DIY RSS 608 Install - Harmonically Dampened Underdrive Pulley

The RSS 608 Harmonically Dampened Underdrive Pulley has been around a while. Different than other underdrive pulleys in that it contains a harmonic balancer, this is the preferred option if you plan to remove the factory dual-mass flywheel in favor of a lightweight flywheel. RSS claims a WHP increase in their dyno testing, but the bigger benefit is that the slower belt speed will help preserve the OEM power steering pump during track use. There have been reports over the years of the power steering pump overheating the fluid and boiling over, so this pulley should prevent that. Parts needed: RSS Pulley Kit 608 - Harmonically Damped - Underdrive Performance Pulley Kit (986, 987, 996, 997) New OEM crank bolt P/N 900 082 085 01 New Serpentine belt, RSS # 6PK Loctite 242 (blue) Tools needed (not exhaustive): Shortened 24mm socket Torque wrench File, die grinder, air file to cut down timing locator boss on the engine block https://www.amazon.com/Astro-3037-2-Inch-18-Inch-Sander/dp/B00L50MKJS Torx socket sets (male and female) Plastic trim tools Reference: Disassembly We start by removing the passenger seat. Fold the seat back, power it forward, and remove the two rear bolts. Power the seat back, remove the plastic rail trims by lifting up on the front tab, remove the front bolts. At this point, disconnect the car's battery. For the passenger seat, there are two connectors, yellow and grey. Yellow for all functions, heat and airbags, and grey for the weight sensor is how I understand it. Remove the package bar/thing on top of the firewall, and pop the black trim up as shown. Then remove the carpet with plastic trim tools, taking care to note the push clip in the top center of the carpet underneath the upper black trim. Finally, remove the silver engine cover bolts/nuts and we have found the front of the engine: Remove the serpentine belt by "tightening" the 24mm pulley bolt right behind the shifter cable penetration. In the RSS kit, they provide a bolt to lock the OEM crank pulley in place so that you can remove the OEM crank bolt. Super difficult to get a good picture, but one of the holes in the OEM crank pulley is pear shaped. Rotate the crank via the bolt (trans in neutral) to line up the timing boss on the block, and put the bolt in. Then you can remove the crank bolt, and pulley pries off very easily. Here you can see the aforementioned timing boss and crank snout. RSS pulley compared to the OEM crank. A difference for sure, but not too significant. Grinding the Boss This is a necessary step because of the smaller diameter of the pulley compared to stock. The stock pulley goes around the timing boss, while the underdrive pulley goes right through it. First up is masking the engine bay. I neglected to get a picture of this, but you'll want to mask off as much as possible. I used paper and 2" wide blue painter's tape. I papered the entire top-right of the engine bay to keep the aluminum dust out as much as possible. I taped the alternator shut as best I could, and taped the pulleys so that no shavings got embedded in them. I also removed one of the idler pulleys for better access. To grind the boss down, I used an air belt sander. Small enough to fit in the space, very controllable, and relatively quick. One of these: Running the air sander at the same time as a vacuum, I went to work sanding the boss down. This is the end result. Compared to the earlier picture, you can see how much it needs to be sanded to get the RSS pulley to fit correctly. Pulley Install First up, make sure you have a shortened socket. There is very, very little room between the front of the RSS pulley and the firewall, so this is critical. I have a lathe, so it was a simple operation for me to cut this down: With the kit, RSS includes a spacer/shim that goes against the crank. After that, the pulley, then the new crank bolt and reused thrust washer. RSS Torque Spec: 37ft/lbs + 120*. Before putting the bolt in, I set the emergency brake really stiff, and put the transmission in 5th gear. Next, I liberally coated the new crank bolt with loctite blue and torqued it to 37ft/lbs. As you can see, there is almost no room in here, even with the shortened socket. There is no room for the barring tool that RSS includes with the kit, but I assume that barring tool works well for the 911 applications of this pulley. At this point, I put some paint marks on the pulley and block, then tightened the bolt 120* from my initial set of 37ft/lbs. Tough to get there, but I got it. The paint marks are there to show you if the crank rotates, so that you can more accurately hit your 120* point. Reassembly Done with the pulley install. In the last pic you can see the idler pulley got reinstalled. Next is the new, shorter, serpentine belt: Installed: Final vacuum and blow-out of the engine bay is next. Some of the engine bay firewall insulation was disintegrating, so it was trimmed back as well. After that, the interior carpet gets the dust vacuumed out, all panels back in, seat in, and we're done!! Happy motoring everyone.

