Drilling Extra Holes in Kooka Cranks??

[pdc]

I'm picking up some 175mm Kookas. Would it be feasible to drill another hole at 150mm and 125mm to make a variable crank? I didn't know if there were steel thread inserts needed or whether the threads are just in the aluminum. Anyone know? Thanks.

[Brian MacKenzie]

Darren Bedford sold me a set up 127's made from a set of 170 Kookas, he'd be the one to ask

[dale_dale]

dont see why not, u could use a tap to put the threads in aswell, Atleast that what u think the tools called it looks like a drill bit but is for putting threds in holes. My dad uses them a lot

[koebwil]

You could drill the hole and then put in helicoils.

[maestro8]

Originally Posted by pdc

I'm picking up some 175mm Kookas. Would it be feasible to drill another hole at 150mm and 125mm to make a variable crank?

It's possible, but which hole would you re-drill? It sounds like you're planning to drill multiple pedal mounting holes. Think about what will happen when you have the pedals in the 125mm holes... you'll have an extra 50+mm of aluminum swinging up from the back side of the pedal with every rotation of the crank. This could potentially turn your ankles into ground beef... unless you come up with some sort of endcap for the extra crank. Then you'll just get some bruises in a tender area

Originally Posted by pdc

I didn't know if there were steel thread inserts needed or whether the threads are just in the aluminum. Anyone know? Thanks.

You'll do fine threading the aluminum. Get a pair of 9/16" taps from your LBS (one left-hand, one right-hand) and a 33/64" drill and you're set. No helicoils needed.

[pdc]

Originally Posted by maestro8

Think about what will happen when you have the pedals in the 125mm holes... you'll have an extra 50+mm of aluminum swinging up from the back side of the pedal with every rotation of the crank. This could potentially turn your ankles into ground beef... unless you come up with some sort of endcap for the extra crank. Then you'll just get some bruises in a tender area

I'll be using these on a Coker, road riding. I dont think the extra length will be an issue.

[fexnix]

Just make shure the cranks doesn´t catch your pants while riding. Possible painful UPD I predict...

[wobblyjohn]

Like this?
http://bikesmithdesign.com/

Having a second hole between your pedals and the hub would make a weaker point in the crank. Whether it's weak enough to cause trouble, that's up to your judgement. Maybe try 150 first, the 125 holes can always be drilled and tapped later.

[theanswerisnt42]

If you plan to use the 175mm holes also you risk failure of the crank due to the amount of material missing from the inner hole, but if you only plan on useing the inner holes then you should be able to get by with it, though it would seem 125mm would be a better placement then 150mm due to the tapering of the material, with 125mm you have more material outside the hole. Although if you are very light on it you might still be able to use the outer hole without it failing...

[gerblefranklin]

Aluminum will wear somewhat fast if you are constantly removing and reinserting the pedals, but this shouldn't matter. Just grease them and if things get stripped, helicoil the thing.

You might want to get a spiral point (gun point) tap, which will drive the aluminum chips ahead of the tap. Remember to take the tapping slowly, being careful to assure squareness. Every 1/3 turn, back the tap up 3/4 of a turn to break the chip. Use a 2 or 3 flute tap, as these allow mroe chip clearance for stringy materials like aluminum. 3 flute is easier to drive in square initially.

Be very careful to make the threads parallel to the original threads, otherwise the crank will feel as if it's bent. I'd use a drillpress, jig bore, or milling machine for this. Hand drilling these things won't be fun. You can assure the location by centerpunching the location of the hole, preventing drill wander.

Good luck. It shouldn't weaken the cranks too much, but the point Fexnix and Maestro brought up seems pretty important.

[john_childs]

I'll second the recommendation for Darren Bedford. He has the taps to be able to do it. Otherwise a good local bike shop may also have the necessary taps. The left crank requires a reverse threaded tap and only a bike shop is likely to have it.

The Kooka cranks are made from a good quality aluminum (a 7000 series). It is harder and stronger than cheaper aluminum cranks. Whether it is strong enough to support the skinny sections of metal between the multiple pedal holes or not, I don't know. But if any aluminum crank could handle it the Kooka's are it.

[Tellurider]

I am also planning to do this to my Kookas on my Coker. I have 170mm cranks and am planning on two extra sets of holes at 150 and 125 or as close to that as the flat part of the cranks will allow. A friend of mine has the taps for this but they are very expensive so I would also recomend finding a bike shop that has a set. Lots of shops have them for cleaning up threads that have been damaged. I would get some machining oil and bring it with you and follow Gerbils directions, try to get them to let you tap the threads. I think the Kookas will hold up fine with the extra holes and you will save a lot of $$ over buying Davinchi cranks which are almost $200. Good luck.

[maestro8]

Originally Posted by Tellurider

A friend of mine has the taps for this but they are very expensive

I found a pair for just over $25 + shipping... I'd give you the link here but I bought them over a year ago and Alzheimer's has stolen my memories of the purchase.

[gerblefranklin]

http://www.use-enco.com/CGI/INLMK32?PARTPG=INSRAR2

I win, kinda. Enco doesn't have any gun-point lefty taps, but they have these. They're four flute, but whatever, just be more careful and break the chip mroe often. About 1/2 way through the tapping, fully remove the tap and clear any chips. You are looking at about $30 for all the cutters for the job: $20 for the taps, $5 (being liberal) for the drill, and $5 for shipping.

[pdc]

Originally Posted by gerblefranklin

http://www.use-enco.com/CGI/INLMK32?PARTPG=INSRAR2

I win, kinda. Enco doesn't have any gun-point lefty taps, but they have these. They're four flute, but whatever, just be more careful and break the chip mroe often. About 1/2 way through the tapping, fully remove the tap and clear any chips. You are looking at about $30 for all the cutters for the job: $20 for the taps, $5 (being liberal) for the drill, and $5 for shipping.

That addy only brought me to the front page. What are the specific thread sizes for pedals?

9/16 X 18 BOTTOM HIGH SPEED LEFT HAND TAP
Thread Size: 9/16-18
Thread Type: NF
Ground Thread Limit: H3
Chamfer Style: Bottoming
Material: HSS
Finish/Coating: Bright
Number of Flutes: 4
Overall Length (Inch): 3-19/32 ??

Is This it? I don't see any 9/16 right hand tap.