thoughts on static belt tension.

[ericjon262]

I've been looking at my accessory drive, and trying to find a better way to mount the alternator, and at this point, my biggest problem continues to be the belt tensioner. I've given it some thought, and wondered if there was a reason to have a tensioner and not just lock out the tension by way of an adjustable pulley.

Pros:

simple, and very easy to implement.
easy to adjust.
smaller footprint compared to a dynamic tensioner

cons:

requires periodic maintenance compared to dynamic tension.
reduced belt life due to potential over tension.
no compensation for thermal expansion/contraction.
no automatic compensation for belt stretch.

after reading what I just wrote, I see almost no argument in favor of running static tension, but I'll throw it out there, maybe I'm missing something.

[Shaun41178(2)]

If your system isn't broke dont fix it

[ericjon262]

it hangs the alternator out way further than I would like. I made some quick progress on a new layout today, the new setup will tuck the alternator closer to the block, and improve belt wrap on the crank pulley. I'm going to work pretty hard at it tomorrow, aside from paint, I think I can have it complete tomorrow.

[The Dark Side of Will]

If your system isn't broke dont fix it

GM's "standard" FWD accessory drive layout for a couple of decades now has been to mount the A/C compressor low on the front, waterpump above it, PS pump basically right above the crankshaft with the alternator high on the back side of the engine.

The Fiero doesn't need the PS pump and the FWD alternator mounting interferes with the Fiero decklid.

The 3800 crowd has a more-or-less "standard" low alternator mount configuration that works, but the 60 Degree crowd does not. A single solution to handle low mount alternator, spring loaded tensioner and dogbone mount on one bracket compatible with the Gen II and later accessory drive would be quite useful.

[The Dark Side of Will]

after reading what I just wrote, I see almost no argument in favor of running static tension, but I'll throw it out there, maybe I'm missing something.

There's no good reason not to use an automatic tensioner. That's why GM went to it across the board.

Tension and pulley wrap need to balance, as do tension and takeup. As I mentioned in your other thread, having the belt directly in line with the direction of pull of the tensioner provides maximum takeup of belt stretch, but is the lowest tension configuration. Having the tensioner pushing sideways on a straight section of belt provides maximum tension, but minimum takeup. Packaging over-rides both concerns because if you can't build it, how well or poorly it works is irrelevant.