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Old 12-12-2009, 01:49 PM   #1
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Underdrive Pulley Install Guide

I just finished installing the 4" underdrive pulley that forum member Jaay sells, and I documented the process in varying degrees of detail to help anyone else out who's considering this mod.

Tools required:
Jaay's 4" pulley and belt
10mm socket and driver
24mm shallow socket
Breaker bar for above
Grinder, dremel, or hack saw
Porsche crank pulley removal tool (or see below)
Various common hand tools
Highly recommended: A pair of mechanic's gloves

Remove your rear subwoofer or whatever other accessory you might have on the rear shelf so you can get the carpet kit out of the way. Slide both seats all the way forward.

Remove the four plastic anchors so you can move the firewall carpet/insulation panel.



You will see the engine cover.



Remove the 10mm bolts and the two 10mm nuts around the perimeter of the cover.



Once you remove the panel, you will see the pulley to be replaced with the underdrive version - it's the pulley below the belt tensioner.

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Last edited by sd_boxster; 12-12-2009 at 02:07 PM.
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Old 12-12-2009, 01:50 PM   #2
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Use your 24mm socket and breaker bar to crank on the belt tensioner so you can remove the existing serpentine belt.



Get out your Porsche crank pulley removal tool, or be prepared to bust something out on the fly. You need to use the 24mm socket to loosen the bolt holding the crank pulley. It's tight.

Since I didn't have the Porsche part, I made something out of a bolt, my floor jack handle, and some plumber's tape I had on my workbench by fishing the bolt up behind the OEM crank pulley, adding a couple of nuts, and creating a strap to attach the jack handle to the pulley... Hopefully the pics explain better than this text...

First, I fished the bolt up behind the factory pulley. I taped a zip tie to the bolt so I could pull it through the hole.



I used another nut to secure the plumber's tape to the factor pulley.



This image sort of depicts how I used the jack handle for leverage, and the socket on the crank pulley bolt as a fulcrum, to get the bolt loose. The jack handle is in the wrong place in this image - it should be ABOVE the socket (lefty-loosey), but you get the idea:



With the old pulley out of the way, it's time to cut down the boss to make room for the new UD pulley. You can see in this pic the material that needs to be removed. I took off about 3/8" to make the boss flush with the other protrusions on the engine case.

I started out using a dremel, but the best tool I had for this job turned out to be a small hack saw I picked up at Home Depot a while ago - it looks like a stout coping saw and works great for cutting at an angle.



Install the new pulley. EDIT: At least one other write up I found indicated that the crank pulley bolt is not reusable.



This image shows the clearance between the cut-down boss and the new pulley. Make sure you remove enough material so the boss does not interfere with the pulley...



I used a strap wrench on the new pulley so I could apply the requisite torque (i.e. I "tightened the snot out of it" per Jaay's instructions!).

Use a shop vac or other means to remove any shavings you created while cutting down the boss...

Install the new belt (refer to your Bentley to ensure you get the belt routed correctly!).



Once you have cranked everything down and triple-checked the belt routing, fire up the motor with the cover off to verify that things look right. Specifically, make sure the new pulley is flat and unobstructed.

Shut the engine down and perform one last snot-tight torquing on the crank pulley bolt.

That's it! This took me about 2 hours, including taking pictures, lashing together my ghetto pulley tool, and drinking several beers.
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Last edited by sd_boxster; 12-15-2009 at 09:15 PM.
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Old 12-13-2009, 08:58 AM   #3
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nice write up. Did you notice a substantial improvement?
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Old 12-13-2009, 09:10 AM   #4
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Thanks for the write up. I also would like to know what your experience is after doing this. Notice any extra power or other improvements?
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Old 12-13-2009, 09:41 AM   #5
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Just got back from a decent drive. There is a noticeable performance gain - not enormous, but appreciable. Certainly more than I "gained" from my EVOMS intake.

Interestingly, all of the accessories running at a lower speed results in less overall noise. Maybe this is due in part to the new belt - but whatever the cause, I'm very happy with this side effect.

So - I'm happy! Hopefully I'll get an AX in sometime soon and get back with a proper review.
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Old 12-15-2009, 06:40 PM   #6
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Looks good Glad the install went well.


