Help - Engine cover / alternator bracket

Greetings. I'm usually more of a lurker, but couldn't find a lot of information on replacing this part and was hoping somebody here could share some knowledge. A little background: I have a 2002 C4S, with (now) 70k miles. I've had it for about 5 years. I was replacing a noisy idler pulley and discovered this cracked cover/front mounting point for the alternator: The crack was barely noticeable, but as I pulled off the idler pulley (upper bearing - so the mounting bolt supports the other side of the alternator) I could see that it's completely sheared off. With the new bearing and drive belt back in place, there seems to be enough tension to hold the two pieces in place, but this clearly needs replacement. I was able to quickly track down the part number(s), listed in PET as simply a "lid," 996 101 021 51 which was superseded to 996 101 021 52, both of which were superseded to 997 101 021 00. I opted for a good used 997 part rather than pay the $350 (cheapest I could find) for a new piece. I also made sure to get a new gasket. As a side note, comparing the 996 part (left) to the 997 version (right), it's clear they beefed up the supporting material around the upper bolt where the alternator mounts (the area that failed on my car). Here are my questions:. 1. Has anybody else here experienced this failure, or replaced this part? I'd appreciate the sharing of any wisdom learned in the process. 2. I realize there's coolant running behind the lid, but as this is at the top of the motor, can I get away just with partially draining the coolant? Would setting the car at an incline (nose pointing down) before removing the lid help minimize the coolant in that area? (Without opening up a can of worms) I'd like to avoid having to vacuum purge air from the cooling system and am thinking that if I'm only partially refilling I can use the purge valve. 3. From what I understand that hose connector can be finicky and is prone to breaking. Any suggestions or advice for working with it? 4. Does anybody know what the correct torque settings should be for the six mounting bolts on the lid, or the alternator mounting bolt? Any other thoughts/considerations/insults for not regularly contributing here? Thanks for any help, Nate

1. One post I remember here https://rennlist.com/forums/996-foru...install-2.html 2. You should loose at most the whole reservoir worth of coolant. You won't need the purge tool if that's indeed the case. 3. Some has converted that to a brass barb. I'll just get a new OE 99610622652. There's also a stainless steel version for $40 https://www.carpartsdiscount.com/coo...ml?3593=525804 4. 7.5ftlb for the small bolts and 17ftlb for the big alternator anchor bolt Now my turn What's the p/n of your used 997 cover? Have you fitted it and made sure all the holes line up and the alternator anchor hole is at the same location as before?

Thanks Ahsai, you've pretty much answered all of my questions! I did read through the post that you linked. There does seem to be some confusion with the part number. I'm traveling this week, so can't verify 100% - and I haven't taken the old part off yet to compare - that these are identical in alignment. I'm sure hoping that they are. I will definitely let you know what I see when I get in there. I found that the 997 part (997 101 021 00) is stamped on the inside with a different number- 997 101 215 00. And the 996 part number (at least the one that Parts Heaven had on hand) was stamped [phone removed] 9R (instead of 996 101 021 51 or 52). If you look at the picture that you posted in your link, which looks the same as this one on the part page for 997 101 021 00 at Auto Atlanta - it's stamped 997 101 215 00. I'm sure there's some logic behind all of this. I believe they're the same part.

Just closing the loop and updating this thread. I replaced the cover with the 997 part that I received. Fortunately, my part came with all both hoses, to and from the t-connector. Interestingly, the connector from the t-connector is different on the 997 part vs the 996 one, and uses a smaller hose and quick connect type of fitting on the end. I didn't mess with that, and just used my existing hose and the new t-connector. Before I took the old cover off, I syphoned out all of the coolant from the expansion tank to a clean bucket using a new (clean) hose. When i removed the cover, I lost (at most) about a quart of coolant. The new part is an exact fit and I had zero issues installing it. Some pictures below showing the two parts side by side, and the end result. It may look like one is slightly larger than the other - that's just the foreshortening effect of the iPhone - they are the same. Unfortunately, I did hit a snag in removing the lower idle pulley when the mounting bolt sheared off. Fortunately, I was able to get the broken off portion out of the engine case using needle nose pliers (Whew!!) A quick call to Suncoast and a couple days later, and I was back in business. One thing I noted is that the mounting bolts for the idler pulleys (I opted to replaced the upper as well), have superseded to newer numbers. The lower bolt has changed slightly and is threaded the length of the bolt (my original had a smooth shank and then threads). The upper bolt now has a torx head in place of the hex. Part numbers I used were: 900-378-159-01 (lower), 900-385-092-01 (upper).

