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  1. #1
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    Overhauled drivetrain, now it is "crunchy". Ideas for debugging this?

    I'm working on overhauling a 1984 Trek 620. After cleaning/repacking adjustable BB, installing a new 7-speed freewheel, new derallieur, shifters, etc. Everything is back together but when pedaling under any kind of load, I hear "crunching" from somewhere. Can't hear it under light load (like using the granny hi gears) or on the bike stand.

    My suspects:

    1) BB-- I initially replaced the two caged bearings with loose ball bearings (9 each side). I put it all together and heard the crunching. But then I read that I should have used 11 bearings on each side, so I took it all apart again and re-did it with 11 loose bearings. The adjustment cup is pretty tight so that there is no knocking/play yet is smooth when turning it on the stand. On the other hand, this is my first attempt at rebuilding/repacking an adjustable BB.

    2) 7-speed freewheel. Bike originally had a 5-speed freewheel on this 126mm rear. The freewheel went on no problem with plenty of axle space, but to get enough chain clearance for the bottom cog, I ended up removing a spacer. It seems ok, but I haven't yet tried reverting to the 5-speed freewheel. Nonetheless, I hear crunching on any of bottom 3-4 cogs.

    3) 8-speed Ultegra bar-ends with 7-speed freewheel (with alternate derailleur routing). I eliminated this suspect by just using friction-mode shifting for now. Still crunchy. I'm hoping that once I solve the crunchy noise, that this combo might just shift ok even though the spacing isn't exact.

    4) KMC Z50 6-7-speed chain on a new Tiagra 9-speed derailleur. I tried the old Shimano 600 derailleur. Still crunchy. With 7-speed freewheel and 7-speed chain, seems like there shouldn't be a problem here even though it looks like there is very little space between the chain and the rear adjacent cogs.

    Tomorrow I guess I'll try the original freewheel and if I still hear the crunches, I guess I'll either go back to the caged BB bearings or go for a new cartridge BB.

    Anything else I'm missing?

  2. #2
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    Quote Originally Posted by ppg677 View Post
    I'm working on overhauling a 1984 Trek 620. After cleaning/repacking adjustable BB, installing a new 7-speed freewheel, new derallieur, shifters, etc. Everything is back together but when pedaling under any kind of load, I hear "crunching" from somewhere. Can't hear it under light load (like using the granny hi gears) or on the bike stand.

    My suspects:

    1) BB-- I initially replaced the two caged bearings with loose ball bearings (9 each side). I put it all together and heard the crunching. But then I read that I should have used 11 bearings on each side, so I took it all apart again and re-did it with 11 loose bearings. The adjustment cup is pretty tight so that there is no knocking/play yet is smooth when turning it on the stand. On the other hand, this is my first attempt at rebuilding/repacking an adjustable BB.

    2) 7-speed freewheel. Bike originally had a 5-speed freewheel on this 126mm rear. The freewheel went on no problem with plenty of axle space, but to get enough chain clearance for the bottom cog, I ended up removing a spacer. It seems ok, but I haven't yet tried reverting to the 5-speed freewheel. Nonetheless, I hear crunching on any of bottom 3-4 cogs.

    3) 8-speed Ultegra bar-ends with 7-speed freewheel (with alternate derailleur routing). I eliminated this suspect by just using friction-mode shifting for now. Still crunchy. I'm hoping that once I solve the crunchy noise, that this combo might just shift ok even though the spacing isn't exact.

    4) KMC Z50 6-7-speed chain on a new Tiagra 9-speed derailleur. I tried the old Shimano 600 derailleur. Still crunchy. With 7-speed freewheel and 7-speed chain, seems like there shouldn't be a problem here even though it looks like there is very little space between the chain and the rear adjacent cogs.

    Tomorrow I guess I'll try the original freewheel and if I still hear the crunches, I guess I'll either go back to the caged BB bearings or go for a new cartridge BB.

