How the Timing Belt Tensioner Actually Moves

[familyMAN]

Too much "tension." Funny if that was intensional

BTW, I use a stock tensioner, belt too. Does that put me back in your "cool club?" 8400 rpm with the 280's and no instantly broken belt or tensioner. Not sure where anyone was saying stock components are crap.

Hey, before hitting the track or dyno today, maybe you can bounce over to the thread stating you are 800hp uncorrected now and post your chart.

[Boost4VR4]

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

I would take SOHC out of the equation since the tensioner is a basically a solid tensioner which is comprised of a tensioner pulley tensioned once and then secured in place with tensioner pulley bolts with a spring attached to it as safety mechanism.

The belts do stretch, the fiberglass cords do not stretch. The OEM belts from the dealerships are not the same as any newer Gates belts that are manufactured for the 3/S even in OEM form are far different from OEM belts seen from the factory.

[Jimvr4]

And we should believe this:

The belts do stretch, the fiberglass cords do not stretch. The OEM belts from the dealerships are not the same as any newer Gates belts that are manufactured for the 3/S even in OEM form are far different from OEM belts seen from the factory.

After seeing this:

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.

[Boost4VR4]

Explain why timing belts break without any outside interference causing the break if they don't stretch?

[Chris@Rvengeperformance]

I have never seen a belt fail that didn't come from one of the pulleys locking up or foreign object damage.

[Boost4VR4]

I have never seen a belt fail that didn't come from one of the pulleys locking up or foreign object damage.

I suppose you're right something always tends to get in the timing area and touch the belt while moving causing it to start to wear faster.

I mean, what about when a belt is subjected to hot/cold spells, does the belt expand/contract at all?

[sergechronos]

Coefficient of expansion for regular nitrile (not highly saturated as is used in most timing belts) is 235e-6 C.
For 1 meter of regular nitrile with no reinforcement, that's a total of about 2cm to go from 0C to 100C.
Considering HSN is bonded tighter and the belt has fiberglass cords, I would expect it to likely be smaller.

Again, speculation and just basic physics knowledge, but would seem unlikely to be a large change.

HSNs operating range is from -30F to about 300F

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[sergechronos]

I would take SOHC out of the equation since the tensioner is a basically a solid tensioner which is comprised of a tensioner pulley tensioned once and then secured in place with tensioner pulley bolts with a spring attached to it as safety mechanism.

This is why the SOHC tensioners were even brought up. What is it about the DOHC that requires it have the hydraulic system that the SOHC doesn't? Does the DOHC see that much more load on the belt? Does some kind of thermal expansion of the heads push the cams apart and dynamically change the tension or something? Or is it just related to the way that the belt can relax depending on cam position when the motor is shut off? Knowing exactly why the SOHC can get away with a fixed tensioner and the DOHC can't could help provide light into the decision that plays into a new hydraulic or a solid.

[Boost4VR4]

Ok in that respect, if you want to know why, I think it's pretty simple. The load would be greater because the DOHC heads have double the components compared to SOHC. For better flowing heads with more intake and exhaust ports, the sacrifice is additional intake ports and exhaust ports, smaller piston to valve distance and longer belt.

[familyMAN]

I haven't messed with SOHC much, but I did do a waterpump and timing belt on my dad's old Chrysler New Yorker, sohc 6g72. No need for cam lockers. You put the gears at the marks and they stay, perfectly. I'm sure someone can explain, but I assume it has to do with the intake and exhaust springs acting on the cam in exact opposite forces? No idea if that has anything to do with the lack of hydraulic tensioner, but it was an observation based on my only experience with it.