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OK this must sounds stupid . . .

Old 10-29-20, 06:30 PM
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OK this must sounds stupid . . .

While adjusting the FD on my bikes, a slight out-of true on the chainrings of my lovely 1980 Fuji Gran Tourer SE, and 1974 Araya became apparent. This was while they were in a bike stand so I was able to observe this accurately. They appeared a little out when I restored them, but I have a bad habit of standing up on the pedals as I whizz around and am now wondering if this made things worse. I am 150 pounds and a fairly energetic when pedaling - using higher gear with more force. Might I have instead bent the axle? The worry of causing uneven wear on the BB bearings on these beautiful, original bikes is haunting me. And it'd really like to get ride of the once-per-revolution occasional scrape against the FD cage if it could at all be avoided.

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Old 10-29-20, 07:26 PM
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If there's no play in the BB, it could be the crank spider arms themselves. Older parts are often a bit off. Alloys were softer, castings not as rigorously maintained. During my time wrenching in shops, I was taught to whack it straight with a shop mallet. Try to hit it right about where the chainring bolt is (and be sure all of them are tight).
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Old 10-29-20, 08:30 PM
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Originally Posted by Albion View Post
The worry of causing uneven wear on the BB bearings on these beautiful, original bikes is haunting me.
Overhaul the bottom brackets.

really like to rid of the occasional scrape against the FD cage.
Rotate/move the fd clamp to the most efficient position. You can also try to bend the chainring(s), but that can be difficult.
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Old 10-29-20, 08:43 PM
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Originally Posted by Dylansbob View Post
If there's no play in the BB, it could be the crank spider arms themselves. Older parts are often a bit off. Alloys were softer, castings not as rigorously maintained. During my time wrenching in shops, I was taught to whack it straight with a shop mallet. Try to hit it right about where the chainring bolt is (and be sure all of them are tight).

It's not that hard to straighten with a wood or hard rubber mallet. Just don't get too agressive and do it a little at at time.
Done it on a number of my vintage rides.
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Old 10-29-20, 09:35 PM
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If both chainrings are slightly off by the same amount, I'll just remove the cranks and reorient them on the four spindle flats until I find a combo with the least wobble. So far, so good, on my bikes with square taper BBs.
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Old 10-29-20, 09:56 PM
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This has been covered a few times. It is often the adjusting of the spider's tabs with a big wrench that can make the corrections. However, these days, I find it easier to embrace the non-indexing feature of my front derailleurs and trim when necessary.

But...I am curious, how many millimeters out of plane do folks tolerate? As much as I might want to remove that annoying 1mm runout, it is a lot of-- remove, adjust, reassemble, test, remove,...
A hammer/mallet? I might give it a try.
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Old 10-29-20, 09:56 PM
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Most likely to have bent something while shifting under too much load small to big ring.
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Old 10-29-20, 09:58 PM
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Never seen a bent spindle outside of a violent crash.
bent pedals, bent spider, bent arm from whaps of some sort.
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Old 10-29-20, 10:31 PM
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^^^^^Agree, highly unlikely, too much force required even though you are 150lbs and hammer.
Best, Ben
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Old 10-30-20, 06:50 AM
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Originally Posted by canklecat View Post
If both chainrings are slightly off by the same amount, I'll just remove the cranks and reorient them on the four spindle flats until I find a combo with the least wobble. So far, so good, on my bikes with square taper BBs.
I'm old enough to have put on brand new Campy or Shimano cranksets over 50 years ago. Almost all of them have a bit of wobble the 1st time I installed them. They wobble more or less depending on which of the 4 possible squares of the BB axle they were on. Before I tightened them down, I looked for which of the 4 possible options the crank had on the BB that the rings wobbled the least. There was almost always some variance and some little wobble even on the best option.
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Old 10-30-20, 06:56 AM
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Originally Posted by Albion View Post
While adjusting the FD on my bikes, a slight out-of true on the chainrings of my lovely 1980 Fuji Gran Tourer SE, and 1974 Araya became apparent. This was while they were in a bike stand so I was able to observe this accurately. They appeared a little out when I restored them, but I have a bad habit of standing up on the pedals as I whizz around and am now wondering if this made things worse. I am 150 pounds and a fairly energetic when pedaling - using higher gear with more force. Might I have instead bent the axle? The worry of causing uneven wear on the BB bearings on these beautiful, original bikes is haunting me. And it'd really like to get ride of the once-per-revolution occasional scrape against the FD cage if it could at all be avoided.
If you only noticed on the stand it's fine.
​fine. If it doesn't show up when ridden it's not a problem. You could never bend the spindle no matter how strong you are.
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Old 10-30-20, 08:14 AM
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You BEAST!!!
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Old 10-30-20, 09:15 AM
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Thanks to all!

