New KX500 converted to snowbike owner with some questions

[Bcsnowbiker]

Hey everyone,
New KX500 owner here, that I have converted to a snowbike. I have owned some big bores way back in the past, a PE400 and a couple IT465's but never a 500. Kind of dates me I know...
I've ridden and raced dirt bikes for over 40yrs, snowmobiles for 30, but snowbiking to me is the new latest greatest thing. I've been interested in snowbikes for years, and I always said the day I build one it has to be a 2 stroke 500. I picked the KX for the powervalve and Nickasil cylinder.
Bought a 91 in decent shape for the vintage. Tore it down to the frame and rebuilt the bike but left the motor alone as everything was in spec and decent looking on the top end, bottom end was still tight. I figured I only had a half dozen rides on it this year anyways, so ride it stock and find it's short comings. As far as add ons engine wise so far I got some new rads, a PC Plat 2 pipe, snowbike intake and an Intellajet carb set up for altitude adjustment. A Scalvini carbon shorty silencer is on the way as well.
So the bike rips, and makes a perfect snowbike. I can pull 4th gear up huge alpine bowls (it's big mountain riding where I live in BC). My only complaint is the top end signs off too soon. Bottom to mid are a monster, but missing some top for those big long pulls. As a caveat I have not pulled my PV apart yet to assure proper operation.
So on to my questions. Summer is here, I have a bit of play at my main bearings at the FW and it is time for a full motor rebuild. Easy parts, rebuild and balance crank, replace all bearings and seals, replate cylinder, new piston etc. Possible clutch rebuild, PV assembly, hopefully trans is happy.
My questions come to porting, head work and timing. Two things I want to keep with a snowbike in remote big mountains is easy starting and reliability. She's a one kick wonder right now and reliability? well it is a 91, enuff said.
What kind of squish is considered tight but reliable on the KX5? On my RM250 I shoot for 1.2mm but thinking a little extra clearance on the KX wouldn't be a bad idea. My thought was to have squish tightened but then the head recut to stock or slightly higher compression.
Porting ideas? Again nothing too crazy but looking to keep what I have down low and adding a bit more to the top.
Anyone play with their ignition timing much? Particularly retarding timing looking for top end.
Fuel wise I have some leeway as I have access to Avgas and typically run it 50/50 in the KX now.
Thats all I got for now, I'm sure more later.
Cheers 

[reklessj]

Welcome aboard man!! Sure you will love that thing once ya get her all straightened out. Check this out http://www.kxriders.com/forums/index.php/topic,16933.msg137454.html#msg137454 and maybe pm member 1901306708 I think he's the man for SNOWBIKE tuning a K5

[Bcsnowbiker]

Thanks man. I've read through this thread and pretty much anything I could find here and on KxGuru.
1901306708 is pushing the limits of the motor more than I would like to,but I should shoot him a PM, I'm sure he has some good ideas.

[Bcsnowbiker]

Figured out how to post a photo here. From last week and last ride on the snowbike this season.

[Foxx4Beaver]

Welcome aboard!

Nice pic!

[reklessj]

Figured out how to post a photo here. From last week and last ride on the snowbike this season.

f**kin sweet man!! Snow getting rotten up there in B.C. too?

[Bcsnowbiker]

Figured out how to post a photo here. From last week and last ride on the snowbike this season.

f**kin sweet man!! Snow getting rotten up there in B.C. too?

That day it was rotten until treeline and then just perfectly transformed in the alpine. A little bit of powder on the very high north faces. Since that day it has actually been cold and the snow has stayed icy all day. Would not be fun.
Biggest reason to hang up the hat for the season around here is all the dirt riding you have to do on the access roads. You will hit lots of snow, unload from your truck, and then a mile down the trail hit a sunny section and be dirt riding. Painful for you and the bike.
Where abouts are you located?

[Bcsnowbiker]

Here's what the snowline looks like looking into the valley

[reklessj]

Figured out how to post a photo here. From last week and last ride on the snowbike this season.

f**kin sweet man!! Snow getting rotten up there in B.C. too?

That day it was rotten until treeline and then just perfectly transformed in the alpine. A little bit of powder on the very high north faces. Since that day it has actually been cold and the snow has stayed icy all day. Would not be fun.
Biggest reason to hang up the hat for the season around here is all the dirt riding you have to do on the access roads. You will hit lots of snow, unload from your truck, and then a mile down the trail hit a sunny section and be dirt riding. Painful for you and the bike.
Where abouts are you located?

We still have snow at most trailheads here in Colorado but it's starting to go fast. I'm gonna go out beginning of the week for a couple days n see how many times I get stuck!! Lol

[1901306708]

I don’t like doing things part ways.

