Manual Tighten Belt Tensioner? Supercharger Boost Drop Related..

[MisterM52]

Hello Fellas, Are the OEM tensioners good for supercharging And are there any way to manually over tighten the tension on the serpentine belt on these cars, M50/M52 based motors that is.

This one is the mechanical spring loaded tensioner, original one 150K Km on it, seems to wiggle even at idle now without any blower attached.

I had boost drops at higher revs anywhere from 3 - 5 PSI Drop! I have ruled out everything and found out the tensioner was going bad.

So I'm replacing it with a new one but also looking for any room for improvements!

[someguy2800]

Take it apart and find a heavier spring to fit in it?

[geargrinder]

there's a lot to be said for a spring tensioner in terms of coping with wear and belt stretch and not OVER-tightening which most manual-tensioners result in. not to mention ease of maintenance.

given those miles I'd just toss a quality new one in and see how it goes.

what does your belt setup look like, Mister? can you post a pic of how it routes? there are options to add idlers to get more wrap etc. - philly here just fabbed a rig like that for our V8's that looks like it works really well and allows to keeping a spring-loaded tensioner... basically getting better wrap means not having danger of overtension and having the downsides associated...

[MisterM52]

I ordered a new mechanical spring loaded one, $140 (ouch).

But this is how it usually looks like, Gear. The pic below is from an earlier incarnation on a S50B32 but the belt routes the same, mind the hydrulic tensioner on this one, while mine is a 150k old spring loaded mech. Would like to see some of philly's work, if you have a link. And let me know if you see room for belt routing/pulley improvements! I guess I could squze in another idler pulley just between the sc and alternator, but unsure.

(press ctrl + to enlarge the pic.)
P030612_15.450001.JPG

[someguy2800]

does that belt go around the alternator with the ribs facing out? Did you machine the grooves off the pully or something?

[geargrinder]

Looks right side to me...

Yeah Mister I think this is an easy wrap issue - you've got less than 180 degrees of wrap on the blower.

Dude - honestly this is a fix right up your alley as Mr. FabIt. Cook up some solution with an idler to get the belt wrapped up around that blower pulley. Then just grab a catalog and buy a couple longer belts and figure out what fits.

Here's philly's work in progress on our V8's but it's a classic approach - mount an idler up in there to get good wrap. Before this mod, the VF & Dinan kits have no idler so the belt comes straight off the small blower pulley so you can imagine its a huge difference.

http://www.bimmerforums.com/forum/sh...-the-Stock-M62

He hasn't updated his thread but he's since gone triple nutz on the fab-train and has made a new version with 2 idlers.

[someguy2800]

Looks right side to me...

Yep, your right.

[MisterM52]

Looks right side to me...

Yeah Mister I think this is an easy wrap issue - you've got less than 180 degrees of wrap on the blower.

Dude - honestly this is a fix right up your alley as Mr. FabIt. Cook up some solution with an idler to get the belt wrapped up around that blower pulley. Then just grab a catalog and buy a couple longer belts and figure out what fits.

Here's philly's work in progress on our V8's but it's a classic approach - mount an idler up in there to get good wrap. Before this mod, the VF & Dinan kits have no idler so the belt comes straight off the small blower pulley so you can imagine its a huge difference.

http://www.bimmerforums.com/forum/sh...-the-Stock-M62

He hasn't updated his thread but he's since gone triple nutz on the fab-train and has made a new version with 2 idlers.

Thats very good approch to the issue to address that VF/Dinian, such a long belt and so little tension! thanks gear your a pal alright, got a light bulb in my head right now..its so simple, why didn't i think of it earlier, I could just bolt it in there without even having to touch the welder..brilliant! here's another incarnation one done to a M52, I think I will put the spare idler pulley I got here somewhere just between the sc and alternator pulleys, so I get good wrap! yep



- - - Updated - - -

does that belt go around the alternator with the ribs facing out? Did you machine the grooves off the pully or something?

oh no no, thats the alternator tensioner pulley, the alternator is just right to it in its usual position, a lot of the M50/S50/M52 motors I see seem to be missing it!