This is great! The scraping was despite adjustment with the bikes on a stand, and after a BB bearing service. It occurs only at extreme combinations (high front, low rear, and vice versa). Dylansbob first gave me the confidence to gently strike the side of the chainring, backed up by Doug - so, using a soft plastic-head deadblow hammer, with less force than would drive a brad into softwood, tapped the web on the chainring where the runout was the worst. It worked - on both bikes! Now down to about 1mm. Interestingly, the runout was worst at about the 10 o'clock position, not directly opposite the crankarm, scotching my theory that it was standing on the pedals that did it. And the runout was the same when R&R'ing the crankarms through 180 degrees, so no bent axle (phew!) Repechange made me think - I may well have used too much force changing up to the larger chainring. All this demonstrated to me how chainrings may be strong radially to pull the chain along, but they are far weaker axially.

The advice I have received here is invaluable - I'm glad to have a Bike Forums subscription. Than you all again!

Last edited by Albion; 10-30-20 at 03:12 PM.
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Old 10-30-20, 12:55 PM
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BITD we used the BFS (Biggest Frickin' Screwdriver) as a pry lever (never use the proper tool for the job!) to straighten the spiders on brand new bike builds. There was usually a bit of wobble that needed straightening. Wedge the end of the screwdriver between the crank and bb cup, align the shaft with the offending spider arm, and lever gently outwards. We're talking like a 2' long screwdriver. It was safer to do that than to try to smack the arms inward with a mallet, being that if you missed the mark with the mallet, even by just a little, the chances of damaging the rings was high, and though a mallet is softer than a hammer, it could still leave a mark. No bueno on a brand-new bike. As long as you aligned the screwdriver properly, never left a mark, no chance of damaging the rings.

Although triple cranks were tricky, at least the 110/74bcd ones, since the granny gear got in the way of the spider arm.

How much force was needed to straighten the arms was generally proportional to the quality level. Cheap steel cranks needed a lot of care and little force, it was easy to pry too far. Mid-level swaged Sugino Maxy cranks were medium, forged Mighty cranks took some effort.

We didn't get a lot of Campy in our shop, but the Campy cranks we saw were usually dead-on. The fit between rings/spider was also usually tighter. That said, they were considerably more expensive than the high-end Japanese cranks, so it made sense.
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Old 10-30-20, 01:23 PM
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I'm not in favor of hitting anything that involves bearings with a hammer or mallet. Ball bearings are point-contact and the peak shock load of the hammer strikes may print a little dimple or initiate a microcrack into the bearing race(s). It will likely still feel okay immediately after, but the seed of failure has been planted and an area of spalling initiated.
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Old 10-30-20, 03:21 PM
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I am getting a BFS from Harbor Freight - even easier than a deadblow hammer. Thank you so much for your kind reply, I cannot put a price on advice like this.
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Old 10-30-20, 03:26 PM
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Thanks for this, I am going to use the PCB Technique (I'm calling it that from now on, along with the Dylansbob Method).
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Old 10-31-20, 09:06 PM
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I always use a hammer, but first position a wooden dowel on the bolt as a drift, to allow the hammer force to impact accurately.

I advise against any prying or bending on the outer ring itself, as I have known the chainring mounting tabs to fracture from the resultant bending torque.
I've used the hammer and drift on literally hundreds of cranksets to true the rings, and never broke a tab using the 2 and 3lb hammers.

I do also endorse canklecat's approach of first repositioning the crankarm on the spindle at each of it's four 90-degree positions, I've achieved true-running rings many times this way without needing the hammer!

I haven't known either of the rings to go out of true from any shifting event, other than when the chain found itself between the chainstay and the inner ring (and which often bent the inner ring). I suppose it's possible, but the big ring will happily flex a good bit before taking a set out of true. I think that most out-of-tru big rings on road bikes got that way from getting bumped around in the garage or in the back of a vehicle, or from crashes. Probably half of the used bike's I've bought needed some attention in this area.
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