On my way to changing my serpentine belt, I found something interesting. Continental makes the ContiTech serpentine belt that is the BMW/MINI official part (BMW 11288573253 aka Continental 6PK1715, both of these are printed on the belt I got straight from BMW). For Continental's aftermarket "Multi V-Belt" line (in this case whose analogue belt is part 4060675) their "Belt Nomenclature Explained" PDF document specifies with a big giant graphic:

- 60,000 mile inspection interval
- 90,000 mile replacement interval

In a separate PDF, "Belt Tensioner Kit", Continental states: "Continental Multi V-Belts, tensioners and idlers work as a system. Therefore, replacing a single component in the system is not recommended. Instead, replace all the accessory drive components at the same time to prevent premature and uneven belt wear, belt slippage and loss of tension."

The lack of a defined maintenance interval for either the belt or the tensioner has been a discussion point here before. I was trying to sort whether to replace the tensioner on my F56S at the same time I do the belt (I am just above 100K miles), and I dug this up by dumb luck (thank you random YouTube video that happened to get me pointed to the Continental site to eyeball that packaging).

What do you think of this approach for the MINIs whose BMW-official belt is made by Continental?

 

I'd do tensioner if I was going to do the belt, but that's me. Had a tensioner problem on another car (not Mini) sold me.

 

So in my case, the things I'm wondering explicitly, especially given that the car has hit 100K miles, are:

(1) How long before I can expect the tensioner to develop an issue
(2) How long before I can expect the crank pulley/harmonic balancer to develop an issue
(3) How obvious is it going to be that either has a problem before it takes out something else.

As an example of (3), on my other vehicle I had the crank pulley start to separate (similar construction -- two metal rings with a rubber ring bonding them together, the rubber fails due to age/wear). It wasn't obvious until someone took a look at it for the sake of looking at it. Easy enough replacement, but didn't sort that until literal years after wobble in the pulley, in turn causing the alternator belt to do "stuff," had started to destroy the bearings on the alternator. I didn't end up with any real downtime, but I would rather not find out that the crank pulley or tensioner has an issue by way of breaking something more critical.

What I've come to for the moment is to pull the belt and inspect it -- was going to do that anyway -- but while it's off, inspect all the various spinny bits the belt runs, and pay particular attention to inspection of the crank pulley.

I might also just slate replacement of both the tensioner and the crank pulley for 120K miles if I can find nothing wrong with them at present.