KTM 520 too much in the woods?

trewent

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#1
I am currently enjoying life on a KTM 400 exc and am wondering if it would be worth the bother to go for a 520. I ride track and trail (sometimes trials tight) yet the temptation to either throw a 520 piston/cyclinder on the 400 (which would make it a 454 cc) or just buy the 520exc goes unanswered. Anyone experienced in 520 exc woodworking out there?
 
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#2
Seems like the common feedback is that the 400s are better in woods than the 520s or 640s (LC4). I guess there's more control at lower RPMs. I cannot agree or disagree with this first hand, but I believe that I would be just as happy with a KTM LC4 400 than I am with my 640. There's so much power with the 640, it seems that a lot of it is lost with wheel spin and loss of traction on dirt anyway. When I nail it, my back end is floating around under me.

There is physics behind spinning wheels for speed, as the dirt becomes a jet. This is seen at monster truck shows. I'm not sure it is true with motocross bikes, though.

Hope this helps.
 

BCR-Bob

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#3
I rode/raced a 97 620 and now do the same with a 520 EXC. With regards to that comparison the 520 is much easier/fun to ride, the little black button and weight being the biggest things. As far as woods riding goes, I really don't see where you gain much by increasing your displacement. I've ridden the 400's and thought they were great in the tight stuff.
 

Shaw520

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#4
Trewent, It was recently determined, (in some previous post) the 520 jug and piston will not work on the 400.
1. The crank/rod stroke is too short
2. The parts are not interchangable, (con. rod and crank are different)

I do NE woods with the 520 every weekend, Its comparably as light and flickable as your EXC400, but it may require a bit more throttle control.
<its all good>

Gulliver, You cant compare the LC4 to the RFS, two different animals in every aspect.
 
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#5
let us see

After looking in my littile spare parts manual it looks like the 400&520
use the same Head, Case & pin . YES just shim this and mill down that.
Now which cam do we use? {maybe this winter}
 

Shaw520

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#6
Wrong!

Read; crank stroke on 400 = 64mm
crank stroke on 520 = 72mm

If you bolt a 520 top end on a 400 you will have close to 0 compression, not good for performance!
 

trewent

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#7
Shaw,

Are you running stock gearing? Any stalling problems? What do you do when you go moto?

Thanks,

Trewent
 

Shaw520

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#8
No,..... stock gearing is waaay tall for NE woods. I went to 14/52 much better!
What do you do when you go moto?
Fake it! :cool:

Suspension settings are directly related to the type of riding you do and your ability. Start with 3.5 inches of race sag.
 
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#9
Right

Thats a 8mm stroke diff. Which is 4mm crank pin diff. So go get your favorite lathe and spin some off {providing the piston pin center to deck is not to great}
My klx has 3.5mm peice of stop sign for a base gasket
 

Shaw520

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#10
OK

Your right,...with some fancy millwork, you could cut the 520 cyl down to achieve 64mm's of stroke.
Hmmm,... then why cant you just bore the 400 cyl to 95mm and install a 520 piston, providing the pin to piston dome is the same?
The wrist pin is the same,...The cylinder bolt pattern is the same, there should be enough meat in the 400 cyl. Hmmmm Let me try to find that old thread.
 
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#11
For what it's worth -

I ride my 520exc in very tight stuff - it might sound funny, but my own back yard is -really- tight, 80% first gear, 20% second. It took a while to get used to the wheelspin and somewhat control it, but... I did, and so will you. I have not ridden a 400 by comparison, but I think anybody could adapt to the 520. In my opinion, the power is not 'viscious', just builds very linear. I must admit, though, that I rarely get past 1/2 throttle.

I love my 520, not because it's the fastest thing out there (let's face it - the problem is all me, not the bike), but because it can be so darn fun when you do get crazy with the throttle and eat big long ruts when you slide through corners, etc. Waaaaay funner than my 1100 streetbike.
 
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#12
Hey shaw did I see you at the CATRA H.S. this past weekend in Fish House NY just West of Sarratoga Springs off RT29?

FWIW- I was on a wait list for several months for the 400EXC. It was the bike I initially wanted, but as months past I got impatient and bought the 520E at another shop. I'm glad I did. I am 6' 250lb with gear and race NETRA hare scrambles. I don't think you'll find a better test for this bike than that. Throttle control is everything with this bike. If your use to riding a 2 stroke banging a corner, dumping the clutch as you twist the throttle full back, you'll be in trouble. This thing will kill you. The power can be intense and it hooks up great it doesn't spin, it's a 2 wheel tractor.

The gearing for me is alright and although I have a couple different new sprockets (13t 14t 50t 52t) waiting to go on, I haven't changed gearing yet. It actually isn't too bad stock (14-48) I run mostly 1-3 in race conditions and on some trail rides around here I can open her up (wide in 6th) on a couple of long power line runs. Yes it is fast IMO it can be fearfully fast, but boy is it fun now and again to blow past everyone from the rear of the pack. ;) In the tight stuff if your tired you can get your self into trouble with the blip of a tired wrist but I could also do that with my 00'DRZ. Throttle control, focus, and conditioning are the keys to staying out of trouble.

IMHO I'm glad I got the 520 it fits me and my riding style to a T. I do occaisionally wonder if I wouldn't have been faster on the 400. Naaah, I'm 110% satisfied with the 520 she's a keeper and envied by all!