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Diagnosis Help Needed

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Diagnosis Help Needed

Old 07-30-20, 09:44 AM
  #1  
jethro00
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Diagnosis Help Needed

We have ridden our DaVinci Grand Junction just about every day since we bought it new in 2016. We started to feel/hear what appears to be the chain slipping on the front chain ring. I tightened the chain and it stopped for a number of days. But, it has reappeared and getting worse and the chain is plenty tight. It happened once or twice on our ride this morning. Do we just need to have the chain replaced or is it likely the chain ring is worn? I can post pics of the chain ring this weekend if that will help. What is the typical life expectancy of a chain ring? If the chain ring needs replacing, is this a DIY project or LBS project? Pre-Covid-19, we would run this by our LBS. But now, our LBS is busy assembling and selling new bikes and may not readily have time to work on something like this. Thanks.
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Old 07-30-20, 12:50 PM
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Not a Davinci Guy

If your timing chain is as tight as you say, the chainring would have to be worn down to nubs - almost smooth - before what you describe would happen - and that you would clearly see. Doesn't this bike have an independent pedaling system, as is typical for Davinci's? I don't know much about these kinds of systems, but it seems more likely to me that there is something going on with the independent pedaling system, that 'freewheel' between the two cranks, rather than the chainring being worn out. I mean, the front chainring could be worn out, but if it slipped the way you describe, it seems to me it would just as likely to throw the chain off as have it slip. The chain could also be worn, but worn enough to 'slip?'

Usually, putting on a new chainring, is a DIY project, though again, I don't know Davicini. It sounds like, with a few years of daily riding, it wouldn't hurt to put on a new chain, and maybe a new chainring.

Last edited by joeruge; 07-30-20 at 12:54 PM.
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Old 07-30-20, 12:58 PM
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Yes, it has ICS. The chain does not slip off. The issue arises when we are riding slowly and for some reason need to push hard on the pedals, like to cross in between traffic or starting up a hill. I will feel and hear something slip causing a hesitation in pedaling power.
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Old 07-30-20, 01:29 PM
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If one of the 3 chains themselves are not actually skipping on a chainring or a cog, I would look at your cassette freehub and the ICS double block freewheel mechanism as possible sources of the slippage.

We have enjoyed 19 years of trouble-free miles on two da Vinci Joint Ventures with only the usual regular maintenance.

Last edited by Joint Venture; 07-30-20 at 01:33 PM.
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Old 07-30-20, 03:56 PM
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Chainrings do not usually wear significantly. Most last for the lifetime of the bike. Cassettes and chains on the other hand do wear. "Everyday since 2016" sounds like worn chain and/or cassette, and the advice is usually to replace both together, if either one is found to be worn.
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Old 08-01-20, 02:52 PM
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Originally Posted by Leisesturm View Post
Chainrings do not usually wear significantly. Most last for the lifetime of the bike. Cassettes and chains on the other hand do wear. "Everyday since 2016" sounds like worn chain and/or cassette, and the advice is usually to replace both together, if either one is found to be worn.
I'm replying to this post because I replaced chainrings on two bikes recently. Both 36T middle rings on old 110 BCD cranks. Both bikes exhibited "crunchy" feel in the middle ring with a new chain. A new ring resolved the problem. And oftentimes (and in one of my cases) chainring wear is invisible. "Looking" at a chainring is useless to diagnose a chainring wear issue. You have to test ride it (and know chain replacement history of the bike in question). And while working on the wife's single mountain bike, I realize her middle ring may need replacing as well. Chainring wear manifests itself two ways: simply worn teeth (pulling edge wear) and chain suck. Now the latter is not an issue with timing chains, but it's a good indicator of wear in triple-chainring scenarios where visual chainring wear is not obvious.

So, "Chainrings do not usually wear significantly" is not really true. Chainrings wear far more slowly than cassettes, but they do wear. And four years on a tandem could easily wear out chainrings on a tandem. And the ICS system uses much smaller rings:

"ICS also allows a great range of gearing because the chainrings are half the size of those on conventional drives. The 12-, 18-, 24-, 30-tooth chainrings are equal to conventional 24-, 36-, 48-, 60-tooth chainrings."

