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MG MGB Technical - Air Conditioning and Fan Belt Routing

I added air conditioning to my '67 GT a while ago. Everything works well, but I have to make the fan belt tighter than I like to keep it from squealing when the compressor comes on. The fan belt now goes around the crankshaft, fan, compressor and idler pulley, forming an almost square figure (figure 1 in the attached drawing). To tighten the belt, I move the idler pulley outward, making the square a little larger.

I'm thinking I wouldn't have to tighten the belt so much if it made more contact with the compressor pulley. I could accomplish this by moving the idler pulley to the outside of the fan belt, where it would push it inward. The belt would then form a sort of hollow L figure (figure 2). Of course, I would trade the grooved idler pulley for a more suitable, flat-surfaced wheel to push on the flat side of the V-belt.

I have seen this done with serpentine belts, but never with a V-belt. My question is, would this (bending it backwards) cause the rapid demise of the V-belt? -G.

Glenn G

I've never seen a V belt bent backwards, so damage is likely.It's why serpentine is replacing V belts. Most V belt systems will run two belts, rather than bend backwards. My Subaru had a smaller belt being run off the compressor to run the alternator.
peter

Glenn,
Don't know much about V-belts configured like that, but I'd bet they will not do well.
On a connected note, how does the air-co do in your GT? I have thought about it, but am worried about overheating with the extra load on the engine.

Pat
'73BGT
Patrick Callan

I have A/C in our 79 MGB LE, and run 2 belts. 1 going round the engine driven fan, crank, and compressor. The other from the compressor to the altenator mounted above it. The unit is an original one made by Cool Aire and installed by BMC Dealers. Belts always stay tight. no squealing. I replaced the original rotary compressor with a new rotary unit that runs smoother and takes less power to run it. A one belt system is definatley not the way to go.

Kim R.
K Rutherford

O.K., guess I won't try rerouting the belt. It does work pretty well the way it is configured, but I'm accustomed to leaving more play in a fan belt. I am using an old Sanden rotary compressor -- possibly a new compressor would work better. Also, I am using a separate belt for the alternator, running off the compressor pulley, similar to Kim's setup. It is not shown in the diagrams. Ideally, the compressor would have its own belt driven by a dual-groove crankshaft pulley, but I haven't found one of those yet.

Overheating in summer has been a problem with every old car I've owned, and air conditioning makes it worse. Remedies include larger radiator core, new radiator, supplementary radiator electric fans, and micro-managing the car in summer heat. This would include such innovations as using the choke to raise the engine idle (after adjusting the linkage to avoid enriching the mixture), turning off the compressor when stopped at traffic signals and operating the radiator electric fan switch when appropriate if you don't have the fan connected to a thermostat.

On the bright side, air conditioning does cool the interior of the car somewhat. On 100°F days, the temperature inside the car feels about 80°-- much better than the 110° or so it would be without air. In a city with hot summers and many traffic signals, a/c is almost a necessity. -G.
Glenn G

Glenn,

As an Industrial Designer I tend to look at things a little different sometimes.

Could you change to a two belt system?

Belt One: Crankshaft - Fan - Idler

Belt Two: Idler - Compressor

It would mean getting a double pulley for the idler; and either moving the compressor out slightly or adding a double pulley to it and only using the outside slot.

...or something to this configuration. It is just a thought for something to think about...

Robert
Robert Browning

Robert,

Off topic, but I can't help hailing another Industrial Designer. Wonder how many of us are B owners?

I teach now, after thirty years of practice first in the UK and then for most of it in France. Many stories to tell, and my students love some of the archeology of how the high tech products from the 70's through to today were born.

I'm currently looking for a good job in France if anyone out there has any leads.

Regards

David 78 BGT
D Balkwill

Since at least two of you don't seem to understand my feeble attempts to explain the setup, I've redrawn the picture to show how the belts are currently arranged on the front of my engine. This has nothing to do with my question, which was whether a V-belt could withstand a reverse bend. I just wanted to show the setup in case anyone else is considering adding a/c. I've seen a lot of MGBs with this setup, which is not a factory arrangement, but seems to be the most popular way to add a/c to the car.

Glenn G

Glenn,

I don't know the answer regarding bending a v-belt the other direction, but I suspect it would work better than letting it squeal in it's current configuration.

There are two types of v-belts that I am familiar with. There are those that are notched on the inner diameter, and those that are not. I expect the notched ones would take a reverse bend better than the other, but maybe not.

If it is not too difficult to try it, I would suggest you give the reverse bend a try. Keep a spare belt with you, and see how it goes. I bet it works okay, and maybe just requires a more frequent belt change.

Most belt manufacturers suggest a 4-year change interval. If you do the reverse bend, maybe you would need a 2-year change interval. That would not be a big deal.

Charley
C R Huff

Again, this is off subject, but David Balkwill, please drop me an email.

Thanks,

Robert
Robert Browning

Glenn,

It may not be practical, but if you could drive the alternator with the water pump instead of the AC, it may take enough load off the AC to prevent the belt from squealing.

Wayne
Wayne Pearson

Glen,
My A/C setup has a large shroud so that air is drawn in and is a more effective way of cooling the engine using a faily large multiblade fan. Also in front of the condenser I have it so the electric fan also comes on to further cool the 134a in the system if it gets above a certain temperature. I set the idle at 1200 rpm and find that it runs smoothly at lights etc.
Have copies of the original BMC installation if you would like one. Our temperature here in the summer does not get much over 95f on the hottest day, however the engine temp runs is half way on the gauge, slightly over if in heavy traffic and crawling along. The temp inside the car runs 70/75f. Super effective unit.

Kim R.
K Rutherford

This thread was discussed between 11/08/2009 and 19/08/2009

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