scirocco some years back I happened to
>> be
>> at idle, at a stop light. Everyone said that that was what saved me
>> because
>> it (somehow) increased the probability that the engine might be in one of
>> those two position when the belt went. The shop put in a new belt, timed
>> the engine, and it ran fine for another five or six years. In fact, it
>> was
>> running fine until I took it off the road a few months back.
>>
>> When I lost the belt Tuesday I was coming down an exit ramp, clutch on
>> the
>> floor, engine at idle. The shop put in a new belt, timed the engine, and
>> it's running fine (so far, anyway).
>>
>> My question is, was I misinformed that the 1.8L 16Vs are "interference"
>> engines, or have I just been really really lucky twice?
>>
>> - Bill
>>
>

"dave AKA vwdoc1" > wrote in message
...
> Twice lucky. ;-)

Even more so. About 30 seconds earlier I'd been up around 4,000 RPM on the
highway I was exiting from when this one went.

> Change that belt every 40K miles and then it won't strip or break on you.

Thanks. I was trying to remember if it was 40K or 60K. I have the service
records for the car and it claimed it had been done about 30K back. But
I've also just discovered that the odometer slips during warmer weather, so
that "30K" could be 50K for all I know.

> I have seen 2 belts snap while the interference engines were at idle.
> Owners were lucky like you.
>
> Don't push your luck and change that belt more often and before it breaks!

No. I'll have to fix the odometer so I don't miss doing it.

Thanks.

- Bill

"Craig" > wrote in message
...
>I call really lucky twice.

I was running around 4,000 RPM about 30 seconds before this too.

> Don't forget at higher RPMs you are usually accelerating in gear. This
> gives the rotating mass in the engine more momentum which allows it to
> continue rotating after it dies. Also the force of being in gear will
> force the pistons around for another HIT.

I'd figured on momentum, but didn't think the cam shafts would really have
enough to keep it spinning. On the other hand, as you mention, at high RPM
there's a lot of rotational energy stored in there.

Someone mentioned that, if it's going slow enough, there's a "snap back"
from the valve springs which would tend to take the valves to one of the
safe positions.

> I have seen 1.8T motors survive broken timing belts while at idle & those
> are most definatly interferance engines.

Related question: Are the 8V (as in 1990 Corrado, 1980's Sciroccos and
Rabbits) also interference types?

- Bill

"Lost In Space/Woodchuck" > wrote in message
...
> my 2 cents, at low RPM the oil pressure is lower and the lifters aren't
> pumped up as at higher RPM.

I hadn't considred oil pressure at all. In fact, I guess I hadn't even
considered that they were hydraulic lifters.

- Bill

"Bill Leary" > wrote

snip

> Related question: Are the 8V (as in 1990 Corrado, 1980's Sciroccos and
> Rabbits) also interference types?
>
> - Bill


AFAIK If they are 8v, they are not usually an interference
engine.........unless they are diesel engines which are interference.

Some belts have age as well as miles listed in their service interval.

On Sun, 31 Aug 2008 20:57:57 -0400, "Bill Leary" >
wrote:

>"dave AKA vwdoc1" > wrote in message
.. .
>> Twice lucky. ;-)
>
>Even more so. About 30 seconds earlier I'd been up around 4,000 RPM on the
>highway I was exiting from when this one went.
>
>> Change that belt every 40K miles and then it won't strip or break on you.
>
>Thanks. I was trying to remember if it was 40K or 60K. I have the service
>records for the car and it claimed it had been done about 30K back. But
>I've also just discovered that the odometer slips during warmer weather, so
>that "30K" could be 50K for all I know.
>
>> I have seen 2 belts snap while the interference engines were at idle.
>> Owners were lucky like you.
>>
>> Don't push your luck and change that belt more often and before it breaks!
>
>No. I'll have to fix the odometer so I don't miss doing it.
>
>Thanks.
>
> - Bill

The older 1.8s are non-interferance. You can break belts all day long at
redline & they wouldn't care. The newer ones AEG & newer technically aren't
but they are extremely close & I have seen them hit due to carbon buildup on
the pistons.

Craig

"Bill Leary" > wrote in message
...
> "Craig" > wrote in message
> ...
>>I call really lucky twice.
>
> I was running around 4,000 RPM about 30 seconds before this too.
>
>> Don't forget at higher RPMs you are usually accelerating in gear. This
>> gives the rotating mass in the engine more momentum which allows it to
>> continue rotating after it dies. Also the force of being in gear will
>> force the pistons around for another HIT.
>
> I'd figured on momentum, but didn't think the cam shafts would really have
> enough to keep it spinning. On the other hand, as you mention, at high
> RPM
> there's a lot of rotational energy stored in there.
>
> Someone mentioned that, if it's going slow enough, there's a "snap back"
> from the valve springs which would tend to take the valves to one of the
> safe positions.
>
>> I have seen 1.8T motors survive broken timing belts while at idle & those
>> are most definatly interferance engines.
>
> Related question: Are the 8V (as in 1990 Corrado, 1980's Sciroccos and
> Rabbits) also interference types?
>
> - Bill
>