Correcting Mega-9 Hollowtech Chain Line?

[Oracle]

Howdy farkin home/professional mechanics,

Noticed the other day that my chain line is not pefectly parallel to my frame so pulled my LX hollowtech II BB/crankset apart late last night to see whether I could simply swap the plastic spacers around and inspect/regrease threads whilst I was at it. I've a 68mm BB and currently have 2 spacers on Right (drive/chainwheel) side and 1 spacer on the Left (crankarm only) side and am using the hollow plastic tube in the BB.

The Chain Line as seen over-looking the bike in relation to the top tube (with chain on middle chainring and 5th rear cog) diverges quite obviously from the 5th rear cog to the middle chainrings of the bike, by ~1cm as an estimate from the two ends of the chain. This translates to the chain line being near parrallel whilst using 44 chain ring and 11 tooth rear cog, and very out of line when using 22 chain ring and 30 tooth rear cog.

Looking at the BB cups last night I realised the Left and Right cups were not identical length with the Right (chain rings side) being longer, to account for two spacers as compared with the Left (crank arm only side) with one spacer. Consequently I didn't swap the spacers over as the left side cup would not thread as deep into the BB (68mm) as the right side cup would if I swapped the plastic spacers. The casette is about as close to the frame as I would like it so can't really move it more than a few mm's.

So my question is can/should I:
(1) reverse the cups keeping the 3 plastic spacers and BB adapter (the hollow plastic tube), or
(2) remove the plastic adapter/tube and one or both spacers on the Right (drive) side cup, or
(3) just leave everthing as it is and not worry about running a non-parrallel chain line?
(4) anything/something I might have missed?

Cheers and thanks in advance!

 

[udi]

1) won't work as the thread orientations are different between left and right, and definitely don't do 2). Hollowtech II cranks rely on correct spacing for correct non-drive crank to spline contact area.

What you CAN safely do is move 1 spacer from say driveside to non-driveside, as long as you are running the correct number of spacers for your setup as per the manual instructions.

The thread contact area isn't really an issue, should be fine IMO. If you don't want to do that, then your only option is 3).

 

[spyderman_au]

IMO the time you want the chain to be straight is in top gear, which is where it is.

There is the most force going through the chain at this time so least amout of damage is being done.

 

[Oracle]

1) won't work as the thread orientations are different between left and right

Slaps myself in the head... can't believe I even posted that now I think about it!

Hollowtech II cranks rely on correct spacing for correct non-drive crank to spline contact area.

What you CAN safely do is move 1 spacer from say driveside to non-driveside, as long as you are running the correct number of spacers for your setup as per the manual instructions.

The thread contact area isn't really an issue, should be fine IMO. If you don't want to do that, then your only option is 3).

I did try this last night but I don't think the Right side (chainrings) threads weren't cut deep enough into the BB, so I'd likey strip the outer threads of that cup. I'll need to pull the BB/Crankset apart again and measure more accurately.

The cups not being equal lengths is what surprised/confused me and my bike bible (Zinn and the art of MTB maintenance) didn't really offer any great solutions that I could find at 2am. So I just put it all back as previous, i.e. as per Shimano instructions.

 

[Oracle]

IMO the time you want the chain to be straight is in top gear, which is where it is.

That's something I didn't consider - what do others think?

IMO the time you want the chain to be straight is in top gear, which is where it is.

There is the most force going through the chain at this time so least amout of damage is being done.

Wouldn't the most force/tension in the chain occur when I'm in low gear and climbing a monster hill, rather than when I'm in high gear on the road and cranking at a more even cadence? I'll have to think about this some more!

 

[Dicky]

Wouldn't the most force/tension in the chain occur when I'm in low gear and climbing a monster hill, rather than when I'm in high gear on the road and cranking at a more even cadence? I'll have to think about this some more!

I tend to agree with this line of thought.

A less-than-fantastic chainline should be set up in favour of the gear combination most stressful to the components - taking into account the most commonly used combinations.

There is much, much more torque available in the smallest chainring. Consider the diameter difference between the circle made by your pedal spindle (crank length x2) and the 44 tooth ring. Now substitute the diameter of the 22 tooth ring into the equation. BIG transfer gear difference.

Factor in that it results in less effective distribution of load (and thus more chain wear), with a less effective guidance system holding it in place (front mech vs rear mech), and thus more margin for error.