Well, "half the size" translates to "twice the wear" since now half the chainring teeth are sharing chain loads. Additionally, a bike that hasn't had appropriate and regular chain replacement will wear out chainrings even faster. Timing chains can wear faster than main chains on tandems under many circumstances. (I spoke to a DuMond Tech rep at Interbike one year and he and I were discussing tandem timing chain wear. He said their tests indicated timing chain wear was THE issue with tandems.)

So the OP's symptoms point directly to chainring wear in my opinion. I'd at least inquire into what maintenance the bike has gotten over its four years, specifically chain replacement intervals. At the VERY least, I'd ask the OP to hold a ruler up to the chain and see how much "stretch" is observed. Since it's a timing chain, I'd suggest measuring 24" of chain to better reveal the amount of stretch. Just multiply the usual wear metrics by 2: So 1/8" wear (or more, obviously) in 24" means it's at "replace" stage. More than that means the rings have been suffering increased wear with every ride and skipping is a very real possibility if wear has gone off the charts and really affected chainring teeth.
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Old 08-02-20, 07:30 PM
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<<So the OP's symptoms point directly to chainring wear in my opinion. I'd at least inquire into what maintenance the bike has gotten over its four years, specifically chain replacement intervals.>>
There has been minimal maintenance. A LBS did a tune up once. A shifter has been replaced. I replace tires and tubes. I don't recall any chain replacement.

<<At the VERY least, I'd ask the OP to hold a ruler up to the chain and see how much "stretch" is observed. Since it's a timing chain, I'd suggest measuring 24" of chain to better reveal the amount of stretch. Just multiply the usual wear metrics by 2: So 1/8" wear (or more, obviously) in 24" means it's at "replace" stage. More than that means the rings have been suffering increased wear with every ride and skipping is a very real possibility if wear has gone off the charts and really affected chainring teeth.>>
I can put the bike on the bike stand and measure 24" of chain. What exactly am I calculating in that 24"?
I am wondering if I can replicate the issue with the bike on the stand so I can see what is happening. It only happened once in the 1hr 15 min ride this morning.
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Old 08-03-20, 05:26 AM
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After 4 years of daily riding, I would suggest you change the drive chain and cassette as a first resort. To check for chain “stretch,” measure 12” from one rivet. It should be exactly 12” to the next. If if it is only slightly more, the chain has “stretched” and should be replaced. Do similar for the sync chain, but use 24”.
Cassettes usually outlast chains by 2 or 3 to one, in spite of what your LBS might tell you, but in your case, I would change both. This is doable with the right, inexpensive tools: chain breaker, chain whip, adjustable wrench, cassette removal tool. You can see details on YouTube GCN How to change a bicycle cassette.
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Old 08-03-20, 09:06 AM
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New data emerged on the ride this morning. When I felt the chain slip, my stoker said she saw the chain come off of the front chain ring and then go back on. Thanks for the details on measuring chain stretch. I will try to put the bike on the stand this evening and measure the chains.
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Old 08-03-20, 04:24 PM
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If you ride any bike regularly you need to have a "Chain Wear Indicator". For literally a few bucks you can monitor your chains any time you want and know exactly the condition without guessing or waiting too long and damaging other components.
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Old 08-03-20, 04:26 PM
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Originally Posted by jethro00 View Post
<<So the OP's symptoms point directly to chainring wear in my opinion. I'd at least inquire into what maintenance the bike has gotten over its four years, specifically chain replacement intervals.>>
There has been minimal maintenance. A LBS did a tune up once. A shifter has been replaced. I replace tires and tubes. I don't recall any chain replacement.

