Do we have hydraulic or mechanical serpentine polyribbed drive belt tensioners?

That previous 318i post is unbelievable. What on earth happened to the education system in the years since I graduated from high school?

Anyway, a great thread today confirmed, in addition to what ElwoodBlues posted, there's yet another type of mechanical tensioner that looks different than the ones pictured prior.

Since the identification of the type of tensioners is visual, I'll repost the picture here from a 2003 BMW 525i.

Notice the lack of the raised molded nut. Instead there's a sunken Torx #60 indentation. Who knew!

Originally Posted by bluebee

That previous 318i post is unbelievable. What on earth happened to the education system in the years since I graduated from high school?

Anyway, a great thread today confirmed, in addition to what ElwoodBlues posted, there's yet another type of mechanical tensioner that looks different than the ones pictured prior.

Since the identification of the type of tensioners is visual, I'll repost the picture here from a 2003 BMW 525i.

Notice the lack of the raised molded nut. Instead there's a sunken Torx #60 indentation. Who knew!

For record purposes, the picture shows the lower (AC) belt tensioner (new and original). Part #11287512758. According to realoem.com it is for vehicles manufactured "from 9/2002" that have a mechanical tensioner. This is NOT the upper accessory belt tensioner.

Again for cross referencing purposes, here is a photo of a BMW E39 M54 hydraulic tensioner where the author advises against removing the pulley with the T50 Torx.

Personally, I don't advise replacing a mechanical tensioner with the so-called hydraulic tensioner (which is merely a spring in a tube of oil) ... because of the myriad complications and increased cost and non-proven value.

Here's a recent post today of someone who mentions some of the drawbacks:
"Oh BTY BMW dosen't sell the pulley wheels for the spring loaded tensioners but they will gladly sell you an upgrade for hydralic tensioners at four times the price of a replacement wheel fro the spring type, oh and the special wheel for the hydralic type is extra" (sic)

I wonder if anyone recommends a hydraulic replacement kit over a simple replacement of the mechanical tensioners with like tensioners?

As a cross reference, I came here to quote a diagram of the mechanical belt-drive system and was surprised I hadn't posted it here before.

So, for reference in the future, here it is (for my 2002 525i) from the threads:
- One users' example of total electrical failure (AAA towed away) alternator repair (1) (2)
- Video of cold idle engine squeal (1)
- Recommended parts list for a complete belt drive system overhaul (1)
etc.

There was a strange post this week where the owner had half of a hydraulic tensioner hanging there ... without the other parts ... so we suspected the previous owner could have started a conversion of mechanical to hydraulic but left it undone ... and didn't add the compressor belt back (if you can believe that).

Anyway, in looking up help for that person, I had to go again to the mechanical to hydraulic conversion kit parts thread and just in case that thread disappears, here are the photos from that thread:

- Changing from Mechanical tensioner to Hydraulic tensioner for your serpentine belt drive

Here is the Hydraulic tensioner from realoem that you will need to buy:
http://www.realoem.com/bmw/showparts...90&hg=11&fg=18

Here is the mechanical tensioner from realoem note: This is just a comparison so dont buy this one)
http://www.realoem.com/bmw/showparts...05&hg=11&fg=18

And, here is a conversion kit from mechanical to hydraulic (although not for the E39) from that thread:
- autohauz mechanical to hydraulic tensioner conversion kit

Here are pictures of these respective links from that reference thread:
Quote:
*******>********>*******>********>*******>********>*******>********>

Here is the Hydraulic tensioner from realoem that you will need to buy:
http://www.realoem.com/bmw/showparts...90&hg=11&fg=18

Here is the mechanical tensioner from realoem note: This is just a comparison so dont buy this one)
http://www.realoem.com/bmw/showparts...05&hg=11&fg=18

