mrmb

How much slack measured in inches can you safely have?

I have a bike that has about 1in at the loose spot and about 1/8 in at the tight spot. That means push the upper portion of the chain as far up as I can, then let the chain relax. The chain travels 1in when I do this. There is no pushing down. I am mildly concerned by this.

I can not center the chainring to improve this. It is a campy record crank, campy record chainring and it is seemingly not centerable, not by the sheldon method or any other method I know. I am using a phil wood threaded cog, no centering to be done there either.

Matt Gaunt

You definitely don't want to get into the habit of having 1 inch of vertical movement due to slack at any point in the chain IMHO. I try not to run any more than 0.5 inches as I've had chains jump off with much less than an inch of slack in them. It's not fun.

In case it's useful, I run a Miche crank, Miche chainring and a Dura-Ace cog.

Good luck.

TimothyH

Something is wrong with the bike if the chain goes from 1" slack at the loosest point to 1/8" at the tightest point. Something is bent or not installed correctly.

The answer to the question isn't a number. If the chain can't be forced off the chainring or sprocket with a screwdriver then it is not too tight.

Do NOT try to force the chain off the ring or sprocket with your fingers.


-Tim-

Colnago Mixte

Biopace chainrings? Do they make Biopace cogs too?

mrmb

What do you advise I look into TimothyH?

cpach

This is pretty surprising with campy crank/chainring. Is the bb axle bent, or the bb loose?

If the chain is too tight it will destroy bearings in the hub and bb, of it's much too loose you risk derailing the chain. Can you do this? If not it's okay, except for more slop when backpacking.

Andrew R Stewart 

With some crank arms and ring combos there's a bit of clearance/slop with the ring bolts, the ring's bolt holes and the crank spider's ledge (that the ring sits on, if any). For minor out of round rings one can loosen the bolts slightly, rotate the crank so that the tight chain position is established and by grabbing the top and bottom run of the chain slightly shift the ring to be more on center. Not much correction is possible but sometimes it's enough to make a difference in the amount of tight to loose chain "tension".

As already mentioned by TimothyH said 7/8" of difference (1"-1/8") is a HUGE amount. I, too, wonder what's going on. Of course the first thing to revisit is the measurement. Andy

ThermionicScott 

Have you tried mounting the chainring in different orientations on the crank spider to see if a combination of tolerances are causing your issue? (IOW, perhaps mounting the chainring two bolt holes off in one direction will cause it to run better.)

If nothing else, you could find the spot where the chainring pulls the tightest and file down the bottom of one or two chainring tabs to allow the chainring to be centered. Might only take a pass or two of light filing to accomplish your goal.

To answer the question that was asked: I don't shoot for a particular number when setting my chain slack anymore. I just spin the cranks, and confirm that there is a tiny amount of chain droop the whole way around. I get behind the rear cog and sight down the top run of chain to do this. If it seems like there is excessive droop, I'll try tightening the chain a little and spinning the cranks again. If the chain ever pulls completely straight at some point, I know I've gone too far.

79pmooney

Sheldon Brown has a routine you can do to minimize this difference if you have play in the chainring bolt holes and sleeves. I've never gotten it to work. I suspect you need to get the bolts very tight is you make a practice of skip stops.

I have had good luck buying quality track cranksets (Sugino 75 running Sugino and Campy rings), decent cogs (I like the Eur-Asian ones; they run a little rough but seem pretty round and resistant to chain throw. I bought one Surly, a 17 and don't trust it to not throw a chain on a less than perfect setup. Of my three fix gearrs, only one has the Sugino 75. The others are 110 BCD Sugino road cranks with1/8" rings. On those bikes, I will only run the Eur-Asian cogs. (Its a little backwards. Because I don't trust it, that Surly gets "relegated" to my best bike. I run the $20 Isuzue 1/8" chains. Again, other chains run smoother, but those ones I trust to stay on.

I do a lot of hills and some very fast descents on my fix gears, Not as crazy as I was 30-40 years ago, but still ... I want gear that is still in place at the bottoms. Means far more to me than some mystical smoothness or silence.

Ben

mrmb

Well, I tried, tried and tried. Not going to happen. This thing is like a camshaft lobe and there is no centering this this. I machined the tabs a little and oversized the bolt holes a little to allow for some centering....................nothing.

Nothing is bent, there is no wobble to anything.

I just can not get chain tension to be even close to uniform. My other 4 bikes are perfect in this regard so I know what it takes to get good chainline and good uniform chain tension. It is just not going to happen.

I am moving on to a dura ace crank set, shimano bb and not sure on the chainring yet.

Anyone want a campy record crankset, phil wood bb and phil wood bb wrench? If so, pm me.