<<At the VERY least, I'd ask the OP to hold a ruler up to the chain and see how much "stretch" is observed. Since it's a timing chain, I'd suggest measuring 24" of chain to better reveal the amount of stretch. Just multiply the usual wear metrics by 2: So 1/8" wear (or more, obviously) in 24" means it's at "replace" stage. More than that means the rings have been suffering increased wear with every ride and skipping is a very real possibility if wear has gone off the charts and really affected chainring teeth.>>
I can put the bike on the bike stand and measure 24" of chain. What exactly am I calculating in that 24"?
I am wondering if I can replicate the issue with the bike on the stand so I can see what is happening. It only happened once in the 1hr 15 min ride this morning.
The rule with chain wear and replacement is when there is 1/16" of stretch in a 12" length, it's time to replace. If you have over that, you have probably changed the teeth spacing on the smaller rear cogs and will have to replace the cassette. The whole goal is to replace your chain regularly so you do not prematurely wear out your cassette. And if chain wear gets extreme, then you also affect the chainrings. So a REALLY bad chain can result in needing to replace the cassette and middle chainring, or worse, small and large, too. But wearing a large ring takes a LOT of effort! But we're talking about a timing chain here, so we're worried about affecting chainring teeth spacing. I just threw in the rule about cassette wear since that's the usual concern.

Measuring the chain entails lining up your ruler EXACTLY at one spot on the chain at 0 or 1 (1 is easier), usually pin center or one edge, and then looking to see where 12" or 13" lines up by comparison. You're looking for 1/16" or less offset. But on a tandem timing chain, you have more to work with, so I recommend measuring 24" and seeing how much variance you have. It's easier to see and measure 1/8" than 1/16". Plus, with 1/8" being the threshold, it's easier to see how close to 1/8" wear you have (assuming your chain isn't beyond that). And for those of us over 50 years old, doubling the scale makes for much easier visual evaluation!

This is what you want to do: measure your chain to see stretch. If your stretch is below the threshold, replace it anyway. A four year old chain is due for replacement. If you're lucky, you just need a new chain and you'll have no issues with mesh at the cassette or chainrings. However, since you have skip, you'll probably end up replacing other stuff. If you're lucky, your chain "skip" is caused by another problem: bent chainring tooth, chainring, or tension problem. Or perhaps the chain has been twisted by a foreign object, causing your chain to skip. However, since your problem appears to occur under high pedal loads, this seems to be a chain/chainring wear problem.

With traditional timing chain tandems, there's a trick to prolonging chainring life: switch them! As it is now, each chainring is getting wear on one side. And with many timing chain set ups, you can reverse front and back. Doing this changes the edge of the chainring teeth doing the work. So one side of each ring tooth may be worn or mis-spaced, but the other side should be pristine. So if possible, you may be able to remedy your skipping problem by switching. Probably not with the ICS since you don't have two identical timing chainrings to swap. But I thought I'd throw that out there anyway.

Oh, and skipping under load CANNOT be replicated on the bike stand. Successful and effective chain replacement at the LBS entails thorough test ride and mashing all the gears to confirm no skip. There's no other way to check, unless you have a way to do a precise digital scan of all the cog teeth profiles. But that would cost a fortune! I know of no tool that measures this.

Stiff links in main chains also cause skipping, but due to other factors. If you have no idea what I'm talking about, get yourself to YouTube and you'll find ample instructional videos on chain issues and problems.

Good luck.

Last edited by LV2TNDM; 08-03-20 at 04:35 PM.
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Old 08-03-20, 07:40 PM
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Thanks for the detailed and helpful responses. We are 30+ years into riding tandems and on our third tandem. With our first tandem (Trailmate cruiser), we rode no more than once or twice a week and a LBS did maintenance. We bought our second tandem (Trek T900) from a LBS walking distance from where we live. So, that LBS did most maintenance, but not always cheerfully. They frequently had to order the parts and were less than enthusiastic about working on a large bike that took up a lot of room. So, I started doing some things myself. We bought our current tandem (DaVinci Grand Junction) from House of Tandems in Spring, TX. They are great, but not even in my state. I have a second LBS walking distance away. It's a one-man shop and he is good to deal with. But, he has a small shop and can only deal with a tandem when he's got the time and space. So, I have gradually tried to acquire tools and learn how to do more. We ride every day. So, things are going to wear. Unfortunately, I have limited time to work on our tandem. One of the reasons we keep our Trek T900 as a backup is for when it takes me a while to get to doing maintenance on the Grand Junction.