*******>********>*******>********>*******>********>*******>********>

No.	Description	Supplement	Qty	From	Up To	Part Number	Price	Notes
i	Only applies to hydraulic belt tensioner
01	RIBBED V-BELT	6PK X 1538	1			11281706545	$39.18
02	Base plate		1			11281726774	$67.76
03	Bush		1			11281748718	$8.39
04	Pitman arm		1			11281726773	$61.13
05	NEEDLE SLEEVE		2			12311713153	$18.45
06	ADJUSTING PULLEY		1			11281748131	$45.97
07	Fillister-head screw	M10X25	1		07/2007	07119920150		ENDED
07	Fillister-head screw	M10X25	1			07129905534	$1.50
08	Hydraulic belt tensioner		1			11281717188	$112.15
09	Hex bolt	M8X40	1			07119901161		ENDED
09	Hex bolt	M8X40-ZNNIV SI	1			07119905549	$1.05
10	Hex bolt	M8X50	1			07119912652		ENDED
10	Hex bolt	M8X50	1			07119904533	$2.84
11	Hex bolt	M8X105	1			07119901785		ENDED
11	Hex bolt	M8X105	1			07119904532	$1.78
12	Flat washer		3			11281440369		ENDED
13	Hex bolt	M8X35-8.8-ZNS	1			07119913111		ENDED
14	WAVE WASHER	B8	1			07119932121		ENDED
15	Deflection pulley		1		07/2007	11281748130		ENDED
15	Deflection pulley		1			11287841228	$46.81
16	Hex bolt	M10X150	1			07119904677	$3.82
17	PROTECTION CAP		1			11281730349	$2.37
18	PROTECTION CAP ADJUSTING PULLEY		1			11281727159	$2.37
19	PROTECTION CAP		1			12311713143	$0.42
20	Mudguard		1			11281730532	$2.37
21	Complete hydraulic belt tensioner		1			11281722789		ENDED
21	Complete hydraulic belt tensioner		1			11287838797	$69.64

For those of you who have curious mind, you may want to read the following article discussing the pros and cons of mechanical vs hydraulic tensioners.

Those of you with engineering background will like this article. Also, for those who want to read about Hydraulic Tensioner: it is basically like a car suspension with a Spring + Strut (to absorb sudden shock).

In the Hydraulic Tensioner, the Spring maintains the proper tension. The hydraulic oil works like a Strut to absorb sudden changes in TB tension.

Here is a very good link to read on how Hydraulic Tensioner works.
I also uploaded this pdf file to this forum in case they delete the pdf from their website in the future!
See attachment below for pdf.

http://www.gates.com/europe/file_sav...Tensioners.pdf

I am attaching a picture for a quick read:

For the cross linking record, dcotti wrote up his hindsight recommendations over here for what he'd do differently the next time he replaces his 2003 tensioners and belts.
- Belts / Tensioner s/ Idler Pulley Replacement

Notice that he had two mechanical tensioners, one of which was the TORX and the other the HEX pry point.

It seems that only the 2003 is so afflicted with the torx pry point.

Also dcotti described what he'd remove next time he contemplates the same job.

For the record, G. P. Burdell, over here, kindly provided a pointer to the following BMW alternator-belt tensioner retrofit service bulletin:

Originally Posted by G. P. Burdell

There's a BMW service bulletin (SI B 11 04 03) that recommends replacement of noisy mechanical tensioners with hydraulic tensioners. The bulletin applies to most BMW models equipped with the M54 engine.

Thanks to Nando & Starless, attached below is a copy of that Technical Service Information Bulletin (I created the SIB JPEGs for ease of viewing).

Note the following BMW SI B 11 04 03 details:

• It applies only to the upper tensioner on the M54 engine (alternator belt)
• It applies only when a customer complains of noise
• It requires a "kit" to allow switching from 2 bolts (mechanical) to 3 bolts (hydraulic)
  • Upper bolt: BMW PN 07 11 9 901 785
  • Lower bolt: BMW PN 07 11 9 912 652
  • Left side bolt: BMW PN 07 11 9 913 111

The question I would have is, since most cases of noise are in the bearings, not in the spring, what is in a so-called hydraulic tensioner that would cause it to be less noisy than a mechanical tensioner?

Note what cn90 said: Both are mechanical; one is a spring in oil, the other doesn't have oil ... but noise is usually from the bearings, which, presumably, both have.

The Gates technical bulletin posted by cn90 states that hydraulic tensioners are "mainly used on applications with high loads and/or angular vibrations, where a mechanical automatic tensioner can not provide sufficient damping or tensioner movement." It may be that the mechanical tensioner, while less expensive for BMW to install at the factory, wears its pulley bearings out faster and becomes noisy because it's less capable of handling the loads of the belt drive system compared to the hydraulic tensioner.

Originally Posted by G. P. Burdell

It may be that the mechanical tensioner ...wears its pulley bearings out faster ... because it's less capable of handling the loads ...

This is enlightening and interesting.

I copied your response over to this specific thread I opened on the topic:
- WHY would a hydraulic belt tensioner be any quieter than a mechanical belt tensioner?