[Def]

Yea, increasing the wrap is likely easier than anything else at this point.

The relationship between transferring power is Tension = Force transmitted * e^coefficient of friction * wrap angle in radians

If you take tension and coefficient of friction to be constant (should be in this case) and substitute some reasonable numbers like 60 lbs of tension and a mu of 0.4, and increase your wrap angle from the roughly ~165-170 degrees it looks to be now up to say 210 degrees, then you can transmit 46 lbs on the pulley face vs. 41 lbs. It may not sound like much, but that's an increase of 5/41 = 12%.

If you bump the tension up a bit more, you can get up to about 15-20% more power transmission.

Just putting some numbers up there. It makes me feel better since I'm burning out on studying for my PE exam and am looking for distractions. This is like studying but more fun...

[MisterM52]

Always like a bit of theory good sir, brings out the mad scientist within so that's definitely appreciated

Figured out where I will put the new pulley to help wrap it up, will use a moduler plate, as did philly on his thread above. In my case however there is about an inch's dept which I may solve with some washers or nuts or other means, trial and error. but overall solid idea to allow more power transmission.

New Tensioner arrived today, not genuine BMW(Yea after $140 I would expect not a Hans Piers Knockoff) But hey..It looks good..The old tensioner wasn't only lose as in I could move it somewhat on my hands, meaning the spring had given in and lost its resistense, it also had a tab broken! T

he new on on the other hand..wont move a bit..

In with the NEW
2016-04-14-833.jpg

Out with the old!
2016-04-14-830.jpg

[geargrinder]

The nice thing about an idler too is that it doesn't have to be super aligned... you can source a slightly over-wide pulley and not have to worry about exact axial location. Although a pulley with shoulders is nicer, and that means having some axial alignment, the plain jane idlers seem to work fine for OEM so you should be fine here...

[philly98540]

Cool, another wrap adder! It works really well. I updated my thread showing the addition of another pulley. I'm hitting almost 16 psi now and no slip.

Looking forward to what you come up with.

[MisterM52]

Okay Fellas, So this is what I am going to be incorporating (the V2 belt orientation).

I already bought an extra pulley, will do this sometime next week and post back with pictures.

Thanks to Philly and also Gear for bringing this into light.

[philly98540]

That looks great. It's on the higher tension side of the SC, so make sure the bracket is strong!

[geargrinder]

Agreed. Of course on a big serp with multiple accessories like that, both 'sides' of the belt are loaded, so it would have to be pretty strong either way, not like our simple little dedicated belts where the return off the blower is unloaded

[MisterM52]

Thanks Guys, Yea I am thinking the same thing, but I also need to keep it modular, and not a one off thing (which again can be done) but will reduce the simplicity of my designs, specially for my customer base who might use different sized pulleys so I had in mind something that can of course be bolted on and off.

I also need about 1" of protruding for the pulley to sit flush with the other pulleys, So I figured for ease of build and installation if I ought to use simple square tubing like this with the pulley on one end and couple of bolts on the other with the choice of being to move it at a few different angles for various sized pulleys. Or am I gone nuts again?



Notice the rough idea in red below..
SCV2 Belt Idler.jpg

[philly98540]

Concept looks good. I think that square tubing may squish when you tighten up everything. May need a thick washer or something to get the force to the sides. Good luck.

[MisterM52]

The square tubing was just to get an idea, I couldn't allow myself to use it, So this is the final concept. Cut out of 2mm Sheet metal, this is V1, where I messed up the mounting holes, V2 will improve upon it tomorrow and it will have more space for various angle's for the second pulley tomorrow.

Finally V3 will be cut from 25mm aluminum and slot right into place.

V1.



Basically Sandwitches itself between the top and bottom mounting points.





How it got there..

First we go back to the drawing board, Caveman fabrication 101.


