How the Timing Belt Tensioner Actually Moves

So I have always been curious how much the timing belt tensioner moves while going through the rpms. I built an engine test stand for a different project and decided I would try to measure how much the tensioner moves. I always assumed that the tensioner plunger moved inward as the rpms increased. I thought this was because the belt would get forced outward more and more as rpms climbed. I wouldn't say I ever analyzed the system though.

Anyway I took a video today of a dial indicator that I placed against the lever arm for the tensioner pulley. Its hard to get in that area in general and I couldnt get an exact measurement relative to the plunger. However you could assume the movement is more than the dial indicator shows. The video is boring and unedited but the first part of it was with the engine starting at 1000 rpms. Every ~10 seconds I increased the rpms by 1000 up to 5000.

http://youtu.be/1Xa8m4oocDc

I was surprised to see that the tensioner plunger actually moves outward as the rpms increase. I thought maybe the magnetic base of the dial indicator was moving around but when I let it go back to idle, the plunger actually slowly moves back inward. In the second part of the video I increase rpms to 5500 and slowly bring it back to idle. Again you can see the tensioner does the same thing. Its very repeatable which makes me think the measurements are fairly accurate.

I don't know exactly why the system is working this way but my assumption is the belt is stretching slightly and the placement of the crankshaft pulley and tensioner pulley prevent the belt from moving outwardly in that area. From the tensioner pulley to the first cam gear I can see the belt expand outward as you would normally expect. From idle to 5500 rpms the dial indicator shows movements of about 40 thousandths. The plunger itself will actually move more than that.

Thoughts about related subjects:
I wonder if a kevlar belt makes the tensioner act the same way? They claim they dont stretch... Anyone want to send me one to try this out on? :rapture:
If you are using a solid tensioner, are you actually loosing some performance as the cam timing would be off a little because it can't expand outward?
I was always worried the washer mod for the tensioner would potentially cause the tensioner pulley bolt to loosen up because the plunger couldn't move inward and the belt would be trying to push it that way. It appears this isn't the case.

Thanks
Dan

Not surprising at all... When you put a greater load on the belt, it pulls all the slack out of the belt in the loaded areas, (and attempting to stretch the belt) which creates slightly more slack on the non-loaded section of the belt. The auto tensioner moves out to take up that slack.

I would expect the same behavior from a kevlar belt, although it may not be to the same degree being the belt teeth are stiffer and won't flex as much.

The change in tensioner length you are seeing will not equate to a measurable change in cam timing. If you do the math on a 20 inch length of belt, pushing the middle of it .100" off center, you've only changed the length of the belt span by about .001"

Regardless of which way it moved, the forces on the tensioner are the same.... I don't understand the fear of the pulley coming loose? Unless you somehow overtightened the belt, and had it bottomed out, there will always be the same pressure on the tensioner.

I agree it is just taking up slack from the front cam back to the crank, where all the slack ends up at the tensioner side (unloaded). Cool vid for sure!

Great vid- at idle, you can see that the plunger is depressing as it gets hotter. Do you think you got enough temp in her to see the full expansion of the heads & block?

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Originally Posted by RealMcCoy

Not surprising at all... When you put a greater load on the belt, it pulls all the slack out of the belt in the loaded areas, (and attempting to stretch the belt) which creates slightly more slack on the non-loaded section of the belt. The auto tensioner moves out to take up that slack.

I would expect the same behavior from a kevlar belt, although it may not be to the same degree being the belt teeth are stiffer and won't flex as much.

The change in tensioner length you are seeing will not equate to a measurable change in cam timing. If you do the math on a 20 inch length of belt, pushing the middle of it .100" off center, you've only changed the length of the belt span by about .001"

Regardless of which way it moved, the forces on the tensioner are the same.... I don't understand the fear of the pulley coming loose? Unless you somehow overtightened the belt, and had it bottomed out, there will always be the same pressure on the tensioner.

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I am surprised that the belt stretches that much that the tensioner needs to take up that slack. I assumed the centrifugal force was greater than the spring force inside the tensioner. I had never seen anyone post that the plunger would actually move outward as rpms increase. I'm not an ME and I didn't do any real analysis. I just knew it allowed movement in both directions. After watching the video its easy to assume whats happening.

I don't know how the belts are made but I assume that the length of the belt has very little to do with the teeth flexing. I would assume they might be inner woven but there is some cording or something that controls the stretch of the belt independent of the teeth.

