[subframe]

Before I get to the nuts and bolts, I want to say that it feels a bit weird to discuss something as trivial as my e90 during the COVID-19 crisis; for me it is a welcome distraction from the troubles. That said, I hope all of you, your families, loved ones and friends are infection-free and holding up well under the circumstances.

Now to the car. Last weekend I did a DIY replacement of the serpentine belt, tensioner, and idler pulley on my '06 325i (n52 engine). For the parts, I purchased the OE kit from FCP Euro, which has the contitech belt and other parts made by INA. The tensioner includes the replacement bolt. The job went well; however I have a lingering uncertainty. (Note: others have raised a similar concern in other threads.)

The concern is the alignment of the belt on the tensioner pulley. The front edge of the belt is aligned with the front edge of the pulley. There is no overhang, thankfully, but the belt is not centered on the pulley. I am the original owner and this is the first replacement of these parts. The belt on the original was centered on the tensioner pulley, as confirmed by the wear on the original pulley. I have not been able to determine why the belt is riding off-center on the new one. I am concerned that the center of the force imparted by the belt on the pulley is off center, which could lead to premature failure of the tensioner pulley.

So, what caused this? The belt looks to be correctly aligned on all other pulleys. It is centered on the idler pulley, alternator, power steering, etc. That suggests that the problem is with the tensioner itself. Do any of you have any experience with this issue? Any insight appreciated.

Thanks and take care all.

Jim

[OLI77]

That is about what mine looks like as well and I replaced the idler pulley recently. On the idler pulley, there is ~2 mm between the belt and the front of the pulley.

[subframe]

Originally Posted by OLI77

That is about what mine looks like as well and I replaced the idler pulley recently. On the idler pulley, there is ~2 mm between the belt and the front of the pulley.

Is you tensioner original, or has it been replaced?

[OLI77]

Original, uploading pics....

[OLI77]

[OLI77]

I guess on the tensioner there is a little space between the edge of the pulley and the belt.
That distance appears larger on the idler pulley.

[subframe]

Originally Posted by OLI77

I guess on the tensioner there is a little space between the edge of the pulley and the belt.
That distance appears larger on the idler pulley.

Yes. I'd say yours looks better positioned than mine. I have not extra pulley surface in the front; the extra surface is all in the back. It's strange since the idler is centered and on the factory tensioner pulley the belt was centered. I am wondering if the replacement is slightly off-spec, or if I did something wrong when I installed it.

[OLI77]

Hopefully others will chime in with data. I have never done the tensioner on the E90 so can't comment on steps that could have been mishandled.

[Pittz1]

Interesting. I am about to to the same thing. I will have to take before and after pictures. Original belt and idler. 160k miles.

[subframe]

Originally Posted by Pittz1

Interesting. I am about to to the same thing. I will have to take before and after pictures. Original belt and idler. 160k miles.

Just curious, what replacement parts are you using.

[marvinstockman]

First, you didn't purchase an OE kit from FCP, which would have come with BMW stamps. You may have purchased an OEM kit, which means original equipment manufacturer, this means the same company that makes parts for BMW made your part.

Second, I bought the same kit from FCP because my belt was running over the edge of the tensioner pulley, and I was surprised that after I installed all the new parts, the belt was riding just at the edge of the pulley. Not over the edge, but at the edge.

I'd go have a beer, and not worry about it.

[subframe]

Originally Posted by marvinstockman

First, you didn't purchase an OE kit from FCP, which would have come with BMW stamps. You may have purchased an OEM kit, which means original equipment manufacturer, this means the same company that makes parts for BMW made your part.

Second, I bought the same kit from FCP because my belt was running over the edge of the tensioner pulley, and I was surprised that after I installed all the new parts, the belt was riding just at the edge of the pulley. Not over the edge, but at the edge.

I'd go have a beer, and not worry about it.

I like the beer idea. To explain why I said OE, I was using the "quality" designations FCP uses, which are "OE" "OEM" and "Genuine BMW". They define each of those designations. If I recall (no time now to grab the link or a quote) OEM is supposedly the same manufacturer that makes factory parts, but the part is not necessarily identical; OE is the same part as factory but without the logo; and Geniune is the part you would get at the dealership parts counter. Each part description includes a "quality" designation. The parts I bought were in a kit and the quality designation was "OE". At lease that's what I recall.

[clegg]

The aluminum tensioner bolt is TTY. Did you torque the bolt to 18 ft lbs and then another 90 degrees?

