Shortening steel cranks

[Hyena]

OK, so I dun went and stuffed up...

I bought this cruiser bike, got it fairly cheap on ebay (new) and when it arrived it was massive!

Here's a pic next to my other 2 bikes (excuse crappy phone camera)

The white bike being a dirt jumper is a little on the small side and the blue bike is large-ish but fine with the seat right at the bottom.
You can see how much the cruiser towers over it.


So in my wisdom I took a look at the rigid forks, and the triple clamps and thought "hey, there's still plenty of clearance here, I'll just cut a heap off"



And that dropped the height down perfectly. Awesome. Then I went to put the pedals on and found I only had less than an inch clearance. DOH!
I tried to ride it but the slightest lean and the pedals dig into the ground. :x

So I thought I could just cut an inch or 2 off the length of the crank arms, tap in a new thread and be done with. I'm not too worried about how the bike pedals with teh shortened cranks, just as long as it can still be pedalled if necessary.
The only problem is they're cast steel and all of the bike shops I've approached refused to tap the thread.
They've also got this funny hexagonal bottom bracket I've never seen before (like the square taper ones, but not tapered, and 6 sided)

My options are I see it are

A: try and make something custom (alot of stuffing around and/or big $$)
B: swap out the bottom bracket and hunt around for some cranks off a kids bike (I need around 150mm)
C: cut the bottom inch or 2 off the crank arm and weld it further up the arm - this is a bit dodgy and probably won't be that strong although I won't be putting alot of torque through it as it'll only be 'token pedalling'
D: Hack the frame up and move the bottom bracket (I'd really rather not do this)

Anyone got any other suggestions ?
How do you guys who put 20" back wheel on mountain bikes get on ?

 

[AussieJester]

Cant you just get a new bottom bracket axle and buy some new 160mm cranks for it? I am
assuming the diameter of the axle is similar to the more conventional non hex job you have now?

You could always chop the threaded end off remove the 2inches for more clearance and weld the threaded piece back on...
need to find someone that will weld cast iron though, think ARC with right rods does it not positive though never welded
it myself.

KiM

 

[full-throttle]

..or get some alloy cranks, drill another hole for the pedals then go to a bike shop and thread them. remove excess later on.

just wondering what did the lowering of the fork do to the steering angle??

 

[Hyena]

I'd really need ~150mm cranks, and shortened cranks from what I've seen seem to be quite expensive.
And by the time I buy them and a new bottom bracket it's probably 2/3rds the cost of the bike.

As for cutting and welding, they're not straight up and down, they kink out as they go down so the pedals stick out from the axle but sit parallel to the road.

Another option I just thought of is trying to remove the hex bits from the existing cranks and transfering them to softer alloy cranks to be cut and drilled.
Upon closer inspection there seems to be a large round hole with this hex section "glued" in. I'm not sure what sort of glue it could be but no doubt it's strong as shit.

edit: i missed your post before full throttle - I'm not sure about steering angle. I also cut about 4-5" off the length of the handlebars so that's changed the feel a bit but has made it nicer to steer. They were huge before, sorta like driving a bus steering wheel. They're still a bit that way but atleast your arms are forward now and not almost by your side!

This pic shows the original geometry of the bike - a bit odd looking!
I guess the steering angle has stayed the same, its just dropped the frame down to be flatter across the top bar rather than pointing upwards

 

[02jze]

Just resell it on ebay know one will know the crank arms are too long.lol

 

[AussieJester]

No offensive buddy i mean this in the nicest way, but that frame is as pretty as a bucket full of assholes man! what were you thinking!
The forks at least are triple trees we can reuse them at a later date i hope

Lowering the forks also decreased the head angle thus the bikes geometry, looks like the designer/builder started out wanting a chopper frame then changed his mind when he couldnt find a decent fork with enough trail that would allow to rake the head angle out hahaa... Bend that head tube back another 15-20 degrees and throw a set of springers on it it would completely change the look...



^that photochop has the head angle another 20 degree on stock Trail on the forks isn't correct but you get the picture, would of looked better IMO


KiM

 

[Hyena]

haha yeah its not the best and I didnt even buy it for me, it was for a work collegue but because its massively too big and I've now stuffed it it's mine - I'll factor the purchase price into the final cost of their ebike when I deliver it :wink:

Agreed, it definitely needs more rake but I'll probably make do for now with it like this:
Moving the seat back a few inches and lower down makes it more comfortable sit on and steer ( a little more like yours AJ rather than being perched up high) It doesn't look like much but there's a huge difference in feel and stand over height just moving it back slightly

 

[cell_man]

My God Jay that pic of the cruiser as it arrived is a beauty :lol: I can honestly say I am pissing myself laughing and as Kim said 'What were you thinking?' :lol: It's defo looking a bit better with the shortened forks though mate :wink:

 

[Geebee]

I have shortened older steel cranks by hacksawing in half, V'ing the ends and then bronzed back together, they are still going strong years later.
Option 2 buy a set of kids MTB cranks, gives the option of three rings and cost less than $25 at a LBS, still need the correct BB though
Cheaper option visit your local tip shop and grab a kids bike with the BB and pedals you need, maybe $5.
Cheapest option leave them alone and lift the inside pedal on corners, my lowrider chopper has exactly 1" clearance from the ground to the pedal and it has covered many miles powered and unpowered, mind you the pedals do have some scrape marks on them.

