How the Timing Belt Tensioner Actually Moves

[aaronatstate]

First off, awesome vid Dan! Love to see videos of things like this!

In belt design there is always a slack side of the belt, and this is where the tensioner pulley is located. As the slack in the belt changes, the tensioner is there to take up the varying slack. As my earlier quoted post said, timing belts with fiberglass cords do not stretch. The reason the belts appear to get longer as the motor is running at higher rpms is because the force on the belt is higher. As the force goes up, the teeth begin to compress and the belt starts to get more slack, and the tensioner is there to make up for that.

The stock Mitsubishi belt is the basic design as the Gate aftermarket belt, the Gates racing belt, and any other aftermarket belt. Synchronous belts all have three basic elements, a nylon jacket that is on the face of the teeth, tensile cord members, and rubber. It is there to prevent wear, and to reduce noise.

The tensile cords, which can be made of many different materials. We make belts with fiberglass cords, polyester cords, aramid (kevlar) cords, carbon fiber cords, and even belts with steel tensile cords. All cam timing belts have fiberglass cords, because fiberglass does not change in length. Polyester cord shrinks as it sits over time, aramid soaks up water and grows, and steel just wont break first.

The last component is the rubber. There are many different rubbers we use from EPDM to neoprene, to nitrile, and chloroprene rubbers. The HSN rubber used in cam timing belts has a very high temperature range that it works over, and temperature does not effect the length of the belt. Our racing belt uses nitrile rubber that is reinforced with aramid fibers to make the teeth stronger and less prone to sheering off and compressing at high loads.

Now in production when we build the belts, we actually use a large mold that is up to 48 inches wide, and we basically build a belt that is 48" wide and then grind it to the correct thickness, and cut it to the correct width. After the belt is in its finished state, a certain number of belts are taken and measured for the pertinent dimensions. One of those is length. There is a specified length for every belt we make, and we verify that the belt meets this specification before it leave the facility. The calculation to figure out that length (with two equally toothed pulleys) is:

((#teeth of the belt - #teeth of one pulley)/2) * Pitch of the belt

Just to prove that timing belts do not stretch over time, I measured the timing belts out of my dad's 1980 Honda Goldwing at work after he replaced them. The belts on his bike were probably made in 1979. Even after 40,000 miles and 32 years on his bike, they were still within the specifications!

Lastly, I will try to answer why timing belts seem to break unexpectedly. By far the most common reason we see a timing belt break, is due to mis-installation. There is a minimum bend radius for the belt, and if it is bent beyond this, it can crimp the tensile cord and severely weaken it. Fiberglass is great in tension, but not in compression. Believe it or not, but you could lift a stock AWD 3/S off the ground with the timing belt, it takes that much force to break one. When the cord is crimped, it can reduce this force by over 50%! I will look up at work on Monday what the minimum bend radius is for an 8mm pitch timing belt.

I can measure the belts if you want to send them to me Dan.

If anyone else has any other questions feel free to ask, and if I cannot answer them, I will find the answer out from some of the design and application engineers at work.

Oh and PS just a fun fact, the stock Mitsubishi belt from the dealer is a Gates belt, made on the same line as the racing belts (in Japan). There is no difference in the dimensions of the belts between stock and aftermarket whether its a Gates belt or not. The only difference between them is the materials that go into the belts.

Whew long post...

[j2k4]

Been waiting for you to show up.

Tooth compression, eh?

[sergechronos]

In belt design there is always a slack side of the belt, and this is where the tensioner pulley is located. As the slack in the belt changes, the tensioner is there to take up the varying slack. As my earlier quoted post said, timing belts with fiberglass cords do not stretch. The reason the belts appear to get longer as the motor is running at higher rpms is because the force on the belt is higher. As the force goes up, the teeth begin to compress and the belt starts to get more slack, and the tensioner is there to make up for that.

Given that the kevlar reinforced teeth shouldn't compress (or compress at much) wouldn't that mean that the belt wouldn't get as much (or any) slack and therefore a hydraulic tensioner would be unnecessary (or less necessary)?

All cam timing belts have fiberglass cords, because fiberglass does not change in length. Polyester cord shrinks as it sits over time, aramid soaks up water and grows, and steel just wont break first.

I don't see a downside listed for CF, curious what (if any) it may have aside from likely being expensive as hell. Is it actual CF cords in place of fiberglass, or is it similar to the way that the kevlar is used in the kevlar belts? While not related to the topic explicitly at hand since there is no CF belt for our car (and likely no need for one) I am incredibly interested as I can't imagine the kind of environment that you've got where you would even need a CF belt..Or an application off hand come to think of it. Except maybe some kind of massive supercharger belt drive or a timing belt for a 2000+ hp engine of some sorts.

