Found a cheaper alternative to buying the whole serpentine belt idler assemblies....

[vwleadfoot]

Just got done with my top end rebuild and it came out great. The car has a lot more power and idles like a dream now. Turns out my intake gaskets were so old and cracked that they were producing a massive vacuum leak. I also solved a lot of other problems on the way in and out too.

On my m70 there were two idler pulleys for the two belts. BMW wanted 150(wholesale) each for the whole assemblies. Aftermarket wanted 120 each. I went down to my local carquest and my manager friend let me look through the selection of pulleys that they had. Lo and behold I found an exact replacement for the pulley itself, which unbolts from the assembly. Part # 38071 is a direct replacement for our pulleys and costs about $50 per pulley.

Thought someone out there would appreciate knowing this.

Thanks for your help fellas!

[ross1]

That's a Gates part #. Available for <$30 online

[shogun]

New Gates 38071 Belt Tensioner Pulley on Ebay cheapest US $14.55 up to $40. But when I select an E32 750 the system there tells me: "This part is not compatible with 1990 BMW 750iL Base Sedan 4-Door 5.0L 4988CC V12 GAS SOHC Naturally Aspirated. "
Maybe they never checked it for the 750.

Spec is shown as : Manufacturer Part Number: 38071 ,Belt Tensioner Pulley, Drive Belt Idler Pulley
Notes: Description--Thermoplastic Smooth/Backside (70 mm x 24.5 mm x 8.2 mm x 24.5 mm), Features Advantages--Reinforced polymer pulleys built to resist under-hood contaminants.
Height--1.9100 IN
Length--4.8250 IN
Weight--0.32 LBS
Width--5.0000 IN

[vwleadfoot]

All I know is that two of them are on my car and are working perfectly:-)

[shogun]

Then we know it fits perfectly. Thanks for that information.

[biasvoltage]

It turns out the Gates 38071 isn't quite a perfect match for the pulley on the E32 750il tensioners. They are the same width, but slightly different in a couple of other measurements:

The original pulley measures 75mm in diameter, the Gates 38071 measures 70mm. The hole in the center on the original measures 8mm, the hole in the Gates is 10mm.

I'm giving them a try anyway, having already purchased them. I centered the pulleys as best I could before torquing them down onto the brackets. I don't think the difference in diameter is going to be material, it will spin a little faster and thus wear out the bearing a little faster, but the originals lasted 100k miles so these may well outlast the car.

I discovered the reason that the whole bracket gets replaced; there is a pair of needle bearings pressed into the bracket that allows the bracket to rotate as the belt wears and the tensioner spring takes up the slack. Given that they see a fairly static load, instead of pressing them out and replacing them, I just I flushed them out with brake cleaner and lubed them up with fresh grease.

[biasvoltage]

FAILURE. I can unequivocally state that the Gates 38071 is NOT a direct replacement for the 750il tensioner pulleys. Besides being 5mm smaller in diameter, and having a center hole that is 3mm larger in diameter, it turns out the backspacing is about 2mm off so when the pulley is under load, it scrapes against the backing plate of the tensioner and squeals like a stuck pig. I suppose you could make up for that difference with some washers, but given the other dimensional problems I decided it was a bodge repair on top of a bodge repair and went ahead and ordered the correct, albeit expensive, INA pulleys with brackets.

[vwleadfoot]

FAILURE. I can unequivocally state that the Gates 38071 is NOT a direct replacement for the 750il tensioner pulleys. Besides being 5mm smaller in diameter, and having a center hole that is 3mm larger in diameter, it turns out the backspacing is about 2mm off so when the pulley is under load, it scrapes against the backing plate of the tensioner and squeals like a stuck pig. I suppose you could make up for that difference with some washers, but given the other dimensional problems I decided it was a bodge repair on top of a bodge repair and went ahead and ordered the correct, albeit expensive, INA pulleys with brackets.

It was three years ago when I did the original post on this. I can't remember if I had to do something to them to make them work but I haven't had to fiddle with the pulleys since then. I may have put a washer behind them but I want to say that if I did I would've included that info as well.