Adjustable Cranks - Kooka mod ?

[trailguy]

Adjustable cranks would be great.

I'm thinking about milling and tapping a second set of pedal holes into my Kooka 170 DH cranks, making them adjustable between 170 and about 150mm using a pedal wrench. Problems might include:

-- heel catching: would extended crank end bump my heel upward pushing foot off pedal?
-- strength reduction: would 2nd holes weaken Kookas too much?

Any feedback? Does anyone have experience along these lines?

I like riding my 36" Coker and would value being able to switch between crank lengths of 170 and, say, 150. I have read a forum post on expensive telescoping cranks here (a bit pricey at over $400). I also spotted a reference to daVinci cranks here with 3 pedal holes and just got a quote for $200 (they look great, but still a bit pricey). At a bike shop I saw some kids BMX bikes with crank arms having 2 and 3 holes each, providing for growth, but they didn't offer the right lengths nor did they seem strong.

I like my Kookas and am planning on milling off the nub at the hub end. (Thanks for the post on this, George Barnes.) While modifying, I'm mulling the new pair of pedal holes. Proper alignment would obviously be critical. An experienced fabricator says he'll help if I decide on the new holes.

What do you think?

[johnfoss]

Kookas are really fat cranks, so should be good candidates for drilling an extra hole as you suggest. In my experience, cranks usually bend rather than breaking. So the question is if this new hole will cause the cranks to bend when you're cranking hard on the 170 holes.

Well, it would be interesting to find out. Only you can decide if you want to make the experiment.

The extra end of the crank going around has not been reported as a problem from anyone I've read about. Several people have tried pre-made multi-hole cranks or made their own. If your feet get bumped around on the pedals this could become a problem, but I don't think it will be a major issue.

[daino149]

Do you think it would be a good idea to drill and tap 1/2 inch pedal holes instead of 9/16? It would mean that you wouldn't be able to use the pedals, but it would mean drilling a smaller hole and weakening the cranks.

This is a product I was wondering if anyone has experience with

[TheObieOne3226]

Originally posted by daino149
Do you think it would be a good idea to drill and tap 1/2 inch pedal holes instead of 9/16? It would mean that you wouldn't be able to use the pedals, but it would mean drilling a smaller hole and weakening the cranks.

If you're going to do that and only using the cranks on a coker or something not uber hardcore, you might even consider retapping the cranks for a 1/2'' pedal hole. You may even be able to get a 1/16'' helicoil that makes a 1/2 out of 9/16 so you don't have to retap the cranks.

[trailguy]

Thanks guys.

John, I appreciate the input that suggests, "The extra end of the crank going around has not been reported as a problem..." That's helpful info, especially since I have never used cranks with multiple pedal holes. Regarding the strength, I'm far from hardcore and the most likely problem may be a Coker slammin' UPD. I think I will move forward with this Kooka modification and add another set of pedal holes.

High end, cranks at daVinci are tempting. Three pedal holes: 130, 150, & 170. Billet process reportedly produces a strong crank, with each piece being milled from a solid block of aluminum. I visited with Todd today; he said they need orders in by Thursday of this week, Feb. 3, 2005, if anyone wants a pair. To keep costs down, they apparently manufacture only once a year and that begins Friday. Uni crank pairs have proven to be slow movers, probably due to the stout price of $200. Still, I am tempted. It would be great to easily change crank lengths using a strong, well manufactured set.

Daino and Obie, I will consider the 1/2 inch size, as well as helicoil. I am guessing: is a helicoil is an insert threaded on both inside and outside that shrinks the pedal hole size?

Thanks again.

[TheObieOne3226]

Originally posted by trailguy
Daino and Obie, I will consider the 1/2 inch size, as well as helicoil. I am guessing: is a helicoil is an insert threaded on both inside and outside that shrinks the pedal hole size?

Correct. I'm actually not recommending the 1/2 pedal threads. I think Kooka's are beefy enough to take the extra 16th easily. But if you do wanna get all anal and do that you might as well get an extra set of half inch helicoils and not have to carry around or buy extra pedals.