Torn Serpentine Belt repair process

[maxwmiller]

Hey all, I had my first breakdown in the E84 this weekend. Serpentine belt tore off about a mile from home, AC and charging suddenly went out.

Fortunately I didn't need to go anywhere and have a spare car so I stopped driving and am now trying to figure out how to repair. I believe the leak originated from the front main seal, as I proactively replaced valve cover gasket and OFHG in the last year. Not sure if belt penetrated the seal, which would be a major hassle. Anyone have tips or tricks? 2013 US xDrive2.8i

[maxwmiller]

If I find belt that may have snuck past the seal, I will have been have to drop the oil pan, which requires subframe removal on the AWD cars. Done it twice before, not fun. However I could stand to replace my motor mounts, so at least I could get a few birds with one stone.

[wheela]

Sorry to hear this. I haven't done that so I can't offer any tips, but I hope you let us know how it goes.

[maxwmiller]

Hey all,

I'm happy to report that the X1 is back up and running. I was out of town a bit, so it took a few weeks to make sure everything was ok.

The serpentine belt failure has two possible reasons. First, I previously had a leaking OFHG. This was replaced in February 2024, but the belt was not changed after. CHANGE YOUR BELTS IF THEY GET OIL LEAKED ON THEM. Second, the tensioner pulley was old and crusty. I believe it was the original on the car.

Steps I took:
1) Remove all debris from engine. The belt shredded into small pieces (looked like greasy, black cotton balls), so those had to be removed.
2) Degreased the engine bay twice, for cleanliness and to see my workspace better
3) Removed intake and breather pipes (I have an ECS tuning catch connected to the breather pipes)
4) Inspected front main seal. This is the main cause of concern, as debris can wrap around the main crank and be sucked into the engine. Fortunately, the seal was undamaged and no belt material was near the crank.
5) Replaced the belt tensioner. It was likely the factory item.
6) Re-installed intake and breather hoses, added fluorescent dye to oil reservoir.
7) Started engine, ran for 15 minutes at idle, no leaks observed. Drove for five miles around city, no leaks observed.
8) Took for extended freeway drive, no leaks observed.

I have started using high-mileage oil as well. Most of my gaskets are recently replaced, so ideally I shouldn't be having leaks in the first place, but its a BMW.

[maxwmiller]

Hi all, wanted to provide an update.

A few weeks after inspecting and finding no belt material or tears, I unfortunately did conclude that oil was leaking from the front main seal (FMS). This took a while to diagnose as I had a resurgent leak from the oil filter housing gasket (OFHG) which I had replaced less than six months before. Also, oil was somehow getting on the belt or a pulley, causing it to sling in the engine bay.

The FMS leak was very slow (maybe a few drops per hour). About a week after my initial UV test (which alerted me to the OFHG leak) a friend noticed it had caused a minor but noticeable oil spot when parked overnight after driving for an hour. Minimal leakage was confirmed when I changed my oil and drained the engine for over an hour, I got about 5 liters back (5.5L go in to AWD N20s) but I don't like leaks so seal was replaced.

To replace the seal, you need to remove the crankshaft pulley, which requires belts to come off. The tool I used strongly recommended to remove the water pump as well. Additionally, I found that a flywheel lock tool (like CTA Mfg. 2801) is highly useful so the center crankshaft bolt doesn't have to be counter-held when undoing pulley bolts. The first pulley (power steering) came off like butter, the second (alternator/AC) required a crowbar. This was surprising as I took the pulleys off when doing the timing chain and it was much easier.

The tool kit to pull and re-seat the FMS was available for ~$60 on Amazon, and worked perfectly. I installed an OEM Corteco PTFE seal with Mega Gray gasket sealer for extra insurance. Notably, the old seal was slightly extruded from its housing, possibly due to not having sealant applied when installed during my timing chain replacement. Sealant is not required, but generally good practice.

Will update again if leak was solved or not. The new (non-OEM and cheap) tensioner I installed in May has a slight wobble, so it's getting a OEM replacement and new belts. Should be a happy N20! Suspension refresh coming next