Vee belt problems

[solarman216]

Anyone on here expert on Vee belts, I am having problems with my air compressor, I think I know the problem but do not know how to cure it other than put an idler pulley on the slack side, so here it is, 12 HP 4 stroke motor driving a large horizontally opposed twin compressor, (do not know its CFM but it was made to drive a road drill with only the tubular frame as a receiver, petrol driven with twin belts, engine blew up (might have been twin but cannot remember, it was many years ago) so I grabbed it) so my motor being single cyl 4 stroke the power kick is high, couple that with the twin pulses from the compressor and you can begin to see why the slack side of the belts start to jump wildly near full load, just fitted a matched pair of Gates A belts but no better, if I continue to run it as is the belts will fail in no time, so you see the problem, maybe they make stronger non stretch belts but I have no idea, Rick

[panelbeater]

i made my first compressor from a train shunting engine.
i had the twin vertical high out put pump in a frame i built and a 5ft high big round freestanding reciever next to it.
the 10hp 3phase motor mount next to pump on slider so belt ajustments could be made.
i put a pair of the biggest v thickness v belts on to the pullies that i machiened up,much bigger than what was on pump to start with.
this was run through a pressure switch so on/off was auto with a top pressure cut of with blow of valve.
this over enginered pully system worked as the ones pump came with could not cope with the big motor.
i did think about an ideler pully under spring tention but i did not need it.
the cfm was huge as it copped with apto 3 people drawing a lot of air all the time and it would still cut out.
so maybe a spring pully ideler might help or can you go much bigger on belt thickness.

[macabethiel]

Just throwing this in - on some Mercs the alternator pulley has a spring type clutch mechanism - to reduce load on engine start up I assume.

Only know this as a friend B class kept on stalling just after start up when cold - not good on an automatic! Turned out the clutch mechanism in the pulley had seized.

[Wallace]

Does the new setup use the same pulleys and belt sizes as the old one?

[solarman216]

Does the new setup use the same pulleys and belt sizes as the old one?

The compressor pulley is original and not easy to change as it incorporates a fan, it is 185 mm diameter, (fan much bigger) the engine pulley is 125 mm, recently re grooved for the wider A belt, before it ran an alternator with narrower belts, dictated by the pulley on the alternator, current belt length 1650La I have the makings of a substantial idler pulley, cannot get the engine much closer as only few inches between them and space needed for maintenance, Rick

[Wallace]

My thoughts are what differs from the original setup, pulley size and difference between driver and driven as that might change the contact area add slippage. As the drive pulley has been re-grooved, have you tried pulling the belts off and clocking the pulley whilst turning the motor over? Maybe try taking plug out with the belts as they are and checking run-out.

[solarman216]

Pulley run out with belts on is only 8 to 10 thou, but I did notice when straining the belts that there was 10 to 15 thou deflection on the engine, so maybe need to stiffen the engine mounts, but putting idler on for now as need air, Rick

[solarman216]

OK well got the idler sorted today, ace sorted the top slack no problem, now the bottom drive side is flapping, nothing like as bad but want to cure it, at around full load (120 psi) I tried a smooth bar with gentle pressure and yes that is the way forward, so now in the process of making a lower idler, pics to come later, Rick