Ktm 380 custom build

[eric82930]

Any engineers out there tell me what I'm doing wrong.

This bike will never see the dirt again so i choose to mount it without a heavy swingarm backbone. It's a 10 inch wide 141 power claw so the pegs can mount right on the side plates and my feet are the same place as stock or i can move an inch back if you think it may be better. The jack shaft will be far back so my heel won't rub the chain.

The only problem I see so far is the 141 3" pitch makes an extra paddle in one spot that isn't semetrical so it will climb better on left side hills than on right side hills.....

 

[eric82930]

The long aluminum bar in the pic is just flat plate I had laying around to estimate where the top frame spars will go. I plan to use 3/4" aluminum square tube that will have two slight cold bends so they will be pretty close to straight. The home depot aluminum tube seems pretty soft is there a better alloy I should try to order? Once the jackshaft and exhaust are on, I will add some light crisscross braces between the spars and between them and the tunnel. I have no CAD design options so it will be a trial and error design. I plan to bolt all the aluminum so it doesn't get soft from welding.

I may be able to ditch the subframe entirely and possibly lower the seat height in the process.

The 2.4" power claw only weights 30lbs as it sits.

I used 7 tooth 3" pitch drivers with one center extrovert like polaris used on the dragons.

The 136 summit rails will be set back kind of far with a 141" track but they have lots of curl on the tips compared to most rails. The attack angle will be very flat.

The 380 is already pretty light on the front so I'm not sure I should try to move the pegs back. When It was attached to my LT kit, I could stand up ride very comfortably.

I'm worried the single bolt through the front of the side plates might tear out if I hit something, Should I try to steel plate around it like they do on the sleds front tunnel mount?

This will be my deep powder machine. My other one has a 120sx kit on it for harder snow.

 

[idahoskiguy]

Very nice work! Keep posting!

 

[eric82930]

Making progress.

 

[eric82930]

Top left: The suspension is a standard scissor flipped upside down. It was tricky getting it to fit between the inboard wheels on the 10" wide track.

Top right: The main spars are aluminum bolted to a 16 guage steel sheet welded to the same cross bar the subframe bolts to. It will get web cross braces before its done.

Middle: It has VERY progressive rising rate. The suspension is sagged out an inch in this photo but it still has more travel left over front and rear than a fully extended timbersled and the seat height is the same. The attack angle is so flat the height is deceiving.

Bottom left: This is the reason I started this project. I wanted to test this idea. There is no spring in the back and it can freely pivot to this position before track tension dampens it. Under power I'm hoping the torque from the rear swingarm will keep the nose down but I'm guessing it will not be enough for steep spring climbs. But I have another bike with an sx kit for that. This bike will mainly be for the deep powder days. What do you guys think? Am I crazy?

Bottom right: This is the kind of snow I'm building the 380 for. There is a stock 250sx 2 stroke under me in this photo! No pipe wrap, no carb heat, bone stock, I had to ride it like a 125 to get the 50hp but it really was an amazing snow bike.

 

[wwillf01]

Excited to see this in the wild... Hopefully snow like that comes

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[olymon]

Way to think out of the box on the suspension. Great build so far. KEEP US UPDATED

Making JIS screws into junk

 

[Norma Stitz]

Look for a Metal Supermarkets near you. They aren't super cheap but they carry wide range of stuff and they are even open saturdays.

Otherwise onlinemetals.com is a solid source for anything.

Great build!

 

[eric82930]

Its almost done and I am waiting on one more back ordered bearing housing from polaris. They can't even give me an eta.... Any one have one forsale? I chose to use the TS double bearings on all four ends and the upgrade kit only comes with 3 hence the problem. I really need the long track right now, my short track is just digging holes in this early fluff.

I hate to publicly bash a company but I am also waiting on a mototax ski mount I ordered in June and they just kept telling me it will ship immediately 4 times since september. Now they won't return my calls or emails.... I know they are busy but It sucks they can't be more honest about the ETA. At least polaris can just say they don't know the eta.... I am getting to the point I might just build the missing parts from scratch but I always prefer to buy parts if I can't build it better. I would rather be riding than building right now...

 

[eric82930]

The jack shaft is on two plates that pivot in a way that tighten both chains equally. The tricky part is getting the pivot in the right place. I can't finish until i get the last bearing to make sure the jack shaft is square when i drill the pivot hole. I am making the assumption that the chains will stretch at the same rate but the longer chain will probably stretch faster..... I have enough room to drill many alternate pivot holes but it will look like swiss cheese. Or i could put a ts idler on the lower chain pretty easy.