My fear was that yes by doing the washer mod (welding or putting washers at the end of the tensioner to prevent a gap between the lever arm and tensioner body) , it would bottom out the lever arm and the belt would put a force on the tensioner idler pulley that rotates it counterclockwise causing the bolt to loosen up.

Primus the coolant temps started at 190F and went up to 213F. I have an old radiator hooked up and a box fan blowing some air across it so it can only do some much when im revving the engine that high. I wanted to make sure the block, belt, and components were up to temp before doing any measurements. I have a video of the movement from a cold start to warm idle.

What types of scenarios would cause the plunger to go further inside the tensioner? Changing from high rpms to low rpms like shifting gears would put a force on it but the orifices inside of the plunger should prevent much movement. I'm still trying to see if the washer mod has a downfall. Better yet you could just set tension so that the lever arm is almost contacting the tensioner body. If the tensioner fails, it should keep enough tension that the belt wouldn't slip. Just thinking out loud.

Awesome vid. Thanks for posting. Always had concerns with kevlar and fixed tension. Guess you could run a kevlar belt with stock hydraulic and see if you get similar movement. If so, I would assume running fixed tension would be less than ideal, even with kevlar belt. If it doesn't move, or very little, then kevlar and fixed may be a good combo if you fear stock component failure.

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Originally Posted by familyMAN

Awesome vid. Thanks for posting. Always had concerns with kevlar and fixed tension. Guess you could run a kevlar belt with stock hydraulic and see if you get similar movement. If so, I would assume running fixed tension would be less than ideal, even with kevlar belt. If it doesn't move, or very little, then kevlar and fixed may be a good combo if you fear stock component failure.

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Given unknown lengths of time that the OEM tensioners have spent sitting on shelves, I absolutely do fear stock component failure at this point.

Surely someone has a used kevlar belt that they can send to get this tested. Would love to see the results. Also Maddog, didn't see a video on your youtube of the cold start to warm idle, have you posted it yet or do you just have it? Did you have the dial indicator there for that as well? One of the biggest arguments heard against the solid tensioner and kevlar belt is that the hydraulic is supposed to adjust for the expansion of the engine components as it heats up, but your video starting at warm idle shows a pretty small spacing there anyhow, so not sure how much movement that there is. Throw that video together with one with a kevlar belt (push comes to shove I'll send you mine when I order it from Chris just to get a definitive answer) to show stretch during running, would pretty much answer most questions and concerns folks have about it.

Great info Dan, I think I spy bonsai in the background :suspect:


You going to make NG?

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Originally Posted by sergechronos

Given unknown lengths of time that the OEM tensioners have spent sitting on shelves, I absolutely do fear stock component failure at this point.

Surely someone has a used kevlar belt that they can send to get this tested. Would love to see the results. Also Maddog, didn't see a video on your youtube of the cold start to warm idle, have you posted it yet or do you just have it? Did you have the dial indicator there for that as well? One of the biggest arguments heard against the solid tensioner and kevlar belt is that the hydraulic is supposed to adjust for the expansion of the engine components as it heats up, but your video starting at warm idle shows a pretty small spacing there anyhow, so not sure how much movement that there is. Throw that video together with one with a kevlar belt (push comes to shove I'll send you mine when I order it from Chris just to get a definitive answer) to show stretch during running, would pretty much answer most questions and concerns folks have about it.

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the tensioners are stamped on top with the date. I ordered mine from IPS and even that way it was manufactured at the end of 2012. If you are worried about a tensioner sitting on a shelf in an oiled bag for 1 year then I think you'll worry yourself to death. Probably the ones from cherry hill are even newer, they are definitely still making these parts.

I have to imagine one of the functions of the hydraulic tensioners is to dampen harmonics that the belt may experience, which are caused by the valvetrain. Even just a spring would be better than the solid tensioners IMHO.

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Originally Posted by Forest Gump

the tensioners are stamped on top with the date. I ordered mine from IPS and even that way it was manufactured at the end of 2012. If you are worried about a tensioner sitting on a shelf in an oiled bag for 1 year then I think you'll worry yourself to death. Probably the ones from cherry hill are even newer, they are definitely still making these parts.

I have to imagine one of the functions of the hydraulic tensioners is to dampen harmonics that the belt may experience, which are caused by the valvetrain. Even just a spring would be better than the solid tensioners IMHO.

