Serpentine belt won’t go back on

Hi all. I have a 987.2 Boxster S (2011). The belt tensioner bolt snapped so I bought a new one from Porsche . Now I cant get the belt back on. I’ve checked so many times and the route of the belt is correct. But even when I’m putting heaps of pressure on the tensioner, the belt just doesn’t have enough slack to fit back on. The tensioner seems in good order, it has oil in it and springs back when released. Everyone says this is an easy job. What am I doing wrong?!?!?!

Is this the belt you were driving with? If anything, it should be stretched a bit. If you bought a new belt check for size against old. Check the tensioners side by side as well and the mount. If everything checks out change your approach. Threading the tensioner first, compressing said tensioner and sliding the belt over a roller might be the ticket.

Thanks mate. Yes it’s the belt that came off. I’ve measured it and it’s still exactly 1853. I changed my approach to try and spool it over the adjuster last, then the alternator last and now I’m trying the air con spool last. But with the tensioner fully de-tensioned (as far as it can go) I’m still a good 2-3cm off getting the slack of the belt over any spool. Will persevere more tomorrow but it’s confounding me as to why I’m finding such an easy job so tough. I wonder whether the 30mm tensioner is working as it should, but I have no reference other than a couple of old YouTube vids

Something just doesn't sound right. It's not a stretch belt design where driving the assembly to complete the installation is part of the job, especially true with an old belt. Stepping back and looking again another time with fresh eyes is ALWAYS a great call. Lastly, regarding the tensioner, don't you have the old part to compare with the new one?

Yeah I’m really hoping a fresh set of eyes tomorrow will help. As for the tensioner, it’s the same. The only thing I’ve replaced is the bolt that sheared off.

Yeah, it's definitely tight. I've done it twice and both times it's been a struggle. What's worked best for me is to get a second person to hold the tensioner, that way you can use both hands on the belt. Then get it around everything but the upper right pulley (looking at the front of the engine) and do that one last. Just try to get the belt started on one end of the pulley and then between wiggling the belt on and rotating the pulley you should eventually be able to get it on fully. Note that you don't want to crank hard on the tensioner when releasing the pressure, just hold it against the stop in the released direction. Applying more pressure beyond that won't give you more play, it'll just put strain on the tensioner bolt. I realize it's not a stretch belt but next time I'm going to try a stretch belt install tool, see if that helps.

Thanks mate, really helpful advice. Appreciate your perspective and ideas

I kind of skipped down here - since BTDT. I did a 60k service on my '09 2.9L PDK . As part of that I ordered idlers and the belt (and water pump and a bunch of other "maintenance" stuff) from FCP -Euro, my go-to source for parts. Imagine my surprise when my mechanic tried fitting the new belt onto the engine and it was just too damn short. After talking to FCP who had no explanation (it's what was specified for the engine) - he finally called the local NAPA dealer to see if they had a next -size belt (based on the size marked on the belt, part of the part# I believe). The next size one from NAPA was the correct belt. I have no idea why Porsche spec's a belt that's too short. The one that we put on is still working just fine about 15,000 miles later. I do wonder if at some time there was a change in one of the pully sizes and they didn't change the belt specification. If you have to force it on, imagine the force it's putting on the idlers and the bearings in things like the water pump. The correct size belt should have the spring/hydraulic loaded idler somewhere near the beginning of it's range in tensioning the belt, allowing it to take up slack as the belt stretches with age. The idler should not be hard against it's stop - it's supposed to supply the tension on the belt. If it's hard against it's stop - it's stretching the belt and that stretch is what's providing the tension, and likely to be way too high. It's also probably the reason the tensioner bolt broke. And yes - the "wrong" belt was the 1853... I think the next size up whatever that was worked just fine. And is still working. EDIT: BTW - saw the other thread you commented in - see (2) 987.2 Serpentine Belt Replacement | Page 2 | Planet-9 Porsche Forum for someone who had exactly the issue I had and did exactly what I (and my mechanic) did. I believe the belt from NAPA was from Gates also.. take the old belt to a supplier (see you're not in the US so you probably don't have NAPA there) - but take the belt and tell them you want the next size larger. They'll have a tool to measure the belt. BTW - 2 - in that other thread - there were numerous people reporting the tensioner bolt broke (spontaneously - they weren't working on it) - that's a HUGE clue that something simply isn't right, and what isn't right is the spec for the belt is simply wrong. BTW - 3 - Welcome to Planet-9 - the Porsche Enthusiasts Intelligent Forum! I see this thread was your first or 2nd post here.. how about heading over to (2) New Member Introductions | Planet-9 Porsche Forum and introducing yourself and your Porsche. We love photos!