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Old 12-15-2009, 07:01 PM   #7
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anyone know the torque spec for that bolt holding the pulley?
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Old 12-15-2009, 07:47 PM   #8
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Did you happen to take a picture of the new and old pulley next to each other or weigh them? Is there a reduction in size, weight or both? Why only change the crank pulley and not all the accessary pullies, seems like there would be a more profound effect and free up some more hp?
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Last edited by Adam; 12-15-2009 at 07:51 PM.
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Old 12-15-2009, 09:13 PM   #9
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It's in the Bentley manual - I'll add it to the write up tomorrow, as it's too darn cold to go to the garage.

BTW - and I'll revise my writeup above - I read somewhere else that the crank pulley bolt should not be reused.

Quote:
Originally Posted by tommy986
anyone know the torque spec for that bolt holding the pulley?
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Old 12-15-2009, 09:21 PM   #10
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Quote:
Originally Posted by Adam
Did you happen to take a picture of the new and old pulley next to each other or weigh them?
Nope.

Quote:
Originally Posted by Adam
Is there a reduction in size, weight or both?
Both. I bet you're gonna ask me to quantify it for you, but I can't.

Quote:
Originally Posted by Adam
Why only change the crank pulley and not all the accessary pullies, seems like there would be a more profound effect and free up some more hp?
I'm not sure how much you can underdrive each specific system - but underdriving the crank pulley does them all at once, rather than having to replace each accessory pulley. I'll have to defer to the experts - like Jaay, Jake, and others - I'm just a guy who bought one and installed it.
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Old 12-17-2009, 06:48 PM   #11
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Step 1: Torque to 37 ft-lbs.
Step 2: Tighten an additional quarter-turn (90 degrees)

Quote:
Originally Posted by tommy986
anyone know the torque spec for that bolt holding the pulley?
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Old 12-31-2009, 06:05 AM   #12
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Thanks for the write-up, as this is a mod I'm currently considering (always need a spring project). Anyone know what the protrusion is for, that needs to be milled down? Almost looks like a point where a bolt would go to lock the pulley (not sure it lines up)...it must be there for a reason.
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Last edited by jmatta; 12-31-2009 at 06:08 AM.
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Old 12-31-2009, 07:00 AM   #13
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It could be a couple of things; the M96 is used in multiple configurations, so it could be a mounting boss for something not use when in a Boxster. A lot of casting bosses on these engines are used as anchor or alignment points during initial machining operations in the factory, and not used again.

Considering its location so close to the factory pulley, it probably is not used when the engine is actually in the car.
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Old 12-31-2009, 11:44 AM   #14
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I believe jmatta is right. The boss in the casing that must be cut down is a top dead center locator. You align to TDC and slip a retaining tool through the stock pulley to hold the crankshaft in place. It is useful when changing timing chain tensioners to keep everything aligned so don't cut it all the way off. There are other ways to fix the crankshaft at TDC but this is a quick way that techs are familiar with. On one car in our club the casing boss was completely cut off and the Porsche techs had to get creative as they could no longer use the tool.
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Old 01-01-2010, 09:04 AM   #15
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Fig. 25 confirms it's for TDC.

http://www.pelicanparts.com/techarticles/Boxster_Tech/Disc163/BoxsterTech-163.htm
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Last edited by clickman; 01-01-2010 at 09:09 AM.
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Old 01-02-2010, 05:33 AM   #16
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Very good visual, indeed. Do you think the point is strong enough to hold so you could loosen the crank bolt? The only experience I have is that is remotely close is the tool that holds the pulley for removal in an older air cooled 911.
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Old 02-26-2010, 09:14 PM   #17
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It is strong enough. The bolt is on there way tighter than the fan/alt nut on the air-cooled 911s incidentally. (just did this mod today)
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Old 03-01-2010, 10:14 PM   #18
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Why not remove the stock pulley with air tools?
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Old 03-04-2010, 01:40 PM   #19
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Quote:
Originally Posted by CapDunn
Why not remove the stock pulley with air tools?
There's no room in there. You could do that if you dropped the engine.
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Old 03-04-2010, 02:17 PM   #20
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It is strong enough, I just cut a large hex key to fit in the hole and it worked like a charm. You will need a large breaker bar and a 24MM socket to get it loose.
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