Where the three related questions are asked:

1. Is the bearing loading any different between hydraulic & mechanical tensioners?
2. Are the bearings themselves any different between hydraulic & mechanical tensioners?
3. Is the problem only related to the alternator tensioner or does it also apply to the AC belt tensioner?

"BMW dosen't sell the pulley wheels for the spring loaded tensioners

While BMW won't sell you "just" the pulley for the mechanical tensioners, apparently the pulley "can" be bought separately.

At least it says so in this E46 reference:
- a/c belt tensioner pulley

And, in this E39 reference:
- Squeak

For the record, another user today reported you can replace "just" the pulley on the mechanical tensioners:
- Belts / Tensioner s/ Idler Pulley Replacement

Originally Posted by fiat84

Appears you can replace only the pulley separately on both the mechanical AC assembly and mechanical tensioner assembly, both use the same pulley. Before finding this out had replaced my entire tensioner assembly with an Ina brand and plan on doing the AC assembly later in the spring. Came across a E46 DIY where they only replaced the mechanical pulley's as the assembly was still in great shape. http://forum.e46fanatics.com/showthread.php?t=735884

Gates part #38018 brand at Napa in Canada $21.09 each heard good things about Gates belts, etc so will buy this one local.
GoodYear #49024 pulley $15.35 at partsource.ca http://74.208.162.181/part-source.ca...ulleys&mode=PA
Dayco #89133 Bumper To Bumper Canada $30.71 - at Autozone as Duralast #231133, both manufactured by Ina

Note the mechanical pulley is different from the hydrolic pulley.

Originally Posted by jayee_2003

Hmm. I've had a few cars with this series of engine. They all had the mechanical tensioner. Guess I buy outside the curve.

this
I have 2001 and 2003 and both have mechanical tensioner
I believe all M54 has mechanical tensioners
both have been replaced to the same mechanical on 80k miles
0 issue, will last another 80k

Together, we're a team (alone we're nothing) ...

For the record, many people (including me at first) are confused whether to twist on the mechanical tensioner pulley centerbolt or to leverage on the raised knob (or sunken Torx in the 2003 E39) on the side of the tensioner.

To make matters worse, folks with the hydraulic pulleys often unintentionally mislead we mechanical tensioner people by talking about the pulley Torx centerbolt (which, unless you're replacing 'just' the pulley, which most of us do not do, then it buys you nothing to loosen the pulley centerbolt on the mechanical tensioner).

Anyway, the topic came up, again today, over here:
- Serpentine Belt Replacement

To which WagonTheDog posted a wonderfully succinct picture that I reproduce here for all to benefit:

Thanks for for the cross-reference, BB.

Originally Posted by bobdmac

Thanks for for the cross-reference, BB.

Thanks for noticing.

For every thread I ask a question on, I go to great pains to ensure there is a complete & comprehensive answer, which just gets better and better (over time), always aiming toward the goal (but never reaching) of having every single possible question answered. That takes a LOT of cross links because you want one place to find the answer, even if the answer is scattered all over the place.

The worst thing, to me, is when someone asks a common question, and the respondents are so jaded that the OP gets no response, or jokes, or half answers. Even worse, as it seems to have happened even in this thread, well-meaning people give WRONG answers.

In the end, everyone who asks this question finds out the right answer (if by no other reason than by trial and (expensive) error) ... so it's just wrong for them, once they find the answer, to not edify the rest of the team.

By way of example of how the process 'can' work when it's well honed, today someone asked the simple question:
- Belt tensioner hydraulic or mechanic ?

We pointed them here! And, that makes me feel good that the OP in that case has a ready-made answer, a one-stop-shopping combination of all our collective tribal experiences.

The OP's job, now, is to improve our collective knowledge ... any way he can (as we're always improving our tribal answers).

Today, fiat84 reported anecdotal experience with changing 'just' the mechanical tensioner pulley in:
- Belts / Tensioner s/ Idler Pulley Replacement

UPDATE: Changed the AC pulley only with a Gates #38018 and a few weeks later it made an intermittent rattling grinding sound. Got loud when the engine ran for awhile so it DOES NOT appear to match factory specs. Put the old factory pulley back on which is still in great condition and no more rattling. Maybe try the Dayco #89133 since it is made by Ina. Had recently changed the AC belt a month before.

Today, someone struggled with the wrong bolt attempting to remove a hydraulic tensioner:
- Need help changing my belt - problem with hydraulic tensioner

Luckily, folks set him straight with nicely edited pictures, which I reproduce below for the edification of those who need to know.

