Is a drive belt really considered "old" after only 5 minutes of engine run time? - Toyota Nation Forum : Toyota Car and Truck Forums

Camry 3rd & 4th Gen (1992-1996 & 1997-2001)/1st Gen Solara (1999-2003) Toyota Camry Discussion for years 1992-1996 & 1997-2001, as well as Solara discussion for years 1999-2003. Topics of discussion range from fuel economy, safety, modifications, performance all involving America's favorite family car, the Toyota Camry.

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post #1 of 21 Old 05-17-2017, 09:05 PM Thread Starter
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Is a drive belt really considered "old" after only 5 minutes of engine run time?

Looking over the TB and drive belt replacement in the FSM I see they list two values for the tension on the drive belts. One for a new belt and a lower one for a used belt. It makes sense since a new belt will stretch and end up at the value for an old belt at some point. It goes on to say that a belt is considered to be in used condition after 5 minutes of run time Will a new belt actually do all of its stretching after only5 minutes of use and if so why isn't the procedure just to run a new belt for 5 minutes before setting the final tension?

1992 Camry 4 cylinder manual 5S-FE 295,000
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post #2 of 21 Old 05-17-2017, 09:57 PM
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Originally Posted by brianappj View Post
Looking over the TB and drive belt replacement in the FSM I see they list two values for the tension on the drive belts. One for a new belt and a lower one for a used belt. It makes sense since a new belt will stretch and end up at the value for an old belt at some point. It goes on to say that a belt is considered to be in used condition after 5 minutes of run time Will a new belt actually do all of its stretching after only 5 minutes of use and if so why isn't the procedure just to run a new belt for 5 minutes before setting the final tension?
To quote the Dayco drive belt manual:

"Our engineers recommend careful belt tensioning. A normal but significant reduction of installation tension of a new belt occurs as a result of belt seating. To prevent slippage it is very important that the belt be retensioned after running engine for 3 to 5 minutes to seat belt. Do not over tension the belt."

The first time you install the belt it has never experienced tension or load before (bear in mind that a drive belt can be transferring several kilowatts of power to accessories), so they undergo a fairly significant stretch the first time they are run. After that point they have been "conditioned" to the load so only stretch at a slow rate over time. You still need to set the belt at the "new" tension before the first run otherwise it won't seat properly and stretch to the "used" tension, and you'll end up with an under-tensioned belt in no time as the run-in stretch continues after you thought you'd fully tensioned it.

Imagine the two scenarios below:

A) Correct way:
1) Install new belt
2) Tension to correct "new" belt tension of 100lbs
3) Run engine for 5 minutes to bed-in the belt
4) Re-tension to the "used" belt tension of 90lbs (tension may only have been 60lbs after the run-in due to the initial stretch)

B) Incorrect way:
1) Install new belt
2) Tension belt enough to take up the slack and stop it squealing or slipping off pulley (say 20lbs)
3) Run engine for 5 minutes to bed-in the belt
4) Re-tension to the "used" belt tension of 90lbs, however because you didn't bed it in from the "new" belt tension it has only stretched a small amount, so even though you've set the tension at 90lbs it'll continue to stretch afterwards (as if you were applying the "new" tension), requiring re-tensioning AGAIN in a couple of days back to 90lbs

Consider that most things are considered "used" the second they are started/turned on/opened. The value of a new car drops by ~10-20% the second you drive it out of the dealership. Also, bear in mind the difference between "used" and "old". Old implies time, whereas used implies operation. Something can be old but not used (for instance an unsold car that sits on the lot for years), or vice-versa (a current model car that has racked up a quarter million miles as a taxi and is flogged out) or both (that clapped-out old Ford your grandfather has that has driven to the moon and back) or neither (obvious).
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post #3 of 21 Old 05-18-2017, 04:21 AM Thread Starter
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That is it. Someone always knows the answer to the most obscure question. The FSM has a new and old tension value with a definition of 5 min of run time for old but I didn't see anything about retensioning a new belt set at new tension back up to the "old" tension value after its first 5 minutes of run time. They make it sound like you just set tension once new or old and are done. Your correct way is what I was thinking should be done and makes sense. Maybe the FSM just assumes a standard practice of rechecking belt tension for a new belt after that first 5 minutes of use.

