PA50 Crankshaft in NU50 Case

If you've ever ridden an Urban, you're probably familiar with that screaming sound the stock crank makes at high RPMs (also, no thrust washers on stock). Or maybe you're not, but have a desire to upgrade to a stuffed crank anyway, only to find that such products (amazingly) don't exist (yet). Below is a synopsis of how I took an aftermarket PA50 crank (Treatland) and modified it to work with the stock Urban lower half.

First, the right (electrical) side of the crank is nearly identical between the two - which is great due to the high potential for error in cutting woodruff key slots.

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The actual stock crank is about 1mm wider, but this can easily be corrected with washers, or simply left as is (as long as it's centered in the case; I also used a much thinner gasket paper on the rebuild, which about compensated for the lost width). Overall, not much to worry about.

Now the drive side. The taper of the PA is entirely different, save for the first centimeter or so (i.e. the part that the bearing sits on). After that point, three areas need to be modified; in all cases this involves adding to the existing diameter.

First, the area immediately adjacent to the portion holding the bearing should be brought to about an equal diameter so as to hold the NU50 seal, which is different from both it's own right side seal, and PA50 counterparts (i.e. 20x31x7 rather than 15x25.5x7). I choose to use brass for this fitting because of its naturally lower coefficient of friction (also, it's easier to cut, which makes forming an interference fit a bit easier).

Next, the kick-start gear. This is perhaps the most difficult part to manufacture (it's event a bit tricky to remove some of these from long-standing stock engines in the first place). The taper angle at which the inner diameter of the gear receded, and the taper angle of the replacement crank (for the latter ~14mm of the gears 17mm length) are both 7 degrees. This makes cutting a bit easier, although he small bore (i.e. starting as 12mm) makes cutting a challenge (I had to significantly trim down my best internal cutter to prevent unwanted contact even at that low angle).

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The tolerances of the finished product provided a very light interference fit, but came out true, which I feel is more important.

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Re: PA50 Crankshaft in NU50 Case

Lastly, the spacer for the stock variator. This part is both simple and rather fun to cut; think of this as a 20mm OD cylinder with a 10mm hole extending half way up the center axis before transitioning to a 12mm hole.

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This part is the only to not hold an interference fit, but should fit well. Mine fits closer than stock since as the last .05mm was brought down with sanding. The completed modifications are shown below.

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This is a very small portion of a much larger build I'm working on, but felt like contributing something (hopefully) substantive to the MA in the meantime.

Re: PA50 Crankshaft in NU50 Case

Hepatitis J [OFMC] /

Hell yeah.

Re: PA50 Crankshaft in NU50 Case

Captain Janeway /

wow. when will you be shipping me mine? ;)

You cut that gear yourself? cool.

Re: PA50 Crankshaft in NU50 Case

> Captain Janeway Wrote:

> -------------------------------------------------------

> wow. when will you be shipping me mine? ;)

> You cut that gear yourself? cool.

Not the gear itself, but the insert spacer that allows one to fit it securely onto the PA crankshaft. My original plan was to construct a one-piece sleeve, but the internal boring operations would have been waaaay to difficult, so I made spacers for only the areas where they were absolutely necessary.

I'd also be willing to cut a few more if the interest was there, although my time these days is really really limited.

Re: PA50 Crankshaft in NU50 Case

Hepatitis J [OFMC] /

I would be interested in one.

Re: PA50 Crankshaft in NU50 Case

The issue I saw was that the hobbit clutch bell hits the urban case all the way around. You'd have to cut off the hobbit bell then lock the hobbit vario to that kickstart cog then tighten it to lock the hobbit vario minus the bell, to the crank. Oh yeah, flip it around backwards while your at it for the belt to line up. Unless u have a better idea, I kicked it around for a minute then found better things to do. :) have fun!! I'd like to see it gO!

Re: PA50 Crankshaft in NU50 Case

I did it on my ghetto blaster fa50. Cut off the bell, flip it, weld it to whatever lockS IT ON!! The stuffy crank. Yea! Crappy basement pics,

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I guess I could take it for a spin and let u know, only rode it once about 2 years ago.

Re: PA50 Crankshaft in NU50 Case

That's awesome! I like the idea a lot, but a bit different than what I did. Mine is all Urban, except for the adtermarket crankshaft, which is for the hobbit. The custom spacers let me use all the original NU stuff with the NU case. Although I'm modding that in other ways too - things gunna be insane when I'm done next year; sparin' no expense on this build.

Nice pull start set up btw; maybe it's the angle, but that looks like one of the nicest conversions I've come across.

Next steps for me: cut a new off-centered crankpin to add 2mm to stroke. Then mount the hobbit mini-CDI.

Re: PA50 Crankshaft in NU50 Case

Following!

Re: PA50 Crankshaft in NU50 Case

I am in need of the adapter pieces for my NX50 (same crank as NU50) and willing to pay!

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It's worked out well, but took time get right; kinda suprised that there's no "adapter sleeve" on the market already.

The day job's taking up most of my life, but I've got time off between xmas & new years; I'll make an effort to cut more sets, but no guarentees.