Rock Auto sent me a short belt that was guaranteed to fit the Ford Duratec V6 too, strange coincidence.

Wow Don! I hugely appreciate your wisdom and experience on this. You’re absolutely right about the tension on the bolt. I’ll look into a slightly longer belt. Will also go say hi in the intros section. Really loving the community spirit in this group! Thanks again

I did the coolant pump, pulley and tensioner along with a Continental belt this summer. As I said on another forum I was nearly in tears installing the new belt. It took several attempts and when I released the tensioner it all settled out ok. I threaded the belt leaving the alternator till last and getting it over the flange was the critical move. I applied a small amount of Simple Green to a two inch section of the belt to add some lubricant. Cleaned it off and was good to go. I have also used Isopropyl Alcohol as a lubricant since it evaporates almost immediately and will not damage the rubber since it is a limited application.

That's a good idea, and I probably should've used some sort of lubricant. For rubber some good choices are diluted Dawn dish soap or a water-based product like KY Jelly: they won't damage rubber or anything and rinse off clean with water when you're done.

Ok update with photos. You can see that with the tensioner fully de-tensioned (to the point where it’s putting stress on the bolt that originally snapped) I’m still way off getting the belt over the alternator pulley. I’ve tried all the other pulleys and its the same. I honestly think that this belt is too tight. The bolt that pivots the tensioner shearing (when it’s not under any torque) I think is a sign of this. Porsche maybe have some specific method of putting this belt on but at the end of that day, the belt needs to be snug enough to gain traction on the pulleys. This tightness, in my humble opinion is excessive. I’m going to opt for a slightly longer belt and let the tensioner do it’s job of springing part way back and pulling the belt tight. Thanks again everyone for your input. I really appreciate it.

Hmm. That does seem too tight. I checked my records and the last belt I got from Pelican Parts was a Continental 6DK X 1853 Contitech. I assume 6 is the ribs and 1853 is the length in mm. This one was tight but went on okay, maybe compare the length to what's on the label of the one you got.

Yeah 6 is the ribs. I took my belt to a mechanic and we measured it to be exactly 1853. Crazy that everything on paper is correct but it just doesn’t fit

I hear what you're saying, Don. At the same time, I got the Continental 1853mm belt on okay, and I assure you the tensioner is not bottomed out. So I don't know what to tell you.

Do you remember how you threaded it on?

I've changed mine and changed the tensioner and had no issues with tightness. I followed these instructions. Hopefully it helps with the routing:

Yes thanks mate. This was what I was working off when I started the job. I agree that it should be easy, but something I just can’t work out is not making that the case for me.

It's been a while, but IIRC trying to get it on the tensioning roller last did not work for me. I believe I did the upper right pulley in the diagram (4) last. I got it around everything but that pulley and used a strap to hold a wrench on the tensioner in the released position (if you have another person handy that'll work too, lol). Then I just got one edge of the belt over the pulley and between rotating the pulley and pushing on the belt was able to get it on. That said, in the picture you showed the belt looks tighter than I remember. But I pulled up my receipt and both times I've done it it's showing as a Continental 1853 mm belt so I'm not quite sure what to tell you. You're absolutely sure you've got all of the slack out of the rest of the belt?

I agree, it’s very puzzling. The only thing I can think of is that the tensioner is somehow now working properly to make the belt lose enough to fit and the spring back to tighten. I’ll order a new one and see if that makes any difference. Might as well order a new belt at the same time.

Well everyone. I have to admit I’m beaten. I’ve removed and refurbished the tensioner, it’s fully working. the belt just won’t fit back on. Time to throw in the towel and go to a mechanic. How frustrating. Thanks so much for all your advice! Cars are pain

Sorry mate. Hopefully it's something simple. I can also confirm that the replacement belt I got was 6DPK1853 (10x1853). Not that it helps much...

Are you 100% sure your belt routing is correct?

Yep 100% mate. I’ve checked and rechecked so many times. My original drawing of how it was matches the factory spec. The tensioner just doesn’t seem to be allowing enough slack. But it does seem to be turning as far as it is supposed to.

Are you putting the belt on all of the ribbed pulleys first? I don't have a 987.2 , but every other car I have done belts on, which is a lot, the easiest way is to make sure the last pulley to get the belt on isn't ribbed or flanged. Usually this is an idler or the tensioner itself. If you try to put it on a flanged pulley last, the flange will often make it impossible. Sorry if you've gotten this advice already, I read through most of the replies, but may have missed it.

