Just had a timing belt job and it is like a newer car,

Did your replace the timing belt?

The old timing belt looked OK so I can only attribute the improvement to eliminating belt stretch. I see that access plug to get to the tension pulley. I hope to reset the tension all I have to do is remove the spark plugs.

You don't have to remove the plugs.

If that is the case I will definitely try it at the 3 year mark. Before when I went to pass I could never get decent (any) acceleration. Now I can accelerate like a normal small car should.

The poor performance was not likely the stretch... it may have been out of time altogether.

Now I would like to know why resetting the tension is not part of the service interval chart. Why not list it as a recommended procedure at 3 years/40,000? They went to the trouble of putting an access plug there so why not at least mention to use it? I guess your car won't quit if you don't but the increase in performance, and I would assume gas mileage, is quite obvious.

I don't know why the don't do it. It could be that by the time it stretches that much, you need a new one.

If I reset the tension do I need to get in there and check the timing marks or will they just line up like when the belt was new? When done at the proper spot is the force of the spring supposed to match the resistance of the crankshaft pulley?

If you only reset it, the timing will not change. The belt is kinda like a flexible light weight chain. If it stretches, the belt gets loose all over. If you turn the engine sightly until all the tension is on the pull (front) side, hold it there, and loosen and then tighten the tensioner, all you have done is to put the excess stretch on the back side, lift the tensioner to take the slack out and tighten it. It does not change the timing. It tightens it all up, so there is no slop or fluctuation in the timing, but it doesn't change the timing. Usually by the time there is significant looseness in the belt, the spring is no longer able to pull the tensioner up high enough to take all the slack out, so you may have to go in there after all. After the belt has stretched that much, if you were to check the timing you would find that the cam is slightly retarded, because the belt stretch has allowed the cam to lag behind as much as the stretch. That won't be all that much. You won't be able to change the timing unless you remove the belt and physically set the cam "forward" or advanced on tooth. Then the cam will be over advanced and you will likely lose performance.

I don't know how much they actually stretch. I might be surprised. But another thing to consider is that the distributor on that car is run by the cam, so when the cam is retarded so is the ignition timing, and that will make a big difference. Changing the belt actually advances the ignition timing. It probably wouldn't hurt to check the ignition timing either.

So I don't know if it is really worth retensioning the belt in the long run or not. Glad the belt helped you!

 

If you only reset it, the timing will not change. The belt is kinda like a flexible light weight chain. If it stretches, the belt gets loose all over. If you turn the engine sightly until all the tension is on the pull (front) side, hold it there, and loosen and then tighten the tensioner, all you have done is to put the excess stretch on the back side, lift the tensioner to take the slack out and tighten it. It does not change the timing. It tightens it all up, so there is no slop or fluctuation in the timing, but it doesn't change the timing. Usually by the time there is significant looseness in the belt, the spring is no longer able to pull the tensioner up high enough to take all the slack out, so you may have to go in there after all. After the belt has stretched that much, if you were to check the timing you would find that the cam is slightly retarded, because the belt stretch has allowed the cam to lag behind as much as the stretch. That won't be all that much. You won't be able to change the timing unless you remove the belt and physically set the cam "forward" or advanced on tooth. Then the cam will be over advanced and you will likely lose performance.

I don't know how much they actually stretch. I might be surprised. But another thing to consider is that the distributor on that car is run by the cam, so when the cam is retarded so is the ignition timing, and that will make a big difference. Changing the belt actually advances the ignition timing. It probably wouldn't hurt to check the ignition timing either.

So I don't know if it is really worth retensioning the belt in the long run or not. Glad the belt helped you!

I disagree. As a toothed belt stretches the tooth pitch increases (centre to centre distance between two adjacent teeth) all around the belt. This means that the part belt length on the driven side (non-tensioner side) between the crank and cam sprockets increases. This means that the cam(s) will increasingly retard as the belt stretches over time

 

then what is the purpose of leaving a service hole there?

 

I guess it could skipped a tooth when loose and been out of time but from what I have read if that happens it will barely run. It ran fine but passing on a single lane country road was not a good idea. It makes sense that this lack of power was due to the spark being retarded and the new belt got everything back in line. I thought the tensioner access plug was there to take up the slack and get everything back in time between changes.
I thought the spark plugs should be removed so you can rotate the crank to 45 BDC to set the tension. This is the position the FSM says to put it in when setting the tensioner.

 

Depending on the age and mileage on the timing belt, the stretch could be the equivalent of a couple skipped teeth.
Even though the belt looks fine, the stretch can be easily measured and compared against a new belt.