The HSN rubber used in cam timing belts has a very high temperature range that it works over, and temperature does not effect the length of the belt. Our racing belt uses nitrile rubber that is reinforced with aramid fibers to make the teeth stronger and less prone to sheering off and compressing at high loads.

What separates the type of nitrile used in the kevlar with the aramid fibers from highly saturated nitrile? Is it just the aramid fibers and it's still otherwise identical to HSN?

There is a minimum bend radius for the belt, and if it is bent beyond this, it can crimp the tensile cord and severely weaken it.

This would then provide something to look out for when ordering a t-belt from a vendor to make sure that it's not super bent when you open the packing I would assume. Is there any kind of visual way to verify before installation? I would be curious what the bend radius is all the same.

I can measure the belts if you want to send them to me Dan.

If Dan wants to send the Kevlar (and I guess keep it packaged with the tensioner) to you after he's done with it, I'm fine with that. Just so long as it makes its way back here by May.

[aaronatstate]

Been waiting for you to show up.

Tooth compression, eh?

Yup, take a caliper and measure the thickness of the belt. Then push harder, it gives

Given that the kevlar reinforced teeth shouldn't compress (or compress at much) wouldn't that mean that the belt wouldn't get as much (or any) slack and therefore a hydraulic tensioner would be unnecessary (or less necessary)?

I will always, always recommend a hydraulic tensioner. The drive was designed with a hydraulic tensioner for a reason. Kevlar reinforced belts will still give some, and the engine will expand as it heats up. All these things change the effective length of the belt, and that is why a tensioner is needed.

I don't see a downside listed for CF, curious what (if any) it may have aside from likely being expensive as hell. Is it actual CF cords in place of fiberglass, or is it similar to the way that the kevlar is used in the kevlar belts? While not related to the topic explicitly at hand since there is no CF belt for our car (and likely no need for one) I am incredibly interested as I can't imagine the kind of environment that you've got where you would even need a CF belt..Or an application off hand come to think of it. Except maybe some kind of massive supercharger belt drive or a timing belt for a 2000+ hp engine of some sorts.

Carbon Fiber's biggest downside in a drive like this is that it is too strong, just like the steel. Look up our Polychain GT2 belts with carbon cord. They are used to drive machinery mostly, where you need something very strong, and efficient. We run all of our machinery with them. There are some of our Polychain Carbon belts that take almost 100,000lbs of force to break! Another interesting fact is that most of the Top Fuel drag racers use Gates Polychain belts (with Kevlar cord) to run their superchargers.

What separates the type of nitrile used in the kevlar with the aramid fibers from highly saturated nitrile? Is it just the aramid fibers and it's still otherwise identical to HSN?

They are all HSN rubber. The racing belts just have aramid (Kevlar is Dupont's brand name for aramid) fibers to make the teeth stronger, mostly to resist sheering off in high torque/load situations.

This would then provide something to look out for when ordering a t-belt from a vendor to make sure that it's not super bent when you open the packing I would assume. Is there any kind of visual way to verify before installation? I would be curious what the bend radius is all the same.

It won't be crimped being put into the box. All of our employees are trained to not crimp belts to prevent them from breaking prematurely.

If Dan wants to send the Kevlar (and I guess keep it packaged with the tensioner) to you after he's done with it, I'm fine with that. Just so long as it makes its way back here by May.

OK. I'm good either way!

[sergechronos]

I will always, always recommend a hydraulic tensioner. The drive was designed with a hydraulic tensioner for a reason. Kevlar reinforced belts will still give some, and the engine will expand as it heats up. All these things change the effective length of the belt, and that is why a tensioner is needed.

They are all HSN rubber. The racing belts just have aramid (Kevlar is Dupont's brand name for aramid) fibers to make the teeth stronger, mostly to resist sheering off in high torque/load situations.

Would you see any reason why the kevlar with hydraulic tensioner would cause failure? After the thorough analysis and information you've provided I doubt it since the overall length of the belts should still not experience drastic change, although I'm unsure if the OEM tensioner would see any premature failure from perhaps not being worked much.

Would the kevlar be a better choice for higher load applications due to upgraded valve springs? Or is it likely still complete overkill? I guess in short for this, why produce a kevlar belt if the OEM should still be satisfactory (and has been proven to be satisfactory) for builds up to and over 1000awhp? I would assume money (or rather, just because there's a market for them), although I'm not sure what kind of difference in profit you guys see for the kevlar belt vs the original.

