jimmuller 

I haven't been doing much bike work lately, nor even much riding or visiting BF. I've been out a few times this summer and we have taken the tandem out a few times. Been having trouble with the tandem's drive train. Time to do some investigation.

Do you see anything wrong here?


Time for new rings and chain (not installed yet). Ignore the dirty bits. I guess 15,000 miles will have an effect.


New tires too.

rumrunn6

was it exhibiting any symptoms, doc?

jimmuller 

Ah, yes. Skipping teeth when we pushed hard. (The Rear Admiral didn't like that.) We didn't have to push very hard and it was getting worse. I measured the chain. 12 inches covered just a bit more than 11 links!

Surprisingly, the new SRAM PC870 chain fresh out of the box was 56 outer links plus Quick Link, exactly the same as what the bike had. I expected it to be longer, with a few "extra" links I'd have to remove.

We don't use the granny ring all that much, which is why it looks okay.

Sir_Name 

It’s always a mixed bag when your chains grow up.

P!N20

The big ring teeth in the first image look hammered.

nlerner

I think a shark is missing its teeth.

Hondo6

My first thought on seeing the large chainring was, "Cue up the theme from Jaws." (smile)

momoman

Those links above “38 Sugino Japan” don’t look like they are fully engaging the teeth.

ThermionicScott 

While you're at it, that bar tape looks a little tired.

non-fixie 

Seeing it's mainly the teeth on the big ring that are worn, you guys must be real fast!

francophile 

I wouldn't rule out stuck pawl on freewheel or similar freewheel related slippage when under any load. I've had more cases of older, heavily- (or under-) trafficked freewheels causing slippage than worn rings. Easy to test for also - toss on another rear wheel with a known-good freewheel, or just swap on a known-good freewheel.

But sure, could be related to chain or ring wear.

jimmuller 

It's great when people gang up to tell you everything that is wrong.

Yes, the big ring teeth are hammered. The middle ring teeth are hammered pretty badly too. And the chain is badly stretched. That's the reason the chain isn't engaging the teeth fully, or the teeth not engaging the chain if you prefer to put it that way.

The bar tape is, um, experienced. You really think it should be replaced? Okay, if you say so...

Hobbiano 

What about the other chain, and rings? Are they worn also? And the freewheel may be (probably) toast too.

Bad Lag

You'll be needing this:
https://www.peterwhitecycles.com/tach.php#competition

You're welcome.

nlerner

No, you don't look at all worn, Jim.

jimmuller 

No, the other chain ("timing chain" in tandem parlance) and those rings are okay because I replaced them not so long ago. The freewheel is good because I replaced it no long ago with one Pastor Bob rebuilt.

Good suggestions though.

I tried to build this bike with as much original or original-like equipment as I could manage. That rear crank is a modern crank cut down to 140mm but the front is original Stronglight. That means I had a spare timing gear, since the rear crank is a modern arm with (I think) 74mm BCD. Eventually I'll have to switch over to newer stuff, I guess.

Road Fan

yes I do see something wrong. I think the front derailleur cage is too close to the teeth on the big ring. Campy at least says to set the height of the derailleur for 1.5 mm to 3 mm vertical clearance. I use this spec for all my bike setups. With the cage too low, the cage tries to drive the chain through the outer chainring rather than helping it sneak through.

Bad Lag

(deleted by author - posted in wrong thread).

Bad Lag

(deleted by author - posted in wrong thread).

thook

it may not be. if the front derailleur is inboard of the outer ring, the FD cage will look too close/set too low from a side view since the cage swings down while also moving inward

Road Fan

True dat, but Dr. Jim is looking for what we see. If it was mine, this is one of the reasons I’d put her up on the stand and make a better measurement. I just did this on Mrs. Road Fan’s Campy triple, and the big ring is flush with the derailleur outer plate when the chain is on the middle ring.

Hondo6

That's actually a pretty impressive statement about just how strong the original chain really was. That's over 6 1/2% elongation - which means a helluva lot of metal had been worn away and it still didn't break under load.

Was the original chain also SRAM?

jimmuller 

I see what you are saying, or rather hear what you are saying, or more accurately, see what you were typing, but @thook has it right. That proximity is merely an optical illusion, or rather optical delusion, from the perspective of the camera lens and from the downward movement angle of the cage when centered on the middle ring. FWIW, that FD is a new-ish Simplex triple. I don't know if it is still made but it was one of those new, seemingly retro models. It works extremely well. I bought it some time in the last decade to replace a true vintage Simplex triple which was never better than just okay. The new one made all our front shifting problems disappear. (They probably didn't go away but are hiding under the bed, and will jump out to haunt us at some random time in the future.)

Yes, the previous chain was SRAM PC870, like this one. A wear spec I had seen here in BF was to replace a chain at 10% elongation which seem like a lot, or else I totally misunderremember it, or rather misoverremember it. Of course, we are not a monster-masher team, total team weight under 275 lbs and I prefer to spin rather than mash. In any case, we are taking about 1 inch of metal spread over 112 pins and some of the wear might be on the sleeves instead of the pins. So it's a bunch, but apparently not yet fatal to the chain. (That chain got tossed into the recycle bin along with the rings.)

Now you wanna' talk about chains breaking, I once tried restoring a Motobecane Le Champion which came to me with all its original parts. So I assembled it for an easy test run around the block, got about 30 yards and the chain broke. I believe the chain was a SedisSport but perhaps not. Closer inspection showed that a third of the outer side plates had visible cracks. That chain got retired immediately. I eventually sold bike and parts to another BF member. The full restoration was bigger than I wanted to jump into.

Another chain-break episode involved the Masi when I was about 30 miles from my car into a planned 75 mile ride. Apparently the Quick Link broke or came apart. I couldn't find the missing half along the 50 yards of roadway where it must have happened. I wondered if there was a bike shop in the nearest town. After foot-pedaling the bike for a quarter mile I asked someone on a riding mower in his front yard. He said the guy who lived next door was an avid cyclist who had just come in from a ride so I should go ring his doorbell. Wow, talk about being in a lucky place and time. The guy did indeed have a chain tool I could use to splice my chain. He had to show me the chain ring from his older-days track bike. The teeth on that ring looked like needles. We had a great conversation and I made it safely back to the car. I have carried a spare Quick Link pair ever since. For want of a few grams of metal the ride was lost, but not the rider or the horse.

Hondo6

I think you might be misremembering it. Recommendations I've seen elsewhere say one should replace 5-10 speed chains at 0.75% elongation (Park Tool goes on to recommend replacement at 0.5% elongation for 11- or 12-speed and at 1% for single-speed). If a chain wears much farther than that, chances go up that you might also have to replace the freewheel/cassette and/or chainrings due to wear.

https://www.parktool.com/blog/repair...n-on-a-bicycle

If it took only a bit more than 11 links to measure 12" when under reasonable tension, you might have been a wee bit past 0.75% elongation. (smile)

Reminds me, I probably should use the chain wear checker before today's ride.

Classtime 

The freewheel was good when you got it from Pastor Bob, and you put it on the bike with an old chain, it might not be good anymore and could be where the chain is skipping. Worn rings for me cause stickyness not skipping.