New mountain tandem questions
In February we purchased a Ventana ECDM from Alex at MTBtandems.com. We've been loving the bike and have almost 80 hours on it since we bought it. I've always done my own work on our bikes, but we've never had a mountain tandem before. A few questions on things I'm noticing...
1) It seems that every other ride or so I have to torque down the captain's crank bolts. The stoker cranks need tightening maybe every 5 rides. We are using the FSA bottom brackets and square taper Middleburn tandem cranks that came with the bike. I'm not very familiar with square taper maintenance, but we find that the cranks will start to creak if I don't tighten them. Is this normal? Am I damaging the square taper by tightening all the time? Should I be removing and greasing on a regular basis?
2) We have a Hadley rear hub and the other day noticed the axle was slightly loose during a descent. I re-tightened the axle without a problem. I also removed the cassette to clean and noticed the freehub body is developing some minor grooves where the cassette sits. When tightened, the cassette still has a minimal amount of play (no different than I've seen on our other bikes). I've seen our single bikes develop this after a long time, but should I be concerned about this after only a few months?
Riding style -- we do a lot of climbing and push the tandem pretty hard on the descents. Live in southern California, so it's dry and dusty, but we had quite a muddy winter.
Thanks in advance!
Jeff & Katie
Maybe others will chime in on this one, but it's my understanding that square tapers should be clean and dry and assembled with NO lubricant.
Originally Posted by jeff^d
They should not be coming loose or making a lot of creaking noise; what torque spec. did Alex / Middleburn provide for the crank bolts? Also, did Alex indicate if Middleburn recommends grease or no grease on the tapers?
Originally Posted by jeff^d
Here's the deal, old-school suggests no grease be used on square tapers... but it really doesn't matter. They key is making sure that the bolts are torqued per the manufacturers spec. The only trick I know when it comes to square tapers on mountain tandems (we've used daVinci cranks with Shimano UN-72s since the late 90's on our Ventana tandems, and had Sugino Fuse 500's before that) is substituting Blue Loctite (242) for grease on the crank bolts IF you find your bolts are backing out. I'm not sure why it's a problem on the off-road tandems since it's never happened on our road tandems (which all use daVinci + square tapers), but the Loctite takes care of it.
Two other cautions:
1. You'll want to be sure that your 'creaking' noises aren't coming from the bottom brackets and eccentrics, as they tend to be the source far more often than the crank interface on new tandems. The Bushnell eccentric needs to be torqued to 90 in lbs per the manufacturer's instructions: http://www.bushnelltandems.com/eccinstructions.pdf. Nine times out of ten, if I have any noise coming from the cranks on our tandems, it's the eccentric that needs to be loosened and then retorqued, rarely if ever are the square tapers the source. I've also made a habit of installing my bottom brackets using Yellow Teflon tape on the threads... the same stuff you use when threading pipes that carry natural or propane gas. It makes for a nice, tight interface while also acting as an anti-seize product and has cured many a noisy bottom bracket cup.
2. You can permanently damage your square tapers if they come loose while you're riding. The press-fit only works so long as the flats of the tapers stay flat. If they get rounded by riding with loose cranks, it becomes very hard to get that press-fit to hold. Mind you, you'd need to be ignoring what were clearly loose cranks to do that kind of damage... but it bears mention if only to reinforce the need to make sure you're installing your Middleburn cranks to Middleburn's specs.
Both of the conditions you note are fairly normal for tandem hubs.
Originally Posted by jeff^d
All hubs that have adjustable bearing pre-load need to be tightened after about the first 100 miles, usually less with an off-road tandem given the massive torque loads that granny-gears help to generate when attached to two people moving 300lbs or more of bike and riders up a hill. I forgot to do this on our Chris King hubs and was quickly reminded that it needed attention when the engagement mechanism started to act-up: CK hubs have incredibly tight tolerances.
As for the indentations in the freehub, off hand I'd guess that Hadley uses a steel freehub for its tandem hubs. Even with steel, the torque generated by off-road tandem gearing will typically leave small indentations under the loose cogs that aren't attached to a spider. Most of the cassettes that we and others use on our off-road tandems have the four or five largest sprockets mounted to a carrier or machined spider, otherwise they'd mangle the freehub. Aluminum, hard-anodized aluminum and even titanium cassette freehubs will typically have far-more pronounced wear than the steel freehubs, which is why they aren't typically spec'd for tandems.
Not sure what you mean by "play" in the cassette. Once the lock ring is torqued down on a cassette that cassette should be rock solid. If not, then a spacer is needed between the largest sprocket and the freehub.
Last edited by TandemGeek; 05-17-10 at 03:22 PM.