I presumed BMW did this to make the M3 seem much more special, and maybe that's part of it, but there's another reason too- When you rev these things they explode in a fucking massive, engine wrecking, nothing worth salvaging, kind of way. Ever wondered why 325 and 328 engines are cheap and common and 330s cost so much more despite being so similar? It's because most of them are fucking broken!
My engine was running great, totally reliable and great, being both my hard used daily driver and used on drift days all over the UK with no problem. Then one day, at 6700rpm in 5th gear, the oil light came on, and stayed on, and it sounded like a bag of nails. I knew this meant game over for the engine, and seemed likely the oil pump failed. But I didn't know why. Well, it turns out it's because of this...
So what happens? Well, the nut falls off, which then means the chain and pulley falls off, so the oil pump stops, meaning instant zero oil pressure, which as you can imagine, writes an engine off pretty instantly.
If you catch it super quick and at low rpm you'd likely get away with rebuilding the engine with new bearings etc, maybe a crank polish. That's debatable if it's worth doing over buying a good used engine, but mine fell off at 6750rpm and 3 figure speeds, and I likely didn't notice for at least 5 seconds, so it was deffo game over.
I limped it 5 miles home, and then thought 'fuck it, I'm not rebuilding it' so limped it as far as I could to my mates garage 10 miles away. Amazingly, it made it! Well, it got to about 200m away before it expired, and I coasted it the rest of the way.
What was the damage? Well, this...
So what the hell fuck can you do about it? As it's mega common, and pretty flippin' disastrous lots of people have looked for a solution. There's a few expensive things that 'seem' to fix it, and a few cheaper things that seem to just delay the inevitable...
Another 'solution' is lockwiring the nut in place (top left). You can even buy kits for this, but again, it delays it, not fixes it. The entire pulley ends up shearing off.
Next up is almost the same solution and same 'in the end' fail, spot welding the nut in place, as the top right pic shows.
A better solution is a modified pump with a 4 bolt pulley, as per center bottom. Shame it costs about 750quid, which is nearly twice what a used engine costs.
Because it's crank harmonics that cause it, an ATI crank damper (bottom left) supposedly helps too, but again, it's big money, which turns most the appeal of a 330i in the UK (ie they're cheap as chips) down a little.
Best of all, but serious money that would certainly make you wonder why you didn't buy an M3 in the first place, would be a dry sump setup (top centre).
So what have I done on mine? Well, I picked up a low mile engine for £450, got the nut spot welded in place, which deffo isn't the full solution, BUT I hope it lasts a long time. Finally, partly as I wanted one anyhow for performance reasons, and partly as it's entirely possible it will change the damaging harmonics to a different RPM that it's no danger any more (but literally no way to know, it's SWAG- Scientific Wild Ass Guess, but a hopeful one) I've got a super lightweight flywheel to replace the fucking mental heavy dual mass setup they come with.
If it does fail, I'll let you know!