    Anything else I'm missing?
    I should note that the BB worked just fine before I overhauled it. I had the cranks off to change a chain-ring so thought I might as well repack/clean.

  3. #3
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    You did not mention replacing the chain. The chainrings might also be worn down.

  4. #4
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    Quote Originally Posted by peterw_diy View Post
    You did not mention replacing the chain. The chainrings might also be worn down.
    Chain has 100 miles on it (with the old cogs).

  5. #5
    Senior Member chriskmurray's Avatar
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    what about the chainrings? It may quite down after a little break in time.

  6. #6
    Senior Member oldbobcat's Avatar
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    Better try the first freewheel. You said it only crunches on the bottom 3 or 4 cogs with the new freewheel.

    When you moved spacers on the hub you may have messed up the wheel bearings. Does the rear wheel spin true and quietly?

  7. #7
    Senior Member mrrabbit's Avatar
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    Quote Originally Posted by ppg677 View Post
    I'm working on overhauling a 1984 Trek 620. After cleaning/repacking adjustable BB, installing a new 7-speed freewheel, new derallieur, shifters, etc. Everything is back together but when pedaling under any kind of load, I hear "crunching" from somewhere. Can't hear it under light load (like using the granny hi gears) or on the bike stand.

    My suspects:

    1) BB-- I initially replaced the two caged bearings with loose ball bearings (9 each side). I put it all together and heard the crunching. But then I read that I should have used 11 bearings on each side, so I took it all apart again and re-did it with 11 loose bearings. The adjustment cup is pretty tight so that there is no knocking/play yet is smooth when turning it on the stand. On the other hand, this is my first attempt at rebuilding/repacking an adjustable BB.

    2) 7-speed freewheel. Bike originally had a 5-speed freewheel on this 126mm rear. The freewheel went on no problem with plenty of axle space, but to get enough chain clearance for the bottom cog, I ended up removing a spacer. It seems ok, but I haven't yet tried reverting to the 5-speed freewheel. Nonetheless, I hear crunching on any of bottom 3-4 cogs.

    3) 8-speed Ultegra bar-ends with 7-speed freewheel (with alternate derailleur routing). I eliminated this suspect by just using friction-mode shifting for now. Still crunchy. I'm hoping that once I solve the crunchy noise, that this combo might just shift ok even though the spacing isn't exact.

    4) KMC Z50 6-7-speed chain on a new Tiagra 9-speed derailleur. I tried the old Shimano 600 derailleur. Still crunchy. With 7-speed freewheel and 7-speed chain, seems like there shouldn't be a problem here even though it looks like there is very little space between the chain and the rear adjacent cogs.

    Tomorrow I guess I'll try the original freewheel and if I still hear the crunches, I guess I'll either go back to the caged BB bearings or go for a new cartridge BB.

    Anything else I'm missing?
    Rear view pic of the hub, freewheel, and derailleur with the chain on the lowest cog would be nice.

    =8-)
    4000+ wheels built since 1984...

    Disclaimer:

    1. I do not claim to be an expert in bicycle mechanics despite my experience.
    2. I like anyone will comment in other areas.
    3. I do not own the preexisting concepts of DISH and ERD.
    4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
    5. My all time favorite book is:

    Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life

  8. #8
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    New chain with old freewheel will do this. The old freewheel's teeth may have been slightly reshaped by a stretched old chain. This happens most on the gears used most - which could explain why it's only a few of the gears playing up.

    If this is the case then a new freewheel will fix it.

    Indicative diagnosis would be to run the old chain if you still have it. If it's quiet with the old chain then it's unlikely to be the BB.

    You can only run a new chain on an old freewheel if you change the chain before the old one stretches beyond a certain point.

  9. #9
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    Here are pics. While this is supposedly a 7-speed chain (KMC Z50) with a 7-speed freewheel, it looks pretty tight such that the adjacent cog could be rubbing. Perhaps this is my problem?

    IMG_6162.jpgIMG_6163.jpgIMG_6164.jpgIMG_6165.jpg

  10. #10
    Senior Member mrrabbit's Avatar
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    Shimano HG-37 7-speed....