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Not only are they still making them, they still USE them in Hyundai and Kia.

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Originally Posted by RealMcCoy

Not only are they still making them, they still USE them in Hyundai and Kia.

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Hmm my 2012 Kia shortage has a chain. I know 2011s had a belt.

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Originally Posted by Forest Gump

Hmm my 2012 Kia shortage has a chain. I know 2011s had a belt.

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It's possible I overstated that... I really haven't payed much attention to what they are offering in the last couple years, I was primarily stating what I'm seeing in the shop, which is often at least 2-5 years old.

I'm still seeing DOHC 6G74's in pretty late model vans and SUV offerings from Hyundai/Kia, hence my statement they still use them.

Great footage. Thank you! The gauge needle is basically a blur @ 5000 rpm's swinging over a ~10(?) mil* range... Do you think that's due to vibrations, actual movement of the tensioner, or both?

*mil = .001" for the newbs

Interesting. I would be really surprised if the timing belt is stretching. Would be interesting to see how the slack event is impacted when using solid lifters.

Well, solid lifters are out of my price range, but I was going to buy a solid tensioner and kevlar belt anyhow, so Maddog if you would be so kind as to do a video showing OEM hydraulic with the kevlar belt and then the solid with the belt, I'd happily have Chris ship it to you first and then you can just ship it to me once the videos are done.

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Originally Posted by sergechronos

Well, solid lifters are out of my price range, but I was going to buy a solid tensioner and kevlar belt anyhow, so Maddog if you would be so kind as to do a video showing OEM hydraulic with the kevlar belt and then the solid with the belt, I'd happily have Chris ship it to you first and then you can just ship it to me once the videos are done.

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I would be happy to test a kevlar belt with a stock tensioner. I'm not sure what I could measure or look for with a kevlar belt and a solid tensioner.

I do have a video of the engine warming up. Basically it pushes the tensioner in around 30 mil as the engine warms up. Its 12 minutes long and I havent uploaded it. I can if someone really wants to watch 12 mins of and engine idling.

green-lantern I should be at NG. thanks for the thanks

Adam, I think the movement is due to vibrations of the engine acting on the mount. When i press on the body of the dial indicator it seems to dampen it but I dont want to mess with the readings so I have been looking at the middle of the needle blurr :) for an idea of where its actually at. I dont think the tensioner would be able to move that quick but I could be wrong.

J Fast if the belt isn't stretching what do you think is causing the movement? I'm open to ideas.

I can't imagine that the solid tensioner and kevlar belt would move at all, but would be interesting to see if there is any movement from anything with the solid and kevlar set up. If increasing RPM/load causes any kind of flex or movement or undue strain on any of the gears or pulleys. I think that the kevlar belt with the hydraulic will be the most telling of anything as far as measurement (if the movement from before is due to belt stretch or something else.) PM me your address, and I'll have Chris ship it out to you when I order it.

I thought McCoy hit it on the head. The belt isn't stretching (much at all), the slack is just shifting. There is a little slack all throughout the belt when the engine is sitting still, but that slack gets shifted over when you increase rpm. That's also why I'm not real fond of the solid tensioners. Sure they aren't hydraulic which means they won't fail, but they also don't take up the slack. Increase rpm with a solid tensioner, and you will get a significant (comparably to stock) amount of slack in the belt. I'm not sure how much a belt stretches out over a period of 50,000 miles but its possible that an old, stretched belt could get so much slack that it would skip a tooth on the crank if using a solid tensioner. I don't think it's likely at all, just possible.

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Originally Posted by futurevr4man

I thought McCoy hit it on the head. The belt isn't stretching (much at all), the slack is just shifting. There is a little slack all throughout the belt when the engine is sitting still, but that slack gets shifted over when you increase rpm.

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I'm a fan of this theory also.

I love that we have people running tests like this, helping to explain why Mitsu engineers did what they did.

Agreed with Larry - the crank is the driver, so it only stands to reason any slack - due to stretch or not - would manifest immediately after the crank pulley where the tensioner is.

I would've assumed as much, except aren't idler pulleys usually for slack side in applications? Yet our slack side is supposed to be the side with the tensioner (and tensioner pulley) and our idler pulley is on the opposite side of the crank cog.

