Chain suck

[data]

Carlos, I'm still trying to figure out my chainsuck problem and I found something that I thought was weird but not sure. From the center of the frame it is 55mm to the end of the ds bb spindle, meaning, and measuring 58mm on the nds. Shouldn't that be 56.5 and 56.5 for a 113mm bb. I also have noticed that the low set screw on the fd is all the way out and I still have a very slight rub while in the 22f 32 rear. Let me know if I'm onto something here. Oh yea, it's of course an ES-70 bb.
Thanks!

[carlos]

what is the measurement of the center of the frame to the middle chainring with the cranks installed?

47.6 - 50mm is your target.

most frames, even hardtails have the bottom bracket shell pitched a bit to the NDS. this is to accommodate the front derailleur and chainrings and the profile of the cranks.

even on single speed frames, the BB shell is a bit pitched to the NDS to make room for the single ring and cranks.

sometimes, the low set screw can be turned all the way out. this ensures that, for your particular set up, the front der. swings all the way to the frame when dropping the chain from the middle ring to the small ring. mine is set up the same way.

to get rid of the rub, you can shift to the largest cog and the smallest chain ring. since we know that the Shimano BB has a flange, it can't be adjusted to get rid of the rub.

SOOOO, what you'll need to do, is, in that gearing mentioned above, turn the barrel adjuster on the left hand shifter till you get slight resistance.

take a 5 mm hex key and loosen the bolt for the frame clamp just enough so you can move the front derailleur on the seat tube. make sure that you don't change the height of the front der. you only want to change the angle of the cage.

next, push the tail end of the front der a few milimeters toward the frame. tighten the bolts and check for rub.

you don't want a ton of room between the chain and front der. cage. you only need to get rid of the chain noise.

repeat if the noise is still there. work in increments.

once you get rid of the noise, stay in the largest cog and shift to the middle ring.

if the der hesitates or doesn't make it, shift back to the small ring and turn the barrel adjuster ont he left shifter counter clock wise two whole turns.

try to shift to the middle again.

if it hesitates, shift back to the small ring.

turn the barrel adjuster on the left shifter out 2 or 3 more turns.

try shifting to the middle. keep turning the barrel on the left shifter until it makes it to the middle ring.

when you can get to the middle ring from the small, shift to a middle back cog and check to see that the chain shifts smoothly from one ring to the next.

if you encounter any other small problems, feel free to PM your number to me. front ders can be tricky.

[data]

Thanks again!! The advice is always great!

[data]

I guess I should have said that I was using the center of the bb shell to measure? Shouldn't it sit evenly in the middle of the bb shell?

[TechniKal]

It sounds like you could be running a 68mm bb in a frame that has a 73mm shell. The spindle would still be the right length, but your chainline would be off by 2.5mm on the drive side. 2.5mm off would be enough to cause problems with chain suck.

What frame are you using?

[carlos]

as you can see from the photos. the BB shell on any frame, even on a track bike, never sits in the center of the frame.

to check the chain line, you'll need to measure from the center of the seat tube out to the center of the middle ring.

on the BB, there is always more spindle protruding on the NDS side.

on Shimano BBs, remember that there is a flange on the DS that preven'ts adjustment toward the NDS. adjustment toward the DS is possible with the use of BB spacers.

as for the chainsuck. i'd say, get out the WD-40 and clean the chain.

remove the chainrings as well and clean them from both sides. note the position of the rings as you remove them so that the gates (the parts of the ring where the chain enters and exits a chainring) don't get misplaced.

clean the cassette as well if possible or if it's really dirty.

reinstall everything bone dry and lube.

you'll need three applications if it's wax based so make sure to wipe off the two initial applications by holding a rag under the chain while turning the cranks backwards.

also, and this is as important as keeping thengs well adjusted and cleaned.

-never shift under load. shift before you need to.
-even if there is not a substantial load on the cranks, too low a cadence can cause the chain to hesitate moving from one ring to the next and BAM, chainsuck.

also, Technikal has a good point. what is the width of the BB shell and that is the width of the BB cups?

[carlos]

.

[data]

The bb width is 68. I changed back to my old square tapered bb, what came with the bike, and had 3mm of chain clearance on the fd. With the splined I had less than 1. I put another splined in, exactly like the original splined ES70 68x113, and had 3mm of clearance. Put the other ES70 in and back to 1mm clearance??? I can see the difference in chain alignment just by looking at it. It now measures ~50mm from center of seat stay to middle ring.:confused: I'm tempted to change it again just to take pictures...

[TechniKal]

Sounds like a mislabed bb - or possibly a damaged one. The ds cup on shimano bb's is just a press-fit, so it's conceivable that it could have been knocked over a couple mm somewhere. However, my money is on it being a mislabled 73mm bb. That would give a perfect explaination to the strangeness you saw - and I'm pretty sure that the only difference in 68 & 73mm shimano bb is the offset of the spindle on the fixed ds cup.