I will get a "Chain Wear Indicator" and start staying on top of when the chains need to be replaced. I didn't get to measuring the chains tonight. I'll try to get to that tomorrow and check out the front chain ring. The detailed information on what to check really helps.
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Old 08-03-20, 07:59 PM
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Would the Park Tool CC-3.2 Indicator be a good choice?
www.amazon.com/dp/B000BR3LHQ/ref=emc_b_5_t
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Old 08-03-20, 10:35 PM
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Originally Posted by jethro00 View Post
Would the Park Tool CC-3.2 Indicator be a good choice?

www.amazon.com/dp/B000BR3LHQ/ref=emc_b_5_t
Just get a steel ruler and measure carefully, in a good light, along 24 rivets, as per @LV2TNDM. If distance is more than 12 1/16 inches, replace the chain. I find it easier to measure from the front or back edge of the rivets rather than trying to place the zero of the ruler exactly in the middle of a rivet. The chain should be under some tension so use the top run of chain with an assistant putting some gentle pressure on a pedal. Make sure the ruler doesn't slide or creep as you shift your attention from one end to the other. The ruler needs to be longer than 12", otherwise it's hard to tell if it is just under 12 1/16 (OK) or just over. In a pinch you can measure to 23 rivets at 11 1/2 "


Alternatively, get a good caliper and open it to 130 mm. Insert the inside-measurement jaws into the spaces between outer links and butt the jaws up against the rollers. If you get more than 132.60 mm anywhere along the chain, it is worn. This is the principle of the Park tool but has the benefit of being a tool that you can use for all kinds of other measurements, and it gives you an actual number, rather than your having to take Park's word for it.

Last edited by conspiratemus1; 08-03-20 at 10:38 PM.
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Old 08-04-20, 06:10 AM
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Originally Posted by jethro00 View Post
Thanks for the detailed and helpful responses. We are 30+ years into riding tandems and on our third tandem. With our first tandem (Trailmate cruiser), we rode no more than once or twice a week and a LBS did maintenance. We bought our second tandem (Trek T900) from a LBS walking distance from where we live. So, that LBS did most maintenance, but not always cheerfully. They frequently had to order the parts and were less than enthusiastic about working on a large bike that took up a lot of room. So, I started doing some things myself. We bought our current tandem (DaVinci Grand Junction) from House of Tandems in Spring, TX. They are great, but not even in my state. I have a second LBS walking distance away. It's a one-man shop and he is good to deal with. But, he has a small shop and can only deal with a tandem when he's got the time and space. So, I have gradually tried to acquire tools and learn how to do more. We ride every day. So, things are going to wear. Unfortunately, I have limited time to work on our tandem. One of the reasons we keep our Trek T900 as a backup is for when it takes me a while to get to doing maintenance on the Grand Junction.

I will get a "Chain Wear Indicator" and start staying on top of when the chains need to be replaced. I didn't get to measuring the chains tonight. I'll try to get to that tomorrow and check out the front chain ring. The detailed information on what to check really helps.
Over the years I've scheduled our tandem repairs for later in the day and bring our tandem in at that time. My shop then works on it till done and I hang around and take it home. Helps them out to not have our giant bike taking up space. :-)
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Old 08-04-20, 09:09 AM
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Originally Posted by jethro00 View Post
Would the Park Tool CC-3.2 Indicator be a good choice?
www.amazon.com/dp/B000BR3LHQ/ref=emc_b_5_t
Yes.

Not completely fool proof, but very easy to use with less potential for error than manual methods.

The Park tool has two gauges: (1) worn, but has additional life, and (2) Replace now.

I try to play it safe and simply replace at the first wear line. Chains are cheap, cassettes and aggravation from poor shifting are not.

Good luck
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