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Dual Belt Pulleys??


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12 replies to this topic

#1 cobcob

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Posted 14 April 2008 - 04:23 PM

OK, so I've finally got my '88 DL 5spd wagon back to running condition. I have to make a 30 mile trip into town to get it inspected prior to licensing it. Question is this. I currently have 1 belt on it, that belt runs PS, ALT, AC, and Waterpump. I know I can get a second belt for it from the shop that I'm going to tomorrow but do we reckon it'll be OK to run with just 1 belt for the trip into town?

#2 Flowmastered87GL

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Posted 14 April 2008 - 04:27 PM

it should be.... generally the second is a backup to keep you moving. Some models it follows the exact same path, others it skips an accessory or 2.

#3 cobcob

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Posted 14 April 2008 - 04:28 PM

Cheers... the second belt will skip the Alt. I figured that if the first let go then I'd certainly know about it before I over heat due to lack of coolant flow!!

#4 msteel

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Posted 14 April 2008 - 04:41 PM

Mine has the AC between the PS and Alt. Without the second belt the AC will not run because the pulley slips too much and the system disengages the compressor clutch. Everything else works fine.

Some engines have the accessories arranged differently, I have no personal experience with that setup.

#5 mudduck

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Posted 14 April 2008 - 07:09 PM

I've benn running just the one belt for 3 years and havn't had any problems. It will be ok.

#6 92loyale

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Posted 15 April 2008 - 05:29 PM

Having the 2 belts more evenly distributes the pressure on the bearings. Therefore, only using 1 belt will prematurly wear water pump bearing and the like. Yes, it will run that way for a long time. However, it's cheap insurance to get both belts running on there when you can.

#7 Andy FitzGibbon

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Posted 15 April 2008 - 07:47 PM

Not true. One belt or two won't make any difference to the bearings. The reason for the two belts is for the A/C compressor.
Andy


Having the 2 belts more evenly distributes the pressure on the bearings. Therefore, only using 1 belt will prematurly wear water pump bearing and the like. Yes, it will run that way for a long time. However, it's cheap insurance to get both belts running on there when you can.



#8 GeneralDisorder

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Posted 15 April 2008 - 08:47 PM

Two belts is not for insurance - if one breaks the chances are good that it will slip under the good belt and either snap it as well, or pop it off the pulley.

It was designed with two belts entirely based on power transfer needs. These are type "A" classical industrial V belts. Individually they have a power transfer of around 2 to 3 HP at around 1000 RPM. A single belt is not sufficient to drive the AC compressor, Power steering pump, and Alternator according to standard v-belt power transfer guidelines.

Now in reality, you can run with a single belt all day long and twice on Sunday's because they are over-engineered, and belt technology has progressed since 1985 just a wee bit. But the REASON for the twin belts is purely engineering - there is nothing about redundancy here. If you replace the belts at the reccomended intervals you should never need any redundancy, and besides the only way to truely accomplish that (as I said above) would be to run belt gaurds that prevented broken belts from being sucked into the other pully grooves.

I build large compressors at work and am often faced with the questions of how many, how big, how long, and what type of V belt's I will need when building a package - it depends on the size motor and pump I'm running, what RPM I want the pump to turn, the HP and RPM of the motor, ect, ect.

GD

#9 Andy FitzGibbon

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Posted 16 April 2008 - 07:34 AM

Two belts is not for insurance - if one breaks the chances are good that it will slip under the good belt and either snap it as well, or pop it off the pulley.

It was designed with two belts entirely based on power transfer needs. These are type "A" classical industrial V belts. Individually they have a power transfer of around 2 to 3 HP at around 1000 RPM. A single belt is not sufficient to drive the AC compressor, Power steering pump, and Alternator according to standard v-belt power transfer guidelines.

Now in reality, you can run with a single belt all day long and twice on Sunday's because they are over-engineered, and belt technology has progressed since 1985 just a wee bit. But the REASON for the twin belts is purely engineering - there is nothing about redundancy here. If you replace the belts at the reccomended intervals you should never need any redundancy, and besides the only way to truely accomplish that (as I said above) would be to run belt gaurds that prevented broken belts from being sucked into the other pully grooves.

I build large compressors at work and am often faced with the questions of how many, how big, how long, and what type of V belt's I will need when building a package - it depends on the size motor and pump I'm running, what RPM I want the pump to turn, the HP and RPM of the motor, ect, ect.

GD


Additionally, two belts are needed because of the poor belt wrap on some of the accessory pulleys, due to the path of the belt. Depending if you have Panasonic or Hitachi A/C, either the alternator or the A/C compressor pulley has barely any belt contact if one belt is used.
Andy

#10 cobcob

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Posted 16 April 2008 - 07:59 AM

Correct on all counts, in this case the AC pulley has poor wrap on it.
It's a moot point now anyway. The front right brake caliper seized onto the brake rotor last night so the car isn't going anywhere for a little while.

#11 GeneralDisorder

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Posted 16 April 2008 - 09:10 AM

Yep - and poor pulley contact will result in over-tightening to prevent slippage, which will cause bearing failure.

GD

#12 Quidam

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Posted 16 April 2008 - 10:50 AM

Yep - and poor pulley contact will result in over-tightening to prevent slippage, which will cause bearing failure.

GD


Here is something else to consider. I own and have used a belt tension gauge. What I saw with a lot of DIY'ers was that they don't get it tight enough.

Doug

Edit: I hardly ever use that belt gauge anymore. Last time I did was to demonstrate to a guy how they should be. He had just swapped a motor, thought he had it tight enough, an hour later it was squealing with the altenator draw on it. Used single belt...there is a setting for that.

It's a good hands on teacher and it measures the belt strech, after you install and calibrate. Mine is plastic and it was inexpensive. It has scales for single or double belts, old and new alike. I'm talking V belts here. New stuff has that all built into the system...and you don't even have to think about that. Last serpentine I did there was nothing to it, slap the belt on an go.

Once you clamp it to a belt, make sure you remove it before starting the engine...or it goes blammo.:) I've bought two in my lifetime.

Doug

#13 GeneralDisorder

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Posted 16 April 2008 - 06:57 PM

Here is something else to consider. I own and have used a belt tension gage. What I saw with a lot of DIY'ers was that they don't get it tight enough.

Doug


Belt tension is a tricky business. As one of my co-workers like's to say - it's a "1/4 turn before it breaks" sort of thing.

As long as it doesn't slip and it runs straight - it's tight enough. Any tighter is just putting uneccesary strain on the bearings - regardless of what a tension gauge tells you. Not a single tech that I work with uses those things - and some of the guys have been doing these for 30 years.

Basically you are looking for it to be tight enough to not slip, run true without flopping on the slack side, and make it to the next service interval taking stretch into account. Generally a single adjustment once in the life of the belt is all that's required to accomidate stretch - they only stretch so much and then they will stop.

If it makes you feel better by all means use one - but a good eyeball check with it running and an ear for slippage will do just as well. Don't go crazy and pull out your pry-bar and 6 foot cheater to tension your alternator either though - it's a feel and it's something you just have to learn IMO.

GD




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