[TechniKal]

On second thought, that's not correct. If you have a 68mm frame and put a 73mm bb in it, you'd have the opposite problem - the chainrings would be too close, not too far away...

[carlos]

the change in clearance has to do with the splined system.

while the BB and cranks have a stop, on initial install, the stops on the BB or cranks never touch. unless you get the cheater bar out.

also, chainlines change when you switch from square to splined.

50mm from seat tube to middle ring? you're good to go.

Technikal, mislabeled is possible. there were a ton a BBS that had no sticker on them. :(

also, the DS side cups on XT bbs are always fixed. unless it's an old bb.

the difference between 68mm and 73mm is the offset of the flange on the inside of the NDS cup AND the length of the bare NDS side and the DS flange.

wacky but true.

this just helps to sit the bearings as outboard as possible to prolong their life.

also, regardless of the shell width, the DS spindle still pokes out the same length. everything on the DS is fixed (assuming the BBS have the same spindle length but a different shell width) for splined stuff. the ammount the spindle that protrudes is the same.

on the NDS it's a whole different story.

[data]

Can you say Type "E" bb. Without enough spacers to set the chainline right. It is functioning perfect now with the correct bb in place.:cool:

[carlos]

ahhhhh......ha!

yeah, that'll screw it.

cool!

[been_jammin]

Carlos,

You have earned the honorary title of "Batman" - whom everyone should realize is easily the most intelligent and well-educated of all the superheroes.

Your explanation of bbs and advanced front derailleur adjustment reminded me of episodes of the original tv series, when Robin would say something like, "Holy bottom brackets, Batman! How did you know that he'd need to turn the barrel adjuster on the left shifter out 2 or 3 more turns?"

Batman replies, "It's simple to the logical and educated mind, the Shimano technical manual for 1997-2000 XT front derailleurs, clearly states..."

[Chongo loco]

Originally posted by carlos
the change in clearance has to do with the splined system.

while the BB and cranks have a stop, on initial install, the stops on the BB or cranks never touch. unless you get the cheater bar out.

also, chainlines change when you switch from square to splined.



Got a Q Carlos, I changed the OEM POS Bontrager cranks w/square BB to xt splined and the driveline moved way left. I pulled the BB first and got the same size 73x113...think I check it against the parts spec for the bike. Was I wrong in assuming the same size BB when switching square to splined?

I adjusted the stops on my F der to compensate, but when I get chainsuck from a few too many creekcrossing on long rides it has occasionally (twice) gotten wedged between the middle ring & chainstay. What happened was on a shift to the granny, a link got hung on the middle so when the crank rotated around it carried it right into the chainstay...got a fear of gouging my frame..pearls of wisdom from the master please :confused:

[carlos]

hey been, just saw this post. Batman? hmmm..... i'm not wearing any body suits though.

hey Chongo....got some questions.

8 or 9sp?

three rings or two?

what kinda bike?

is your front derailleur clamped to the seat tube or mounted on a plate to the BB?

as for keeping the BB size the same, i'd say it's possible that this is the culprit BUT, there are only two slpined BB spindle lengths.....113mm and 118mm so the choices are limited.

also, check your chainline as show in the photos below. it's measured from teh center of the seat tube to the center of the middle chainring. the measurement should be between 47.5 and 50mm.

all frames are different....not all frames work well with, say, a 73X113 (square spindle for this example) so some would buy a 73X110 and BAM-O! shifting like a dream. whatever that means. anyway, another example would be the cranks themselves. all after market cranks are different, throw in all sorts of different frames on the marrket and "suggested" BB spindle length can be tricky......even with shimano.

[Chongo loco]

It's a Fuel 98...came OEM w/Shimano UN-72 BB & Bontrager Race Cranks (9 sp). The POS Bontrager cranks w/Shimano chain & Der's never was smooth so I wasn't disappointed when I bent the spider on a rock :D Upgraded to Shimano ES-70 BB & XT cranks. It shifts like butta now...just a little worried about moving that chainline too close to the chainstays.

It's a clamp on f der, I'm pretty sure the angle's good if that's what you're thinking. Per Zinn it's at the correct angle or close to it ;) I guess if I think about it I probably moved the stop on the F. Der about 3 or 4mm so I should just switch to a 118 spindle length...didn't know they came that wide. thought 113 was the widest or is that just square :confused:

[carlos]

if the shifting is good on all rings you should be ok.

every frame is differnt so sometimes cranks sit in differnt spots on differnt frames.

naaaa....118 will make it shift as smooth as Jim Beam.

113 and 118 are what shimano sells for the cranks that take a splined BB.

in square you get 107, 110, 113, 118, 122.....and lots of others.

[Chongo loco]

I leave the mojo board yet again knowing a bit more ;) ...Thanks Carlos

[carlos]

anytime.