Sumo is love. Sumo is life. Follow the one true path!

Or so people kept telling me. Listening to people is not how my brain is wired, I learn by doing, probably why I have so many scars.  For those that haven’t heard the good word a supermotard is a motocross bike set up for riding on pavement, generally bigger brakes, smaller rims, street tires and cranked damping. Those that own them love them, they are agile, quick and tolerate crashing.

My first supermoto experience happened on the snake, corner # 9, you know the one before the short lap turnout. I was up there early, cars who fail to understand the concept of a double yellow typically don’t show up to ruin someones life until after 10. The neighbors probably don’t like it, but I am not there often and never there for long. You can’t really wind it out until you pass the houses anyway.

I paused at the top, letting a herd of cyclists complete their climb unabused by 112bhp through what could barely be considered a glasspack. Have a little respect for them skinny tire folk. They love being on two wheels just as much as we do but haven’t heard the gospel of Otto. I followed a cyclist down some steep twisties (84 up in the bay) once, I had a bizillion times the contact patch and 98 times the power (1 people = 1.2hp). I actually had to get off idle to keep up in the corners, I was wearing full gear, he had on spandex, dude was bananas.

A couple runs in and I was cruising, the road was warm, my tires were hot, no cyclists, no fishermen, no people, just how I like it, time to let that three cylinder engineering marvel sing.

A wild corner wizard on a ktm exc appeared and schooled me. I was easing off the brakes and cranking it over into 9 and this Austrian missile flew by on the inside.  Just smashed any hope I had of keeping up in the corners. Alright fine, if that little dirtbike could destroy my naked rocket on my favorite type of road, maybe I need to learn a thing or two.

Mostly I just wanted to learn how to do dank whoolies on something I could crash repeatedly. This is the story of how I made that whoolie machine, in logical not chronological order.

The Bike

My new hooliganmobile, as advertised

I ended up spending a day with socalsupermoto and decided to jump off the deep end. The day I started seriously looking a good friend mentioned that he had a Husqvarna 510 SMR for sale with a dropped valve for cheep (like that valve had some serious rage issues and took them out on the cylinder and head cheap).

Husqvarna has other people assemble a pretty decent motorbike with their logo on it. They have phenomenal suspension (Marzocchi/Sachs), great brakes (Brembo with rotors that don’t suck) and an awesome MV motor…when it works. Unfortunately this particular bike had a cracked piston from running on bad gas. When the guy before me replaced the piston I don’t think the head was torqued right and it dropped a valve after less than an hour of racing.


You ever get that feeling when you order something off the menu and it doesn’t look like the picture.

I bought it on the spot.

Now I had a bike with a topless engine. Things going topless can be good or bad. Topless engines have really really low compression which puts them solidly in the bad category. 510 heads did not exist on ebay, luckily the 510 and 450 head are identical and interchangeable, unluckily the only 450 head I could find at the time was 2100$, from Europe. 2100$ is more than I paid for the whole rest of the motorcycle.This is why people buy Japanese things, at least parts exist. I can do a whole engine swap for less than that, right impulsive Jacob? yeah totally engineer Jacob! speaking of which a WR450 motor makes about the same power, weighs about the same and the whole darn thing can be had for waaaaaay less than 2k. Bonus points, the FCR off of the 510 fits the Yamaha, so you don’t need to buy a carb, but you do need to re-jet it. We got this!!! there will be zero problems and you will only buy exactly the parts you need the first time, it will be super cheep.

Now I don’t know about you, but if I valued my time on projects I probably would have just bought the head and been done with it. I don’t put a price on hours spent hacking things together in my garage with friends and beer. I  wanted another project because I don’t have enough half finished projects and and engine swap sounded fun (I’m weird, I like these things). A large wooden crate with a Yamaha motor showed up in less than a week, it’s go time.

Furniture is for grownups, car parts are where its at.

The Build

Cramming the motor in the frame*

*you know, so you can see what else you have to do, because we are totally winging this

I didn’t know if the motor would fit when I ordered it. The only dimensions or cad models I could find were behind paywalls or on old university FSAE sites that had links but wouldn’t serve me files. I ordered it anyway, the WR450F swing-arm bolt was shorter, it had to be possible. Lazy me didn’t feel like going to a dealer and measuring, two beers me has a welder and forsees zero problems.

Very little work needs to be done to the WR45o motor itself for this swap. The rear motormount is pretty narrow and has steel bushings pressed into each half of the crankcase. These bushings center the motor between the swing arm bushings and a big bolt holds the whole thing together and to the frame. The Yamaha swingarm bolt is the wrong diameter and the motor bushings need to be wider. Good news, they are easy to remove with a hammer and a screwdriver which is nice because that is what I had. Bang away, then measure a bunch of stuff to get the drive sprocket lined up right, oh you measured everything without installing it in the frame? it’s ok, that’s what they invented belt sanders for.

