Machinery like sound from drivetrain at largest sprockets

[Tebbybabes]

I'm posting this because I've just about come to the end of my wits or my rope or both.

I have a Merida Speeder T2 with this load out.

FRONT DERAILLEUR Shimano R443 34.9
REAR DERAILLEUR Shimano Tiagra
GSSHIFTERS Shimano SL-R440
BRAKE LEVERS Avid FR5
BRAKES F/R Avid Single Digit 3
CRANKSET FSA Tempo 52-42-30
BB SET Shimano Cartridge
CHAIN Shimano CN-HG50
HUBS F/RAlloy QR / Shimano 2200
RIMS Speeder Pro V
FREEWHEEL Shimano CS-HG50-8 12-25

I'm experiencing machinery like noise whenever I'm on the largest sprocket and I'm on the middle chainring and this only happens when its loaded. When the bike is on the repair stand, its just fine and dandy. I've mentioned this to my LBS, who's a wonderful fellow, and he said that, without seeing it, it may just be the chain not meshing completely well with the chainring in that position. I've looked everything over and adjusted everything to within an inch of its life and can't see anything causing it.

I guess the main reason I'm irked by all this is because I've owned several bikes before, all what would be described as department store cheapies. MTB style with definitely cheap breakable components. (One reason I've become handy with my bikes). Anyway, when adequately maintained, they were all whisper quiet, at any gearing. I've been riding/maintaining these cheapies for a few thousand Kms and they're still good, albeit they weigh a ton. Steel is real. LOL. But seriously this is bottom quality stuff.

This Merida is actually my 1st 'fancy' bike. It was a gift, but I know that it cost a whole heck of lot more than my other bikes. I was really hoping that this could be as whisper quiet like my others. Any thoughts as to why or to see what I can do?

Some things that don't seem to be the problem:
- The jockey pulley is not hitting the large sprocket
- The chain isn't hitting the FD, although that's what I initially thought it was. The sound is 'similar' but NOT the same. Intentionally hitting the FD with the chain generates a much louder sound. It's almost as if its just only 'brushing' against the FD, but I can't see that. (of course that's when it's on the stand, unfortunately, the sound only occurs at load)

Some observations on my part
- Since this is my 1st 8 cog cassette, and my first compact frame, I'm surprised at the amount of flex in the chainline of the chain.
- All of my other shifters were friction shifters and as such trimming was so easy... (I keep thinking if this damn thing was just friction then I wouldn't even have this problem.) But anyway, after some visual comparisons, I've noticed that the clearance inside the FD cage on my cheapies was huge compared to the one Shimano R443. This is in spite of the fact that my cheapies actually had wider chains!
- If I can't make this go away, I'm considering just skipping those gears. Am I actually supposed to be able to use those gears?
- Since this only occurs at load (light load - occasional noise, heavier load - more frequent noise), could this be related to the frame or something else flexing? If it is, is there a way to fix that?
- Bike hasn't been ridden anywhere close to the distance I've done with my others. If I had to estimate, it's only probably in the 300km mark. Meaning I certainly hope its not wear. Also, I've had the noise problem pretty much since I got it, but I've only found the time to tinker with it recently. I thought it was just something that I could fix so I kept putting if off.

That's all I can think of ATM. Thanks for reading and TIA for any input.

[__PG__]

Is the chain lightly brushing against the outer chainring?

[Tebbybabes]

That's an idea that I haven't thought of.

Thanks.

Will take another look at it as soon as I can get to the bike.

[im_no_pro]

Is the chain lightly brushing against the outer chainring?

Cross chaining was the first thing that came to my mind also, but on the largest cog wouldnt it be brushing the little ring?

[bychosis]

BB or cranks loose causing lateral movement in chainrings onto the derailleur? I had a bike that would rub on the derailleur under load, but only in a particular point in the crank rotation. BB needed adjusting ( non sealed unit)

[jacks1071]

Is the cassette lockring done up?

[Tebbybabes]

Sigh, real life has caught up with me and I haven't had a chance to fiddle with my little push bike just yet. I'm hoping to be able to get some time in on it by Tuesday.

@Jacks1071 - I'm going to have to look up how to secure a cassette lockring. Haven't had the need to fiddle with a cassette just yet. Now seems a good time to learn.

@bychosis - that's an idea I'll have to check as well. It didn't occur to me because the bike hasn't been ridden all that much and also because the noise was limited to only a few gears. I've realized now that if it was flexing just enough, then it might be the cause for the problem under load. Silly me. Anyway, I'll be fiddling with the bottom bracket ASAP, but is there actually any adjustment possible with a cartridge type thing?