There is no mention of this but maybe the TB itself should also be retensioned after its first 5 minutes for the first time for the same reason. They just have you turn the crank through two revolutions, set it to 45 BDC, then tighten down the tension pulley. Maybe we should also re do this TB tension setting process after we run it for 5 minutes to seat the drive belts as well.

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post #4 of 21 Old 05-18-2017, 09:50 AM
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Dunno about others brian, but I've always re-checked & confirmed TB belt tension, and proper alignment on pulleys after 1st start here, regardless of vehicle - and have had to go back and re-adjust / re-tension a few times.

* Nothing wrong with taking your time, & re-checking work, especially on a DIY project.
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post #5 of 21 Old 05-18-2017, 11:44 AM
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This discussion is very useful. But why couldn't the belt makers run the belt 5 minutes in factory so that they are 'used' out of the door? Can't they make people's life easier? From the big picture, this is a very inefficient way of doing things.
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post #6 of 21 Old 05-18-2017, 05:29 PM
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Because it gets expensive if they need to run every belt for 5 minutes. Besides, good designers use automatic tensioners so the belt slack and tension are always kept in the proper range. The stinking manual system is cheap and more timing consuming.

Usually new tension is about 25% over the "old" tension. That said, I find that you're likely having to retension it again after several warm up cycles. I was hesitant to use higher "new" tension than specified, but Hiro has a great point in the reason behind it about seating it.
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post #7 of 21 Old 05-18-2017, 06:27 PM
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Originally Posted by JohnGD View Post
Because it gets expensive if they need to run every belt for 5 minutes. Besides, good designers use automatic tensioners so the belt slack and tension are always kept in the proper range. The stinking manual system is cheap and more timing consuming.
Exactly. A factory pumping out a belt every 10 seconds would either slow to a crawl or need a massive bank of tensioners, both of which cost money (either in slower production, higher costs, or more equipment). There's a reason why things rated to MIL-SPEC are more expensive, because they have the stress-testing done in the factory to cut down the infant mortality rate (nothing to do with children by the way) portion of the bathtub failure curve so things are less likely to fail early in the field. Same goes for burn-in at the factory for high-end electronics, to stop the smoke escaping the first time you turn your new $5000 hi-fi on.

And that same Dayco manual I quoted earlier says that for systems with auto tensioners you don't need to re-set after the initial run-in....


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post #8 of 21 Old 05-18-2017, 10:14 PM Thread Starter
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This has me wondering how a TB can keep the crank and cam in sync as it stretches. On the side of the cam-crank pulley opposite of the tensioer pulley there is a set number of teeth between their timing marks. This number of teeth is not going to change as the belt stretches. Now, later after the belt has stretched and you go to reset the tension pulley to take up the slack on the opposite side between the cam and crank there is nothing to take up the slack like there is on the other side. Won't this lead to a properly tensioned belt on one side and a floppy on the other resulting cam turning back on its timing mark to keep the forces on each side equal?

Maybe whenever you mess with the TB like this you always have to go back and check the timing marks and reposition the entire belt.

It sounds like all the stretching is done after the first 5 minutes and if you go back and redo the timing belt adjustments after this it will not stretch much more over the rest of its life.

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post #9 of 21 Old 05-18-2017, 11:31 PM
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Timing belt use cogs so it doesn't seat into the grooves like drive belts. Tension wise I think that's a difference.

Timing belt has strong fibers that will eventually stretch, retarding the timing. That's a reason why I change out the belt 5-yr/60K instead of the 6-yr/90K or even Honda's 7-yr/105K intervals.
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post #10 of 21 Old 05-18-2017, 11:53 PM
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Quote:
Originally Posted by brianappj View Post
This has me wondering how a TB can keep the crank and cam in sync as it stretches. On the side of the cam-crank pulley opposite of the tensioer pulley there is a set number of teeth between their timing marks. This number of teeth is not going to change as the belt stretches. Now, later after the belt has stretched and you go to reset the tension pulley to take up the slack on the opposite side between the cam and crank there is nothing to take up the slack like there is on the other side. Won't this lead to a properly tensioned belt on one side and a floppy on the other resulting cam turning back on its timing mark to keep the forces on each side equal?