If you're a bit masochistic and go looking for things to climb, then I'd bring the driveside crank inboard a touch, maybe one spacer swapped to the non-drive side.
I only run the 32t/44t on my commuter / XC machine, have made this change, and there seems to be a touch less resistance in the 32t / largest cassette cog combo. No perceivable difference with top gear though.

Too many spacers to the non-drive side, and there may not be enough thread insertion of the BB cup to let you sleep at night.

The benefits of any change of this magnitude are not going to be all that obvious - for example, you may get 3000km out of a chain instead of 2700, just to pick some numbers, and with all other variables staying the same.




If only 5 bolt cranks were still the norm, with sensible 2x9 combinations i.e. 29/42... ohwell.











Just run 32:16 and be done with it.

 

[AngoXC]

I was very hesitant before I got these cranks for this very reason (I think i even PMed you Oracle about it...) But it all turned out fine. I think the difference probably lays with the fact i run an 8 Speed but other then that, our frames would be very similar.

 

[udi]

I just had a look on one of my own HT2 BB's, and the thread contact area is a little low with two of the 2.5mm spacers on the non-drive side. One thing that might be worth trying (although it may not make as noticeable a difference) is using 2x 1mm spacers instead of 1x 2.5mm spacer.

Then use one of each spacer on each side. That *is* reducing the required total spacing by 0.5mm - you might be able to buy 0.5mm spacers (not sure) and run one on the side of your preference to correct this. I think it'd be fine personally though.

Might help you get the right balance of chainline and thread contact area.

 

[k3n!f]

Does it actually effect your gears? Does the chain ever jump on the cassette?

I ran my Race Face ISIS cranks with a wider bb than it should have had which meant the chain got pulled off first gear on the cassette all the time. That was hell because your only in first on the back when the going gets steep...

All I'm saying is that if it ain't broke...

 

[Oracle]

I tend to agree with this line of thought.

A less-than-fantastic chainline should be set up in favour of the gear combination most stressful to the components - taking into account the most commonly used combinations.

Yeah, this is what I thought last week, and considering I couldn't find any relevant posts, thought I'd find out what other members have done.

If you're a bit masochistic and go looking for things to climb, then I'd bring the driveside crank inboard a touch, maybe one spacer swapped to the non-drive side.

Hills are a little hard to avoid here in Tassie, but on that note I certainly don't try to go around them, as I really don't mind a bit of a climb! Therefore, I do tend to use the full gear ratio on my bike.

If only 5 bolt cranks were still the norm, with sensible 2x9 combinations i.e. 29/42... ohwell.

I'll try riding using just 32/44 chainrings to see whether I can drop the inner/22 chainring. However, considering my current riding style/locations, don't think this is going to be a viable option for now. Might be easier if I was running 11-34 rather than 11-32 cassette?

Just run 32:16 and be done with it.

Not a chance

 

[Oracle]

Does it actually effect your gears? Does the chain ever jump on the cassette?

Doesn't affect gear changes and the chain doesn't jump, although the chain rubs on the front derailleur (when in 32 chainring and 11 or 30 cassette combinations) without playing with the gear tensioner of the front shifter (SRAM X-7) on the fly. And I have played extensively with the high/low adjustments and angle of the front derailleur (Shimano XT)..

All I'm saying is that if it ain't broke...

Not broken yet, but I can only assume that the chain rubbing on the front derailleur and/or being twisted more than it probably should (e.g. 32t chainring and 30t cassette) is going to cause excess wear on either the chain, cassette, front derailleur, chainrings or all parts more than they normally would?

But mostly I was just wondering if my setup was the norm and/or whether I should leave it or correct it depending on the response of other senior members!

 

[Dicky]

I'll try riding using just 32/44 chainrings to see whether I can drop the inner/22 chainring. However, considering my current riding style/locations, don't think this is going to be a viable option for now. Might be easier if I was running 11-32 rather than 11-30 cassette?

Yeah, a 11-32 or even 11-34 should make life a little easier.


My next rig is a 5" ish full squish trailbike... I'd love to run 28/38 up front again, but nobody makes 38t ramped chainrings anymore, except DMR, but D*rt W*rks don't bring them in.

Think it'll be 28/40 instead, as 36 is no fun.

 

[Oracle]

Yeah, a 11-32 or even 11-34 should make life a little easier.

Bugger, just realised I wrote wrong cassette ratio in my previous post (I've just edited it) that you quoted!

I currently have a PC990 11-32 cassette and should have written an 11-34 might be better if I were to drop the inner chainring.