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Beyond sourcing a used factory dampner, are there other options or good aftermarket alternatives? Thanks in advance.

My high school physics didn't prepare me for this. What I know is less than what I don't know, but I do know a little.

It might be super simple, I don't know. I have heard on domestic V8s that the wrong dampener caused engine failure. Although not specifically exactly what. I do know there were 2 different ones for 533s, slightly different in weight. Slightly. I think the later one was the same as US spec 535s. But it might have been where the weight was. Think, Realoem is your friend. Earlier M30s, 2.8/3.0 used different, lighter dampeners. 2.5's probably used still lighter ones but I no longer have one of them. Same as a lighter flywheel, or a critical mass. I have a suspicion, but without technical knowledge I won't share it because I don't want to tell you the wrong thing.

I think long ago, I posted a question about this and received no feedback. Don't be surprised if you get the same. No hostility, just nobody really knows. Or maybe they do...

There's a place called Damper Doctors in California that rebuilds harmonic balancers. They don't list anything specifically about BMWs on their website but you could contact them to see if they can rebuild yours. https://www.damperdoctor.com

M30s do not have a harmonic damper.
What we have is just a tuned mass damper AKA a chunk of weight, to have some inertia. There is nothing to rebuild or replace, unless it's so rusted out that it's out of balance.

You can upgrade to an ATI unit if you are worried.

szacsi72 wrote: Sep 18, 2024 12:17 PM M30s do not have a harmonic damper.
What we have is just a tuned mass damper AKA a chunk of weight, to have some inertia. There is nothing to rebuild or replace, unless it's so rusted out that it's out of balance.

You can upgrade to an ATI unit if you are worried.

While neither agreeing or disagreeing, if it's just a mass, why does it have rubber in it and why do different throw cranks have different dampeners?

for anyone interested:

https://www.schaper-automotive.com/en/d ... 850b258991

pavulon wrote: Sep 28, 2024 2:56 PM for anyone interested:

https://www.schaper-automotive.com/en/d ... 850b258991

Yeah. It's a ton of money.
370 just for the adapter and then another 500euros for the adapter.
Unless its an all out race engine, I don't think this is worth it. Stay under 6500 and you won't have issues. Most M30s don't make power over 7k anyway.

Mike W. wrote: Sep 18, 2024 3:15 PM

szacsi72 wrote: Sep 18, 2024 12:17 PM M30s do not have a harmonic damper.
What we have is just a tuned mass damper AKA a chunk of weight, to have some inertia. There is nothing to rebuild or replace, unless it's so rusted out that it's out of balance.

You can upgrade to an ATI unit if you are worried.

While neither agreeing or disagreeing, if it's just a mass, why does it have rubber in it and why do different throw cranks have different dampeners?

Sorry for the slow reply, Mike. Been busy at work.

It doesn't have rubber in it, at least neither the M30B28, and B35 engines that I own, had no rubber in them, they are a single part. I even have M50 and M50tu dampers laying around, that are a solid one piece, no rubber at all.(they do have some kind of a rubberized coating tho, so they are tricky.) They are possibly from a B20, I'd need to check that.

Different cranks can have different dampers, because even without the rubber part, they can act as a damper, we call this the "tuned-mass-damper". This is very un-true mechanically, but you can think of it sort of as a timer. It can help you time the harmonics of the crankshaft, to cancel out some of the unwanted resonance.
Let's say cyl. #1 fires, which would twist the crankshaft compared to the rear end, so the flywheel(inertia) and/or driveline. But since there is a chunk of metal at the front, there is more momentum for the same amount of force derived from the cylinder pressure, which results in slower acceleration = less or slower torsion of the crankshaft. If you time this right, the crankshaft should not be able to "rock back and forth" (twist).
An M54B30 crank can twist as much as 1.4 degrees without damping.

If you are interested, I recommend to research the topic tuned mass dampers, because I am an idiot and cannot explain anything in a way that is understandable and making sense at the same time.