Anybody work on old BMX style bikes?

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skep419

skep419

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I have a Schwinn ZFlash that I saved up and bought new when I was a kid. I kept it for my son and now the pedal shaft loosened up and got hogged out. I'm wondering what I need to do to replace the crank assembly, and also convert it back to 6 speed (have the gears but lost the grip selector) Here is what it looks like.................

s-l1600.jpg

schwinn z flash bmx | eBay
 
Hopefully new bearings will take care of it, a lot of times junkyards have piles of bikes. Around here we have a yearly city wide clean up day with bikes on every block!
 
skep419 said:
I have a Schwinn ZFlash that I saved up and bought new when I was a kid. I kept it for my son and now the pedal shaft loosened up and got hogged out. I'm wondering what I need to do to replace the crank assembly, and also convert it back to 6 speed (have the gears but lost the grip selector) Here is what it looks like.................

View attachment 1716105431
schwinn z flash bmx | eBay
Click to expand...

I used to race BMX and started one of the first "sponsored" BMX freestyle teams in MN back in the mid/late 80's. My bikes were single speed but the rest I can help with.

You mentioned the pedal shaft loosened up and hogged out, then asked about replacing the crank assembly. Are you saying the hole in the crank itself wore out?

Switching out the crank assembly is pretty easy. The arms will come off and you'll be left with the main crank shaft. That also comes out easily. The bearing cups, those are probably sealed, can be a pain but it's not that bad. Installing new beairngs/cups is as simple as putting a long bolt through the crank hanger and sandwiching the cups between large washer and crank it down (pun intended). There is nothing rocket science about it and working on cars is far more difficult. I'd take my entire pike apart and grease everything after lake jumping in less than 30 mins weekly. Could lace new rims and straighten time in about an hour taking my time.
 
Pound said:
Hopefully new bearings will take care of it, a lot of times junkyards have piles of bikes. Around here we have a yearly city wide clean up day with bikes on every block!
Click to expand...
The crank arm is messed up (below is a picture I found that looks similar)
I doubt I'd be able to find a replacement, figured a new assembly would be the best option if I could find one that'd work.
ng-some-and-then-the-crank-backed-v0-v8wofsbslnza1.jpg
 
skep419 said:
The crank arm is messed up (below is a picture I found that looks similar)
I doubt I'd be able to find a replacement, figured a new assembly would be the best option if I could find one that'd work.
View attachment 1716105448
Click to expand...

Yeah that's toast. Could be welded but probably not worth it.

The crank hanger (short tube the crank shaft goes through) are pretty standard sizes. The crank arms might have a length stamped in, that's the starting point. Mine were 180mm, but that was long for the leverage I needed with the large front sprocket etc. I don't recall if the mounting point (size of the square hole) is standard, but you "might" get away with just replacing the arms. Call around to local bike shops and explain what you're doing and why. I bet you get lucky quick and someone has a pile of spares they will sell cheap of even give you.

There might be no reason to replace everything.
 
I was real hard on 3 piece cranks back in the day.
Had to have a one piece and full Cr-Mo.
Some bottom brackets can only be used with a 3 piece, though.
I agree- replace just the arms, if possible.

As for the shifter, I bet any mountain bike style grip shift would work, provided it had the number of steps you need. Would probably need to re-use your cable due to length.

I'm not a big grip shift fan, though. I prefer trigger shifters.
 
YY1 said:
I was real hard on 3 piece cranks back in the day.
Click to expand...

Same except I went with the redline flights. Cro-Mo 3pc and bulletproof. I actually saw a pair of solid Cor-Mo bend from riding (falling off of) big quarter/half pipes.
 
Takagi 185 for the win in my case.

Everything else either broke or bent real bad from landing.
 
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