N55 serpentine belt - too short?

[LoloHaole]

I'm replacing the serpentine belt and pulleys with the kit from FCP Euro: https://www.fcpeuro.com/products/bmw...-11287628653kt

I also put in a new alternator, which was a VERY tight fit but bolted into place nicely after some gentle tapping with a dead-blow hammer.

But now when I go to put the new belt on, it's not long enough. The tensioner retaining pin is in place, and cranking it the little bit more that's left only gets me a couple mm closer. I'm using this pic for routing the belt:
https://i2.wp.com/diyautogalaxy.com/...pg?w=750&ssl=1

I used calipers to verify that the new pulleys are the same side as the old ones. The only difference is the new tensioner pulley is smooth where the old one was grooved. FCP says that's the correct part and it's ok for the ribbed parts of the belt to be on a smooth pulley.

The belt package reads Continental 7K1860 -- When I measure it against the old belt, it seems only *slightly* smaller, like I'd expect a brand new belt to be.

In my frustration with taking the belt off and putting it back on, verifying that it's on correctly, measuring pulleys, cranking on the tensioner, etc, I didn't think to try installing the old belt. I'll do that tomorrow.

In the mean time, any help is appreciated. Could it be possible that the alternator is somehow different enough to cause this? It looks exactly like the old one, minus the 75k miles of leaked oil and dirt caked onto it...

Am I just missing something really obvious? Everything I've read and watched about this job indicates that putting the new belt on is easy, so I'm frustrated AF right now.

Thanks,
LH

p.s. Pic attached of how far the belt will go below.

[zx10guy]

I had to take out the retaining pin in the tensioner to get the belt on. A serpentine belt tool worked wonders for me in getting the leverage I needed onto the tensioner.

[dtla1]

Originally Posted by LoloHaole

I'm replacing the serpentine belt and pulleys with the kit from FCP Euro: https://www.fcpeuro.com/products/bmw...-11287628653kt

I also put in a new alternator, which was a VERY tight fit but bolted into place nicely after some gentle tapping with a dead-blow hammer.

But now when I go to put the new belt on, it's not long enough. The tensioner retaining pin is in place, and cranking it the little bit more that's left only gets me a couple mm closer. I'm using this pic for routing the belt:
https://i2.wp.com/diyautogalaxy.com/...pg?w=750&ssl=1

I used calipers to verify that the new pulleys are the same side as the old ones. The only difference is the new tensioner pulley is smooth where the old one was grooved. FCP says that's the correct part and it's ok for the ribbed parts of the belt to be on a smooth pulley.

The belt package reads Continental 7K1860 -- When I measure it against the old belt, it seems only *slightly* smaller, like I'd expect a brand new belt to be.

In my frustration with taking the belt off and putting it back on, verifying that it's on correctly, measuring pulleys, cranking on the tensioner, etc, I didn't think to try installing the old belt. I'll do that tomorrow.

In the mean time, any help is appreciated. Could it be possible that the alternator is somehow different enough to cause this? It looks exactly like the old one, minus the 75k miles of leaked oil and dirt caked onto it...

Am I just missing something really obvious? Everything I've read and watched about this job indicates that putting the new belt on is easy, so I'm frustrated AF right now.

Thanks,
LH

p.s. Pic attached of how far the belt will go below.

That picture you are using for reference is of an N54, regardless, below is my diagram I made when I changed by belt a couple years ago. I tried to label a couple things, "idler" really should be tensioner, and the other poor attempt at labeling is the balancer.

I literally just sketched this on my phone before I took the belt off two years ago so please excuse the sloppiness of it.

[LoloHaole]

Thank you! I'm going to try that asap!

Originally Posted by zx10guy

I had to take out the retaining pin in the tensioner to get the belt on. A serpentine belt tool worked wonders for me in getting the leverage I needed onto the tensioner.

[LoloHaole]

Thanks for that, dtla.

I dug a bit and this motor is an early n55, which looks to have quite a bit of n54 design still in it. The tensioner I see for later N55s is only one pulley, where mine has two. Mine looks exactly like that N54 pic, except for the engine cover and the 2nd turbo hiding in the back.

N54 / early N55(?)
https://s2.qwant.com/thumbr/0x380/c/...=0&b=1&p=0&a=1

Vs later N55s:
https://s2.qwant.com/thumbr/0x0/d/b/...=0&b=1&p=0&a=1

I hope I have this right...

Originally Posted by dtla1

That picture you are using for reference is of an N54, regardless, below is my diagram I made when I changed by belt a couple years ago. I tried to label a couple things, "idler" really should be tensioner, and the other poor attempt at labeling is the balancer.

I literally just sketched this on my phone before I took the belt off two years ago so please excuse the sloppiness of it.

[dtla1]

Originally Posted by LoloHaole

Thanks for that, dtla.

I dug a bit and this motor is an early n55, which looks to have quite a bit of n54 design still in it. The tensioner I see for later N55s is only one pulley, where mine has two. Mine looks exactly like that N54 pic, except for the engine cover and the 2nd turbo hiding in the back.

N54 / early N55(?)
https://s2.qwant.com/thumbr/0x380/c/...=0&b=1&p=0&a=1

Vs later N55s:
https://s2.qwant.com/thumbr/0x0/d/b/...=0&b=1&p=0&a=1

I hope I have this right...

I'm not sure about the whole early/late N55s to be honest, my car is a 10/2010 build so I supposed I would also be "early" in this case?? Regardless. It looks like the sketch I drew matches your first link for "N54 / early N55(?)", and that my sketch/link does not match your picture of the N54 from your first post (Easiest way for me to identify N54 vs N55 is the placement of the oil filler cap).

Specifically, the red lines in your newest link ("N54 / early N55(?)"), are what differ, the routing of the belt goes straight down from the AC Compressor to the Power Steering, and then loops up to an idler(?), then back down and around the crank/balancer.

[dtla1]

You might have already found this OP, but just in case: https://www.1addicts.com/forums/show...1190224&page=2

[Gizmo135i]

There are a couple different belt routings for the N55 depending on the car, the one for the 135 and 335 is different from the other models... I think the difference is on one style the belt is routed from the crank to an idler before going to the p/s pump and then directly to the a/c, and on the other style it goes straight from the crank to the pump, and then from the pump it goes to an idler before going to the a/c if that makes any sense.

[LoloHaole]

dtla1, thank you for that thread and the details on how yours is set up. You saved the day for me today!

All of you did, actually. Thank you ZX10guy and Gizmo135i, too!!!

I had to use THIS routing, not the n54 one that I was trying to use (all of the pulleys look the same, but the routing is different.)
https://www.1addicts.com/forums/show...7&postcount=26

Once I had the correct belt routing, slipping it on was easy. I didn't even need to remove the pin.

[dtla1]

Originally Posted by LoloHaole

dtla1, thank you for that thread and the details on how yours is set up. You saved the day for me today!

All of you did, actually. Thank you ZX10guy and Gizmo135i, too!!!

I had to use THIS routing, not the n54 one that I was trying to use (all of the pulleys look the same, but the routing is different.)
https://www.1addicts.com/forums/show...7&postcount=26

Once I had the correct belt routing, slipping it on was easy. I didn't even need to remove the pin.

Good to hear that you were able to figure it out!
Yeah that routing looks to be the same as my sketch as well as that first link you previously sent "n54/earlyN55". Some of the pulley labeling is different, but overall same same.