Misc. update: I've pot-committed myself to the current build; gunna go all out. Recently electropolished the frame:

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Re: PA50 Crankshaft in NU50 Case

Whoa. Sexy frame! How did you perform the electropolishing?

I'm willing to prepay for adapter sleeves! :D

Re: PA50 Crankshaft in NU50 Case

Ive found eletropolishings to be more of an art than science, but the basic idea makes use of a DC Bench Supply, some beefy leads, and bottles of sufox T & N (came out cheaper than mixing my own acid). There's a good instructable that covers the basics. Watch for arcing, acid burn - this really deserves its own thread... might make one Monday.

And no need to prepay; money's no issue - just time. You've got your spot in line if/when i get these cut (Jan maybe?). Or I can detail out everything I've learned if anyone wants to try themselves.

Re: PA50 Crankshaft in NU50 Case

Thinkin more about it - def gunna make that electropolishing thread when Im done. I really dig the finish - not only reflective, but seems to never rust. Plus is feels different too - like it's too smooth to be metal - cool stuff.

Re: PA50 Crankshaft in NU50 Case

That is so awesome.

Re: PA50 Crankshaft in NU50 Case

I want one! What can I do for one? money is no issue.

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I would use one and even skip the kick starter gear, I wish someone would

make these available for the NU.

Re: PA50 Crankshaft in NU50 Case

First, thanks all for the positive feedback.

Never planned on marketing there, but due to the obvious interest, I promise I'll cut a few more en masse; my current company has a shut-down period between X-Mas and New Years Day (and now I get to honestly say that I've got holiday plans...).

Sets will have the three pieces (Variator boss, kick-stater spacer, and seal spacer), unless requested otherwise, and cut to the best of my abilities from 1148 and/or 316 Stainless. These have worked fine for me so far (the kick-starter even held in place after being pressed on only by hand) - still - the attorney in me is having heart palpitations about selling engine parts. Don't want to deal with refunds, or claims of "my-bike-exploded-and-the-spacer-went-through-my-spine..." I'll post a disclaimer when I'm ready to ship; this also means I'll probably NOT accept payment(s) for the labor or parts themselves (but, yes, you will need to cover material costs and shipping - that shit adds up fast on my end).

I'm using this thread to benchmark the demand.

Unrelated, has anyone tried to press the pin from this particular crankshaft? I'm having one hell of a battle with it; had 20 tons on it last night and the fuckers only budged ~7mm. About ready to just drill that shit out. At least the elctropolishing continues to surpass my expectations.

Re: PA50 Crankshaft in NU50 Case

I tried to press the crank pin out with a 20ton and got 0mm, Im here and waiting if you ever get a chance to cut some adapters :)

Re: PA50 Crankshaft in NU50 Case

> bob john Wrote:

> -------------------------------------------------------

> I tried to press the crank pin out with a 20ton and got 0mm, Im here and

> waiting if you ever get a chance to cut some adapters :)

Yeah, she's quite the bitch to remove (come to think of it - a lot of things on that bike seem to take excessive force to remove...). The magic number seems to be around the mid to upper 30's.

Even managing to press it, the pin bore evidence of the struggle (not enough to affect the press fit this time - but it likely cannot withstand another remove/insert cycle).

Could easily cut another, but it wouldn't be nitrided/carburized, and I'd want to use a minimum of something like 8620 (which I don't have on hand right now).

Also, someone experienced suggested that you might be able to save yourself the trouble by using a Moby crankshaft (not my idea, never tried it myself, but seems very clever).

Re: PA50 Crankshaft in NU50 Case

Go to Ebay and type in " con rod kit nc50"

Re: PA50 Crankshaft in NU50 Case

I had Cafe Racer in KCMO press a different rod into my NX50 crankshaft (which is the same exact crank as NU50), you might give them a ring and ask about it! PM me for more information.

> alex ganz Wrote:

> -------------------------------------------------------

> I'll post a disclaimer when I'm ready to ship; this also means I'll probably NOT

> accept payment(s) for the labor or parts themselves (but, yes, you will

> need to cover material costs and shipping - that shit adds up fast on my

> end).

^ You could set up a "donation" fund? The release of liability / disclaimer is a great idea, especially if you set up a Google Form with a signature field for people who wanted to get in line and order these. (I would also be happy to help coordinate this!) And again, I would be happy to pre-pay for a few sets :)

Mine:

Re: PA50 Crankshaft in NU50 Case

Merry Christmas!

Re: PA50 Crankshaft in NU50 Case

Count me in.

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the lack of nu50 crankshaft availability is the reason why I quit building these engines. broke 4 or 5 and gave up . I need to get one of these if you have the time . definitely count me in!

you wouldn't believe how many engines I bought just to rob the crankshaft.

Re: PA50 Crankshaft in NU50 Case

Hey guys, just recently received more stock metal, but back at the day job. No promises pertaining to if/when I'll get more cut, as I'm neglecting even my own projects a this point, but I'll keep everyone posted.

Re: PA50 Crankshaft in NU50 Case

Yasss!!!! :D

Re: PA50 Crankshaft in NU50 Case

woah rick ems in the house!

Re: PA50 Crankshaft in NU50 Case

Im itchin to donate to the cause.

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