Do Timing Belts Ever Stretch?

I have been an auto hobbiest for qiute a while and wondered what this
Forum's best and brightest think about the following: I noticed a very
simple proceedure to adjust timing belt tension in my factory maint book
on my 95 Civic by removing a plug on the lower timing cover to get at the
adjusting bolt and removing the top timing cover to check for loosness.
This prooceedure would be quick and should be a piece of cake to perform.
This makes me wonder if it might be a good idea to check belt tension at
45,000 miles and adjust if needed? Do these belts ever stretch or not? Of
course I mentioned my 95 Civic EX timing belt having excessive looseness
(over 1.5" in 78,000 miles) in a previous post and had several good
responses. I have seen an 85 Nissan 300Zx (mine) have a loose timing belt
at 70,000 original miles way back when..... Some manufactures use an
active hyrdraulic tensioner(Mazda V6 89-98 for example) versus a lock down
system like Honda uses. I have not seen this issue addressed anywhere, but
think this discussion could be of benefit to the entire Honda community
because our engines have such a long timing belt change interval and are
of interference design. So,I'm still wondering? Thanks in advance for
your thoughts and recommendations.

 

I've some knowledge of this type of belt on industrial equipment. These are
not like fan-belts. Typically they have Kevlar cords and extremely little
tolerance for stretch - less than a metal chain. That is they maintain their
length right up to the point of catastrophic failure. So I don't think this
sort of inspection would be much help.

rj

 

Yes, timing belts stretch. But I'm not sure I understand your question,
because you already stated that you had past experiences with loose
timing belts, so doesn't that already answer the question?

 

Thanks for the input Ron. And Bucky, you have made a good point. But to
answer that point....I have to say the following: I did not install
either of those timing belts, so I'm not sure they were installed
properly. I have read sooo many posts on Google on "stretched timing
belts" that I'm convinced there is about a 50 - 50 split on the issue. I
would say that timing belts are not supposed to stretch, but some
do......for whatever reason. The timing belt and its tensioner is
operating in an oven type enviroment, and might be starting out the day at
the same temperature as cold your freezer..........I'm very glad I opened
up my timing belt cover on my 95 Civic EX with 192,000 miles (78,000 on
the belt, seals and water pump) after hearing an unusal but not loud
noise. First, I found a very loose timing belt with over 1.5" of
deflection and second, the tensioner was in very bad shape with no grease
left in the bearing. Cheers.

 

Oh I see, so what you're saying is that you discovered you had loose
belts, but you were not sure if the belts got loose because they
stretched, or if they were loose when they were installed.

Well, I had a friend who had an old Honda Accord with about 80,000
miles. One day (while I was riding with him), the engine died. After he
had it towed to his mechanic, the mechanic told him that the timing
belt (original factory) was stretched and loose, so it needed to be
replaced. To me, that's proof that timing belts stretch. How else could
you explain that scenario?

 

there's minimal wear, which can cause slight looseness, but the belts
don't stretch - as stated by ron jones, their length is the same
throughout their life. if you have one that's loose, it wasn't set
right - an apparently common problem since it's spring tensioned, not
manually tensioned. if the factory tension procedure is not followed to
the letter, you'll have problems.

on a side note, ability to retain tension and lack of stretch are a
couple of the reasons why belts are superior to chains in this application.

 

Bucky, you make a very good point. You're on the side of the fence that
says: timing belts stretch. And then there is Honda that allows us to
drive their newer cars to 105,000 miles on a timing belt while other
manufactures are changing them at 60,000 miles. I agree with you to a
point. So, I'm straddling the fence by saying: some timing belts stretch.
Ron, on the other hand, works with this type of belt and says they don't.
I wonder what would cause timing belts to stretch when the're not supposed
to?

 

Thanks for weighing in again on the issue Jim, I know which side of the
fence you're on. I'm straddeling it. I set my tension by the book and am
getting about .25" of belt deflection versus over 1.5" deflection of the
old belt on my 95 Civic EX. The previous job was done by the dealer 7
years and 78,000 miles ago. How could a dealer screw up something as
simple as a timing belt? Anyone else out there have a loose timing belt
when doing their car's first belt change or the first belt change after a
Honda Dealer replaced the belt like me.

 

fine, but check the data on belt materials. do tires "stretch"? the
same aramid fibers.

easily. i've repaired many vehicles screwed up by dealers. you
wouldn't believe. a friend came to me the other day because his car was
making a "strange transmission noise". the dealer wanted to change the
transmission for thousands of dollars. it was simply a broken motor mount.

yes. me.

bottom line, dealer mechanics should know the most because they
specialize and work on the same vehicles again and again. but fact is,
some individuals are not good with their hands and/or didn't pay much
attention in class. so they're not good at their job. statistically,
the dealer gives you a good chance of the job being done right, but it's
absolutely /no/ guarantee.

 

Thanks again Jim. There are very few guarantees. A friend of mine and I
asked a tire dealer to change both passanger side tires on her van and
made it very clear we wanted to keep the passanger rear tire as a spare
The driver's front was brand new with less than 2,000 miles on it. The
passanger front was well worn had the belt breaking loose which was
visible. The Dealership proceeded to change both rear tires , one of
which had less than 10,000 miles on it and kept the better of the two back
tires!...........
If you find a good mechanic, tip him or her and send him more business.
If he makes a mistake, work with him and you will be rewarded 10 fold.
Just my opinion of course.

 

So Jim what you're saying is that if a belt is loose, the only
explanation is that it was equally loose when it was installed. In
other words, if a belt deflection is at 1.5" after 80,000 miles, it
must have been around 1.5" out of the factory.

What if the following situation occurred: You get a new car out of the
factory. You check the tension, it's at 1.25" deflection. 80,000 miles
later, you recheck the tension, and it's at 1.5" deflection. Would that
prove that timing belts stretch?

Like I wrote in another post, my friend's car died after 80,000 miles.
Mechanic checked it out, said it was a loose timing belt and replaced
it (he still had the original factory timing belt). It obviously was
not as loose during the first 80,000 miles, otherwise the car wouldn't
have started. So how do you explain that?

 

pretty much, yes. as i stated before, you do get a small amount of
wear, but that's not stretch.

no. see above.

car wouldn't have started??? would this mechanic also say the blinker
fluid level effects starting too? your friend needs a new mechanic if
they tell b.s. stories like that. if the belt has not jumped, the cam
timing remains and the car therefore will start. even if it's jumped a
tooth, it'll still start. performance will suck, but it'll start. if
the timing is any further off, there will probably be interference and
therefore severe damage. looks like your friend got hosed for a
premature belt change to me.