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Rex also has a mini

4K views 31 replies 10 participants last post by  CK 187 
#1 ·
In idea i have several, but for now gonna focus on one maybe another in a while

so as some of you might know my good friend Matti got a free kx65 with a dead engine for electric bycicle project. that failed for him. But i had this urge to get a minisupermoto for a while. so he offered me his, because he was going to junk it anyway.
so i got it brought to Latvia by a "relative" tucked it in my car on our visit

did a quick assembly one evening(i know the forks are wrong way in, it's already fixed




since the lump was bad one and new cylinder kit is 400eur, i decided to crap that shit ad get something cheap to fit in. so after an ebay browsing i stumbled upon 40eur EBE engine from bultaco astro(derbi senda, i think some aprilia, well it's popular)

since they come as 200-300eur in decent state i took a gamble, that i might lost


will try to drill this out



as for head, well two head studs came out one was already snapped and one is quite stuck
also the piston doesnt move, so it looks i will need a new crank, or iļl give repressing a bearing one this one a go

took some fight to get it off

head has a crack in it aswell





clutch side looks good tho




good thing about engine is...
they're cheap for an engine
new crank starts around 50euros, cylinders has a lot of aftermarket, with bifferent crank can be made up to 110cc( and thats two stroke we are talking about)

about the chassis, it's okey, plastics needs to be sprayed, one of fork legs leaks, missing front numberplate, steering clamp.

my aim? to get it ridable within less than year, so i can take it to Smash next year. but i also want to take VF build too, so as always i have bitten more than i can chew
 
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#5 ·
Been digging through the garage some more, got an airbox I have no vehicle for so it`s most probly from the kawi... There was some other bit too I cannot remember off the top of my head that might also belong to the bike, it was plastic but no idea what it was... I did give you the rad grill at smash didn`t I?
 
#11 ·
so... first of all big thank you to Kimmo for donating a lump. Derbi EBE unit with 85cc kit
tried to fit it


kinda fits, except for few isues

a bit heavy on one side, if i want the chain to be aligned. but it will work



water channel for head, will have to be modded in order for cooling to be working


this is already bent for clearance, but yes, this too


and yes, this is where the fun begins






so in order to have a working pipe, i need to angle it straight bend right out of head and turn it around frame. since there's no place on right side of bike, and originally derbi engines has pipe going on the left, that was only logical solution|

so i started to look around for possible pipes. the original kx65 was goingon the right side *this is also a bit on an issue, since i will have to relocate radiator from left to right.

looked around for a cheap pipe options, beside i was looking for tuned pipe, since engine isnt stock. kinda got a great deal for pipe with bashed first part of pipe, i needed to redo anyway, but the guy changed his mind. so i found leo vince 70+ cc pipe with muffler for 30eur, had a dent though.


dent was hard to remove without welding, but... it didnt quite fit the way i thought to fit it. kx pipes other half kinda fitted, but that meant i had to rebuild first part and i have no idea about lenght and diameter it has
 
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#12 ·
so in the spirit of CUSTOMFIGHTERS.com and the fact, that i like to learn and try new things, when it comes around bikes, i decided to take measurements of leo vince pipe, work around web program of cone bending and look what i can do

started with paper model







at this point i unerstood, that paper is flimsy and i should have some issues, but i am stuborn and decided to try it anyway

this is the part i made a small mistake, but later about that


we have a car repair shop next to my work, and i asked some steel sheet, i think it was 1mm thick
layed out templates and marked around them

rough angle grinder cuts

flap disc sanded

hand bent cones against piece of pipes i had at garage


loaded bike up in Tofu and headed for my dads work, where i have acces to MIG welder. keep in mind i'm not too good with it for the rest of part you read. but PRACTICE MAKES PERFECT


yes i grinded the seams




since i bent them by hand they werent exactly round, so i had to work some magic around them with vices and some bending, a bit of hammering

anyway this is how far i ended up doing








so there's where my previous mistake comes to play, i have somehow missed making of two cones i had on paper model. will try to make them this week and weld shortly after test fiting them on bike again.

was the making of pipe fun? yes
challenging? yes
fun? kinda
hard? making cones took me 5 hours of almost non stop, welding was around 7h i think, knda lost track of that, because i also had to weld lower engine mounts before doing pipe.
will i do it again? possibly i have mbx80 i want to make into a road legal mini
 
#20 ·
Made new cardboard cone mockup to see how it fits. Because old and original one was in a bad angle


Then cut it out and welded together

As for muffler. The slip on part snuck easy on an old bars that i used to have on vfr and bent after a crash in track. So yes i have a steering bad as exhaust. Made a slip on part out of sheet metal on chamber side. Have to fab up some brackets to hold the exhaust.







Like how it looks. Now up to fit radiator. Make brackets for side fairings. Clutch cable, cooling, ignition and carb. Wheels
 
#24 ·
@Mattson sent me some carbs, he claimed it as birthday gift. So thanks to him... after being dissapointed in bros i was looking for stuff to do around shed, so i dont feel so bad. took the reeds and intake manifold off ebay lump. of course it wont fit, because carb is 28mm IIRC and original is small. looks like i might try to make one myself from steel i have around


while i was at working on ebay lump. tried to get the cylinder off. it wasnt an easy task, also it already was damaged, so i went full on ballistic, with heat, angle grinder and hammer.





also it finally paid off to have welder at shed, and i could extract the bolt that was PITA from beginning



oh also, i took ylinder off my MBX80... looks like i need to take it for milling and hooning one size bigger
 
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#25 ·
bought a lighty used cylinder from euro3 model. was told it fits, also was told it's airsal. but it's stock one, aluminium though. but hey 10euros

also, cut the mount bolts that are stuck in casings, so i can split the engine. heat and hit them out with less resistance from lenght


if ya squint it's mint



oh forgot pics of cylinder





this is the reason why it was cheap. welding a nut to it and screw it out doesnt bother me much
 
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#26 ·
bought this wonderful tool


so i can do this



the bolts even started to bend... it took some heating aswell. one bearing even cracked and around 30% of outer side fell off. but in the end i did it





now i need to find time to clean it, press the pin out. and head after new bearings

also managed to heat and hit out one of 6 axle halves that are left after i cut them so i can split the engine cases

and all of this, becaus i had nothing to do whule i wait for pulse generators for Bros
 
#27 ·
been a while... so i have carb for it, and daihatsu heater core for cooling, that will be mounted where the headlights usually are, because there's no place for anything due to exhaust. but now i have another idea, but we'll see about that. i also picked up bends and tube to start intake manifold (again not enough space).

but i picked up chinese ktm sx50 ignition from post office. mocked it up. seems that i'll need to mod the inner taper for derbi size a bit. and i started the journey to get an adaptor plate made

Original ignition i had


"KTM" unit
img]https://i.imgur.com/rRsfbbx.png[/img]

3 model of adaptor plate
 
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