crank conversion ?? Help

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Ok I have never done a 3 piece crank conversion into a old bike and the more I look the more confused I get :headbang: wondering if someone can point me in a direction I am looking for the bottom bearing conversion and 130mm bcd (bolt circle) cranks to bolt a sprocket to, prefer probably 165mm long crank arms at least. I have been searching and calling places they seem to draw a blank what I am talking about or yeah have crankarms but no conversion kit so have I no idea what to buy and what will work with what? and don't want to keep spending $ on something that does not work any help greatly appreciated or if someone also owns a bike shop that could help and has parts a plus. Thanks can send my cell # to if easier to explain.
 
Super easy to do, once you know exactly what you're working with. I'm assuming you've got a bike with a one piece crank and an American BB shell, and you want to run a square taper road crank, since you said 130mm BCD. If that's the case, definitely get one of these:
20918__27747.1403892576.1280.1280.jpg

http://www.niagaracycle.com/categories/bb-conversion-bp-american-to-euro (or similar)

I'm realizing that you probably want some specific products, but we'd need to know more to do that effectively. Best move, in my opinion, would be to choose a crank (or give us some info on what you want/need so we can guide you) and to give an exact description of the rear set-up.... what make/model of hub, and if it's a derailer bike, how many speeds you're running, etc. From there, I can usually tell you exactly what BB to buy for the adaptor i linked above.
 
Bicycle808 Thank You! yes it is a '36-7 colson bike 1 piece crank, I will look at what brand/cool crank setup I like that will accept a 130mm. bcd. prefer a bare aluminum crank setup for it but that can vary as I can always bead blast them, one other question is I don't remember seeing a pedal thread size I would really prefer the old 1/2inch thread so guess need to verify that also.
After measuring stock crank length I will need 172mm in length. The rear hub is a Nexus 7 speed, will have to look at model, no derailer.
 
170-175mm crank wont' make to much difference. You will not find a 3 piece crank with 1/2" pedals. It doesn't make much difference, but why are you looking for 130 BCD?

Use that adapter that 808 linked to, then pick a crank off of ebay or your local bike coop. That ebay one comes with a Bottom bracket but you may need a longer spindle length. That will depend on the chainline of the Nexus 7 and your chain stay shape in relation to what chain ring you use up front.
 
cman Thanks! as you can tell I am a newbie to all this conversion stuff I am looking for a 130 bcd specifically for a chainring I want to use on my buildoff bike the link to the ebay one you posted looks good, looks like I need more measuring to do this is a learning curve for me. as for the 1/2 pedal threads have a pair really wanted to use but guess that may change if I get the rest figured out.
 
I came up with three solutions to your pedal issue. Two of the solutions involve a machinist and/or machine equipment...so, really expensive :eek:.

The third is pretty elegant and doesn't require a machinist...and came as a surprise to me. I was looking up how many threads per inch for 9/16" and 1/2" pedals. Both are 20tpi...interesting. So, I looked up left hand heli-coil 1/2"-20 inserts. The kits are ~$130...and you would need one for LH and one for RH...$260...stupid money. This is the interesting part, and 'not confirmed', but...the 'oversized' tap that comes with the helicoil kit uses the same tap drill that a 9/16"-20 crank tap calls for. This means that your 9/16" cranks are already drilled and tapped for 1/2" heli-coils :crazy2:. So, you don't need the whole kit, just the inserts and the installation tool. However, you can't buy single inserts...so, you'll have to buy a pack (probably 8-10 inserts for ~$25-35), one for LH, one for RH. The installation tools are also ~$25, and you'll need a LH and RH.

So, your probably thinking, I just took a solution that was REALLY stupid expensive, and made it just stupid expensive. But wait, there's more :happy:...you just need to find 7-9 friends that also want to use 1/2" pedals on 9/16" cranks and charge them ~$15-20, and viola! Your conversion is free!

...or, you could just go with 9/16" pedals :grin:

Jason
 
I was surprised working on one of my theft recovery Magna's the other day that the 3 pc crank took a 9/16 pedal.
photo 4.jpg

I had picked up a cool pair of Vintage Sakae bear traps at a LBS for $5 like 3 weeks ago.
Well used, but they roll much better than the plastic stock pedals, and look "cool". Serendipity - lots of great options out there!
sr-sakae-mtp-126-pedals-vintage-mtb-made-in-japan-quality-low-fat-2aa9414ddd85c95af13f0e7ef8a626a9.jpg
 
Just run some hot 9/16" pedals. You'll be fine. Once you settle on a crank, we can (probably) get you the right spindle, depending on how weird and Chinese your crank is....
 
Figuring the spindle length will probably be the biggest annoyance (depending on how easily the BB converter goes in), but it's not too bad, but you do have to know how you want to configure the rear end. It may also help to have crank length to check for interference at the chain stays. Sheldon Brown must have put out something on it and he's always a good place to start.
 
image.jpg
image.jpg
I have done 5 conversions now, using the Trvativ converter, and are well worth the trouble considering you will end up with a sealed bottom bracket and no play.
You will find bottom brackets vary in length from around 102mm to 127mm long and you can also get offsets on the left to allow for 3 chain rings. Cranks also have different offsets. You are never going to work it out exactly until you put the thing together so what I do is buy, beg or borrow a range of bottom brackets. It will quickly become clear whether you need a longer or shorter bottom bracket. Too short and the cranks will hit the chain stays as mentioned earlier. Too long and the chain alignment will be too far out. You can move the chainring from the outside of the spider to the inside to fine tune the chain alignment. Don't worry if you end up with a few spare bottom brackets you can use them on the next project. There is always the next one. You are also going to need a bottom bracket tool, and a crank arm puller , don't even start if you don't tool up.
 

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Modbikemax said:
View attachment 25753 View attachment 25754 I have done 5 conversions now, using the Trvativ converter, and are well worth the trouble considering you will end up with a sealed bottom bracket and no play.
You will find bottom brackets vary in length from around 102mm to 127mm long and you can also get offsets on the left to allow for 3 chain rings. Cranks also have different offsets. You are never going to work it out exactly until you put the thing together so what I do is buy, beg or borrow a range of bottom brackets. It will quickly become clear whether you need a longer or shorter bottom bracket. Too short and the cranks will hit the chain stays as mentioned earlier. Too long and the chain alignment will be too far out. You can move the chainring from the outside of the spider to the inside to fine tune the chain alignment. Don't worry if you end up with a few spare bottom brackets you can use them on the next project. There is always the next one. You are also going to need a bottom bracket tool, and a crank arm puller , don't even start if you don't tool up.
Click to expand...

If you're working with a well-known crank, you can typically figure out exactly what spindle you need, before you even bolt anything together. Oh, and i can't believe i didn't already post this, but the smart move is to go with a bmx tubular crank; get adjustable chainline, sealed bearings, and you can even run your 130bcd chainring on a powerdisc, like a real boss....
 
Bicycle808 said:
If you're working with a well-known crank, you can typically figure out exactly what spindle you need, before you even bolt anything together. Oh, and i can't believe i didn't already post this, but the smart move is to go with a bmx tubular crank; get adjustable chainline, sealed bearings, and you can even run your 130bcd chainring on a powerdisc, like a real boss....
Click to expand...
You can calculate till you realise that it's quicker to just try it. Especially if using old mixed parts, even the square taper can vary between jap and Italian cranks for example.
I have never used those BMX cranks, they look like they should work ok but as we know when you customise anything there is always that one thing that bites you in the ..... So I have just given my experience. I'd like to hear from someone who has done a few BMX crank conversions.
 

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