    That's a good choice of freewheel with a 31.9 width - which is right at the limit for a 126mm rear hub with freewheel stop to locknut dimension of 36mm. It looks like the chain also clears the the seat stay. I don't see any outright obvious indication of a misaligned derailleur hanger. I don't see a reason at this point to make any changes to the hub. However, if you did make spacer/locknut changes - then you do need to check the dish of the wheel.

    Other than checking the wheel to ensure that it is properly dished (rim centered between the lock nuts of the hub) and then re-centering the wheel between the chain stays,

    my guess here is that others are going run with this as a chain, freewheel, derailleur adjustment or perhaps a chainline issue.

    Nice photos...exactly what I needed!!!

    =8-)
    4000+ wheels built since 1984...

    Disclaimer:

    1. I do not claim to be an expert in bicycle mechanics despite my experience.
    2. I like anyone will comment in other areas.
    3. I do not own the preexisting concepts of DISH and ERD.
    4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
    5. My all time favorite book is:

    Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life

  11. #11
    Cabrőnista™ dprayvd's Avatar
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    Bro, douse that everloving thing in oil--and ride for a week at least....

    I'm not being glib: it's way dry.

  12. #12
    Cabrőnista™ dprayvd's Avatar
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    Tru dat mrrabbit@thephotos

  13. #13
    Cabrőnista™ dprayvd's Avatar
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    And, and...cassette action, it has its qualities.

  14. #14
    Senior Member mrrabbit's Avatar
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    OP:

    In your original post, you did mention removing a spacer on the hub. That alone suggests that a re-dishing of the wheel is required. Re-dish the wheel such that the rim is centered between the locknuts - done using a dishing tool or the flip flop method.

    Then re-install the wheel centered between the chainstays.

    That will ensure that both the crankset and the freewheel and hopefully the derailleur are ALL operating in parallel to the bicycle frame centerline.

    Then proceed with all else...

    =8-)

    Hopefully when you do this, you'll have smoother operation at the small chainring and one of the middle rear cogs.
    4000+ wheels built since 1984...

    Disclaimer:

    1. I do not claim to be an expert in bicycle mechanics despite my experience.
    2. I like anyone will comment in other areas.
    3. I do not own the preexisting concepts of DISH and ERD.
    4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
    5. My all time favorite book is:

    Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life

  15. #15
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    Quote Originally Posted by mrrabbit View Post
    OP:

    In your original post, you did mention removing a spacer on the hub. That alone suggests that a re-dishing of the wheel is required. Re-dish the wheel such that the rim is centered between the locknuts - done using a dishing tool or the flip flop method.

    Then re-install the wheel centered between the chainstays.

    That will ensure that both the crankset and the freewheel and hopefully the derailleur are ALL operating in parallel to the bicycle frame centerline.

    Then proceed with all else...

    =8-)

    Hopefully when you do this, you'll have smoother operation at the small chainring and one of the middle rear cogs.
    Thanks. I haven't checked dish with a truing stand (or tool), but wheel appears centered between the seat stays. I'll try to get a more accurate look at dish as soon as I procure a better tool.

    I do think this is coming from the rear freewheel area as when I turn things slowly and put my ear close to the freewheel, I'm definitely hearing the noise.

    I suspect it is possibly chain-line related or that maybe just a narrower chain would help.

  16. #16
    bike whisperer Kimmo's Avatar
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    No idea what's causing your crunching, if the chain isn't too wide... nasty sounds are the hardest things to diagnose over the net. If you shot some video, that might help.

    Quote Originally Posted by ppg677 View Post
    I'll try to get a more accurate look at dish as soon as I procure a better tool.
    You don't need a tool to dish your wheel quite accurately; put a zip tie around one of your stays and cut it so it rests against the rim, then pull the wheel and flip it.

    More accurate than a dish gauge that uses the axle ends rather than the locknut faces.