@Im no pro & PG - from memory, it almost seems that the small chainring is quite far below the middle chainring for any rubbing to occur but I will visually determine that as well.

Again, thanks for the ideas, folks. Much obliged.

[ironhanglider]

Inner plate of the front derailler?

Cheers,

Cameron

[danny the boy]

Had a similar problem after changing chains. What confused me more was I changed wheels at the same time. Would only happen on 1 or 2 sprockets on the cassette when cadence got above around 90 rpm and no amount of fiddling could relieve it. Was at the point where I was randomly stopping mid ride without changing out of the gear to try and find a noise similar to chain rub but there was no evidence of it. When the chain was freshly lubed it would disappear completely so I am going with the conclusion of dodgy chain to spare myself further frustration and just live with it until I change it again.

[Tebbybabes]

Ok, I've run into an embarrassing snag. Bike work has been stopped for now. Turns out I don't have a bottom bracket tool! [Can't do the screwdriver and hammer/pipe wrench trick like cup and cone bottom brackets.]

Anyway, the BB doesn't seem to be worn as it performs quite well ATM, neither is there any appreciable play. However, after reading all the suggestions, it does seem that its possible that the chain is rubbing on the inner cage of the FD under load. I've ridden it around a couple of blocks and have noticed that the noise appears when I'm loading the left pedals.

Oh and @Danny - I forgot to say that this is a brand new chain. And it is well lubed. Fact is, when I took off the stock shimano branded ones they felt alright. But when I fished the cheap KMC out of the box, whoa, it felt so 'supple' compared to the shimano's I just removed. Hard to describe, except I guess it just moves like crazy and the stock ones felt stiff compared to it.

[bychosis]

If its a cartridge BB there is no adjustment. If your BB is spinning smoothly and no play then that is unlikely to be the issue. My experience above was with a cup n cone BB

[Tebbybabes]

How flat should chainrings be? Should they be absolutely perfectly flat? (as in one perfect plane)

[colaiacw]

It may pay to check your chain length. If the chain is too short and it pulls the rear derailleur too much, the jockey wheels will be under stress and emit a grinding noise.

This could be possible, does the noise go away when you shift down to the next cog?.

BTW chainrings should be flat and have little or no wobble. Cheers.

[A_P]

top derailleur pulley too close to the larger sprockets perhaps.
B screw adjustment needed?

[Tebbybabes]

Again, much thanks for the suggestions. The chain length is all right. I did the Large-large +1 trick. Not surprisingly, it came out exactly the length of the stock chain.

I also increased the tension in the B-screw A LOT, just to see if would make a difference. It didn't. On a related note, I know its supposed to be as close as possible - but without touching it for better shifting... surprisingly, increasing the angle much beyond the optimum didn't degrade shifting performance for me. Go figure.

Anyway, I had a Eureka moment this afternoon. Took my cranks apart and noticed that when I put my chainrings down on my flat floor they weren't entirely flat. So I put them back on again and checked, they weren't true! It was a difference of only 2mm but that might actually explain the mysterious machinery noise.

I've straightened out bent chain ring teeth before on other bikes because they were visibly out of whack but I have no idea how to true a chain ring. I don't even know how to get the leverage on it. Nor which part to bend.

I'm taking it to my LBS and watch him while he does it.

One strange thing though... the wobble of the chain ring on the floor was much less than the wobble on the bike... would that possibly have something to do with the axle on the BB or maybe even the spider?

[Tebbybabes]

Have just come back from the LBS, and he very very kindly trued my chain rings gratis. Who'd have thunk that it was actually a rather simple affair. LOL.

Anyway, unfortunately the noise didn't go away and since admittedly it is a very very faint noise, when the friendly owner/mechanic and I rode it around the parking lot, we couldn't hear it. (moderately trafficked area)

So I'm riding home and am aghast that along quiet stretches of road, I can still hear the sound. I stopped mid-ride and did my usual inspection but this time since I was clued in to the previously out-of-true chain ring I was looking at a different angle. This time I found it!!!

I had my FD really really low for best shifting and I noticed that my large chainring was extremely slightly out-of-true and out-of-round. Not enough to cause any issues with pedaling or shifting... but I finally noticed that some of the teeth get really really close to the OUTER cage when the FD is trimmed for the middle chainring largest sprocket during part of its revolution. I figured that loading the left pedal might cause enough flex to cause the large chainring teeth to actually hit the outer FD. Looking carefully, I actually noticed a sliver of shinier than the rest chrome right on the edge of the FD.

Suffice to say, I moved the FD a smidgen higher and now am blessed with a lovely quiet ride all around!

Whew!

Again thanks for the suggestions!