Nice job and great follow-up! I'm sure this will help someone down the road. (No pun intended)

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+1 Good job and thanks for confirming the 997 part works. The used ones for 996 are on short supply and a new one is just crazy expensive.

Although I have not fixed my busted mount, yet, I have the same problem on my 997, and I haven't had much luck anywhere else on the web getting info on this issue. I am considering fashioning a secondary brace so as to leave the coolant part in place. Just need something to secure the alternator. Its an expensive part to replace! I have no idea how it broke. Just started rattling one day last week, and haven't done any work in the engine. Thanks again. -russ

I thought this thread was a couple years old or something - started last week! Crazy! That's when my issue started, too!

If I completely replace the mount, will I have to remove the accessory belt? Thanks. -russ

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I would think that's the easiest (will create much more space) and also you don't want coolant to spill on the belt.

Nice job! Thanks for the follow-up!

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Russ- Assuming that these areas on the 997 are the same or similar to the 996... I think if you're willing to replace that cover, taking <5 minutes to remove the belt is a no brainer. I'd also suggest taking both the upper and lower idler pulleys off. On the 996, the bottom pulley is right in the way of one of the cover mounting bolts. I also removed the top one as that pulley's bolt serves as support for the right side of the alternator. It seems more logical to re-attach the alternator to the pulley bolt first before connecting it to the tab on the new cover (which apparently has some weakness). For the cover itself, I'm not sure how you can brace it without taking it off first - and if you're going to go through the trouble to do that, I'd just replace it. I had also considered bracing or finding somebody that welds aluminum, but both of those options felt like inappropriate solutions for a car of this caliber. If you're searching for a used part, look for both the number stamped on the cover (997 101 215 00) in addition to the actual part number that comes up in Porsche's catalog (997 101 021 00). I personally wouldn't put one of the 996 covers on your car, even though it would probably be a direct fit and more readily available. Happy to share anything else I learned in the process if you have any questions. Nate

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Thanks. I have all parts ordered and a new belt on the way. Was driving in my neighborhood and my belt shredded. Guess I should not have been driving with the cracked alternator mount. Everything is ready to install when parts arrive. Even the beefier 997 mount is prone to busting. Wish they made it more substantial.

Update here: https://rennlist.com/forums/997-foru...-2006-c2s.html I had my broken part welded back together, and its as strong as ever. Crazy its a $480 part. If you don't get that primary alternator mount/pulley bolt tightened properly you're gonna break these again and again. I have broken 2 in the last month!

For whatever it's worth I did not experience the aluminum alternator bracket failing, but the plastic component that you will see in post #4. That plastic component was very weak...both of the posts that connect the tubes broke inside the hoses.

And...I can see how that aluminum part could fail because of what it takes to rotate the alternator counter clockwise after removing the longer bolt on the high side of the alternator.

18 year old plastic is going to be fragile...

