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GT3 with light weight flywheel (LWFW) – you MUST replace crank pulley to track! (DIY)

 

Old 12-08-2010, 02:02 PM
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facelvega
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Default GT3 with light weight flywheel (LWFW) – you MUST replace crank pulley to track! (DIY)

As the first round of 997.1 GT3 drivers found in 2007-2008, if you drop the RS light weight fly wheel (LWFW) into the car, you must also replace the GT3 crank pulley with the RS crank pulley. Some of the old threads on this are HERE, HERE, and HERE. If you do not replace the pulley, the car will spit it out after a short period of track driving.

Now that many drivers are trading up to the 997.2’s, lots of the .1’s are on the market at reasonable prices, ready to become track cars. There are many drivers that do mods on the cars for fun, but do not track them. If you pick up one of these cars, you may get one (as I did) that has the LWFW but not the RS pulley. This may be OK for sedate driving on the street, but needs to be changed for the track. I did not dig back into the 2008 threads, so I went to the track and lost the pulley (twice!). The pulley exchange is pretty easy, so here is a guide for the DIY crowd.

My car had about 4000 street miles on it when I got it, and the stock pulley was doing fine. I bought it as a track car, went to the Pat Long event – Pat drove it first session of the first day. When he was done, I made it only 2 laps before the pulley came off. The car went to Topp Racing to replace the pulley, and I was in a spec Miata for the day. Next day, I was back in the GT3. First session was fun. One lap into the second session, the pulley came off again.

I submit that popping loose the pulley is really likely to happen if you track the car, so do not end up in a spec Miata – change the pulley. When the pulley comes loose, the dash warning lights up because the alternator is no longer making power. You also immediately lose power steering, so the steering effort goes up. The car still sounds and runs great (even more power! No drag from the accessories!)but you need to get off track and shut down quickly, because YOU ARE NOT PUMPING COOLANT ANYMORE. I was lucky enough in both cases to be starting a session. If you are well into a session, and the engine is hot, you will overheat rapidly and may do some damage. On the plus side, as long as the engine is cool, there is no problem driving up onto the trailer for the trip home.

From what you can see, everything looks fine in the engine compartment, except the belt is not moving:



To see the issue, remove the air cleaner by unplugging the MAF:




And loosening the hose clamp on the rubber plenum, then lift the air cleaner up and out:




Now we can see where the crank pulley has come loose:




To fix it, we need to remove the bumper and rear center muffler. First, remove the tail lights by loosening two T-27 screws (do not remove, just loosen).




Lift the light back and out, and unplug the wires. Remove the T-30 plastic screw that was behind the light:




Remove the T-30 screw where the bumper meets the wheel well:




And the T-30 screws across the bottom of the bumper to the heat shield:




Finally, remove the T-30 screws across the top of the bumper. You can now lift the bumper off and back. You will need to flex the sides at the wheel wells to get it around the heat shield. Once it is off a few inches, unplug the wires to the license plate light, and set the bumper aside.

Next remove the impact bar and heat shield with a 16mm socket:




Now you can remove the center muffler with a 6mm hex driver. Your muffler will probably look different, but the hangers will be the same (I think).








Now you have exposed the loose pulley:







To get it out, put a 16mm socket on the belt tensioner and rotate clockwise to release the belts:





Then remove the old pulley and bolt. Now you can see the RMS(correction - FMS - thx 911Slow) and crank end. The pin from the pulley will be sheared off in the matching hole in the crank end.





Since the sheared pin is a machine fit into the hole, there is no way to pry it out. Some have written that they drilled it out. Try this first: the pin is steel. Get one of those super powerful magnets (like in parts retrievers), and you can probably pull it out. Worked for me.

You will want to use thread lock on the new bolt, so clean up the threads really well with solvent/alcohol/etc.

The GT3 pulley is steel, 494 grams. The RS pulley is aluminum, 292 grams:




As you can see, the bolt is longer, and the torque spec is different. The GT3 bolt coming off requires 18mm socket, RS going on is 19mm socket.

RS parts that I got from Rhonda at FVD:

993 102 550 80 screw GT3-1 M96.79 04-, GT3-2 RS, M14 x 1,5 x 40
996 102 017 95 Pulley 996 GT3 RS Street, 997 GT3 RS
999 025 174 02 Washer 14x1.5x40 (updated - was 999 025 174 01 )

And from Alex at Sharkwerks, torque is 185 FT-LB (250 NM). This torque will easily turn the engine, so you need to set the parking brake, tighten on the ground with wheels chocked, or brace the wheels (I braced with wheel hangers and jack handles):




Now some thoughts about thread lock. The crank bolt head is less than one inch away from a large, flat plate (the muffler back) which is at a constant 600 degrees F. The surface of the crankshaft is being cooled to about 200 degrees F. There is a temperature gradient from the bolt head at 600 to the crank surface at 200. I do not know what the temperature is at the pulley bolt threads, but if we split the difference, it would be 400 degrees F. Standard thread lock releases at 300 degrees F.