If you're correct, then the only thing I could think is not so much the slack itself but vibrations causing long runs of the belt to potentially whip laterally off and potentially come at least partially off the cam cogs (which would likely lead to skipped timing or a shredded belt.) While maybe on a steady increase in RPM or a slow increase it doesn't matter much, but I would be curious about fluctuating loads (like it would see with actual driving and shifting) possibly inducing far greater vibration than the roughly 10 mil that we could see on the indicator just from the steady climb. Not sure how accurately it could be emulated with this test rig though.

The increased rigidity of the kevlar belt may reduce that possibility (heck, might even reduce the vibrations) so that it is less of a concern. Although, of course, just pure speculation on my part until I get the belt ordered and shipped to Maddog and it gets tested. Curious why the hydraulic on the DOHC and the spring on the SOHC. Are we seeing that much more slack/vibration/whatever than the SOHC?

I'd be interested to find answers to both the Kevlar and SOHC questions...:wink:

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Originally Posted by Maddog

J Fast if the belt isn't stretching what do you think is causing the movement? I'm open to ideas.

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The engine and valvetrain are constantly accelerating and decelerating. If one were to draw a belt force diagram between each gear in the timing assembly ie. timing cog, cam gears, water pump, tensioner etc. and also take into consideration the belt spans in 720° of crank rotation at no place on the belt in between cogs is the tension and compression equal. Due to this phenomena there will always be dynamic slack or run-out. As the magnitude of the engine throw increases so does the differential of tension and compression which is transmitted on the tangental plane of the gears as acceleration and deceleration.

In plain English... as the engine throw magnitude increases the belt is being pushed faster than it's being pulled. The hydraulic tensioners job is to ensure the slack is maintained through dynamic run-out.

On another note, I do not believe a Kevlar belt will change the dynamic run-out. If anything at all I think the slack run-out will be equal, but the rate of slack pickup will be faster due to a higher belt spring rate. Will be interesting to see the outcome... Also makes me wonder if the tensioner pulley was elliptical if the slack would be the same... Mehh. That's just my brain throwing ideas out there.

Cool thread. Haven't had one of those around here for awhile...

Given that the timing belts use fiberglass reinforcing cords, I'm not sure how much they might actually stretch as they age (and 30 mils worth of change as everything heats up isn't exactly super significant given the length of the belt as a whole.)

This leads me to believe, and correct me if I'm wrong (as it often happens), but I'm not sure now that the t-belt changes are due to stretch, but are instead due to the aging of the rubber allowing it to become more brittle. Possibility of teeth becoming damaged as it ages (especially exposed to the heat it sees) likely increases quickly, or even just brittleness of the rubber as a whole, might make it hard to keep contoured properly to the cogs under high load situations? Throw in possibility for the tensioner to weaken as it ages, and lower tension perhaps leading to damaging the brittle teeth as well from poor engagement?

I believe that the SOHC spring is just used when setting the initial tension and then it basically becomes a fixed tensioner?

Update: Solid tensioner and kevlar belt order placed with shipping to Maddog for testing, so we should have some more information in the next little bit.

I hope one of the old fogies chimes in soon, but I'm quite sure that I have seen a comparison pic of an old belt and a new belt, and the old used one was noticeably longer. Like inches longer. But I may be totally off my rocker on that as well.

As far as brittleness, yeah it happens, but it seems like you're comparing rubber that you run into every day with the rubber a tbelt is made of. The tbelt rubber is much more resistant to heat stress, and wearing as well. But I do agree that it gets more brittle over time, it's one of the main reasons you change it as preventative maintenance (and of course because we have interference engines).

I would like someone to confirm or deny if the belt stretches. I guess I could google it but I'm on my phone...

I am curious if the tensioner weakens over time. If so, how long? Do temps affect it... dramatically even? How much would it weaken? The way that tensioner is made, it doesn't push out with much force, but it resists moving inward very hard.

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Originally Posted by aaronatstate

Just as a note, synchronous belts with fiberglass tensile cords do not stretch more than .001-.003" over the lifetime of the belt. All automotive synchronous belts, from the stock Mitsubishi belt, to the Gates aftermarket belt, to the Gates racing belt all have fiberglass tensile members, and will not stretch. The kevlar portion of the racing belt comes from the kevlar fibers they put into the rubber compound to strengthen the teeth. It makes the teeth stiffer and stronger and less prone to sheering off. Being an engineer at Gates, I don't see any reasons why a Gates Racing Belt would require more tension than the standard belt.