  17. #17
    Senior Member mrrabbit's Avatar
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    Quote Originally Posted by Kimmo View Post
    No idea what's causing your crunching, if the chain isn't too wide... nasty sounds are the hardest things to diagnose over the net. If you shot some video, that might help.



    You don't need a tool to dish your wheel quite accurately; put a zip tie around one of your stays and cut it so it rests against the rim, then pull the wheel and flip it.

    More accurate than a dish gauge that uses the axle ends rather than the locknut faces.
    Not quite...flip flop method gets it close...especially if you rotate the axle to catch any deviations in low quality axles, cones and lock nuts. Once you go quality, or CNC end caps - that little caveat tends to fade away.

    The dishing guage however avoids this as the arms rest on the rim - and you see the entire relation of the point to the axle entirely. Flip over and compare...done.

    I do about a dozen electric bike wheels per years, my dishing tool is almost useless with some of the hubs used.

    So I go the flip flop route. Set one way, rotate axle 360 - check the farthest and closest extent at which the rim is from the reference point...

    Flip...rotate axle again...check the farthest and closest extent at which the rim is from the point.

    If the extents are the same, dished - done. If not, got more work to do. I would say that I end up within a millimeter of being "dished".

    The dishing tool is much faster...but there's an even more important reminder. Buy quality hubs to begin with - you don't have to put up with such annoying caveats.

    =8-)

    I use the Park TS-2 so I have no way to guarantee that I've "snugged" a hub perfectly parallel in the arms. I bet someone here has a stand that does...

    =8-)
    Last edited by mrrabbit; 09-12-12 at 01:04 AM.
    4000+ wheels built since 1984...

    Disclaimer:

    1. I do not claim to be an expert in bicycle mechanics despite my experience.
    2. I like anyone will comment in other areas.
    3. I do not own the preexisting concepts of DISH and ERD.
    4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
    5. My all time favorite book is:

    Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life

  18. #18
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    Definitely caused by going to the 7-speed Hyperglide freewheel. I put the original 5-speed freewheel back and everything runs smooth. I'll have to check dish and/or try a narrower chain.

  19. #19
    Senior Member mrrabbit's Avatar
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    I'm thinking you should be able to stick with the 7-speed freewheel and get a chain that will work with it. According to the Shimano doc I'm viewing the chains are:

    CN-HG50, CN-HG40 and CN-UG51

    Yaban makes compatible chains for those and so should KMC / Taya

    =8-)

    In the archive is a post where someone asks if KMC Z50 = CN-HG50, but it didn't seem as though anyone directly answered the question.

    http://www.bikeforums.net/archive/in.../t-162570.html

    =8-)
    Last edited by mrrabbit; 09-12-12 at 10:41 PM.
    4000+ wheels built since 1984...

    Disclaimer:

    1. I do not claim to be an expert in bicycle mechanics despite my experience.
    2. I like anyone will comment in other areas.
    3. I do not own the preexisting concepts of DISH and ERD.
    4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
    5. My all time favorite book is:

    Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life

  20. #20
    Senior Member mrrabbit's Avatar
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    Just talked to a mechanic I deliver wheels to - and he prefers to not use the Z50 on Shimano 7-speed hyperglide freewheel - but rather the actual Shimano recommended chain - or a third party 7/8 speed or 8 speed chain.

    Yaban would be S52 and S8. Don't know the KMC or Taya models.

    =8-)
    4000+ wheels built since 1984...

    Disclaimer:

    1. I do not claim to be an expert in bicycle mechanics despite my experience.
    2. I like anyone will comment in other areas.
    3. I do not own the preexisting concepts of DISH and ERD.
    4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
    5. My all time favorite book is:

    Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life

  21. #21
    Senior Member zukahn1's Avatar
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    ) 7-speed freewheel. Bike originally had a 5-speed freewheel on this 126mm rear. The freewheel went on no problem with plenty of axle space, but to get enough chain clearance for the bottom cog, I ended up removing a spacer. It seems ok, but I haven't yet tried reverting to the 5-speed freewheel. Nonetheless, I hear crunching on any of bottom 3-4 cogs.