I used Loctite 272, which releases at 450 degrees F, and would recommend it for this application. You might also mark the pulley, and be nice to the next person who works on the car (like, when they find it in a barn, 100 years from now), so they do not twist the head off the bolt when they try remove it:

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Old 12-08-2010, 02:30 PM
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Great Thread - you are 100% correct. Any 997.1 GT3 with a LWFW must have the GT3 RS Pulley for tracking. My CPO'd car came with a LWFW but no RS pulley. Even though the car is primarily a street car, my paranoia and advice from Alex at Sharkwerks finally dictated a purchase for the RS pulley and new bolt/washer. My dealer endorsed this for me so no issue with existing CPO. As you have shown removing the rear apron is the best way to get to the pulley. The way to tell if you have the GT3 only pulley is if it has the holes all the way around it. The cost of the pulley is reasonable under $100.00 and the bolt and washer cost around $39-48.00 go figure.
I also found that this was the ideal time to add a Sharkwerks Bypass pipe and new tips....thanks Alex
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Old 12-08-2010, 02:31 PM
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Outstanding post, thanks for the details and photos. I'm proud of my mechanical abilities just from swapping brakes, it's always a pleasure to see a much more detailed breakdown like this to de-mystify the guts of my car.

Aren't you supposed to wear purple gloves, though.
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Old 12-08-2010, 02:34 PM
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Nice thread and a good reminder.

Just a correction the pulley seal is the front one so FMS not RMS : )
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Old 12-08-2010, 03:23 PM
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I remember the original threads a few years ago and still have a few questions. I have a 6-GT3 with LWFW (964 RS parts) that I installed years ago (without changing the pulley) and have had no issues (street+track). Question one: why is this a 997 issue (nobody I know of has changed the pulley on a 6-GT3 when doing the LWFW). Question two: is the RS pulley referenced above the right one for the paranoid 996 GT3 LWFW owner to use?
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Old 12-08-2010, 03:57 PM
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I was using on a 6GT3 the 996RS/997.1 RS LWFW, part number 964 102 239 31 and I upgraded to the LW pulley of the 996RS/997.1RS part number 996 102 017 95.

Now that I am using the even lighter LWFW from the 2010RS (actually it's the older lighter cup flywheel ) I didn't change the pulley to the 2010RS one. There is only one version for both the 997.2GT3 and 997.2GT3RS. I don’t know much it weighs. Probably they use the same because the pseudo- LWFW double mass of the 997.2GT3 is light enough.

I did the change to the lighter pulley based on common sense and elementary physics, rather than actual failure cases of 6 GT3s that had a LW flywheel without the LW pulley. When you remove weight from one side of a balanced stick (crankshaft), you unbalance it and you have to remove some weight from the other side.
Besides no harm is done by removing weight from the very back of a 911..
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Old 12-08-2010, 04:02 PM
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Here's another alternative (aftermarket) solution..

http://www.evomsit.com/EPK_GT3_CS.htm
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Old 12-08-2010, 04:28 PM
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should replace throw out bearing while in there doing the lwfw, for added peace of mind
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Old 12-08-2010, 05:59 PM
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Larry Cable
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I think that the 997.2 GT3 has the RS pulley already installed ... Can anyone confirm this?
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Old 12-08-2010, 06:00 PM
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Yes Larry it's in my last post. : )
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Old 12-08-2010, 06:37 PM
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Sorry! Too much dayquil meds...
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Old 12-08-2010, 06:38 PM
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Don't want to put a damper on your day, but you are missing a very important friction washer that goes between the pulley and crank. It's a very thin feeler gauge thin piece of steel and I believe diamond coated for high friction - p/n 996.102.203.90.

Also although bracing the crank by locking the car in gear and locking the rear wheels worked in your case, there is a possibility of breaking a gear tooth, ring gear, or placing abnormal twist to the crank, so the factory procedure calls for a factory pulley holder that inserts into the two holes you see on the pulley. The tool is quite long and large, and requires the removal of the rear center muffler and rear engine carrier in order to insert.
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Old 12-08-2010, 06:42 PM
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Great post and thread. Copied to the GT3 DIY Forum for posterity!

Best,
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Old 12-08-2010, 06:49 PM
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Evo MS has a pulley installation tool.. I am not sure how this compares to the factory tool..

http://www.evoms.com/Marketplace/vie...-FF328F486653}
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Old 12-08-2010, 07:14 PM
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Originally Posted by Steve W View Post
Don't want to put a damper on your day, but you are missing a very important friction washer that goes between the pulley and crank. It's a very thin feeler gauge thin piece of steel and I believe diamond coated for high friction - p/n 996.102.203.90.

Also although bracing the crank by locking the car in gear and locking the rear wheels worked in your case, there is a possibility of breaking a gear tooth, ring gear, or placing abnormal twist to the crank, so the factory procedure calls for a factory pulley holder that inserts into the two holes you see on the pulley. The tool is quite long and large, and requires the removal of the rear center muffler and rear engine carrier in order to insert.

Good points.

Special tool is not very expensive, but usually requires two people and room to operate it. On the other hand this is a DIY and besides, many indy shops don't use it..

Make sure to check that the straight pin of the pulley aligns with bore of the crankshaft, check the friction plate for signs of damage and replace if necessary.

The torque for the screw in the 996GT3 pulley is 250Nm (185lbft.) and 170 Nm (126 ftlb.) for the 996 /997 GT3 RS lightweight one.
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