New life for an old Mercian

[fenderbender]

That is what I thought until I read this article by Sheldon "It as never given me a lick of trouble" Brown. Velo Orange explanation goes a bit further and blast the myth that JIS and ISO have different angles. Something I was told and believed in many years ago! Without knowing I have used a JIS bb with an old Stronglight triple crank set for many years without any issues.

[Mick F]

Yes, the angles are the same.
It's the length that is the issue.

One is too short for the other, and I can't remember which is which.

If you have a short BB taper, it doesn't mate very well with the "long" C/S taper and can cause problems. The other way round is absolutely fine.

This is another place where SB is not always correct.

[Mick F]

And another thing ......

"typically the crank will be installed once, and will stay in place unless/until the bottom bracket needs to be replaced."

Come on, is anyone ever going to tell me that to leave a BB in place for years and years and years and years is a good thing? Would anyone in their right mind want to leave a modern BB in place until it needs to be replaced?

Sorry SB.
I don't agree with you - again.

[fenderbender]

Yes, the angles are the same.
It's the length that is the issue.

One is too short for the other, and I can't remember which is which.

If you have a short BB taper, it doesn't mate very well with the "long" C/S taper and can cause problems. The other way round is absolutely fine.

This is another place where SB is not always correct.

Sorry, but I forgot to post a link to the VO article. They don't recommend using a JIS crank on an ISO witch fits well with my own experience. I to have issues with some of Sheldon's views like that of using neatsfoot oil to break in leather saddles.

[CREPELLO]

....a Shimano BB with a Campag Chainset. Is that ok to match JIS and ISO that way round?
Personally, I wouldn't mix them either way!

It's what I've done with my new King Of Mercia build. The chainline is perfect. Absolutely no problem for me.

[Mick F]

It's not the chainline I mean. Perhaps it's fine.

It's the taper length that's the problem.
(I can't remember which is which)

One taper isn't long enough for the other chainset. It means that there isn't enough contact area to make a good solid mating surface, so POSSIBLY in the end, you will damage the chainset.

Someone help me here! Which is long and which is short? JIS or ISO?

[fenderbender]

Mick, after all the trouble I've gone through digging up old links, the least you could do is click them!

[Mick F]

Oh Gawd!
Just sat down with a cuppa ........
Swept the chimney, cleaned up, vac'd the house, gimme a break!

(Back soon!)

[CREPELLO]

Just to add, that when I calculated the chainline, I reasoned that as I had a load of UN54 107mm BB's I'd be able to use it with the Record chainset which requires a 111mm ISO BB. The chainset just sits out 4 mm more on the UN54, ergo, perfect chainline.

For reference - ISO chainset mates with JIS BB = good
JIS chainset mates with ISO BB = it'll all end in tears

[Mick F]

Done some searching for info.
Thanks Crepello for clarifying!

Although they look similar they are very slightly different, they both use the same two degree taper, the main difference is in the actual length of the taper, the JIS version is slightly longer, so if you try and put a crank designed for a JIS BB onto an ISO shorter tapered BB which would happen if you use a Shimano Chainset onto a Campagnolo BB, then the crank may go to far up to the end of the taper, so you will be tightening the axle bolt against the axle, as apposed to the crank onto the axle taper, not such a problem vice versa of course as the crank depth will not reach the end of the taper; still not to be recommended.

And this from CTC "Bikes & Bits"

Axles and Cranks – 2000.03
A few years ago I had problems using Stronglight and TA cranks on FAG-type bottom-bracket units. In particular the left cranks easily came loose. This rounded the hole, ruining the crank so that no amount of tightening would make it fit properly again.

I noticed that these cranks did not fit so very far onto the spindle, the reason being that there are two different standards for their dimensions: ISO (International Standard) and JIS (Japanese Industry Standard). Both have the same taper angle but JIS is slightly fatter, so ISO cranks don’t slide on so far by as much as 5.3mm. The longer right-hand taper usually seems to be okay, but the left does not provide sufficient engagement for the crank. Hence it loosens.

Nobody told me that FAG spindles have JIS tapers. Not even the supplier, to whom I wrote when I came across this problem. (I suppose that some people may also have found that JIS cranks push too far onto ISO spindles.)

The answer is to stick to spindles supplied by the crank manufacturer. But be careful: check the spindle or the packet it comes in. Sachs once supplied an ISO crankset (made by Campagnolo) with a JIS spindle (from SKF). And currently Stronglight make ISO cranksets for road and JIS for mountain-bikes! The latter are not easy to come by in Britain, but their spindles are advertised in the CTC mag. These almost certainly have JIS tapers, which are bad news for ISO “Escapade”, “80” and “100” cranks.

The good news is that I have successfully fitted a TA crank, previously damaged by JIS loosening, onto the correct spindle. It seems thus to have found a new lease of life!
Steve Jackson – Albi, France



According to Sutherland’s Handbook, ISO crank on JIS spindle should not be a problem if the crank bolt is tightened sufficiently. Perhaps only the stronger and heavy riders amongst us need to worry about this.
Chris Juden

Hope that helps!!

[fenderbender]

Hope that helps!!

Helps who? Have another cuppa.

[maxwellhadley]

OP here! Remiss of me not have shown my baby off before, but you can see her for yourselves here: http://forum.ctc.org.uk/viewtopic.php?f=15&t=3832&start=735#p308774

Max