    3) 8-speed Ultegra bar-ends with 7-speed freewheel (with alternate derailleur routing). I eliminated this suspect by just using friction-mode shifting for now. Still crunchy. I'm hoping that once I solve the crunchy noise, that this combo might just shift ok even though the spacing isn't exact.
    I would suspect the combination of 8 speed shfiters and likely a cheaper lesser 7 speed freewheel are causing your problems. Your chain and front chain rings are fine. Switching to a good new or used 6 speed freewheel or wheel with a actual 8 speed cassette are likley needed to make things work.

  22. #22
    Senior Member mrrabbit's Avatar
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    Quote Originally Posted by zukahn1 View Post
    I would suspect the combination of 8 speed shfiters and likely a cheaper lesser 7 speed freewheel are causing your problems. Your chain and front chain rings are fine. Switching to a good new or used 6 speed freewheel or wheel with a actual 8 speed cassette are likley needed to make things work.
    friction-mode

    =8-)
    4000+ wheels built since 1984...

    Disclaimer:

    1. I do not claim to be an expert in bicycle mechanics despite my experience.
    2. I like anyone will comment in other areas.
    3. I do not own the preexisting concepts of DISH and ERD.
    4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
    5. My all time favorite book is:

    Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life

  23. #23
    Senior Member zukahn1's Avatar
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    Well the Op has said changing the freewheel back to old 5 makes things work. From experiance I have found 7 speed freewheels problematic even in fricrtion mode they just don't seem to play well with other stuff. I avoid 7 speed stuff on pretty much every bike I build up including free coop builds as a voluteer unless it works good and is complete and already on the bike.

  24. #24
    Senior Member mrrabbit's Avatar
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    Quote Originally Posted by zukahn1 View Post
    Well the Op has said changing the freewheel back to old 5 makes things work. From experiance I have found 7 speed freewheels problematic even in fricrtion mode they just don't seem to play well with other stuff. I avoid 7 speed stuff on pretty much every bike I build up including free coop builds as a voluteer unless it works good and is complete and already on the bike.
    That's because the KMC Z50 (6/7) is likely not the best chain - the Shimano or 7/8 speed is. Most here will say go Shimano and get it over with.

    And you will discover that many people have for 3 decades used 6 AND 7 speed freewheels in friction mode with the correct chain without issues. For me: $count = $count + 1;

    And you seem to be unaware that 7-speed has been the staple for entry level factory MTB, Comfort and Commuter bikes for over two decades. And it hasn't entirely lost that crown to 8 speed yet.

    =8-)
    4000+ wheels built since 1984...

    Disclaimer:

    1. I do not claim to be an expert in bicycle mechanics despite my experience.
    2. I like anyone will comment in other areas.
    3. I do not own the preexisting concepts of DISH and ERD.
    4. I will provide information as I always have to others that I believe will help them protect themselves from unscrupulous mechanics.
    5. My all time favorite book is:

    Kahane, Howard. Logic and Contemporary Rhetoric: The Use of Reason in Everyday Life

  25. #25
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    Quote Originally Posted by zukahn1 View Post
    I would suspect the combination of 8 speed shfiters and likely a cheaper lesser 7 speed freewheel are causing your problems. Your chain and front chain rings are fine. Switching to a good new or used 6 speed freewheel or wheel with a actual 8 speed cassette are likley needed to make things work.
    I gave the 7-speed freewheel a shot because it has a chance of working with indexed (bar end) shifters that I can actually find. I couldn't find any new 6/7-speed indexed shifters, but I read that with alternate cable routing, that the Ultegra 8-speed has a chance of working with the 7-speed freewheel and I was able to purchase those Ultegra bar-ends new for a reasonable $75 price tag.

    If it doesn't shift well enough, my options are to stick with friction-mode or just rebuild with an 8-speed cassette (and new hub).

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