[nsjames]

I replaced mine with the contitech kit 56K miles ago.

the belt has always ridden very near the front edge of the tensioner.

there was a spacer in the box, but when I installed that it was far worse to the rear. There was no spacer on the BMW part I removed and instructions for if you needed it or not were incredibly vague.

I check it every once in a while, but t's never changed and it hasn't been a problem.

[subframe]

Originally Posted by nsjames

I replaced mine with the contitech kit 56K miles ago.

the belt has always ridden very near the front edge of the tensioner.

there was a spacer in the box, but when I installed that it was far worse to the rear. There was no spacer on the BMW part I removed and instructions for if you needed it or not were incredibly vague.

I check it every once in a while, but t's never changed and it hasn't been a problem.

Thank you for sharing that experience, very helpful. The replacement tensioner did not have a spacer in the box, unless it was mounted on the part and I missed it. The idler pulley did come with a large disc, like a washer, on the screw behind the pulley. The original factory idler pulley had the same washer so I installed the replacement with the washer on it.

[nsjames]

maybe that's what it was for.
I remember a spacer/washer of some sort and not using it.

it was 56K miles ago after all.

regardless, mine has always ran right at the front edge of the tensioner pulley and it's been fine.

[e90yyc]

Originally Posted by subframe

I like the beer idea. To explain why I said OE, I was using the "quality" designations FCP uses, which are "OE" "OEM" and "Genuine BMW". They define each of those designations. If I recall (no time now to grab the link or a quote) OEM is supposedly the same manufacturer that makes factory parts, but the part is not necessarily identical; OE is the same part as factory but without the logo; and Geniune is the part you would get at the dealership parts counter. Each part description includes a "quality" designation. The parts I bought were in a kit and the quality designation was "OE". At lease that's what I recall.

I think you're right actually. I've always associated OE with exactly what was on the car when it was made; the part with the BMW logo. FCP describe it as same part/manufacturer as when the car was built, but without the BMW logo and box.

As for OEM, they say it's a company whose quality is high enough that they manufacture original equipment parts for automakers in general. I've always seen OEM as the same thing that FCP would consider "OE," but I do think their description makes sense.

To your original post: I've also replaced my tensioner, idler, and belt with the Contitech kit from FCP. I can't recall definitively if my belt rides right at the edge of the pulley, but it probably does... I seem to remember noticing it, running the vehicle, and then concluding everything looked fine.

[ctuna]

Had mine replaced at local Indy same thing .
The original didn't do that.
I commented on it and he verfied that it does
gives me quesy feeling knowing what I do about the
if the belt come off.
I am wondering if its the mounting bolt.

[mecheng77]

Mine rides 1/16" over the edge, I have 120,000km and it's all original. I don't think it will ever run off, there are 6 grooves tracking it.
I think ppl replace this prematurely, if the belt gets oil on it then yes absolutely. I will eventually change it only because of how it fails

[ricx]

my belt is closer to the front edge by a mil or two. as long as the belt isn't isolating while running and stays at the same position i think it will be fine, based on new oem parts used on my car.

[subframe]

Originally Posted by clegg

The aluminum tensioner bolt is TTY. Did you torque the bolt to 18 ft lbs and then another 90 degrees?

Newtis gives a "jointing torque" of 25 Nm -- and an angle of rotation 90 deg. My torque wrench does not have a metric scale, so I looked up the conversion and saw that 25 Nm = 18.44 lb-ft. I set the torque wrench at roughly halfway between 18 and 18.5 lb-ft to approximate 18.44, erring on the low side. I do not have an angle guage, so for the 90 degree rotation I used a sharpie to make a mark on the bolt head at 12 O'clock. Then I turned the bolt very slowly until the sharpie mark reached 3 O'clock.

Of course, the torque wrench is not 100% accurate, and my method of eyeballing the 90 degree rotation is not precise. I am curious about how forgiving the bolt is to any imprecision in the torque applied. In other words does executing the specified torque + rotation take the bolt close to the failure point, or does it leave a margin for overshooting the mark due to measuring inaccuracy. By the way, I realize I am being obsessive about this thing, but failure of the tensioner pulley would do significant damage to the engine -- failure is not an option.

Jim

[clegg]

You should be good. I had replaced the tensioner on my N52 as I noticed the belt was trying to "walk" off of the tensioner.

I didn't have the time to order the part so I got one from NAPA. I just replaced the tensioner but the belt now sits a few mm's back off of the tensioner pulley.

Just keep an eye on it and have that Corona with a lime.