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Ally bike cranks

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Graham Williams 1116/09/2020 18:08:35
68 forum posts
40 photos

What's the general view on using Ally bike crank arms off mountain bikes to make con rods in model 'diesel' engines replacing HE 15 ?

Michael Gilligan16/09/2020 18:20:40
16422 forum posts
715 photos

If it’s a good spec of crank then it will most likely be forged [no pun intended] and excellent for the purpose.

... But, as with so many things, cheap tat is also available.


JasonB16/09/2020 18:20:55
18930 forum posts
2083 photos
1 articles

without knowing the grade of alloy it's hard to say and it could vary a lot between a set off a cheap £100 bike or a set of cranks alone costing several hundred.

Also if you are not fitting bushes the copper in 2014 is something you would want in a substitute alloy.

For the amount of work that can go into a conrod I'd rather start with known material.

Andy Gray 316/09/2020 19:49:41
24 forum posts
Posted by Graham Williams 11 on 16/09/2020 18:08:35:

What's the general view on using Ally bike crank arms off mountain bikes to make con rods in model 'diesel' engines replacing HE 15 ?

If they're decent cranks, they may well be hollow.

John Olsen16/09/2020 20:50:54
1093 forum posts
91 photos
1 articles

I sawed one open with the idea of using the material once. It turned out to be cast, and had so many blow holes and pores that you could almost say it was hollow. Naturally it was discarded!


Bazyle16/09/2020 21:03:48
5492 forum posts
207 photos

They can be quite tough. I have one from when someone ran into me sideways on a roundabout and it took the punishment bending by about 3 inches which would have been a double fracture and permanent limp if the car bumper had hit my leg. I keep thinking of bending it back to use with the pedal shaft as a mandrel handle.

Graham Williams 1117/09/2020 05:58:42
68 forum posts
40 photos

The crank arms that are on offer are off £800 + bikes that have been pounded round the lakes, step son lives there, but seems that there might be a risk. Think I'll try one in one of the rough looking AM25s I have and see if it holds up as a failure might not be to hard to take. Thanks for all your input. G

Bo'sun17/09/2020 08:50:22
211 forum posts

Might be worth a punt, but beware of metal fatigue in used crank arms. If you do try, stick with quality brands such as Shimano, Suntour, Race Face, Hope, etc.

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