Thread: Routing v-belts for onboard air

Originally Posted by superquag

NOT a full bottle on Vee-belts, but do the experts reckon there is sufficient 'wrap' on each of the pulleys ?
There's 4 of them, - plus the tensioner - which means the average is less than 90 degrees per driven one.

Three on a circuit gives 120 degrees, or 25% more. I'd imagine this would translate as not needing anywhere the same belt-tension as the proposed original.
Which equals as longer belt life, bearing life, quieter (less strain/squealing) and more robust system.

You have a PTO as well ????- Is it noisy in operation? What's its designed duty-cycle ? - Thought they'd died off with the early 'Series'...

- A direct mechanical coupling (obviously) wastes no power in transfer, as do belts/gears/chains.

Just to nit pick...

which way are you counting your angles

180 degrees give a belt that essentially does a u turn
120 degrees 3 of these make an eqiulateral triangle
90 degrees is a right angle turn
60 degrees is your minimum and looks like a deflection
0 degrees is essentialy just a pully thats rubbing or

180 degrees is essentialy just a pully thats rubbing or
120 degrees is your minimum and looks like a deflection
90 degrees is a right angle turn
60 degrees 3 of these make an eqiulateral triangle
0 degrees give a belt that essentially does a u turn

Set the problem aside for today, to concentrate on the more basic task of adding all the bits to actually get the engine running. Main reason I was nutting this out was to figure out the final position of the alternator so I could make up oil lines to suit.

I've come back to it tonight to pass the time, and while the setups that I have seen had the A/C compressor slung underneath the alternator, according to this pic the 4BD1T at least comes in a variation where the alternator sits midway up the engine, and the A/C compressor on top again....



First off, it answers the question re. acceptable belt contact area - the fan pulley and the alternator couldn't be getting more than 50 degrees contact... second, it may be possible to squeeze a second compressor under the alternator....

...Just to nit pick...

which way are you counting your angles...?"

Oops, my mistake.. Did'nt make myself clear-ish...
- I meant the number of degrees of wrap-around, whch is how come 3 pulleys give better grip on the belt than 4 pulleys. -Assuming they're arranged as an equilateral triangle. Better by 33%, not 25%.... can't recall 'what' I was smoking.... so to speak.

A simple 2-pulley setup giving 180 degrees of wrap is the ideal.

IMHO, a 3 and a 2 setup with the onboard air running off the PTO or electric pump is the better way.

Revisited this again while I was sitting in front of the engine bay with a cup of tea...

I've found that quite a few people have raised the alternator and A/C pump on other vehicles to clear steering boxes and such, so it doesn't seem to be an issue reducing the contact area of the fan pulley. I've stacked the compressors in every arrangement to the point of getting into bonnet hump territory, and the best I can do (assuming that it works at all) is as follows:



Any input would be appreciated.

rotate the alternator 90 degrees and hinge it from the outside, this will shift the pully closer to the center and lower it down a little increasing the contact on the water pump (fit a thermo, loose the load of the fan) and more importantly the AC pump which is going to have the highest draw on the belt and is stop/start an may potentially cause belt slip/burn.

So long as you fit an unloader on the Onboard Air you shouldnt have any problems with the idler being on the drive side of the compressor but I would look at fitting a sprung tensioner if you can get one to fit.

For me, not enough drive on the a/c pulley. Could you swap the alt and a/c around. Run a belt from the balancer-fan-alt-on board air. Then run a twin pulley on the onboard air and a/c and run a belt on just those 2.

OR

Scrap the whole idea and just get the damn thing going

Maybe you can chassis mount air compressor with spring idler works but not ideal ,probably drop belt off for most of the time Just a thought

Or just buy an electric compressor like the rest of the world, scrap the endless air idea, and just get the damn thing going.
Hmm think I may have mentioned that earlier