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The Hell You Say!!
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2,956 Posts
I see all these SMs popping up and it makes me want to buy an old dirt bike, slap some USDs on it and some 17'' rims and go see how much trouble I can get in to
 

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Registered
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4,653 Posts
Those wheels look good on there.



Quick question because I know you know your dirt bike shit. I've been looking at possible candidates for a sumo and wouldn't it better to get a 4 stroke instead of say a 2 stroke cr250 because the 4 stroke motor will last longer? just seems like all the ads for 2 strokes say needs new top end or just had a fresh top end rebuild.
 

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moron with a hammer
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119 Posts
Those wheels look good on there.



Quick question because I know you know your dirt bike shit. I've been looking at possible candidates for a sumo and wouldn't it better to get a 4 stroke instead of say a 2 stroke cr250 because the 4 stroke motor will last longer? just seems like all the ads for 2 strokes say needs new top end or just had a fresh top end rebuild.
Depends on the four stroke. Get a dual sport or a tame enduro, and it'll last forever, but you'll be down on power versus a smoker. Get any of the newer four stroke MX-ers, and you're looking at even shorter service intervals than the two strokes. The recent CRF450s notoriously have a 15 hour interval on the top end. They'll go (a lot) longer, but if you're going to rebuild something a lot, doing a top end on a two stroke is a lot easier, quicker, and cheaper.
 

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Remi's Dad
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17,593 Posts
Discussion Starter · #7 ·
Those wheels look good on there.



Quick question because I know you know your dirt bike shit. I've been looking at possible candidates for a sumo and wouldn't it better to get a 4 stroke instead of say a 2 stroke cr250 because the 4 stroke motor will last longer? just seems like all the ads for 2 strokes say needs new top end or just had a fresh top end rebuild.
The top and bottom end i rebuilt on this for $300.

It took me just over an hour to do when the motor was out.

i'd say you can squeeze more hours out of a 2 stroke toy than a 4 stroke with less hassle.

The four strokes are much more maintenance and expensive time/money to rebuild. The only setback with a sumo 2 stroke is the mix oil. They have countless aux tanks and oversize tanks that should do very well. When i see 2 strokes for cheap i will usually jump on them.
 

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Remi's Dad
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17,593 Posts
Discussion Starter · #8 ·
What size wheel/tires and rotors? I might do this swap and ditch my 17" spokes.
110/60/17 and 140/70/17

idk the rotor sizes it looks pretty similar to the stock 250r just needs a spacer of some sort
 

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UnicycleMode
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7,584 Posts
250R wheels on a dirty.... hmmmm.... want some interesting info?





The cush drive is one of the only suitable places to thin down the rear wheel and it only took me an hour or so with the mini mill and it was at a suitable tolerance for a '86 KDX200 swingarm.

The front wheel is a little tricky, had to use a set of very symmetrical modern KDX "blue" USD's. A custom axle/spacer setup centers up the wheel with the caliper bracket on the correct side. The other cool thing was the CBR250R caliper and master cylinder with a braided line run the length of the front legs to keep stopping power at stock stoppie level pressures of the standard CBR. :D


The rear runs a Gas Gas FSE400 Brembo caliper and carrier machined a little to fit, custom spacers too. Was quite a bit of fun to put together a bike that is FAAAAAAAR from road legal. Going out for a run with it tomorrow in the hills, brother in his race suit, me in mine, a pair of supermoto's, and the Wisco twisties in front of us. :D


 

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UnicycleMode
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7,584 Posts
Thus the thread name, "bail me out" lol

i'll have to stud some tires and head up to the lake with you guys this winter




Let me know the sizes and I can have a set ready to spoon onto the wheels when you get here too. Would only be an hour or so of drilling in the studs after mounting them. Gotta add the liners and have them secured, tubes in place, install them on the hoops, then drill in the desired stud pattern. I tend to use 1" Kold Kutter studs (not the Canadian ones either) for my setups on street tires and knobbies alike. I have been considering dismounting my Bridgestones off the SM wheels and getting some slightly thinner rubber for a ice tire setup on 17's, but after the years of sportbikes on ice I'm not so sure I would run anything but the 18/21 knobbies out on the lake at this point... unless some drift training is in the works, then 17's on studs are pretty stellar. :D


Usually mid February is when we hit the lakes hardest. Been meaning to get down to Lake Koshkonong for the epic multi mile road course they run by Sunset Bar. Would be a riot to have a group of us out there hooning like mad men. :D
 

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GURU
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8,827 Posts
very cool project!

As far as the 2 stroke vs 4 stroke. Not all 4 strokes are maint intensive. If you get an early 00's one then yes. WR400-426-450 are stone cold reliable. any ktm pretty much. RMZ and kxf are also good options. 5 speeds version are better. When kaw went 5 speed they just added a 5th. Suzuki messed with all the gear ratios.

Big problems, differences between the two. Engine braking and power deliver. Engine braking isn't a must but certainly helps on the track. The big hit of a 2s makes it hard to keep good traction when leaned over. Especially when you go bigger. a 125 2s just isnt enough. I knew a guy who pulled his 426 wheels off and rode his 125 around the track. Wasnt 10mins before he pulled off and swapped the wheels back.

The really big issue with 2 strokes is the top end lubrication. Its in the gas, so if you are decelrating off the throttle you get no oil to the parts. This can cause you to burn up top ends pretty quick. You just have to be careful. There were lots of 2s SM race bikes and street bikes that ive seen. I would prefer to go older with a 2s enduro like an old KE. Something with oil injection and a rotary valve. The hit will be softer and it would make a better street bike. If you are just looking for a grin, sure build a cr500AF and slap some 17s on it:)
 
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