Now we start off with..Corn Flakes Of course!







Now that we get a rough idea, we cut it out of sheet metal


as it should sit..


- - - Updated - - -

One of the reasons I am wanting to use 25mm thick sheet is basically the pulley needs to sit 1 Inch out wards, other wise I would just opt for 4-5mm sheet metal and bolt the pulley there. Anybody got any suggestions to the setup or making the pulley sit out without going 25mm thick sheet..?

[geargrinder]

Easy. Use a slice of a nice heavy piece of metal tubing to 'sleeve' your pulley mounting bolt and support the backside of the pulley.

Weld it onto your plate so it's not just a big-ass spacer but becomes structural (if you just use a loose spacer-sleeve type of a deal on a bolt, the stress will all go on the bolt and it may bend and/or break over time... if you do it right the sleeve will carry the load as a solid part of the bracket). For extra extra strength you can even weld a little triangular brace or two on the sides of the sleeve to make it rock solid.

Not sure what your proposed pulley is going to look like (ideally it's smooth not a ribbed one that you are using to mock-up) on the backside mating face, but you could potentially go very large in diameter on the tube, then cap the end of it with a center-hole drilled for your bolt. If you do that, cap the tube and drill the hole first before final cutting the back side to length since the cap will add obv. I'd want to miter chopsaw all the cuts to be sure you get good 90's, and/or be sure you have a really really good 90 when you jig it to weld up, but should be easy.

Something like this:
mrbracket.jpg

BTW benefit of non-ribbed idlers is that axial location isn't too important - get one a wee wider than the belt and your location doesn't have to be immaculately perfect.

Also (duh) be sure your backplate is strong enough to not bend, and/or, make sure your braces run out to near the mount points (prob a good idea anyway).

[MisterM52]

That is a non ribbed idler, look close, the ribs are the belt going into sc pulley mockup, I was using my extra 3rd hand to pull the belt, another to wrap the belt around the idler and the other one to take the pic. serious.


You know i thought about just that, but nobody here sells spacer washers like that. might have to use tube. But thats my real plan, to use maybe 3-5mm alloy or mild steel plate (the sc brackets are 7mm mild steel cut with oxyacetylene cutter) so dont think wrap would be a issue when using something half that just to mount the idler? The current pics are merely a template made out of 1-2mm sheet metal. Lets see if I can hunt these down, would make life easier.



Thanks for the input guy.

[geargrinder]

Meh. don't need no fancy spacers. Tubing. Chop-saw. Done.

Those shiny shiny things would need the chrome ground off to weld anyway...

[philly98540]

If the spacer thing is going to be sketchy, just go with the thicker plate is my vote. If you can do the spacer all proper and square it should be fine.

Maybe just a small piece of thick plate could be bolted to the thinner main adapter plate to act as your offset.

[geargrinder]

Or welded down, since Mr is obv an enthusiastic metal melter...

[MisterM52]

I thought about all of these options, don't know what would look better

1. huge block of 25mm metal.. added weight, bulk. problem cutting down, tricky even with a oxyacetylene cutter..

2. something 1/5 that, nice streamlined, machine cut, but has gap needing filled with a pipe/spacer or block for pulley.

a. using a block..
b. using a spacer
c. a pipe.

choices.. choices....I'll see if I can find a nice spacer or two, which would look better then a block, which would be he last option)

[geargrinder]

Using massive 1" plate for the whole thing is def the wrong choice. But cutting some chunks and stacking might be OK - basically make a 'block' out of several slices of plate stock. cut a bunch of little cubes, stack them, weld them into a monobloc, then tack them down, drill hole, grind to make pretty, done.

Honestly, do the picture I drew. will be solid, not too heavy, take a few minutes. Cutting slices of tubing/piping would be fastest and most replicable for your other installs. Make a bunch of slices: Chop. Chop. Chop. Cut a crapload of little triangles. Cut a bunch of backplates. Weld tubes onto back plates. Weld braces. Done.