Damaged cassette when chain at 0,75% Wear

[mtbfreak]

I read through this thread "Chain Replacement on MTB" https://www.bikehub.co.za/forum_posts.asp?TID=51384&KW=chain

and decided to buy a new chain and try the rotation of 2 chains. I currently have 450km (offroad only) on the chain (SRAM 971) and Cluster (SRAM PG980). I thought that this is a good time to try this as the current chain should not be close to the 12 1/8" mark right now (as detailed in this thread: Everything about chains: https://www.bikehub.co.za/forum_posts.asp?TID=43797&KW=everything+about+chains&PID=688598#688598 , and even if the current chain is ready to be replaced, I'll perform the rotation using two new chains, because the cluster should be fine after ony 450km.

 

So I bought a new chain and after installation took it for a Majik ride. The chain started to skip on the first ascent, and as no adjustment could be made to resolve the skipping, lead me to inspect the cluster closely. The cluster now had some nice indentations on the teeth and is basically stuffed.

 

Close up of the offending teeth:

 

I measured the old chain with a ParkTool CC3 chain checker and the 0,75% wear indicator just fit (a really tight fit;), I measured with a ruler over 24 teeth: 306.8mm. I measured with a vernier over 12 teeth: 153,05mm; which equates to 306,10 over 24 teeth.

 

Tool	Measurement	# links	Measurement extrapolated to 24 links
Base (new) [Acc to diagram]	304,80	24	304,80
Base (0,52% wear i.e. 12 1/16")	306,39	24	306,39
Base (1,04% wear i.e. 12 1/8")	307,98	24	307,98
ParkTool CC3 (new)	127,00	10	304,80
ParkTool CC3 (0,75% wear)	127,95	10	307,09
ParkTool CC3 (1% wear)	128,27	10	307,85
Actual Measurement
Vernier	153,05	12	306,10
Ruler		24	306,80

 

My measurement using 3 methods, yielded an acceptable time to replace the chain and cluster wear should not have been significant. However my cluster is clearly damaged and after 450km, I dont believe this should have happenned. By my reckoning, I should have had a minimum of 0,89mm chain wear remaining before cluster damage (307,98-307,09).

 

I have treated my chain well, cleaned at least every second ride, and if it was muddy, it was cleaned after every ride (sometimes with parafin, most times with clean green and a brush) before I cleaned myself.

I understand that the extra weight I carry causes accelerated wear, but the cluster wear is the concern.

 

I have since changed my cluster to match the new chain (15km used on old cluster). A new chain will follow for the first rotation.

 

Was the first cluster of inferior quality?

Was the cluster damaged by the skill level of the rider?

Can I expect the same to happen in the future?

Is the measurement of 12 1/16" still valid or should this be shorter?

 

 

 

 

 

 

mtbfreak2009-06-26 12:33:57

[mtbfreak]

mtbfreak2009-06-26 12:25:00

[Thug]

I'm no expert but that cluster looks normal to me.

 

The PG 980 is a top end cluster and would definitely not wear out after 450 km.

 

 

 

[mtbfreak]

That's what I thought, but if you look closely at the close up, you can see the metal of the teeth folded back. This is especially prevalant on the middle section of the cluster (my favorite gears) i.e. 17, 20 & 23...and that's where it skips the worst under climbing load

[Johan Bornman]

Firstly, dump the chain measurement tool, it is rubbish. Get a ruler with inch increments.

 

Secondly, it is perfectly plausible for a cassette to be worn out after 450 km. Not only chain length, but also environmental conditions wear down a sprocket. If you're riding in gritty stuff you cannot expect a cassette to last as long as one used on the road in clean conditions and enjoying a good bath every so often.

 

Thirdly, that cassette was clearly damaged by a worn chain. The fact that the distorted sections are so high up on the teeth shows that the chain was out of pitch.

 

MTB riding is an extremely hostile envirnment for chains and cassettes and is hard on equipent. 