Thanks for the great writeup and pictures. I have long considered doing the underdrive pulley on my car but have hesitated as some of my friends have had issues with the mod in general across various platforms/cars. Before you decided to DIY the job did you get any quotes from independent specialists? I'd like to potentially do this on my 987 but don't really have the time or the tools on hand to do the job properly (particularly the grinding).

Nope, didn't get any quotes. I'm the type of stubborn person who hates paying other people to do jobs I can do myself. I'd rather buy the tools for the job if I don't have them already, but in this case I had everything I needed already.

Outstanding write-up, @GLTHFJ60 - Thanks for posting! Although I doubt that I personally will have the cash to purchase one of these, surely someone will. Fantastic job!

Great writeup - so - the results? I can imagine the harmonic damper may smooth out the engine just a bit (although a horizontally opposed engine is in balance in all planes.. and a 6 has almost overlapping ignition cycles..) Does it spin up any faster? Any difference you can feel in power (seat of the butt dyno?) I wonder what the boss you ground down was originally used for... the hole is just blank? No threads? Using it like you did does it lock the engine at a certain point?

It's hard to put my finger on it, and it might be a placebo, but the engine does sound different. Doesn't sound like it's going to start to fly apart until redline now, as opposed to maybe 6500rpm before. If it has more power, I can't really feel it definitively. Some day I'll have it dyno'd and see what it actually makes. Big bonuses for me are to slow down the power steering pump for track use, and to add a harmonic balancer for when I move to a lightweight flywheel setup, so I'm happy. This is definitely in the same category of mods as the deep sump, center radiator, lower temp thermostat, meaning the category of mods that makes the car more reliable for track use, but not really faster on the track. The boss that gets grown down is the TDC locating pin in the OEM crank pulley, at least that's my understanding. That's where this bolt is sticking into (through the pulley) in the step below. The boss is still there and can be used for engine timing with the oem pulley if I were to have the engine apart, it's just shorter.

That'll teach me - an AI-BOT tossed bait out there and I took it - another 10 minutes of my life wasted.. oh well. Wonder what a P5 is? He's history obviously. Hi, welcome to Planet-9, the Thinking Man's Porsche Forum! The intent with an underdrive pully is to "underdrive" the accessories driven by the serpentine belt. The pully is a smaller diameter, so the belt doesn't move as fast for any given RPM of the engine, meaning the accessories like the alternator, AC compressor, water-pump, power-steering pump ALL turn slower and require less energy to turn, removing some of the energy they take from the engine to be driven. Underdrive pullies have always been a go-to thing for track cars. Not so much for street cars because on a street car, particularly a Porsche, you'll find that Porsche tried to minimize the "parasitic loads" (accessories) on the engine. Going much below the the stock size means that perhaps the AC isn't quite up to snuff stuck in traffic on a hot day, or short trips won't recharge the battery due to less alternator output, or the power steering would require more effort to turn the wheel. The difference in weight is probably insignificant - the original pully is made from aluminum or plastic - and isn't a heavy item. The replacement with a harmonic damper (weight that damps out crankshaft vibration) actually very likely weighs more. Where a significant difference can be made is with a lightweight flywheel - but again - there are compromises the owner has to accept.. not as smooth an engagement, more vibration in the engine, gearbox chatter in neutral idling - things again that can be ignored at the track but might prove annoying for everyday use. Wen you have a chance - please visit https://www.planet-9.com/forums/new_members/ and introduce yourself and your Porsche., And what's a "P5" I'm not familiar with that..

The factory crank pulley is aluminum. The additional weight of the pulley I installed is due to the inclusion of a harmonic balancer, which will be important when I remove the factory dual mass flywheel in favor of a lightweight flywheel.

Are those non-stock shift cables? I was going to mention that maybe, since you have that part of the car apart, you could easily run a pair of Racing Numeric cables .

It's not apart anymore, lol. This project took me maybe 3 hours on a sunday. I've been driving it since. The cables pictured are stock, but I'll put numerics in at some point.

I have a light weight flywheel on my 987.1 . Resonance and vibration makes it less enjoyable for me. Looking to getting a crank pulley dampener. The RSS solution with grinding the boss scares me a little - with limited knowledge about getting to top dead center for timing - and future maintenance concerns. My 987.1 is my daily, I do not track, and at best do limited spirited runs in city traffic. Can anyone confirm the 997 Carrera S dampener crank pulley is a direct fit with the 987.1 ? Am I overthinking this? Thanks in advance.

You......dont need to put the motor at TDC to change the pulley out. I included it just as a tidbit of info, nothing more. No clue on the carrera s damper.

Is there a reason not to go back to a normal dual-mass flywheel? It doesn't sound as if you needed the lightened flywheel. That seems simpler than adding weight at the other end of the crank to make up for the reduced weight at the output end.