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OEM ///PLUS
2003 M3 6MT Slicktop
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Discussion Starter #1
Ok I have replaced my roller pullies in the past on the V-belt drive. I know those bearings give noises when shot. I have not done my AC mechanical pulley in years.
I replaced my AC belt as it was worn. Placed up against the old belt the new one was ever so slightly smaller. Figured from stretched over time. After the new belt I get a light squeak, but only at first start of day. Goes away after 15 minutes.
Now my question is:
1) is this from the bearings in that pulley going bad
2) is this from the mechanical spring in the pulley unit pulsing from slightly tighter belt.
3) will this stop after the new belt “stretches”
Thanks, figured I’d ask if anyone else has had to deal with this and outcome.
 

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OEM ///PLUS
2003 M3 6MT Slicktop
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Discussion Starter #2
Anyone? I don’t want to waste time/money on new mechanical pulley tensioner if it’s just the belt being new.
It only started after new belt.
 

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the new belt I get a light squeak, but only at first start of day. Goes away after 15 minutes.
The pulley bearing with dried grease making noise. Remove belt and spin by hand, if the balls roll freely and rattle then it need regreased or replaced. Do now or more headache when bearing exploded.
 

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2004 325i automagic
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Maybe drive it a week and see if the squeal goes away. Assuming the tensioner pulley and the compressor pulley bearing test good when you spin by hand.
 

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2003 325xi 5spd Manual
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My vote is #2. Maybe its time for a new mechanical tensioner on the AC belt. but I would hold off and see if it gets better when the belt 'breaks in'.
 

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Everyone should have a mechanics stethescope and they are around 12 bucks at Harbor Freight. Obviously due care around spinning belt but going from pulley to pulley it should take less than 30 seconds for you to 100% know if its a pulley Tensioner and the specific one. If you suspect belt slippage, while its squeaking pour water directly on the belt. If instant stop noise it was indeed belt.
 
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E30M3 Race F10 535 R1150Rt M Coupe
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New Conti belts are quiet.
Furthermore old school belt stretch is almost non existent on serpentine belts. Rather a change in inner diameter due to wear.
 

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2003 M3 6MT Slicktop
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Discussion Starter #8
Thanks all. been unable to get under car and check tensioner/pulley.
just don’t want to replace tensioner if it’s just the new belt. then again the new belt might just be exposing the tensioner/pulley going out??
 

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How are you going to "check" the tensioner/pulley?
 

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2003 M3 6MT Slicktop
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Discussion Starter #10
Either take it out and check the roller bearings and lube the internal spring.
Or lube bearing and spring and see if it stops.
 

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So if you are taking it out I wonder if you can sneak some curative/preventative grease under the rubber dust seal into the bearings? A few years ago I ordered some bearings off a website and was a few bucks short of free shipping. So I found a 7 buck item designed to sneak its tip under bearing seals and relube a nonmaintainable bearing. Its become a valued tool. Turns out you can also use a pick to lift most of these seals and lube these idler pulleys. So perhaps you can here? My experience so far has been a merely noisy bearing can last a lot longer. YMMV
 

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A mechanic specializing in BMW’s showed me a trick, he took a standard screwdriver and applied a little pressure on the engine side of the tensioner while running. It showed me that the tensioner was shot and the noise disappeared after installing the replacement.
 

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2003 M3 6MT Slicktop
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Discussion Starter #13
my ACL injury still making it impossible to get back under car to work on/inspect. but MrMCar has given advice in another thread which makes me lean towards this being a belt squeak. which seems to align with issue and installation of (cheap) belt.
 

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Either take it out and check the roller bearings and lube the internal spring.
Or lube bearing and spring and see if it stops.
If the bearing seems to run dry (very loose like not grease inside) then it needs grease. I added grease every year on Thanksgiving day.

What spring that needs lube? Your is an M3 which has hydraulic tensioner, unless we're talking AC tensioner which has a big spring. I don't think the spring can sing.
 

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2003 M3 6MT Slicktop
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Discussion Starter #15
stated it’s AC belt tensioner, and that’s mechanical.

was only speculation the spring inside the unit at the ends might be under a new tension area and make noise when pulsed.

Don’s (MrMCar) explanation about belt and sound seems to fit (no pun intended).
 

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stated it’s AC belt tensioner, and that’s mechanical.

was only speculation the spring inside the unit at the ends might be under a new tension area and make noise when pulsed.

Don’s (MrMCar) explanation about belt and sound seems to fit (no pun intended).
Well, use a straight edge runs across the crank pulley to check if the belt at the tensioner in parallel with crank and AC pulleys. If yes (which I think) then no belt rubbing on pulley guard and so I don't think the belt in this case. So you're sure if the AC belt is removed the noise disappears?
 

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2003 M3 6MT Slicktop
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Discussion Starter #17
this only started the day the belt was changed with a new one.
 

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this only started the day the belt was changed with a new one.
You did say the new belt is narrower than the old one, otherwise I would suggest to look carefully if the belt is wide enough that its edge rubs the crank/AC pulley guards.
 

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If you suspect belt noise pour water on the belt while its running and the noise will instantly stop. If you have a stream type handheld sprayer thats ideal for minimal water but if pouring, a half pint is adequate. Directly on the belt surface that contacts the pullies. It will spread across the belt and pullies and lubricate the noise away, then harmlessly dry and the squeak will be back. You will have your answer in 30 seconds from a standing position. Wear old clothes...
 
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OEM ///PLUS
2003 M3 6MT Slicktop
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Discussion Starter #20
You did say the new belt is narrower than the old one, otherwise I would suggest to look carefully if the belt is wide enough that its edge rubs the crank/AC pulley guards.
I never said it was narrower.
 
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