"These build journal entries are part of a Special Series on the development of the S85 SMG3 OE+ forged steel lightweight flywheel.

This entry covers the installation notes to the flywheel and the little things to consider. Overall, this is a pretty straight forward for professionals."
- Matt

What to plan for.

The first step is getting to the flywheel. You'll have to remove the exhaust system up to the headers, remove the heat shielding and driveshaft before unbolting and dropping the SMG3. All in all, this is about 6 to 8 hours of billable work depending on any while you're in theres.

Removing the SMG3 from the chassis always presents opportunities to perform while-you're-in-there preventive maintenance. 

It's a good idea to inspect the SMG solenoid wires and repair if needed. Mine were good, although the solenoids' surface rust irks me.

You may also replace the clutch fork and clutch fork pivot pin. I exclusively recommend the original BMW design for the latter. 

Seals should be replaced on a case-by-case basis. The slave cylinder can be replaced as an extra precautionary measure. 

Hardware notes. 

Flywheel bolts. 

The OE+ flywheel is one of the few that was not designed to work with Genuine BMW flywheel bolts as BMW does not sell SMG3 flywheel bolts separately. 

The lightweight flywheel is instead designed to fit with Grade 12.9 bolts in M12x1.5x35mm dimensions. I recommend you use the ARP Chromoly bolt kit #: 664-1003.

New clutch kit. 

Similar to rotors and pads, BMW recommends to replace the flywheel when replacing a worn clutch - and vice versa. Sachs/Valeo also specifies in their instructions to not reuse any clutch that has had the friction discs moved.

If you re-use your used clutch, mark the clutch discs to re-align them properly. Any offset will lead to premature clutch failure. You will need to replace the 9x pressure plate bolts (SKU: 07129905539). 

The clutch kit included with our lightweight flywheel includes the clutch, throwout bearing and pressure plate bolts as of July 2025. 

Comparing the original flywheel. 

My original dual mass flywheel was in relatively good condition. It had slight heat marks - nothing to be alarmed about. This was an indicator the car hadn't been abused in the past.

A key benefit to using the OE+ steel lightweight flywheel is its long operational life due to the lack of dual mass mechanism and its forged steel construction. Should your original flywheel fail, there would be excessive play between the two primary components.

You get a sense of the relative lightness of lightweight flywheel design is when you lift the OEM dual mass flywheel from the ground. The OEM dual mass flywheel is an anvil at 31.5 lbs whereas the lightweight unit is 18.73 bs.

You can clearly where weight is removed you flip over both flywheels to the crank facing sides. The lightweight design eliminates this internal mass entirely - right by the crankshaft. 

The OEM clutch. 

In the previous entry, I touched on how the OE+ flywheels are designed to work with OEM clutches whereas most companies impose their package of clutch & aluminum flywheel

Changing your clutch is quite pointless on a naturally aspirated S85 V10. The clutch has never felt weak contrary to what some aftermarket clutch manufacturers say in the brochure.

Here's why: it comes standard with a dual disc design. It's extremely tolerant to power. 

Installation steps.

You may refer to BMW's original installation instructions here. Please take note of the bolt removal and torquing sequence. 

The flywheel. 

The OE+ lightweight flywheel needs to be aligned properly to the starter motor. You need to identify the unique, slightly enlarged hole and match it with the crankshaft's larger hole.

Follow BMW's recommended torquing specs of 105nm even when using the ARP flywheel bolts. 

The clutch kit.

Prior to installing the clutch, thoroughly degrease and clean the flywheel friction surface. 

The clutch needs to be aligned with the flywheel using a specific BMW centering tool (#21-2-300). A one-time use plastic tool is most often included in Sachs, Luk and Valeo kit. For future servicing, you should mark the alignment of the clutch kit with the OE+ lightweight flywheel. 

The clutch is bolted to the flywheel with 9x pressure plate bolts to 10+2 Nm torquing specifications in a criss-cross manner. Ensure the springs on the clutch align with the machined holes on the OE+ lightweight flywheel. 

Notes on grease. 

BMW provides recommendations to grease the throwout bearing and clutch fork friction areas to ensure long life of your SMG3 to the maximum extent possible.

Notes on software. 

Ensure the transmission the SMG3 has the required the transmission level before proceeding with software adaptations. I do not go into the specifications on the bleeding and adaptations reset process here. I highly recommend you get this done by professionals with experience. 

The OE+ lightweight flywheel does not require a specific SMG tune. It will cooperate with the OEM SMG software. I do recommend increasing idle speed to 900 RPM and eliminating cold start, if your jurisdiction allows it :) We can provide tuning services here.

Notes on break in. 

BMW recommends to break in new SMG3 clutches to be perform 800 to 1,000 shifts under varying throttle conditions and RPMs. Avoid launch control and extended highway usage for the first 500 miles. 

Up next: I finally get to drive it.

I'll cover my first impressions and driving notes over 15,000km and discern the benefits of the carbon driveshaft alongside the lightweight flywheel. 

Is the combination worth it?
Which would I buy first?
Are there any drawbacks? 
Did the SMG get ever more jerky?
Did it blow out my clutch?
Is idle chatter as hell?