Crank bolt bottoming out?

For discussions about bikes and equipment.
Derrek
Posts: 4
Joined: 4 May 2017, 12:32pm

Crank bolt bottoming out?

Postby Derrek » 4 May 2017, 12:45pm

Hi there, newbie alert.
I installed a JIS crank on an ISO spindle after careful consideration. This should have given me a chainline of 44 mm (although I have found conflicting information re the chainline of the crankset). However, the chainline turns out to be 48.5 mm. Does this mean that my crank bolt is bottoming out against the spindle? I then decided to install the chainring in inner position (by the way: do I assume correctly that this needs flipping the chainring bolts and the chainring?), so took off the crank. It pulled very easily (not ridden the bike in between), is this another sign that the bolt bottomed out? Any thoughts would be greatly appreciated.

Norman H
Posts: 958
Joined: 31 Jul 2011, 4:39pm

Re: Crank bolt bottoming out?

Postby Norman H » 4 May 2017, 1:53pm

In addition to the bolt bottoming on the end of the spindle, don't discount that the crank has bottomed out on the shoulders of the taper. You can usually check this visually for either condition. More easily on the non drive side.

If in any doubt don't ride it. You will irreversibly damage the crank.

Sheldon is usually good for this sort of thing.
Last edited by Norman H on 4 May 2017, 2:33pm, edited 1 time in total.

hamster
Posts: 3730
Joined: 2 Feb 2007, 12:42pm

Re: Crank bolt bottoming out?

Postby hamster » 4 May 2017, 2:23pm

What ISO bottom bracket did you use? Many of the Campagnolo ones are not symmetrical.

Derrek
Posts: 4
Joined: 4 May 2017, 12:32pm

Re: Crank bolt bottoming out?

Postby Derrek » 4 May 2017, 4:50pm

The bb is a Campagnolo (probably Veloce) 111 mm, more or less symmetrical. I end up with chainline very close to what you should expect with a JIS crank on a JIS spindle (crank is Sugino RD2R, which is usually listed as 45 mm outer ring with 103 mm spindle). My chainline calculation was based on Sheldon Brown writing " if you install a J.I.S. crank on an ISO spindle, it will wind up about 4.5 mm farther in than it would on a J.I.S spindle of the same length" .When I put the cranks on without bolt, it looks very similar to what I had (also JIS cranks, that was the work of my former LBS, but to be honest it worked). I added a picture.
The problem is that (more than one) other bb's used to turn themselves loose on the left side. My LBS was very vague about the cause (first it was down to italian bb tube threads, then it was down to those threads being worn, then he said that the threads were just fine and that he had installed 'a quality Italian bb'). So I want to avoid having to change the bb.
Image Attachments
IMG_6323.jpg
IMG_6321.jpg

Norman H
Posts: 958
Joined: 31 Jul 2011, 4:39pm

Re: Crank bolt bottoming out?

Postby Norman H » 4 May 2017, 6:40pm

I'm a bit confuse but if I've understood correctly and can summarize:

The Sugino crankset requires a JIS 103mm BB to give 45mm (measured to the outer ring)
Sheldon appears to agree with this listing 103mm & 42mm (measured conventionally)

You have an ISO 111mm BB which gives 48.5mm when you would be expecting about 4.5mm less.

Finally I'm assuming this is a single chainring set up.

Are both those photos taken after the crank has been correctly torqued down?

The thing that strikes me from looking at the photos is that if you were to achieve a 45mm chainline with that crankset, the crank arm would be close to fouling the BB. The more so if the photos were taken before the cranks were torqued down.

A photo of the non drive side crank might be more revealing. As mentioned up thread, its easier to see the shoulders of the taper on the non drive side.

User avatar
Gattonero
Posts: 3730
Joined: 31 Jan 2016, 1:35pm
Location: London

Re: Crank bolt bottoming out?

Postby Gattonero » 7 May 2017, 6:58am

Derrek wrote:The bb is a Campagnolo (probably Veloce) 111 mm, more or less symmetrical. I end up with chainline very close to what you should expect with a JIS crank on a JIS spindle (crank is Sugino RD2R, which is usually listed as 45 mm outer ring with 103 mm spindle). My chainline calculation was based on Sheldon Brown writing " if you install a J.I.S. crank on an ISO spindle, it will wind up about 4.5 mm farther in than it would on a J.I.S spindle of the same length" .When I put the cranks on without bolt, it looks very similar to what I had (also JIS cranks, that was the work of my former LBS, but to be honest it worked). I added a picture.
The problem is that (more than one) other bb's used to turn themselves loose on the left side. My LBS was very vague about the cause (first it was down to italian bb tube threads, then it was down to those threads being worn, then he said that the threads were just fine and that he had installed 'a quality Italian bb'). So I want to avoid having to change the bb.


If you are using the Sugino single-speed cranks, you will notice that the innermost part of the crank is machined, so to not interfere with the BB.
Campag BB's of that kind are fairly flat on the cups so there is a chance that the crank may touch the BB.
How old are the cranks, and what torque are you using to tighten them? And BTw, why not using the Sugino bb, is the frame ITA threaded?
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...

Brucey
Posts: 42310
Joined: 4 Jan 2012, 6:25pm

Re: Crank bolt bottoming out?

Postby Brucey » 7 May 2017, 7:44am

Derrek wrote:
The problem is that (more than one) other bb's used to turn themselves loose on the left side. My LBS was very vague about the cause (first it was down to italian bb tube threads, then it was down to those threads being worn, then he said that the threads were just fine and that he had installed 'a quality Italian bb'). So I want to avoid having to change the bb.