 

[vanilla ice]

I'm with Geebee, find a junk kids bike to pillage.. or better yet ride it the way it is and lift the inside for corners.

 

[johnrobholmes]

cutting the cranks and brazing them back together is probably the safest bet. If you don't have a big enough torch you could cut, drill, and tap the arms for the pedals if there is enough beef in the arms.


I would probably ride it as-is. Who cares about pedal dragging if you aren't going to pedal!

 

[John in CR]

Something to consider if you're going to tap new threads for screw on pedals is that one side has LH thread. That's so the pedal doesn't unscrew as you pedal. I realized this the hard way when I put my chain on the left side. My pedals were coming loose all the time. Screw loctite, I put epoxy and haven't had a problem since. Too bad kids bikes are the 1 piece cranks, otherwise that would be the cheap solution.

An LH thread tap will probably be hard to find and probably expensive if you did. I think the quickest, cheapest, and easiest would be to just cut the length out of the middle and weld it back together, so you don't mess with either end of the cranks. Hit it with the grinder and paint afterward and no one will the the wiser. While you have the metal working tools out slacken that heatset angle, which should help in the looks department.

With that kind of space in the triangle and behind the seat tube, the bike has some real e-bike potential with totally stealthy batts.

John

 

[amberwolf]

Interestingly enough, John, I never had any issue with my pedals coming loose on CrazyBike2, with steel cranks, even though they were like yours--reversed with chainrings on left side, and CB2 has always been setup with the cranks turning if the motor is running; no freewheels on anything (started to fix that a few times but never got any of them working).

 

[Hyena]

I would probably ride it as-is. Who cares about pedal dragging if you aren't going to pedal!

Well the problem is the slightest lump or bump and they hit - I nearly fell off when they dug in just rolling down my driveway.

Something to consider if you're going to tap new threads for screw on pedals is that one side has LH thread.

Yep, this is the reason I can't drill and tap new threads - no one will have a LH tap except a bike shop and none of them will touch my heavy, hard cranks.

With that kind of space in the triangle and behind the seat tube, the bike has some real e-bike potential with totally stealthy batts.

That was largely why I bought it. I can easily fit 100v of lipo in there + a big ass controller in the gap behind the seat tube.



As I said though I originally bought it for someone else but I'm going to keep it for myself new. Because I haven't got enough ebikes already... :?

 

[John in CR]

As I said though I originally bought it for someone else but I'm going to keep it for myself new. Because I haven't got enough ebikes already... :?

Is there such a thing as enough??? This is incredibly cheap for a motorsports hobby, so we can all be Jay Leno and have a collection. 8)

 

[Hyena]

I'm pretty sure Jay Leno doesn't have his wife in his ear though because his collection in the garage means she has to park her car in the driveway :lol:

 

[LI-ghtcycle]

Maybe I'm over-simplifying, but can't you just buy a new set of forks and cut it shorter? Or maybe re-attach the old material you cut off with a slightly smaller diameter tube inside and a bit of welding/brazing?

I don't know the high requirements, or if your friend could have ridden it as it was full size, but I can't believe you have to get another whole bike just because you cut the forks too short. Am I missing something? :?

 

[PJIII]

Cant you just get a new bottom bracket axle and buy some new 160mm cranks for it? I am
assuming the diameter of the axle is similar to the more conventional non hex job you have now?

You could always chop the threaded end off remove the 2inches for more clearance and weld the threaded piece back on...
need to find someone that will weld cast iron though, think ARC with right rods does it not positive though never welded
it myself.

KiM

You can weld cast iron w/ a Ni-rod---one w/ high nickle content---you weld a bit & peen the hot weld & repeat till done. The steel of the crank may well be forged---'don't know.

 

[John in CR]

I'm pretty sure Jay Leno doesn't have his wife in his ear though because his collection in the garage means she has to park her car in the driveway :lol:

If my wife got in my ear about anything, then it would be time to get a new wife, definitely not less bikes. Actually, if my wife complained about something I did, then I must have gone way too far and was being totally inconsiderate, so I'd take corrective action. A complaint level of 0 is exactly how I like it, and one of the reasons I love my wife so much...no more spoiled american girls for me. :wink:

John