 

The 2 chain rotation ploy has nothing to do with sprocket life, it is a convenience issue.

 

Join the white socks brigade, its cheaper.

  

BTW: 2mm is about 1/6th of an inch, way over the wear limit. (Your chain ws 2mm longer over 12 inches).

 

 

Johan Bornman2009-06-28 12:00:11

[mtbfreak]

ok, thanks. So the moral of the story is that when the chain gets to 12 1/16th" the cassette is most likely on it's last...and that I need to save all my money for a new cluster and chain every few months... 

[Cliffhanger]

I have done almost 4000 km on the same chain and cluster. Do you often stand and climb? Do you clean the WHOLE drivetrain properly all the time?

 

 

 

What chain are you using? Maybe you had a Friday chain...

 

 

 

Unfortunately the cluster is a goner..

[mtbfreak]

Do you often stand and climb? Nope

 

Do you clean the WHOLE drivetrain properly all the time? Yep, two brushes, and the elastic part of old undies ;o)

What chain are you using? SRAM 971

 

Maybe you had a Friday chain... or a Monday chain

[Cliffhanger]

yea, it is sad but you are in for a new cluster. You can always use this cluster for a training wheel on a trainer

[Bike Mob]

What would happen if you filed the burred back edges flat again Johann?

 

My cassette is looking the same and my chain is fairly new. Casette has had about 1500-2000km.

[Cliffhanger]

What would happen if you filed the burred back edges flat again Johann?

 

?

 

My cassette is looking the same and my chain is fairly new. Casette has had about 1500-2000km.

 

 

 

It will more than likely skip while riding...as the teeth on the cluster will not longer "grip" the chain

[Johan Bornman]

ok' date=' thanks. So the moral of the story is that when the chain gets to 12 1/16th" the cassette is most likely on it's last...and that I need to save all my money for a new cluster and chain every few months... [/quote']

 

No.

 

12 1/16th is when you replace the chain. Once you've replaced X-numberr of chains at or before this point, you'll have to eventually replace the cassette. We've had people here who logged their chain and cassette replacement carefully and got up to five (IIRC) chains per cassette.

 

What we're dealing with here is an exception of sorts. If all is what it seems, then we most likely have a few sprockets of which the case hardening was faulty....or extremely gritty conditions.

 

 

[Johan Bornman]

What would happen if you filed the burred back edges flat again Johann?

 

My cassette is looking the same and my chain is fairly new. Casette has had about 1500-2000km.

It will more than likely skip while riding...as the teeth on the cluster will not longer "grip" the chain

 

No.  Frictional retention has nothing to do with chain/sp[rocket engagement.

 

[Bike Mob]

So what will happen then?

[Johan Bornman]

What would happen if you filed the burred back edges flat again Johann?

 

My cassette is looking the same and my chain is fairly new. Casette has had about 1500-2000km.

 

Nothing would improve or worsen. The burrs don't interfere with anything. They are an indication though, that perhaps the cassette wasn't case-hardened. Normally you don't get burrs but a very definite 90-degree interface honed perfectly through wear.

 

These burrs are usually present on chainrings that have worn thin from cross-chaining and are then unable to resist the chain pressure.

 

[Shebeen]

BTW: 2mm is about 1/6th of an inch' date=' way over the wear limit. (Your chain ws 2mm longer over 12 inches). 

 

[/quote']

ok, i was born in the 80's so have fundamental problems working this fraction stuff out.

 

bare with me.

 

1 inch  = ~25.4mm, so 1/12 inch = ~2mm, not so?

 

okay, now to put 12 +1/16th inches into the real world = >306.3875mm

and since i have my calculator out and have mastered the in=>cm conversion function 12 + 1/8th inch = 307.975mm

 

I do like the way you took one of those free builder's whorehouse paper rulers, but i have found them to be inaccurate before  (accoring to my Stanley) so be careful.

shebeen2009-06-29 01:46:38