Buildup -'94 Specialized Stumpjumper with MXUS 4504 V2 motor

I bought this CrMo steel frame from an online classifieds website for $25 and its in pretty good shape. Its surprisingly light.
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It looks like the rear dropouts are forged, which is a bonus.
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As per usual I am winging it. My original alum bike was a 2009 Specialzed Rockhopper in which I snapped off my alum rear dropouts pretty easily actually.
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Here are the specs for the bike donor bike. Different RD and Shifters. Went from 8spd SRAM to 9spd Shimano.
http://www.specialized.com/ca/en/bikes/archive/2009/rockhopper/rockhoppercompdisc

I found the '09 forks stem to be too long, but it fits the 1-1/8" tube. The cups are pressure fit. I either push the nut inside the tube down and cut off. Or find shims. I havent decided. Here is a picture of this problem.
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I found I can push down that inner nut.

Not much clearence for my 26x2.10 knobby mtb tires.
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I found out my '94 Bottom Bracket is a Shimano Square Taper.
The '09 is a Shimano BB-ES25, Octalink spline, cartridge bearings, 68mm x 118mm.
BB and Crankset both not compatible.


I can reuse my rear stay bar and seat post mounted "clamp style" rack, I will convert the lower mounts to regular bolt on style, and leave the seat post clamp style.
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Except mine is clamped to bar all the way around.
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See how each clamp is just bolted onto rack, my legs can be bolted onto stay holes. In this picture above, I got the clamps that bolt onto rack, upside down.

Here is the list of stuff I bought.
- MXUS 4504 V2 straight from the manufacturer in China.
- Lyen 18fet RDS
- Ebikes.ca Cycle Analyst
- Throttle
- DC-DC Converter
- 18 HobbyKing 4 cell 14.8V hardcases. Will be going two packs of 74V 10Ah.
- HobbyKing 4mm, 5.5mm bullets, different guage wires, heat shrink, balance lead extensions, balance lead splitters, power cable parallel leads. The "extra hand" is a waste of money, dont bother with their solder, there soldering iron is probably a waste of money too.

*I used power cable 6 (4mm) to 1 (5.5mm) to be most beneficial, 5.5mm bullets and 10,12 guage wire to be most beneficial for building up my battery pack. As usual I overbought* This setup makes it easy to parallel your battery first, then series your individual packs for desired voltage.*

Here are some random pictures.
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I think most likely I will be going one speed in the rear, I just have no idea what an ideal teeth count would be. My front crank will be the typical triple, 42/32/22.

I'm excited for ya, it should be powerful and robust!

I believe 1/1 is good for 5ish mph and about 4+/1 will get you like 30mph, So possibly 20t will give a nice low that's pedalable to 20mph?

I got an issue, my rear Crysyalyte downhill 31mm rim is NOT rim brake compatabile.
My brake rotor hits the chain stay.


A) Try to spread the rear dropouts out with a car jack.
B) Hammer the chain stay
C) Welding

I wouldn't hammer the chainstay or weld unless as a last resort.

The cromo steel should allow 1/4" spreading pretty easily (is that enough?)
Careful with a carjack of course, that's enough power to destroy the frame.

Could a torque arm or washers between stay and hub provide the spacing?

Its a very tight space, I will stretch it by 1/4" then if theres bounce-back or memory to it I will throw in some washers.

Nice old cromo frames are great! But, skinny for tire clearance, not made for disc clearance, they can be a project.

In some ways, the best thing for you to is get a wire feed welder, and stretch it. Add some big steel plate droputs, welded to the original ones. Moving the whole tire back 2-4 inches will get you the clearance, and your brake mount can be built right into the new dropouts. A much bigger tire will fit as well.

See my cruiser thread for how I did it, but I stretched farther than 4 inches.