 

[heliwrench]

Cool project. That 380 should rip! Are you worried about ripping off the little paddle "fingers" that were left from narrowing the track? Maybe better to cut them off now so they don't pull apart the edge of the track? I'm not speaking from experience, just curious. You're probably right about reinforcing that single mount bolt hole at the front as well.

 

[eric82930]

My ts double bearing finally got here and they no longer have grease zerks! So I have 3 with zerks and one without... The outside track fingers will probably tear off someday but might add a little traction until they do. I welded a small plate to the bike frame behind the pegs and got 3 bolts through the plate and front of the side plates. I still have some cross bracing to do on the main spars.

I rode it in the yard with a tire on the front and it does wheelie but you can keep it down with throttle and body position. The wheelie is from acceleration of the cg and has no external lifting force from the rear suspension the way a sled does so it feels pretty bike like. But it will also be bike like on near vertical spring climbs and act like it is a lot shorter than it really is. Speed, momentum and throttle control will be the only way to climb straight up hard pack. (just like a bike).

My chain adjustment idea flopped. I have to rebuild the jack shaft side plates a tad longer and it will add some weight. They will go farther forward and also act as a heel protector to keep my boot from hitting the paddles.

 

[eric82930]

In the last picture you can see the back of the rails are not even touching the track. These rails are straight, not kicked up like a TS LT. It makes it turn and feel like a short track. It will probably wear out the hyfax quickly on the front of the rails. I might have to add a set of wheels to save the hyfax.

 

[eric82930]

Test ride tomorrow

It's done. Hitting the snow this Saturday.
It weighs about 280 lbs with the 141 track. It had about a gallon in it when I weighed it and the front was 114 pounds and the rear was 169. The frame bracing and gas rack turned out great. I built bigger side panels for the jack shaft that now have 6 bolts to adjust the chain but it is way more solid. The MOTOTRAX ski mount showed up just in time. It still needs a chain guard and probably a tunnel cooler for spring.

 

[capulin overdrive]

Looks like the same year as my 380MXC. Don't know if they run much better than a 300, but they sure as hell sound better! Bet yours will sing with that shorty on there!

 

[eric82930]

Yes ive been trying to get the beast to scream like my 300 on top end but the pipe selection is grim. The Gnarly is the only pipe still available and it doesn't like to Rev. It does well with the big torque but kind of boring and vibrates a lot.

 

[wwillf01]

Yes ive been trying to get the beast to scream like my 300 on top end but the pipe selection is grim. The Gnarly is the only pipe still available and it doesn't like to Rev. It does well with the big torque but kind of boring and vibrates a lot.

I see nitrous in your future

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[capulin overdrive]

Yes ive been trying to get the beast to scream like my 300 on top end but the pipe selection is grim. The Gnarly is the only pipe still available and it doesn't like to Rev. It does well with the big torque but kind of boring and vibrates a lot.

How long would it survive with a 300sx ignition? That in theory would give it some revs.




Wonder if Bill's ever made a pipe?

 

[eric82930]

First ride was a success. Nothing broke even though I hit some rocks and logs with the track. I had to adjust the chain once and There was ice in the allen bolts. I used counter sunk allen head bolts inside the tunnel so the track wouldn't rub and had to dig them out so its not a quick procedure out on the trail. I might try to jb weld the bolts in so i don't have to hold them with the allen wrench. I doubt it will work.

THE BRAKE IS AWSOME! Why can't TS figure it out? It always works and locks up with even with the lightest touch. The power claw really hooks in reverse. It is a stock KTM caliper and MC with an yamaha apex rotor, but I used a cheap chinese brake hose from ebay that swells like a baloon.

The front feels very light but it doesn't ever lift unintentionally. It is really neutral under power. It won't stick the ski jumping, crossing ditches or steep drops onto a flat. The forks are stock trail forks and they don't need stiffer springs or any other mods. I didn't even turn the compression up. It is still long and it feels like turning a bus but in this snow it is worth having the extra length. If I only had one bike it would not be a long track.
I look forward to building the same type kit on a short track next time. By then I hope to get a cheap used timbersled sx to hack up and modify to save time then weld it to my snowbike of choice.

I am sad to say the 380 is not that impressive power wise but I am still working on tuning it. My 300 has every bit the same peak power and almost as much midrange. The 380 has more power at idle but what good is that? Even in dirt I could never figure out why people like that kind of power band but that's probably why they don't make big bores anymore.

I might paint it if I get bored next summer but probably not...looks are pretty low on my priority list.

 

[eric82930]

I forgot to mention MOTOTRAX finally sent the ski mount I ordered in june and they apologized for dropping the ball because they were so busy. It is a nice mounting system and may be worth the money to upgrade your ts mount. It doesn't waste that last inch of travel and it is supposed to bend the "d" bar before it bends your forks. The "d" bar is cheap and easy replaceable.