Octalink to Hollowtech Conversion?

[BenDL]

In an old post JB wrote:

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So far, each Octalink failure I've come across was due to a Shimano oversight.

 

Shimano had two shots at this.

 

First it designed them so that there was no press-fit i.e. the

spline simply lined up, fitted in and was tightened. Unlike a square

taper that press-fits quite tightly.

 

A spline that doesn't press-fit has a tendency to cause what is

called an elastic backlach, a phenomena that destroys the splines on

the softer of the two materials. This just happens to be the crank,

which just happens to be the most expensive of the two materials.

 

It was very common on the crappiest car ever made by the British -

the MG and its ilk. They had spline-fit wheels with knock-on centre

nuts that looked like propellers. These continuously destroyed

themselves by backlash. This backlash then caused the retaining bolt to

loosen, which worsened the backlash.

 

On bicycles with Octalink, this was

particularly evident with goofy-footed riders. Goofy-footed means

right-footed, you'll descend with your right foot forwards rather than

the other 75% of the population that'll go left-foot forward.

Left-footedness is more prevalent than left-handedness (10%).

 

Shimano then went to the other extreme and redesigned their

splines by making them longer (which wasn't the problem in the first

place, press-fit was) and unfortunately making them blind, so that you

can't see them line up.

 

Because the second attempt was a press-fit, they were supposed to

be hard to torque down. Aluminium is soft and if the splines aren't

aligned, you're blissfully unaware that you're re-shaping the splines

whilst torqueing it to Shimano's spec.

 

Bad design. Period.

 

The ISIS consortium understood the problem and designed their splines right from day one.

 

Shimano created a mess whilst trying to fix the problem and at one

stage you needed a compatibility table to see what fits with what. It

was a mess.

 

They then abandoned the concept completely and opted for the

one-piece right crank and spindle, and a pinch-fit splined crank on the

left.

 

 

Therefore, don't blame yourself or the mechanic for the destroyed

crank. It is an accident waiting to happen. I suggest you go to a

different crank system now that you're in the market for a crank.

 

JB

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What needs to be done to convert from Octalink to the Hollowtech system?

 

CRC have a

Shimano LX Chainset HollowTech II M582

at R723, while my BB alone cost around R337 (R400 from LBS) so the conversion would make sense if it can be done easily while not sacrificing reliability.

 

(The Octalink has served me well, but is time to replace the BB & chainrings.)

 

 

 

 

 

[Johan Bornman]

Octalink and Hollowtech are two different things - technologies if you like.

 

Ocatlink is the way the (removable) crank fits onto the BB axle and Hollowtech is Shimano's trademark for cranks that are hollow inside. Don't confuse crank with BB axle. Both can be hollow or solid.

 

 

[Guest Big H]

I have a Octalink Hollowtech I crankset on our MTB Tandem. I had two failures on the BB so far. Both were at the back. It is still cheaper for me to replace the BB's than to upgrade to a different MTB tandem crankset. There is nothing wrong with the Hollowtech I crankset exept the horrid BB.