Maybe whenever you mess with the TB like this you always have to go back and check the timing marks and reposition the entire belt.

It sounds like all the stretching is done after the first 5 minutes and if you go back and redo the timing belt adjustments after this it will not stretch much more over the rest of its life.
Remember that timing belts (toothed) are different to drive belts (multi-V) - toothed belts require less tension to operate correctly as they are not reliant on tension to stop them slipping, only to stop it slapping around and/or jumping teeth. Also, it is a known thing that as a timing belt stretches it ever so slightly alters the cam timing, so much so that a timing belt well past its use-by date can actually be a tooth out affecting both cam and ignition timing. Plenty of people have claimed that their car runs significantly better after a timing belt change.

Yes a belt will do a majority of it's stretch in the initial bed-in, but it does stretch after that point too (otherwise there would be no need for auto-adjusting tensioners)


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post #11 of 21 Old 05-19-2017, 03:11 AM Thread Starter
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Oh so,
- The drive belt "bed in" refers to it actually pushing into its V grooves as well as stretching and a TB doesn't have v grooves to push into.
- The TB operates under less tension so is less prone to stretching compared to the drive belts.
- A TB change interval is based on its stretching out to the point of affecting the timing as well as its probability of breaking. I had always thought changing out the TB was solely to avoid the increasing chance that it might break.

I have found out here that the TB tensioner pulley is locked into position at the end of the install so I think the Camry doesn't have any auto adjusting tensioners on its drive or timing belts.

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post #12 of 21 Old 05-19-2017, 08:39 AM
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Regarding the TB tensioner being locked in after the install, the V6 and maybe some year models of the 4-cylinder has a spring-loaded TB tensioner.

I try to run mine to the full 100K miles before changing because I don't believe the stretch and resulting retarding of timing is significant enough to make me do that job any earlier than I have to. One poster said the stretch could amount to a full tooth of difference from the new install. That may be true but wouldn't a full tooth off cause a VERY noticeably rough run? Like all generalizations, maybe we are talking about extremes and special cases that I may not have experience with my particular car...but still wanted to put that out there for further discussion.

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post #13 of 21 Old 05-19-2017, 10:23 AM Thread Starter
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Now I am wondering why they lock down the tensioner pulley on this particular model/year. Why not allow the spring to move the pulley to keep the tension constant for the life of the belt? The designers are pretty smart and must have had some reason why locking it place was better for this car.

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post #14 of 21 Old 05-19-2017, 11:26 AM
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Because the tensioner spec'd is a spring type tensioner - it doesn't have a hydraulic dampener, needed to account for differences in belt tension under engine load.. The function of the spring is to allow the servicer to correctly set the initial TB tension to spec., then lock the pulley in place.

As JohnGD said, a TB has a much greater surface area for power transmission, due to the teeth on the TB belt / the cog pulleys used on the camshafts and crankshaft, therefore the belt has a much lower stretch rate.

Wear, and service life, are more of a concern for a properly tensioned TB after installation.

As a TB wears, fine particles of rubber and fiber are shed within the TB covers - which is why you should replace all pulleys along w/ the belt as a set - the bearings & surfaces of the idler and tension pulleys are also considered a wear item.

Also, an over-tensioned belt is just as bad as an under-tensioned belt - it will accelerate belt wear -> failure much sooner vs. recommended service interval, FYI.

Again, recommend a quick check for any initial 'stretch' as a sanity check, as slack may have been drawn from between the cam pulleys, etc. after 1st start. It only takes another few minutes to check.

Last edited by CamryFL; 05-19-2017 at 11:29 AM.
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post #15 of 21 Old 05-19-2017, 11:59 AM
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Quote:
Originally Posted by brianappj View Post
Now I am wondering why they lock down the tensioner pulley on this particular model/year. Why not allow the spring to move the pulley to keep the tension constant for the life of the belt? The designers are pretty smart and must have had some reason why locking it place was better for this car.
The V6's self-tensioner is heavily damped, like a shock absorber. I suspect if it was a simple spring like the I4 uses, belt tension would bounce like a ping pong ball.

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