Go turn yourself some bushings, stainless would be nice, but you have a bar of mystery ferrous metal on the floor by the lathe, its pretty hard and it will be all greasy anyway.  Install your brand new custom motor mount bushings. Your swingarm bolt makes a convenient tool to align your bushings while pressing them in with inertia (hit them with something heavy). These bushings set all the really critical dimensions, get them right, I didn’t (the swingarm bushings slide in a bit when the swingarm is installed in the frame) and had to remove 60 thou from each side.

Now drink a beer, you deserve it.

Next up, front motormounts, for real this time

This is the part where you get to commit, do you hack up the frame or dont you? Eh we have come this far, I can mostly un-do whatever I totally screw up, its kinda like getting married, except well not, I can still solve all my problems with a welder.

Death wheel time, remove that guard, have another beer (or don’t, you do you, don’t be dumb) and chop off them front mounts.

Mmm Progress, but I don’t like how the motor is angled in the frame, my gut and the carb/intake alignment say it should lean forward more. To do that we have to modify the frame. Chop the bendy bits you don’t like, ratchet strap the motor where you want it and go to town with a metal glue gun, this isn’t a show piece, you are painting everything anyway.

I used some 1″ 4130, because this bike is going to be abused. I don’t have a tubing bender, and notchwelded tubing is for hipster exhausts not structural bits. I found a huge propane burner for boiling mash in my pals garage, heat up your tubing till its a little redish on one side, stick it in a trailer hitch and jump on it, that ought to work. Repeat until you have a couple of 3-5 beer matching bends. Don’t heat it too hot or you will ruin your mat props, how hot is too hot, dunno, dull red is probably safe, you’re an aerospace engineer you know what you are doing, it will be fine, 4130 is decent after a temper and overkill anyway. The bar patrons across the street kept looking at me funny, everybody should melt things with a large propane fire in your Hermosa Beach front yard at 2 am every once in a while.

When you weld the tubes in do a decent job, tack everything enough to avoid warping the frame too badly. If you have porosity fix it, we are using these as the dry sump tank, you don’t want these to leak oil, or your frame to do the splits while you are riding it.

Next up, motor mounts, well go work at your real job for a month, then motor mounts. Angle iron, A36, because you have some and heavy = quality. Put the motor where you want it, you are going to have to notch the frame for the header anyway. You need a m10x160 and a m10x120 bolt for the mounts, the 510 bolts are way skinny. Cut off that goofy little ring, I think its for the coolant drain but I dunno, it gets in the way and you don’t need it.

Now that you have the bare minimum done to the frame, you can throw everything together to see what you need to modify.

Getting hardware to clear

  • Exhaust flange bolt, Notch and weld as necessary.
That little notch at the bottom of the square tube makes it so you can install the exhaust without taking the motor out.
  • Intake plumbing wont clear the frame. You have two options, sledghammer a preform before you cut it, or notch the frame. Sledghammering tubing often takes more than one try, so I went with notching the frame. Welded on a doubler because it looked right and the frame is supposed to be strong.


Lube is important

You will need to add a dry sump tank somewhere because the Japan motor is dry sump and the Italian one is not, but mostly because dry sump=infinite wheelie time. I did this three times, because my first incarnation only held 0.6 qts, which my gut told me was too little and my second try was hackish, also I needed to add a pre pump screen.

Slice the frame where you want the top of your tank to be, don’t cut all the way through, leave a bit for alignment. Insert a plate, weld shut. Then cut and weld that bit you didn’t before. Make a fill port, weld that to the top of your tank. Include some way to attach a 1/4″ ish breather hose to your port (this connects to the little breather on the valve cover).

Why do you need a breather hose? Well dry sump systems typically have two oil pumps, one is bigger and it moves air and oil, you need to let the air out or you will get a really oily air filter, maybe a blown seal or two if you are unlucky. The first pump takes oil from your tank, and crams it into your oil gallerys, lubing up all the bits in your engine that need lubin. The second pump removes everything that’s done lubin from the crankcase. Since oil doesn’t necessarily all flow immediately or evenly to the sump, the scavenge pump (#2) must move much more volume than the pressure pump(#1). This ensures that anything in the sump gets immediately sent to the tank and your tank doesn’t run dry. If your pumps were the same size, you would not be able to fill the tank as fast as your pressure pump drained it which is bad.

Leave the frame runner holes in place, close out the bottom of the frame. It would probably be a good idea to seal the top of your tank with silicone or proof it for good measure. It’s way easier before you weld everything else shut, I didn’t and had a tiny oil leak that took me forever to find. If you don’t want to use the frame runners as oil lines, you could just use the frame tank, which i did the first time around, but I changed this later for more oil capacity.

We want to avoid huge bubbles flowing from the bottom of our tank, as this can cause uneven flow to the lube pump and reduces how much oil we can fit in the tank without choking the breather with oil. Weld a scavenge inlet riser/nipple into your frame tank, you want the scavenge to discharge about 3/4″ the way up your tank, and you want it to spray sideways, away from your tank cap/breather. I also put a little hole close to the bottom of the riser so I when I remove the b-nut, the tank would drain all the way.

