CYCLINGFORUM.COM - Where Cyclists Talk Tech --- Return To Home

 

    Register FAQ'sSearchProfileLog In / Log Out

 

****

cyclingforum.com ****

HOMECLUBS | SPONSORS | FEATURESPHOTO GALLERYTTF DONORS | SHOP FOR GEAR

Return to CyclingForum Home Page CYCLING TECH TALK FORUM
          View posts since last visit

New chain grabbing old chainring
 

Author Thread Post new topic Reply to topic
Nick Payne
Joined: 10 Jan 2004
Posts: 2455
Location: Canberra, Australia

11/22/19 10:31 PM

New chain grabbing old chainring

I just fitted a new chain on one of my bikes, as the old one was at about 0.3% wear, based on the length of 24 links under tension (I try to swap them when at a bit less than 0.5% wear). Anyway, with the new chain fitted, on the work-stand everything seemed fine, and taking it for a quick spin down the road, everything still seemed fine when just spinning easily, but when I put a bit of power in the pedals, it was quite noisy as I pushed each pedal down. When I shifted down to the small chainring, which was less worn than the large, no such problem under load.

After a bit of faffing around, and not having any success, I decided to fit a new chainring, as I had a spare in the same size, and doing that completely resolved the problem. Looking at the photos of the old chainring below, there's some slight hooking on the teeth, but I would have thought I could get another chain's worth of use out of it. Apparently not.

<a href='https://photos.google.com/share/AF1QipO9jQYgYLlFwewrkRKM40WR6adBa3SWVAShPQFUVwVj_jSbXoyhP0UDhtSoFs03xA?key=SW5CVmFWQmlucEJCMWhvMVgyS2ptb2NXZ1UyMWFR&source=ctrlq.org'><img src='https://lh3.googleusercontent.com/yG6-ebHcsZOFo1_oFC4fDYdRvXcUZ4k-I9HfPgOo9SQyKU0M9dyAGP2ygfimusblYOBCHISaNYYYVu9C3CVxpaZnsGlXN_4fWlp0lRNZchQZCVTw5-92Oofi4RiwZwAObmJD0Zn7MJI=w1200' /></a>

<a href='https://photos.google.com/share/AF1QipPm0cSwYw3J1Mfz0o8DhnhhDB4cTNIav9l2-c61h9cdmoM5wzIJrX6sshIfbJ_z-A?key=YktfNDRuZEUwQ29qTWo3V3NKb0x5NnZvREZBQ1FB&source=ctrlq.org'><img src='https://lh3.googleusercontent.com/niJYNf88s_XQllA6xb5EKHfexCXXLNDdKNWhv2gEk0bhBgox8tDHNhJ8zADgduf9ytQazQnAYX2aqpRSd0A6425WIXBMZ5wZBVMAO42bMnZBi_zO_2y4dDJks4NCPNyWQdF4CGIaG6A=w1200' /></a>

 Reply to topic    

Sparky
Joined: 08 Dec 2003
Posts: 17552
Location: Portland, OR

11/23/19 12:15 AM

I can see how a new or like new chain would cause that ring as worn as it looks to meld poorly.

 Reply to topic     Send e-mail

dan emery
Joined: 11 Jan 2004
Posts: 6312
Location: Maine

11/23/19 1:26 PM

Chain noise here too

But that was because the bike had been out in the rain and I forgot to oil the chain. Nothing makes you feel like a Fred like a dry, noisy chain.

 Reply to topic    

Sparky
Joined: 08 Dec 2003
Posts: 17552
Location: Portland, OR

11/23/19 7:08 PM

"makes you feel like a Fred like a dry, noisy chain."

And that was me today. [insert fred emoticon]

 Reply to topic     Send e-mail

dddd
Joined: 11 Jan 2004
Posts: 3285
Location: NorCal

11/23/19 10:08 PM

New chain on worn cogs causes the same occurrence at either the front or rear sprocket, but with different symptoms.

With a hooked tooth, the chain rollers occupy a more-advanced position on a worn rear sprocket, due to the missing metal.
On a chainring, the chain rollers occupy a retarded or less-advanced position along the toothed part of the ring.

But, the metal isn't usually missing near the tip of the tooth, and the rollers still have to fall between teeth during engagement, so the rollers will strike the less-worn tips of the teeth on their way to falling between teeth.