Well, I can't lie, I wouldn't mind having you (or Gates in general) examine the belt after the demonstration video..Or once I'm done with it at 60k miles, I think it would make for a fascinating video to have belts at 60k (or as close to it as possible) of the "OEM", the Gates sold under their name, the Kevlar with a hydraulic and a Kevlar with a solid just to see if there is any kind of discernible difference amongst them. Although, Gates probably already did such testing before (excluding the solid perhaps) and my intuition says that there would likely be little difference, but I'd be curious if at the 60k mile point the Kevlar with hydraulic or the kevlar with solid showed any different signs of wear a wear pattern to teeth or something. Slightly more random question: Why the blue paint on the belts? Seems like it just always comes off and makes a mess of pulleys and such. Couldn't they sell it without that backing? Does it serve any purpose?

[donniekak]

I don't believe they are hydraulic tensioners. They are hydraulically dampened spring tensioners. Like a coil over suspension piece. The spring provides the tension, and the oil dampens the movement.

[sublime_whatigo]

I guess in short for this, why produce a kevlar belt if the OEM should still be satisfactory (and has been proven to be satisfactory) for builds up to and over 1000awhp? I would assume money (or rather, just because there's a market for them), although I'm not sure what kind of difference in profit you guys see for the kevlar belt vs the original.

Well I can give 1 instance where the kevlar belt is superior. A friend had a garage fire, car was a complete loss. He ended up saving the kevlar belt and re-using it for thousands of miles without issue. And the blue paint, that has to be just a marketing gimmick. With that said I always use oem belts and tensioners, I doubt you will see a difference with the kevlar belt as I believe its just the slack being moved around like described and the tooth compression is very interesting concept.

[aaronatstate]

Would you see any reason why the kevlar with hydraulic tensioner would cause failure? After the thorough analysis and information you've provided I doubt it since the overall length of the belts should still not experience drastic change, although I'm unsure if the OEM tensioner would see any premature failure from perhaps not being worked much.

Would the kevlar be a better choice for higher load applications due to upgraded valve springs? Or is it likely still complete overkill? I guess in short for this, why produce a kevlar belt if the OEM should still be satisfactory (and has been proven to be satisfactory) for builds up to and over 1000awhp? I would assume money (or rather, just because there's a market for them), although I'm not sure what kind of difference in profit you guys see for the kevlar belt vs the original.

Well, I can't lie, I wouldn't mind having you (or Gates in general) examine the belt after the demonstration video..Or once I'm done with it at 60k miles, I think it would make for a fascinating video to have belts at 60k (or as close to it as possible) of the "OEM", the Gates sold under their name, the Kevlar with a hydraulic and a Kevlar with a solid just to see if there is any kind of discernible difference amongst them. Although, Gates probably already did such testing before (excluding the solid perhaps) and my intuition says that there would likely be little difference, but I'd be curious if at the 60k mile point the Kevlar with hydraulic or the kevlar with solid showed any different signs of wear a wear pattern to teeth or something. Slightly more random question: Why the blue paint on the belts? Seems like it just always comes off and makes a mess of pulleys and such. Couldn't they sell it without that backing? Does it serve any purpose?

With upgraded springs and other valve train components I would recommend the race belt. It can handle more for longer. The racing belt is superior to the OEM belt. I would be willing to bet on a stock motor the racing belt would last well beyond the 60k mark.

The blue paint is for marketing. That being said only the race belts made in japan are painted. The racing belts we make here in Arkansas actually use blue rubber! If you look at a DSM race belt, both timing and balance shaft, a Supra race belt, or any other race belt made in the US it will be blue rubber.

Interesting fact we make belts in many colors, black, white, red, blue, gray, yellow, and green are a few! If you ever buy any Jesel timing belts for a pushrod motor, it's a Gates belt too. Most pro stock guys run them!

[stealthee]

I don't believe they are hydraulic tensioners. They are hydraulically dampened spring tensioners. Like a coil over suspension piece. The spring provides the tension, and the oil dampens the movement.

Yes there is a spring in the tensioner, but the force is held by the hydraulic fluid. Without the fluid the spring can't hold any amount of forceable tension. I did a t-belt job for a guy and his new out of the box (although non OEM) tensioner failed when I turned the engine over by hand to line up the marks. I pulled it back out and the hydraulic fluid had pushed past the seal. I could easily compress the plunger with my thumb. I grabbed the tensioner we took off and with all my might couldn't close the plunger on it by hand.

[donniekak]

The spring provides the static force, the fluid dampens any movement. I have a couple I should cut apart and look at, I've always been curious how the damper is set up. I doubt it's a stack, probably just a pinhole in a piston.