Wash out your frame with alcohol or gas or whatever floats your boat, then weld the frame drains closed (two tiny holes on the bottom by the swing arm). Pause for a moment before you weld or it will catch on fire, not a big deal but moderately surprising. Then add a cross pipe and another port, I used -6 an hardware because fancy, but use whatever you feel led to weld on, this system is low pressure it will be fine.

The bend is so the sump drain plug clears. Oil system V2 required removing lines from here to drain the oil, super annoying.


Well, I did all this out of order, but this is where you should paint your frame.

Purdy, notice the two nipples into the frame tank, this was oil system V1

Plumb the oilifier.

Put the motor in, then chop the aluminum inlet/outlet lines, route them how you want and weld nipples on the ends. It is cheaper to weld on push to connect nipples and hose clamp lines, but I like having easily removable hoses (and AN fittings make you go faster).

Put an oil screen on the inlet line, you might not need one if you did a good job cleaning out your frame (I didn’t, there are probably chips and nasties in there). Even if you did its a good idea if you are friends with your oil pumps and want that friendship to last for any length of time. An easy way to do this is with an Earls fuel filter, open it up, throw away the little screen and make a new one out of whatever mesh size you want. I brazed together a stainless one with more surface area so it would take longer to clog (because good engineering is lazy, now I never have to clean it).

Now would be a good time to start putting the rest of the bike together to see what else you have to do…..again

Starting to look like a motorcycle

Letting it breath (intake)

Aluminum 2.5″ od 45 degree preform+ 0.1″ plate + Alex = clean air for wheelies. Thanks Alex!

Terrible Picture, Make Better

Dont forget a 1/2″ nipple for your crank breather. I turned one out of a bar, but you can also get them on mcmaster.

Hot gas outlet – How To

You cant weld the stock yamaha header to the husky exhaust, joining Ti to 316 takes some fancy process that is unavailable in my garage, or to my knowledge anywhere. The Yamaha header also pokes out real far and would get crushed when I lowside. Since that is guaranteed to happen often (Yup, first trackday, not a scratch on it btw, good call past Jacob) I made a more compact one out of 304. Also its way prettier.


Turn a copy of the flared end part out of barstock (make it a wee bit smaller, 304 expands more than Ti), bolt it to the motor with the stock flange and old exhaust gasket (so you fab the header with a crushed gasket). Start cutting bends. Woolf makes 1.5D 90s and 180s, they are expensive (like 30$ each) but you only need three and they make the good stuff. You want the good stuff, it makes it easy to look like you know what you are doing.


When welding stainless, backpurge and cleanliness are key, if you start to see oxides in your puddle, stop, clean it, start again. Smaller the gap the easier it is, prep time is worth it.

The Clutch

You have two options, hydraulic or cable. 510s have a magura master cylinder but you need a different slave, hydraulic line, and a custom bracket. Since I had half the hydraulic system (well one part), I decided to finish it.

  • Slave PN: 0120648
  • Line PN: 0722138
  • M6 Banjo Bolt (You dont need a fancy 40$ one, just fill it up with fluid, bleed it as best you can, squeeze it a couple times and leave it over night)
  • Slave to clutch pull thingy, you know, like those little cylinders on the ends of cables, I just made one with two drill bits and a hacksaw out of some scrap aluminum.
  • You also need a bracket dingus to hold the slave cylinder, I tried a couple different iterations and ended up with this.

Putting everything together

Torque everything to probably not going to fall off nm, except dont hulk on tiny bolts that thread into aluminum castings, you will strip those. Everything that doesn’t get bolted gets ziptied.

Now hack the wiring together, throw on the carb and go play. While at the track figure out that the oil system could be better, and the carb needs jetting. Return to the Lube section, build the way it was written, not the dumb way you had it . Also decide to rebuild the top end while you are at it, because why not.

FullSizeRender (3)
1 wheel is good, zero wheels is better

Carb (fun juice meter)

To my knowledge WR450s have 39mm Keihin FCR carbs, The ’07 510 comes with a 41mm FCR. The WR will run with the 510 jetting, but it wont run well, really rich, we want snappy power for maximum whoolieage. I went down a few sizes (from 180 to 168 on the main and 55 to 48 on the slow) and had to swap the needle. JD jetting makes a kit for the WR which is a good starting place. But if you are in LA, just take it to tokyo mods and have them jet it.

Isn’t she beautiful!

Going on an adventure next week, decided to save my race tires, not that slicks aren’t super fun in the dirt.

Taming the electricity monster (The boring stuff)

  • Order a wr450f loom from ebay, like 50$
  • Order a wr450f  CDI box from ebay, like 70$, do the grey wire mod.
    • Must be older than 07, newer WRs are fuel injected.
  • Diagrams and stuff

Untitled picture

  • Vapor instead of the goofy husky display since that is what my bike came with and there is no reason to figure out how to wire up the Husky display. Remember to reset when you plug in the thermometer

Other Stuff

  • I changed the piston (no idea how many hours were on it) and a lifter because it was slightly galled, there are forums for this, google is your friend.