First I want to thank Cru_Jones for the original post, it was instrumental in repairing my car. Our alternator bracket failed 600 miles after I had replaced all of the SAI valves. When replacing the SAI and check valve, everything went back together and the bracket, from my recollection, was fine and showed no signs of emanant failure. After a trip from LA to Vegas and back (by way of Angles Crest) the bracket had failed, the alternator shifted up and to the right, and the alternator pulley started to wear through the oil filler tube. With the air box out I started to piece together what could have happened (and might explain other failures). The sliding bushing had given enough to let the alternator out easily enough but, what I did not realize was, it barely moved when I tightened it. So when I torqued the long bolt to 34ft/lbs of torque I was tightening the bolt to the bushing but not getting the contact between the bushing and the channel that is needed. Over those 600 miles I think that the belt tension eventually managed to get the bolt to slide up and out of the channel. At that point the tab of the bracket had to fight twisting forces it was not intended for and failed. My guess is that the moral of the story is that the bushing is critical to preventing this failure. Also, I decided to replace my lower idler pulley when fixing the bracket and the bolt sheared on the way back in. Like Cru, there was plenty sticking out of the block so it was easily removed. But the sinking feeling of a bolt that is not tripping the torque wrench a few clicks in is a horrible feeling. Again, thank you to all for the advice, part numbers, and pictures.

Been busy on other things for a couple of days, but I put everything back together today... started first time, which is always reassuring ;-) I need to fit a different alternator shroud (from an NA) as the original shroud now fouls the steering rack. Also, I had to bodge a repair on the vacuum line that has the banjo bolt connection to one of the intercooler pipes, which has finally split. Black silicone sealant and gaffer tape. It's not pretty, but it looks like it'll hold until I can replace it with something more permanent. I replaced all the smaller vacuum lines a couple of years ago, but this makes me think it may be time to replace the bigger ones as well.

Does anyone know whether there is suppose to be a support bracket for the back underside of the alternator to support the weight of the alternator or a sleeve that inserts in the upper alternator mounting hole that would stabilize the alternator from twisting. I've already replaced 3 Engine Block Water Cap 996-101-021-51 on my 2001 996. Any suggestion on how to keep this from breaking again?

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Did you read post 18 to the end? He postulates a theory as to why the ear breaks. Does that also apply to yours?

This thread just saved my bacon! Thanks to all who contributed.

FYI URO Parts now have a metal T piece which is identical to the plastic version but all metal. Just installed one yesterday

Do you need to replace the gasket behind the alternator support bracket after replacing? I don�t want coolant coming out, but I can�t find the gasket. is the gasket reusable? I am adding a photo for reference. My broken bracket after top right alternator bolt loosened and allowed the alternator to rotate counter clockwise and lift out of place.

yes, I'd replace the gasket (don't reuse the old one) 996-101-331-50 https://www.pelicanparts.com/More_In...BUeQGv0ugpCgLX

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Very helpful thread ! Thanks vetfever

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Keep us posted on your solution. Would appreciate it 👍

Not sure if Jimbo is still making selling these billet brackets, but they're a nice sturdy piece many like. And last iirr went for $300 without aos coolant outlet or 350 with aos water outlet. I'd give him a shout.... https://rennlist.com/forums/996-foru...bracket-2.html

Check with LN Engineering - an email from them on June 17, 2025 said they (Raby) were working on a billet alternator mount for the 996. The subject line was “Improvise, Adapt, and Overcome” - the story of LN's collaboration with Jake Raby. "A va, currently a middle schooler, now works with Jake, modeling, programming, and CNC machining at Raby Machine Works. As you can see here, she’s successfully programmed and machined one of our newest developments, a billet alternator bracket, for M96 and M97 engines, a part that is sorely needed considering the rash of failures we’ve seen as of late of the factory part and the very high cost for a Genuine replacement that doesn’t have any notable improvements." -Tom

Jim made one for me this year. These are 6061 aluminum machined from 1 piece of billet. I have 2 styles. One OEM style with coolant tube, and the other with the tube deleted for cars with UOAS installed and don't need the coolant hose. $350 with tube $300 w/o tube Paypal [email removed] USPS Priority Shipping included for lower 48 states Let me know if you are interested Jim Yeh

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Thanks 996 CAB. Jim took care of me...good guy!!

Hey guys, I still have a few left. Message me if you're interested. jim