Here's the difference between a used one and a new one.

https://imageshack.com/i/pmIihcaLj


.

 

Wow! I've changed quite a few TB's on various Acura, Lexus and Toyota vehicles. Never saw an old belt which was measurably longer than the OEM replacement.

 

So, in a few years will resetting the tension get me back to the "new belt" timing I have now? Take up the slack in the pulley and have everything line up like it does now.

 

I think no. Because the belt is longer, the length of it going from the crank pulley CCW up to the cam pulley (the side opposite the tensioning pulley) is longer. This is what causes the valve & ignition timing to get delayed. Resetting the tension minimizes the potential for it to slip teeth.

 

Not sure how much a difference in the 5S but my timing belt streched a bit in my 2SE Camry. Engine ran okay, but upon hot restarts, the engine felt like it had a slight miss. It would run slightly rough until I gave it gas and then it was normal. After I retension the timing belt using the similar method above, I noticed two things.

-No more timing belt 'noise', where the belt is chattery upon cold start ups
-No more slightly off idle upon hot restarts

 

First, the tensioner hole may be a left over from earlier models. That is, in later years they did away with the hole entirely. I seem to remember the RM (WAY back) saying to start the car after new belt installation, run it for a designated time, shut it off and then re-tension it.
Second, I have never tested the amount the belt has moved or stretched due to age, but if the picture is accurate... WOW! But even if it is (and I have no reason to doubt it) remember that the maximum distance of change is half what is pictured in the photo. Think of it this way... there is a finite, exact number of teeth on the belt. Every belt that fits that engine will have exactly that number of teeth. When the belt is new and assembled properly, the exact number of teeth with exactly the correct dimension will ALWAYS be the same between the crank gear and the cam gear. If it wasn't the same and exactly correct, the engine would go further and further out of timing with every rotation of the crank. When it stretches, all that happens is the distance between the two gears increases, causing the cam to be retarded. If it is stretched from age and you re-tension the belt, all you do is move all the slack to the tensioner side of the engine, but the number of teeth between gears remains the same, assuming that the belt hasn't slipped. So re-tensioning the belt will NOT change or reset the timing without actually moving the gears on the belt.
2 other things: It was always my habit, when changing a belt, to set the cam timing before removing the old belt. It was just easier and I didn't have to line things up afterward. In all the years I did that (over 23 at just the dealer, 35 in the business), I never saw a cam gear that was more than 1/2 a tooth off from belt wear. Just sayin.
Second, in every case (except 1 that I can remember), if the belt got loose enough to slip, or jump a tooth, the sudden jump of the gears inside the belt instantly caused the belt to strip the teeth off. If it jumps, it is always on the crank because that is where the torque on the belt originates and also it is the smaller gear, hence less surface area. Smaller gear, less surface area, all of the engine torque that can be applied, results in no teeth and a dead engine.
So you guys can extrapolate how you will... I'm just sharing my experiences.
:my2cents:
Have a great day.

 

According to ajkalian's DIY (http://www.toyotanation.com/forum/1...5025-diy-2001-camry-xle-6cyl-timing-belt-water-pump-crank-cam-seals-part-i.html), the T257 timing belt has 211 teeth and stretched 1/2" after 99,700 miles.

So the stretch per tooth is: 0.5" / 211 = .00236" or not even 3 mils. Therefore, I'd say it's very important to have an automatic tensioner to pick up the slack. Because if it does, 3 mils I think is too little to cause belt breakage problems, even if the performance of the engine might decrease a little and might not be noticeable to the typical driver.

On the 4-cyl el cheapo manual tensioning system, that 0.5" slack means a couple of teeth, and if concentrated in one location, could mean the belt teeth slip up against the sprocket teeth. And as they push against each other, the belt snaps. We've heard recently from members with snapped belts. I think this was what happened. Therefore, I'd still retension the 4-cyl timing belt. Besides I'd still stick to 5yr/60K mile intervals for those who can wrench themselves. IMO better than the 5yr/90K interval came up by marketing.

At least kudos to the engineers who thought enough to put in the adjuster plug on the cover. Even if the accountants ended up winning and stuck the manual tensioner to the 5SFE/3SFE. Like I said, engineers didn't put that plug there just for fun. It's the least they could do getting their butts kicked by the accountants.

(There was a motor.com article on a bad batch of 5SFE timing belts stretching like crazy. It was a manufacturing defect I suppose by Mitsuboshi. Couldn't find the article but I'll keep looking. Another reason I don't use Mitsuboshi).