Voith, good points about the material properties. Are the OE belts fiberglass or polyester cord? One thing that I was thinking about is that with a 4 cylinder, you have more distinct torque "pulses" on the belt, especially at idle, because you're getting a power stroke every 180* of rotation. This is where the most stress is really put on the belt, quoting from a different thread:

So I was thinking, if you were going to improve on the OE design, you'd be best off improving its ability to withstand shock loads moreso than ultimate tensile strength. Because Voith is correct, if you're in a situation where you're breaking a belt because of a roller failure, that belt is going to break regardless. You're best off beefing it up for the highest stresses it sees operationally.

 

So, according to the docs you posted:

- Fiberglass is close in tensile strength, yet has "Poor shock resistance" (which is a critical factor to operating in the role of timing belt, particularly on a higher displacement inline 4cyl)

- Polyester has good shock resistance, but less than half the tensile strength of kevlar.

- Kevlar has the highest tensile strength, highest modulus, highest shock resistance, and least elongation at the point it breaks under tension.

So, by your own quoted information it's a no brainer, kevlar wins.

What fancy new very expensive machines come with is irrelevant unless someone knows the composition of those belts regardless of color. The debate here is about material choice not color, no?

If that ~12.5% increase in tensile strength were the only factor at play here, sure your argument makes sense. However this is a big picture scenario, you don't get to pick and choose the one factor that somewhat agrees with your stance and ignore the others.


The part you bolded was prefixed with a reference to use of stepper motors in equipment. Not even close to the application being discussed, and nobody has argued that different materials are more suitable for different environments.

 

Except high modulus is bad low is good so kevlar modulus property is about twice worse than fiberglass and about 8x worse than poly.


Odonell: yep standard are fiberglass.

Torque pulses is a good point but you have to remember ~80% cars in europe are 4cyl belt driven 8 or 16v diesels that sport CR 22:1+ with no problem whatsoever. Diesel pulsing is in another league compared to gas.

 

First 944 timing belt change I did I set the tension using the usual method, left the covers off and ran the engine up to working temp. I rechecked the timing belt tension and it was tight, it hadn't expanded or stretched sufficiently to compensate for the head and block expansion. Over a 500-1000 miles the belt will stretch but in that time it can knock out previously serviceable waterpumps/rollers. I set the timing belt tension slightly lower and a hydraulic tensioners wasn't necessary.

(Use at your own risk)

 

If you change gears as frequently in your car as you do in conversation, you probably need new shifter bushings.

Given that the modulus figures in the quoted material are expressed in psi, it's safe to assume standard Youngs modulus is represented (as opposed to bulk or shear modulus), which is little more than the change in dimension under tension or compression, which in the application of a belt drive, will be proportional to its overall elasticity.

As we've already established that less stretch is better, does it not make sense that a higher modulus is more desirable?

Anecdotal and therefore irrelevant.

 

You need to learn to read before writing. Are you female by any chance?

Bending ability of timing belt is very desirable. As impossible as this might be. To you.

You might want to check diesel anecdote, its a stinky one.

Also you might want to check why diesel belts are thicker glass fibre instead of kevlar.

 

Nihil...let's chill with the personal attacks dude...nobody here means any ill intent.

 

Aww, it's adorable that you've started with personal insults instead of arguing with logic.

Bending ability comes from being able to use thinner material with a stronger tensile strength. Again, you need to consider the operating assembly as a whole rather than picking and choosing singular aspects that somewhat support whatever point you're attempting to argue at the time.

 

It's all good man. Just an observation on the "throw everything but the kitchen sink and hope something sticks" method of discussion.

 

Its not an insult. Its just that 'mouth operates faster than brain' is usually female virtue. That and your avatar is almost as sexy as odu's.

 

I bet women Porsche owners love you. But you're right about one thing, my avatar is dead sexy (in that fun no-homo sense). Gummo screencap for those who haven't seen it.