Italian-threaded BBs very often work themselves loose on the RHS (not the LHS) because they are (in defiance of the usual strictures concerning precession) RH threaded on both sides. Any BB can work loose on the LHS if the threads are damaged or the wrong BB is installed, or the correct BB is installed badly. At one time it was common practice to tap out damaged British threads to Italian size, simply because Italian threads are slightly larger. These days almost any BB can usually be secured well enough using threadlocking compound, if needs be.

Sheldon's comment regarding chainline when using an ISO spindle in a JIS crank ought really to have come with a plainer caveat "if the crank fits at all". IIRC there is a comment to this effect, to check that the back of the taper in the crank isn't interfering with the shoulders at the end of the taper.

Normal engineering practice is to check the quality of a potentially mismatched fit carefully, e.g. by bluing up one part and seeing where they really touch. If there is unwanted interference, sometimes one or other part can be modified to suit. However if this is not possible and the fit is bad (and it does sound as if it is bad BTW), you are going to have to change something; either change the BB to fit the crank or the crank to fit the BB.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Derrek
Posts: 4
Joined: 4 May 2017, 12:32pm

Re: Crank bolt bottoming out?

Postby Derrek » 8 May 2017, 4:23pm

Okay, thanks. I give in, once again. I'll take the bike to a local LBS and end up regretting it eventually as per usual. Interestingly, there was no way I could put the chainring in inner position, no matter how (could not tighten at least two crank bolts properly).

Brucey
Posts: 42310
Joined: 4 Jan 2012, 6:25pm

Re: Crank bolt bottoming out?

Postby Brucey » 8 May 2017, 8:08pm

chainring centres are usually spaced about 7 or 8mm apart or so; thus if the outside chainring position was yielding 48.5mm chainline, the inner position would give a chainline of about 40 or 41mm. You don't say what chainring you are trying to use, but very few frames will accept a chainring of any appreciable size at this chainline; a 39 or 42 might be OK if the chainstay is manipulated to suit, a larger chainring is often not possible.

BTW quite a few JIS BB units have a recess in both cups; it isn't unusual for the centre boss of a RH singlespeed crank to disappear into this recess when a narrow chainline is used, especially if the cranks are based on a double crankset design (everything has to come ~4mm inwards to get the chainline in the 'outer' position). As Gattonero says the campag BB unit doesn't lend itself to this sort of thing, being flat on the end with a thick flange to boot.

If you don't want a trip to the LBS, I'd suggest trying a few different double chainsets on the extant BB spindle; you might get lucky...

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

User avatar
recordacefromnew
Posts: 333
Joined: 21 Dec 2012, 3:17pm

Re: Crank bolt bottoming out?

Postby recordacefromnew » 9 May 2017, 3:30pm

Derrek wrote:My chainline calculation was based on Sheldon Brown writing " if you install a J.I.S. crank on an ISO spindle, it will wind up about 4.5 mm farther in than it would on a J.I.S spindle of the same length".


The main reason why you are getting a greater chainline than what your calculation suggests, is because while Sheldon's opinion on this is often quoted, it is wrong. See

https://forum.cyclinguk.org/viewtopic.php?t=77436&start=15#p801575

If you have a good vernier caliper, you might be able to explain the rest of the difference from careful measurements of the parts you have.

Keezx
Posts: 428
Joined: 20 Dec 2014, 10:44am
Location: The Netherlands

Re: Crank bolt bottoming out?

Postby Keezx » 9 May 2017, 6:08pm

My expirience too, JIS crank on ISO taper is 2-2,5 mm inward which works in 95 % of the cases and gives IMO generally a better fit than ISO-ISO.

Derrek
Posts: 4
Joined: 4 May 2017, 12:32pm

Re: Crank bolt bottoming out?

Postby Derrek » 12 May 2017, 5:37pm

Thanks, very informative. I have seen the Sugino RD2 cranks listed as having 47.5 mm chainline in outer position too, so maybe this could also account for something. Those cranks have a very sloppy finish (they look like having descended straight from hell).
For the sake of completeness: Chainring was a Sugino 130J (many RD2 cranks are fitted with them, the ring appears to be very nicely finished). Crank bolt and chainring bolts (single ring specific) were Sugino too. I have a feeling that I would have gotten away with it. Crank did not hit bb after tigthening crank bolts (still a small gap) and since there is a 7 mm gap (measured it) between ring in inner and outer position, I would have ended up with a very OK chainline of 41.5 mm. The frame can accept a 46 T chainring in inner position.
I finally gave up because I could not properly thighten the chainring bolts having the ring in inner position (no problem whatsoever with ring in outer position).
So, I took the bike to a local LBS with a good reputation, and as predicted, I ended up regretting it. When handed the bike back, I focused on the drive side - it looked ok -, it was only when I got home that I noticed that now I have two completely different crankarms. The right crank is sitting 12 mm closer to the frame than the left one.... Is that acceptable?

Keezx
Posts: 428
Joined: 20 Dec 2014, 10:44am
Location: The Netherlands

Re: Crank bolt bottoming out?

Postby Keezx » 15 May 2017, 4:17pm

Try it and you'll know, I bet most people won't notice it....

aljohn
Posts: 59
Joined: 7 Sep 2012, 9:39pm

Re: Crank bolt bottoming out?

Postby aljohn » 15 May 2017, 6:14pm

I doubt very much if you notice the difference when riding. I bought a Ribble frame to fit all the components from a Decathlon Btwin, which included Campag triple chainset. I automatically fitted the long end of the axle to the drive side and the inner ring was level with the small sprocket - 9 speed. Fitting it the other way the drive side all lined up perfectly, but the non drive side was 1/2" further out. Because I wanted to ride my 'new' bike I rode it like that with the intention of swapping the axle for
one that was the correct size....eventually..... I totally forgot all about it. That was in 2010, No problems riding it like that,so far..... all the best of luck.