M20 Front Engine Whine / Rotational Sound

[Syoder]

Hello all. I'm looking for some insight as to what may be causing a rotational whine near the front of my engine. The sound has been consistent throughout my two years of ownership, is very noticeable around 2k rpm from outside the car, and is definitely RPM dependent. It doesn't seem to have gotten worse or better over time, and there are no obvious external issues I have been able to find. I have replaced the water pump, belts, alternator, distributor, and fan clutch as maintenance items over time, and unfortunately none solved the noise problem. The only remaining external rotating item is the timing belt, which was replaced by a local BMW shop immediately after I purchased the car. I haven't replaced the timing belt again yet, because I may be removing the head for some work soon, and would like it to be fresh with the head refresh.

I think it's also worth noting that there are no shavings or anything visible in the oil that may indicate bearing wear.

I've done some searching, but can't seem to find anyone that I'm confident has the same issue, so any ideas on what this may be would be greatly appreciated.

Video of the sound in question: https://youtu.be/6NpxtjCRxMA

[digger]

Likely the timing belt system, it’s makes that noise when it’s a bit over tensioned.

[varg]

When my M20 was making that sound it was the timing belt tensioner. I disconnected all other belts and it kept making the noise, replaced the belt and tensioner and it went away.

[packratbimmer]

I have had the same problem with one of my cars. I am wondering if I can start the engine with no drive belts attached without harming electronics? In other words, can I start and run the car on the battery for a minute or two with no ill effects? Planning to put one belt back at a time...

[Syoder]

Digger & varg, thanks for the input. Timing belt / tensioner is my main suspect too, just needed to hear it from someone else.

Packratbimmer - Yes, you can definitely start w/o accessory belts to help eliminate the alternator, water pump, power steering pump, etc. This is precisely what I did to rule out those items on my car. Obviously don't run it for long like this. For reference, mine took maybe 20 seconds to confirm it wasn't the water pump.

[Northern]

I am wondering if I can start the engine with no drive belts attached without harming electronics? In other words, can I start and run the car on the battery for a minute or two with no ill effects? Planning to put one belt back at a time...

No issues with this, it won't hurt anything and your battery has more than enough reserve to run it like this for as long as that would take.
Just remember that the water pump is also not pumping while the belt is off, but you shouldn't be running it long enough for that to matter.

[packratbimmer]

No issues with this, it won't hurt anything and your battery has more than enough reserve to run it like this for as long as that would take.
Just remember that the water pump is also not pumping while the belt is off, but you shouldn't be running it long enough for that to matter.

Thanks Syoder and Northern!

[packratbimmer]

Can anyone recommend the best timing belt tensioner brand to buy? I use Continental timing belts and usually buy it in a kit. I am wondering if they have started putting in cheap bearings into the kits to curb costs.

[digger]

OE or INA have worked well for me

[Syoder]

I thought I'd provide an update on the this situation.

Long story short, it does appear to be the timing belt tensioner pulley. There's no obvious play in the bearing, but rotating by hand reveals the movement is a little less smooth than the new pulley I have. The reason I say it appears to be the pulley is that my repair plan snowballed drastically to the point that the engine & trans is now out of the car, the head is at the machine shop, and I'm tearing down the block for the same treatment. I was burning a lot of oil (at least 1qt every 500 miles), and she failed smog. After changing plugs and cleaning & sealing the intake she failed again. I've been wary of the head gasket and the bottom end (specifically rings), as I know the head was rebuilt by the PO, and the bottom end wasn't touched. I thought if I'm tearing the front apart and taking the timing belt out, I may as well go all the way rather than come back in a year and do it all again.

Wish me luck.

Here's a little action shot...

[D.Martijn]

Aah yes, taking the "while I'm in there" to a whole new level!

I too have a whine coming from the front of the engine, I haven't had time to remove the accessory belts yet and listen if it still whines.

[packratbimmer]

Time for a belt again. My car made the noise as heard in the video above during this entire belt service interval and the last if memory serves. The belt seems awfully tight under the tension dictated by the spring. I am starting to think the spring is wrong or maybe the water pump "perch" for the tensioner spring rod is machined wrong and causing the belt to be too tight. Should I be able to flex the belt 90 degrees after the tension is set? I am not even close to that. Also, does anyone set these belts by more modern means?

[varg]

I think quality of the parts is the likely issue, not the tension. The loading of belt tension on a properly designed tensioner is radial, which is what the bearings are designed for. It is increasingly difficult to get parts that aren't garbage these days because of global supply; with suppliers of each individual component scattered across the world, it's more difficult to assure quality of the end product, and it's not profitable in the short term. The springs don't look any different than they used to, and spring rate is fairly constant for a given wire diameter and number of coils, so I doubt that's the issue.

[packratbimmer]

Does anyone use BMW branded tensioners? I think I might go with BMW and a Gates racing belt. I read somewhere that the Continental belt is the culprit. The person swapped out a Dayco and the noise went away supposedly. I might try a Gates next time. Today I finished up the belt job and the noise is still there. The engine is bomber otherwise - despite a little weeping of oil here and there, there is zero consumption between changes and it runs great. Not a big deal right now as it barely gets driven. Bugs me though because I never had the problem - 1999-2015 were fine, but the last 5 years have been plagued by the noise.