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  1. #1
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    20" Hotrock Project Bike

    Well we are going to be updating a 2007 Hotrock 20" 6-Speed Boys bike.

    We are going to be updating this bike over the next 18 months for my Sons 6th birthday. So far the list is to keep only the brakes, seat clamp, frame, headset, & stem. Pretty much everything else will get upgraded or replaced.

    Some of the parts are going to come from my parts bin - others will be bought over time. I will try to update this as we go!

    Below is the before picture - as purchased on Craigslist
    Click image for larger version. 

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  2. #2
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    Looks like a good starting point! Dissasemble the wheels and weight the rims before you discard them. It is very likely that you will not find new rims that are significantly lighter weight as all 20" kid rims seem to use heavy extrusion profiles meant for adult weight rims, just rolled down to a smaller diameter. You can still drop significant weight from the overall wheel by re-lacing the rims with fewer spokes and lighter hubs. Patterns with 24, 18 or 12 spokes per rim are all possible starting with 36 hole rims.

    What are you planning for the fork and the crankset? Those are ususally the two more interesting/challenging parts to upgrade on a 20" bike....

  3. #3
    Havok
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    Very nice, Can't wait to see what it looks like.

  4. #4
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    Quote Originally Posted by GrayJay View Post
    What are you planning for the fork and the crankset? Those are ususally the two more interesting/challenging parts to upgrade on a 20" bike....
    So far the plan is to ditch the fork (it is pretty rusted and beat). I might try to revive it, but probably won't. New suspension fork or a rigid fork?? Not sure yet.

    For the cranks I am looking to get a set of used mtb cranks with 104bcd and cut them down and re-thread them at around 140mm - then use a single ring 32t narrow wide ring for no chain drop. Planning on building it up as a 1x9. The cranks can be re-used on a 24" mtb when he gets older.

    For wheels I am thinking of using some old 28h MTB cassette hubs I have laying around and then getting some new 28h rims. I build wheels all the time so no it is not a big deal. I would do something with the 36H stock rims, but it is more work than the $35 I can get some new rims for.

  5. #5
    GMF
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    Sounds like you've got a plan and the skillz to put it into action. I started with essentially exactly the same bike and have done much of what you are thinking. I cut and tapped some older cranks - but that was in effort to put a double chainring on up front. Swapped to rapidfire shifters, changed out the rear hub to an older road hub (130 spacing back there), and swapped the bars to something lighter.

    We ended up keeping the fork and taking out the travel limit spacers in the bottom. My son now has 60mm of travel that actually works reasonably well for him. The fork does weigh a ton, though, and i've been looking for time to mod an old manitou fok to shave some weight. Realistically, though, it isn't going to happen before he grows out of this bike (currently 8 1/2, average sized - maybe has a year left?). If you only plan on riding pretty smooth trails, a rigid fork is a good way to go.

    Looking forward to your results!

  6. #6
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    Well I was able to somewhat revive the RST 200K fork - it had some of the nastiest muck inside that spewed everywhere when I opened it - a mix of water rust and grease from being left out in the rain! In a former life I worked in a bike shop, so I have seen tons of nasty bikes and parts.

    I was able to polish the stanchions and remove all of the rust using super fine sand paper and polishing compound. Finally, I honed the plastic bushings a bit - and now that the fork is clean and re-assembled with slick honey grease - with just one spring on the right leg - it works pretty good...I will fine tune it once we get the whole bike complete.

    The way things are going - this project might be a 5th birthday present, if my son fits it by then. He is growing like a weed...

  7. #7
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    Bike project done for now

    We had a lot of time to work on this bike over the holidays and such, so thing progressed a bit faster than I thought they would.

    Right now the bike is done for now. We updated most items on the bike and unless we find a lighter fork I don't see much to do. We still have to pick up the new rear tire waiting for us a our local shop.

    Here are some nice pictures of the finished product.

    20" Hotrock Project Bike-img_0305.jpg

    20" Hotrock Project Bike-img_0306.jpg

    20" Hotrock Project Bike-img_0307.jpg

  8. #8
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    I got my son this bike

    Trail 20 Single Speed Boy's

    it has that once piece crank in it.

    I would like to upgrade it, but not sure how the BB would work. Can you tell me more about how you got the cranks drilled and rethreaded?

  9. #9
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    Quote Originally Posted by mjbrox View Post
    I got my son this bike

    Trail 20 Single Speed Boy's

    it has that once piece crank in it.

    I would like to upgrade it, but not sure how the BB would work. Can you tell me more about how you got the cranks drilled and rethreaded?
    Just shortening Adult MTB cranks will still not work as direct replacement for a one piece crank. Bikes with one-piece crank have a different bottom bracket shell type. It is most likely an larger diameter unthreaded American BMX shell. To convert to 3-peice cranks, you need a conversion adapter like;

    Universal Cycles -- Truvativ American to Euro BB-Shell Conversion
    (and then add separate threaded MTB bottom bracket)

    or else;
    American 3-pc Sealed BB by PRIMO
    (but 127mm is awfully wide spindle for a MTB crank).

    Then use short sinz cranks or shorten an adult set. More one-piece conversion info is in thread Novara Pixie 20" project

  10. #10
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    You have a great response above from GrayJay.

    With regards to your question about how I shortened the cranks on the pictured bike; we re-drilled the arms and tapped new threads into them. I do have machine shop equipment to help with tasks like that....

    They are SRAM S600 square taper cranks, with a 104mm BCD and the chainring is a RaceFace 32t narrow-wide version to help keep the chain on at all times, eliminating the need for a chainguide. The bottom bracket is an old 107mm wide Titanium square taper bottom bracket I already had on hand. The chainring is in the middle ring position on the S600 cranks which offers a pretty good chain line.

    The drivetrain is now a 1x9 drivetrain with an 11-32 tooth rear cassette.

  11. #11
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    thanks guys. That helps

    the Universal Cycles -- Truvativ American to Euro BB-Shell Conversion looks simple and gives more options. So I like that

  12. #12
    Havok
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    Very nice, I put those same bars on my sons bike. How wide is yours? My sons is 610mm. I think I'm gonna cut it down to 560mm.

  13. #13
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    They are stock (610 or 620?) right now - but he is still a little bit too small for the bike, being only 4, so I am waiting until he can really ride it to determine the bar width that will be good for him. His other bikes are closer to 550mm right now.

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