[YonexJohn]

Hello. I'm about a 3-4y F10 driver, but first time to post.

Like many of you, I started driving BMW because there wasn't a close second in "bang for the buck" on the used car market. I spend over two hours per day on the road and the driving experience from a comfort, performance, and (lack of) road noise standpoint is invaluable to me. I'm on my second one (first got rear-ended and totaled a couple of years ago) and both were purchased for less than 1/3 of original MSRP with 40-50k miles on them. I afford driving a bimmer by doing almost 100% of the repairs myself. I'm really good about doing all the maintenance I know about on my car. I own carly, and have a friend I can text/call who was a BMW master mechanic for years and can be an escalation for me when I need advice.

I wanted to relay the following in case it saves someone else the same headache. A few weeks ago I was on the way home from work in an area of interstate 30 that doesn't have a shoulder and I heard the dreaded screech of a belt running across a frozen pulley, followed by a pop, and then a dash of lights warning of charging system malfunction as well as the A/C Compressor turning off. I wasn't in a safe area to stop so I slowed down and drove the remaining 2-3 miles to my house. When I got home I confirmed my suspicion that I had broken the serpentine belt, quickly noticed that my idler pulley had exploded (quite literally; ball bearings all over the place, etc.

Over the next hour I confirmed that my local parts suppliers didn't stock the belt and pulley, called BMW and got a quote for the parts (~$400), and eventually settled on ordering the serpentine belt, idler pulley, and tensioner pulley from FCP Euro overnight ($128). The parts arrived on time and it took me a few hours with a good youtube video (link below) to change the pulleys, clean the belt pieces out from the engine compartment, clean the pulleys, and reassemble. It was slightly more painful than it should have been due to my never having removed the fan shroud, fan, etc, but overall a very doable job for a mechanically inclined individual with the right tools.

The best video I found for the pulley replacements:

Within seconds of restarting the car, I got the lean fuel mix codes. I called my aforementioned BMW mechanic friend and he immediately explained what happened. He guessed that the "oil tower" (oil filter housing) gasket was leaking onto the idler pulley which caused it to fail which caused the belt to break which caused the crank seal to be compromised which (probably) caused the engine vacuum to suck belt pieces up into the engine. I validated his theory by stringing some straws together to spray some carb/choke cleaner behind the crank pulley and almost immediately heard the engine increase RPM's.

I called my local dealership and two other reputable european shops for quotes. All three immediately knew what happened, said something along the lines of "this happens all the time", and then proceeded to give me estimates. BMW quoted approximately $8500 depending on what came up during the repair. The other shops were between $4-5,500. I called my friend back and offered to find some way to have him do the repair. He politely declined, but asked for a few hours to reach out to someone he trusted to do the work. We ended up settling on me buying all the parts from FCP Euro, towing the car to the shop in question, and them charging about $1500-2000 in labor depending on whether they had to drop the oil pan or not.

Parts List:
- Valve Cover
- Oil Filter Housing Gasket Kit
- Crankshaft Seal and OE Sealant Kit
- Oil level sensor sensor
- Intake Manifold Gaskets
- Valvetronic Actuator Seal
- Intake Tube O-Ring
- 6 Ignition Coils
- 6 Spark Plugs
- Air Filter
- OE Oil
- Liqui Moly Engine Flush
- Vargas Crankshaft Seal Guard

They ended up not dropping the oil pan, but rather used a camera through the oil level sensor hole. They found a very compromised crank seal and quite a few belt pieces behind the bad seal, no belt pieces in the top of the engine, and none in the oil pan. Apparently my very limited driving after the seal broke limited the damage. The shop had the car for about 2 days and I have driven it about 250 miles since with no further issues.

My takeaway: I will check regularly for any oil filter housing gasket leak that could be compromising the idler pulley and change both pulleys proactively every 50k miles or so. In theory my Vargas guard will prevent this in the future, but I would still rather not have the belt break because of a failed pulley.

Here is what was pulled out from behind the seal as well as the seal itself.

[StradaRedlands]

Fingers crossed no catastrophic damage. An expensive lesson though! The AC compressor froze on my E90 and shredded the belt. No damage to the crank seal though... just got lucky on that one!

[ChiltiCoatl89]

Yeah I dread this, I am so happy to hear you did not destroy the engine! I have a list of parts I am going to install soon before another grand road trip and it will be a complete belt and tension and pulley replacement with Crank guard! Great photos and I am determined to never let this happen to my beloved N55!

[ChiltiCoatl89]

How many miles on the Odometer did all this occur for reference?

[YonexJohn]

Originally Posted by ChiltiCoatl89

How many miles on the Odometer did all this occur for reference?

Good question. It was right at 104,000 miles.

I also forgot to mention that I do the BG EPR/MOA treatment with all of my oil changes and the top end of the engine was beautiful with no visibile build-up. I’m not sure if there is clear correlation there, but figured it was worth mentioning.

[ezaircon4jc]

Originally Posted by YonexJohn

Good question. It was right at 104,000 miles....

I had mine changed proactively at about 6 years (don't remember the mileage). I'll probably do it again in another couple of years. I use years vs. mileage as we don't drive that much since I got fired/retired.

[ChiltiCoatl89]

Yeah I am at nearly 82k and I am making preparations and planning Preventative Maintenance. 104k miles sounds like you had a good run and that was the first time you replaced the belt and tensioner and pulleys correct?

[YonexJohn]

Originally Posted by ChiltiCoatl89

Yeah I am at nearly 82k and I am making preparations and planning Preventative Maintenance. 104k miles sounds like you had a good run and that was the first time you replaced the belt and tensioner and pulleys correct?

Correct.

[ctcarbonari]

Excellent post & write up! Thank You.
Sorry to hear about your experience (especially the timing of where it happened)

I'm looking at the Accessory Belt kit / OFHG kit / Crankseal Guard sitting on my shelf and thinking "don't be a dumba$$" - get off your butt and do this PM work sooner rather than later. (I'm at 78k miles)

[ChiltiCoatl89]

Get on it! Since you have it I would install that ASAP! Im ordering mine very soon.

[OrcaPod]

Thanks for sharing!
I'm at 176K km on my 2011 F10 528i with N52 engine.
I also installed crank seal guard/protection a while ago (just an extra piece of mind). got it from here https://www.maloindustries.com/produ...ection-plate-1 and it took few hrs to install.