KBentley57

I've been dealing with an annoying issue ever since I put the 5800 group on my F5. It has a BB30, and I'm using the wheels mfg adapters to use the Shimano crank. The issue is, that the crank has what I consider to be a lot of runout. It's such that in the big ring trim position, the chain can just barely scrape the outer and inner part of the cage, when the derailleur is installed normally. (appx 2mm from the tallest chainring, parallel to outer ring, backing plate installed, used the plastic cable tool, followed the guide, ect...). To skirt this problem, I've raised the FD to about 4-5 mm above the tallest tooth when parallel and inline to the big ring. It works this way, and I can get it setup to have minimal to no rub in all gear combos. However, it bothers me. My thoughts are about the BB bearings not being perfectly aligned, or the adapters being minimally out of spec, or whatever. I don't doubt shimano's quality control, so I doubt it's the crank itself. Would one of the aftermarket adapters such as the Praxis, Wheels Mfg, KCNC, ect.. be worth trying? Anyone have a clever diagnostic trick to sort out where the problem actually lies?

Andrew R Stewart 

Most ring lateral run out is ring caused, assuming the spindle isn't loose in the bearings. So first recheck the BB and spindle. No end play, no slop that can be seen running from one crank arm/through the shell/to the other arm. No loose ring bolts. Then using the cage as an indicator, looking from above and down past the cage plate to the teeth, slowly spin the ring. I've even used a small straight edge to "extend" the cage plate to just overlap the large ring's teeth to further identify the run out.

To the best of my knowledge there is no stated acceptable run out spec. Instead it's always a question of "does the chain rub too much". Which is also dependent on the rider's strength. So one can't really say to a manufacturer that a ring is wrong/bad. The time honored solution to a "bent" ring is to true it.

various methods exist but they all are the same thing. Pressing/prying/bending the ring in the location you think needs to be corrected. The various sections of the ring, the open stretches and those supported by the spider arms, make this attempt a widely ranging one. Prying tools like Crescent wrenches, caliper toe in tools, channel locks, pedal wrenches, large screwdrivers are common ones. BITD Bicycle Research made a prying tool with two different thickness slots. The modern rings with varying surfaces, thicknesses and lift pins make this job harder. When the DA carbon reinforced rings came out I wondered about their ability to be trued.

But all this is speculation. If your ft der cage height and rotation adjustments fix the problem I say you're good to go. If not you might seek help from a more experienced wrench. Andy.

KBentley57

I just reinstalled the crank a few minutes ago and checked a few things. Ring bolts are tight, preload cap is 'tight to snug' (no real indication of when it's just right here after-all) and the two left arm bolts are tight. No torque wrench on them, but from experience I can say they're tight enough and close enough to uniform. However, I did notice that I'm able to grab the opposing arms and move the crankset slightly, with a little click-like sound'. It's also visible enough that I can see the chain move from close to the inside, to close to the outside of the derailleur cage. I'm not sure if it indicates anything further, but when I rotate the crank backwards there's a definite little clunk emanating from the BB area at the same spot in each rotation; and it correlates well to the spot where the runout is at its worst.

Andrew R Stewart 

What condition were the bearings in with the spindle removed? Almost sounds like worn bearings and/or a lack of lube in them. You need to separate the bearing possible issues from any crank spider/ring ones. Andy.

KBentley57

I didn't remove the dust seals to check the actual balls of the bearings themselves, but they felt smooth enough from a quick finger spin. I've not opened them up since I bought the bike last fall, used but just barely. I'll pull the crank again and do a more thorough inspection. It doesn't seem like the lack of lube would account for the play though. What makes it harder to diagnose is the adapters between the crank and the bearings. I suppose I could pull the rings and lay them on a flat surface to check for uniformity as well.

Andrew R Stewart 

You should be able to detect play between the adaptors (that is enough to cause ring run out) easily enough. Besides the bearing's lube amount and free spin is there end play. Radial cartridge bearings really like some end play. Andy.