To get more real top end you need to do the whole meal deal. 44mm carb, a couple pounds of aluminum shavings on the floor, re-nic, a real pipe, a real head, crank the timing, and then run good fuel. Do just a couple and you get no real change. The thing can’t breathe in or out. Just doesn’t want to rev. Ya you can get it to 9000 but it won’t be moving any more air than at 5000

Honestly...strap a nitrous bottle under the fender.  It’s a pile of work to make decent size changes and without a dyno you are just guessing. I have some boondocker stuff ide practically give you if you are in the Revy area. Start with a small jet to gain maybe 10hp and run straight av. No better bang for the buck, esp if you value your time.

I do a piston every year (barrel of c111) and a crank every 2. Might be overkill but I find they are easier to change when in one piece.  Run that Lucas oil stabilizer in your gear oil at 10%. The dumb stuff at Napa sitting on the bench where you turn the gears and the oil sticks to it. I thought it was a joke but some Ice racers turned me on to it. It lasts way longer and my gears all still look mint  

[Bcsnowbiker]

I don’t like doing things part ways.

To get more real top end you need to do the whole meal deal. 44mm carb, a couple pounds of aluminum shavings on the floor, re-nic, a real pipe, a real head, crank the timing, and then run good fuel. Do just a couple and you get no real change. The thing can’t breathe in or out. Just doesn’t want to rev. Ya you can get it to 9000 but it won’t be moving any more air than at 5000

Honestly...strap a nitrous bottle under the fender.  It’s a pile of work to make decent size changes and without a dyno you are just guessing. I have some boondocker stuff ide practically give you if you are in the Revy area. Start with a small jet to gain maybe 10hp and run straight av. No better bang for the buck, esp if you value your time.

I do a piston every year (barrel of c111) and a crank every 2. Might be overkill but I find they are easier to change when in one piece.  Run that Lucas oil stabilizer in your gear oil at 10%. The dumb stuff at Napa sitting on the bench where you turn the gears and the oil sticks to it. I thought it was a joke but some Ice racers turned me on to it. It lasts way longer and my gears all still look mint  

Super good info 👍
Never thought I would get someone so close to home with good info and another kx5. I am in Pemberton but revy is not that big of trip.
I have to rebuild now anyways just bought the bike last January motor was fine then but now there is a little play at the crank bearings.
So I will get the head cut and a decompression valve put in do some porting rebuild crank and replace bearings seals piston blah blah and get it up to snuff.
Any advice on squish/head mods? Porting?
We should definitely talk on the nitrous.

[1901306708]

Going on memory I think mine is .062 and made to actually look like a squish band. I run straight c111. Because of the silly angled plug, it’s best to find a fella that has done them before or you’ll pay some extra cash to set up a jig. Lots of guys on here can do it. I had Split second do mine. Used him for years on sled motors.

Mine supposedly had motogp porting from gorr when I got it. It looked like an 8yr old fooled around in the intake with a dremmel. To me the cylinder is not worth touching unless you want to do major surgery. Sure someone will charge you $300 to make it look pretty but it will only be marginally better. My exhaust looks like a sled cylinder, or say the 86 kx500.

As far as timing, I keep increasing and it keeps making more power. Thats my setup though, yours may differ. When I went too far, it would start ticking on the midrange at part throttle. So I went up from 100 motor octane to c111 to solve that. Fixing the head allowed it to make the same power with 4 deg less timing.

If you’re going to renic, consider adding a little more clearance. I do .001 more on the bore and then shave a little down on the piston in a few spots. Gets it closer to the clearance a sled would run. Higher loads longer and high cylinder temp variations means you’re more likely to scuff.  Hope that info is usefull. Glad to help. Any other questions let me know.

[Bcsnowbiker]

Going on memory I think mine is .062 and made to actually look like a squish band. I run straight c111. Because of the silly angled plug, it’s best to find a fella that has done them before or you’ll pay some extra cash to set up a jig. Lots of guys on here can do it. I had Split second do mine. Used him for years on sled motors.

Mine supposedly had motogp porting from gorr when I got it. It looked like an 8yr old fooled around in the intake with a dremmel. To me the cylinder is not worth touching unless you want to do major surgery. Sure someone will charge you $300 to make it look pretty but it will only be marginally better. My exhaust looks like a sled cylinder, or say the 86 kx500.

As far as timing, I keep increasing and it keeps making more power. Thats my setup though, yours may differ. When I went too far, it would start ticking on the midrange at part throttle. So I went up from 100 motor octane to c111 to solve that. Fixing the head allowed it to make the same power with 4 deg less timing.

If you’re going to renic, consider adding a little more clearance. I do .001 more on the bore and then shave a little down on the piston in a few spots. Gets it closer to the clearance a sled would run. Higher loads longer and high cylinder temp variations means you’re more likely to scuff.  Hope that info is usefull. Glad to help. Any other questions let me know.

Very cool 👍
I am replating and I had the same thoughts on a little extra clearance. I also was thinking going for a cast piston rather than forged for less variation in size with the big temp swings
As far as fuel avgas is as far as I will go and I would rather keep it to 50/50 pump/avgas.
I get home again next week and then the motor starts coming apart and we will see where we are at.