Also, I would almost always advise against using a solid tensioner. It's not because the belt stretches, but as the engine heats and cools, the geometry of the drive system changes, and the forces on the belt change. By not having something to take up this slack and differences in changes, it may adversely affect the belt.

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^Thanks! Was trying to find that post but couldn't.

Question, even if belt can't stretch (much) can't the teeth give and that end up creating slack?

Would be interesting to see the stock belt at 2500 rpm while it's on the test rig?.

I and a few others have strange fueling issues at 2500 so it would be great to see if there were any odd harmonics going on with the belt..

In your vid the belt threw (sp) a "wobbler" but couldn't work out what rpm it was..

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Originally Posted by familyMAN

Question, even if belt can't stretch (much) can't the teeth give and that end up creating slack?

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Seriously... I thought you were smarter than this? This subject is way over your head Engler.

You don't have to be a dick. It was just a question. Since the belt length stays the same, I wasn't sure if teeth deformation could have any effect on tension/slack. It is still a question, since you are correct, I do not understand fully.

I'm here to learn. Surprised you didn't take the opportunity to write a novel on shit that may or may not apply to the question. Must be an off day for you.

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Originally Posted by familyMAN

You don't have to be a dick. It was just a question. Since the belt length stays the same, I wasn't sure if teeth deformation could have any effect on tension/slack. It is still a question, since you are correct, I do not understand fully.

I'm here to learn. Surprised you didn't take the opportunity to write a novel on shit that may or may not apply to the question. Must be an off day for you.

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I'm sure we will get a copy and paste from Solar Flares 101 about how the belt only stretches if you run 50 weight oil or if Venus is in transit.

Don't need to write novels to know who understands this stuff in real life vs. the internet.

Pics of my Billet TD05's - Page 37 - 3000GT/Stealth International Message Center

You went down the same path ehhh?

I would normally bite my tongue but I noticed Engler took a stab at me on 3si where you guys have green dots... comedy hour... and your cars on tow trucks or jackstands.

Mehh, maybe Ill see you guys at NG and stomp mudholes in you at all the events with the engine I built one time. You can listen to the sound of a harmonious engine turning 7500rpms and speeding 170mph on the straightway.

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Originally Posted by J. Fast

Don't need to write novels to know who understands this stuff in real life vs. the internet.



Pics of my Billet TD05's - Page 37 - 3000GT/Stealth International Message Center



You went down the same path ehhh?



I would normally bite my tongue but I noticed Engler took a stab at me on 3si where you guys have green dots... comedy hour... and your cars on tow trucks or jackstands.



Mehh, maybe Ill see you guys at NG and stomp mudholes in you at all the events with the engine I built one time. You can listen to the sound of a harmonious engine turning 7500rpms and speeding 170mph on the straightway.

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would love to see another good running car at the NG.

Until you come and run good times you are no different than Nelson though. Except he now has some timeslips.





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I haven't seen such an ongoing and comprehensive demonstration of social tone-deafness on an internet board in forever, Jeremy.

You're in a class (that's the wrong word, but) by yourself.

It is really classless to come to a community and make fun of people that have had engine issues.

I don't need to see your car running or read one of your rants to know what kind of person you are.

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You know what's also funny J. Fast? In my thread where I was tuning my engine you were telling me to add ~5 degrees of timing, lol. That would've worked great.

Cool thread link. You do realize what the likely cause of that spun bearing was right? Read some posts about ray having issues and took him multiple spun bearings to figure it out. Wasn't timing/tuning if that's what you are alluding to. Hell I wasn't even tuning it then. One of the best in the platform was until I was able to get more comfortable.

So are you scanning 3si to see when anyone mentions dmbldr? It's too bad your attitude is what it is. I have referenced your turbo sizing thread (not the infamous one, there is another with good info) more than once on 3si. Went downhill since then unfortunately.

You still haven't answered the question. The difference here is that I am asking what is likely a stupid question where others give stupid answers.

Too much tension in this thread. See y'all on the track with my stock belts and tensioners.

FYI, I believe in the stock belt and tensioners as well, lol. The solid tensioner and kevlar belts are just designed to take peoples money. You can tell that since Maddog isn't even a vendor of these parts and is doing more testing on them than they ever will.