It gets worse as the load increases, as the chain elastically pulls slightly forward(rearward) from even it's already-advanced(retarded) position along the rear(front) sprocket, thus causing harder contact with the tips of the teeth.

At the front sprocket, as the chain rollers engage the teeth, the rollers impacting the teeth can be heard and can be felt as a rumble through the pedals as the chain's driving tension forces the rollers past the tips of the worn teeth.

But at the rear sprocket, there is only mere sprung chain tension trying to force the rollers into engagement between the teeth, so as the pedaling force increases, at some point a single roller will hang atop the tip of a tooth and prevent a series of several rollers from engaging at all, resulting in violent slippage followed by engagement as the now de-tensed chain once again resumes engaging the sprocket until the chain again reaches that critical tension.

The fix for either condition is to bevel away the protruding drive/driven-side corner at the tip of the tooth, roughly only a 1mm bevel at about a 35-40-degree angle to the driven edge of the tooth (where the "pocket" wear has formed). This simply lets the rollers follow their hinged arc into engagement without striking the tips of the teeth.

I've done this in minutes using a Dremel stone (without even removing the rear wheel from the bike) with complete success on many hurried occasions.

But on the alloy chainring, a file is the thing to use on the softer metal that would clog a grinding-stone surface.

The OP's pictured Middleburn chainring appears to be just a couple of swipes of a file from having every tooth restored to running quietly with a new chain.

I've probably repaired about 60-70 rear cogs and perhaps a dozen chainrings using the above techniques, and with about a 90% success rate.
A few different rear cogs didn't work out despite following up with a bit more grinding, for whatever reason. I suspect that with a single chain having perhaps worn the cog over a great range of chain stretch, that the wear pocket was bigger than it looked because the hook thus appeared less sharply defined. Somehow there were just a few like this that I couldn't quite fix.

Take a look at the small cog below, where the top tooth marked "ba" has been ground, perhaps just a bit more than I would normally cut. This on a cog that didn't need it, just a sample illustration!

[/i]

 Reply to topic    

Sparky
Joined: 08 Dec 2003
Posts: 17552
Location: Portland, OR

11/23/19 10:31 PM

To be clear, you mean the left side [tip] of the 'ba' tooth?

 Reply to topic     Send e-mail

Nick Payne
Joined: 10 Jan 2004
Posts: 2455
Location: Canberra, Australia

11/23/19 11:22 PM

@dddd - thanks, I'll give your suggestion a try for when I next swap a chain on a bike with a Middleburn crank - I have those cranks on three bikes.

 Reply to topic    

KerryIrons
Joined: 12 Jan 2004
Posts: 3018
Location: Midland, MI

11/24/19 10:32 AM

Wavey

That chain ring definitely looks worn out to me, though quite possibly dddd's trick with the file might revive it fully. Not with the same goal in mind, but I am always amazed how a few se=wipes of the rat tail file will make a chain saw chain SO much sharper.

 Reply to topic    

dddd
Joined: 11 Jan 2004
Posts: 3285
Location: NorCal

11/25/19 4:58 PM

"To be clear, you mean the left side [tip] of the 'ba' tooth?"

Yeah, sorry for the somewhat whited-out photo, attempting to show the bevel applied to the DRIVEN side of the tooth.

On the chainring, it would be the DRIVE side of the tooth, the top-right corner instead of the top-left corner.

With some of today's chainrings and cassettes being rather pricey, I thought that the time might be right to tune up rather than discard. I originally was trying to restore prized freewheels that were no longer in production when I did some analysis on the subject and came up with my fix.

 Reply to topic    


Return to CyclingForum Home Page CYCLING TECH TALK FORUM
           View New Threads Since My Last Visit VIEW THREADS SINCE MY LAST VISIT
           Start a New Thread

 Display posts from previous:   


  
Last Thread | Next Thread  >  

  
  

 


If you enjoy this site, please consider pledging your support

cyclingforum.com - where cyclists talk tech
Cycling TTF Rides Throughout The World

Cyclingforum is powered by SYNCRONICITY.NET in Denver, Colorado -

Powered by phpBB: Copyright 2006 phpBB Group | Custom phpCF Template by Syncronicity