For the record, here is a nice picture of the adjustment arc of the V8 hydraulic tensioner today:
- E39 (1997 - 2003) > AC tensioner installation

NOTE: The I6 hydraulic tensioners do not have this adjustment arc.

Originally Posted by bimmerteck

• I6 E39 mechanical tensioners (no adjustment necessary nor possible)
• I6 E39 hydraulic tensioners (no adjustment necessary nor possible)
• V8 E39 mechanical tensioners (no adjustment necessary nor possible)
• V8 E39 hydraulic tensioners (no adjustment necessary component removal facilitated via the bolted arc)

In addition, cn90 referenced a nice DIY:
- BMW 740il Serpentine Belt

*******>********>*******>********>*******>********>
A. First thing you have to do is take off the fan and fan coupling.

Layout of Serpentine Belt Then loosen nuts (1) and (2), loosen and remove the Serpentine Belt.

Use hex head (1) to preload adjusting plate to end of long bore (2) and tighten nuts (3). Installation:
Fit Serpentine Belt and check it is correctly located on pulleys.

The A/C belt is as easy as it looks. Just loosen the tensioner and replace the belt.

See also:
- How to tell if you have mechanical or hydraulic belt tensioners (1) & how to switch from mechanical to hydraulic (1) and what is the difference between the two types (1) (2) & how to rebuild your hydraulic tensioners (1)

For the record, yet another person (this time on an E46 M54 engine) posted an idler roller that simply fell off the centerbolt, unbeknownst to the owner:
- E46 (1999 - 2006) > Alternator replacement with deflection pulley surprise.



Other related threads show why the idler roller is replaced along with the belts & tensioners:

E46 (1999 - 2006) > Another Possibility of a P00128


- E39 (1997 - 2003) > Mechanical Fan Exploded! Is another one

For the record, a side discussion of which tensioners are adjustable went on today over here ...
- E39 (1997 - 2003) > Battery light on..

Originally Posted by QSilver7

I'm not sure how the I6 is set up...but on the V8 (M62/M62TU) you tighten the tensioner by using 2 sockets, or 2 wrenches, or a combination of the both. You need a 17mm socket or wrench and a 13mm socket or wrench.

When the 13mm bolt is loosened (it's the one that goes thru the slotted part that allows for movement to loosen or tighten)...you place a 17mm socket or wrench on the 17mm bolt (on the right) and turn/push it counter clocwise. This puts tension on the belt/pulley...while turning/pushing the wrench on this 17mm bolt....you tighten the 13mm bolt preferably with a socket wrench.

This is how you put tension on the pulley for the V8. For those that have the I6...is it the same type of set-up?

(image by Arbysnight from BimmerBoard)



>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<

(#8 = the 13mm bolt & #9 = the 17mm bolt in the image above)

Originally Posted by pleiades

Best I can tell, it's not adjustable on the i6 cars.

For the record, yet another 540i owner was confused today about the 'ability' to adjust belt tension on the hydraulic tensioners with the arc:
- E39 (1997 - 2003) > Alternator Swap, Loose Belt, Help!

Originally Posted by russelltickle

I put in a new alternator today and need help getting the serpentine belt tight. The Bentley says "turn hex clockwise" to pretension the belt, then tighten the idler arm bolts. I don't know what that means. The tensioner pulleys have a 45 torx bolt if that helps. I also have a tensioner pulley to the lower right of the alternator that doesn't show up in the Bentley or any DIY's I've seen.
How do I get the belt tight on an '02 540? It's on, but squeals at me. I also broke a fan blade, broke a pop pin on the fan shroud, and caused an oil leak by the oil filter housing. But the alternator works!

Here are the links I referred him to for details:
- How to tell if you have mechanical or hydraulic belt tensioners (1) & how to switch from mechanical to hydraulic (1) and what is the difference between the two types (1) (2) & how to rebuild your hydraulic tensioners (1) & the answer to the question of adjusting the 540i hydraulic tensioners' belt tension (1) (2)

For the cross-linked record, the question of how to tell, hydraulic vs mechanical, came up again today:
> E39 (1997 - 2003) > Cooling system! be safe than sorry?

Originally Posted by colombianoe39

Still not sure in regards to Belt tensioner Mechanical Type or hydraulic?

Luckily, I think 'this' thread has all that anyone would need to answer that question!