Thanks mate. I’m grateful for all the advice! Sadly though I have tried this. It completely makes sense not to be dealing with a flange, especially when the belt is already tight. I’m going to explore the tensioner more as I think I must not be de-tensioning it enough to make this job a simple as it’s supposed to me. Thanks again

After I installed my Continental belt I sat in the car with the bulkhead cover removed and watched the tensioner as I started and rev'd the car. On initial start I could see the tensioner compress momentarily then settle. Revving didn't seem to do much, but that little bit of compression and rebound told me things were as they should be and the tensioner was doing it's job

Mark did you ever figured out why the old belt did not go back on? I'm having the same problem, it when on and off fine but this time when I changed my tensioner pulley. The old belt will not go back on, like's it's too small. I know it's the right size because it fit fine before.

Hi Mark did you ever figured out why the old belt did not go back on? I'm having the same problem, it when on and off fine but this time when I changed my tensioner pulley. The old belt will not go back on, like's it's too small. I know it's the right size because it fit fine before.

Could the pulley be bigger than the original? It's strange that we're seeing many post with this problem after the 987 has been out for so long.

UPDATE - Issue solved! Ok so the reason the belt didn’t go back on will partially remain a mystery but somehow it did shrink slightly. The mechanic bought a new belt and it fit perfectly first time. He was amazed too but it seems the only way to explain it. Save yourself the hassle and buy a new belt. Cheers for all your advice and ideas

Hi mate. Yes and no. Reply below. The TL-DR version is… buy a new belt

Glad you've got it solved. Now I'm wondering about that spare belt I bought years ago that's been hanging in my garage. I bought it to carry when traveling cross country where parts would be slow to arrive in an emergency. The few times I've loosened my original belt to work on driven accessories I never had any issues reinstalling (with the help of a large braker bar) so it's hard to imagine a new belt shrinking enough. I wonder if it is a production quality control issue.

Ordered the new belt and it went on smoothly just how you see the guys on vids do it lol. You would think the old belt would be stretched but it the opposite like Mike said. They shrink….

I wonder if the belt shrunk - that's counter to any aging process for belts that I've ever seen. I'm wondering about the pully diameter. When I did mine (well, I and my mechanic), we had the pulley and idler assembly (complete with hydraulic damper/spring) from FCPeuro and the belt from them. A Continental. And that belt just wasn't going on the new pully and idler, no way, no how. We had the idler back to its fully retracted stop, and it wasn't going on. The 987.2 2.9L uses a double-sided ribbed belt. We ended up checking the dimensions on it, then calling up NAPA to see if they had 1 size larger - and they had one in stock (US brand, not Conti ) - got it - and it went right on and has been on there for about 15,000 miles. Something changed in size. We did replace the water pump at the same time - and the new pump came with a new pully attached, a metal pully instead of the plastic one the Porsche pump uses.. despite all the parts being sold as a "kit" from one vendor - it just didn't fit. FCP -Euro refunded me the money and told me to throw the not-fitting belt away. I gave it to my mechanic - maybe it will fit something else that wanders into his shop.

yes it is certainly a mystery. In my case I changed absolutely nothing except the hydraulic cylinder on the tensioner. So strange why the belt that had been there for 60,000kms didn’t go back on

Both new belts I've put on my 987.2 over the years have been a freakin' fight. Like, I was almost certain there was no way they were going on until I finally with a lot of effort got them over the final pulley...whichever one is upper right facing the engine. Just a freakin' bear of a job both times. They were both Continental brand from the typical suppliers. Maybe trying a different brand or going one size up is the way to go. Don, do you recall the belt length you ended up using?

Offhand no - one size bigger than the one FCP sent. I was thinking next time I have the engine exposed I could look at the markings on it - but there are none since it's a double-sided ribbed belt. @Mark 987.2 comments about the only thing he replaced was the tensioner piston assembly makes me wonder if the fully compressed length of the old vs new is different, and the new one can't be compressed enough to get the old belt back on.

Just read this post and needed some clarification. You state that the new water pump you installed has a metal pulley, instead of the plastic one that Porsche uses. My previous research indicated that there are two choices selecting a replacement water pump. One has a plastic ‘impeller’ and the other has a metal one. Does your water pump actually have a plastic ’drive’ pulley, where the belt rides? Seems like an incredible amount of force and stress on the driven pulley to be made of plastic. And searching past posts regarding the serpentine belt reveals many members reporting replacement belts not fitting, being smaller than the one previously fitted. Has me scratching my head as to why this is occurring. If the pulleys are the same size, there should be no issues. Are there differences in the size of the pulley on the water pump, or are there simply wrong sized belts out there on the market? For reference, the belt on my ‘08 Boxster base is a Continental 6PK2115, which was just replaced with none of the aforementioned problems.