Purpose built snowbike

fgauvin7

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Did you get any more snow yet for further testing?

Yes I have done few more little test, we have enough snow so I can just pull it out and go direct from the house so it is easy now! The upgraded cooling system with the tunnel cooler and thermostat is just perfect now. The now coupled rear suspension keep the font end on the ground, we will see If I need to add some preload in the deep stuff when we get some. For the rest, everything is just working as it should! I have a bit of an hard time keeping all the bolts on the bike but it is managable with a good amount of loctite thread locker. :D The shaking aspect of the YZ250 is certainely something that I don't like about my engine choice.... But I will have to live with it for this year at least. I have the bearing on my output shaft extension that I will machine a better housing than the cheap sheet metal clamshell, maybe this will solve a small part of the vibration.

Right now I'm on building a new tank on the tunnel to increase the fuel capacity from 6L to 18-20L. Most of the tank is done, the hard part is to find a way to fill the small tank with the bigger one... I need a pump to transfer the fuel with an overflow that drain back in the big tank or a little pump that I can turn on when needed. The best way would be a standard diaphragm pump with an overflow but this solution need a crankcase vaccum port that I dont have.... maybe when I doa rebuild I will go this route. But for now I think I will simply put a small electric fuel pump with a switch to fill it up when needed. I will need a small battery pack anyway for an headlight.

Feel free to let me know if someone have an idea about an other way to trasnfer the fuel.... The top tank is maybe 12in higher.

Here is a few seconds of clip that I have from the last test.


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Dec 19, 2007
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I use these pumps. Light and cheap and don't make too much pressure to cause the floats to dribble. I drill the pulse hose hole right behind the reed, it doesn't need to be in the bottom end.
For the vibration problem try connecting a strut from the swingarm bolt close to the engine center castings back at a 45 to tie into the frame spars under the seat. This helped a lot on my 380. My first build just had an unsupported swing arm bolt like yours and it vibrated so bad I couldn't see straight. The bolt must resonate like a banjo string if you let it.
 

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fgauvin7

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Oct 14, 2012
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I use these pumps. Light and cheap and don't make too much pressure to cause the floats to dribble. I drill the pulse hose hole right behind the reed, it doesn't need to be in the bottom end.
For the vibration problem try connecting a strut from the swingarm bolt close to the engine center castings back at a 45 to tie into the frame spars under the seat. This helped a lot on my 380. My first build just had an unsupported swing arm bolt like yours and it vibrated so bad I couldn't see straight. The bolt must resonate like a banjo string if you let it.

Thanks for the idea! I have tought about drilling a port in the intake, it is easy as I can get to the inside and catch the chips but the casting is maybe only 1/8'' thick here... It is doable but did you use a standard npt fitting ore something else?

For the chassis brace I think you have something here... I'm sure it could help a lot to add a triangulation to the swing arm bolt. I have done a quick sketch of what I huderstand. This brace would still lack of up and down rigidity but it could help....
IMG_2108 bar.jpg
 
Dec 19, 2007
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My ktm reed walls are pretty thin too. I couldn't find any really small npt at the hardware store and I didn't want a big hole so I just used a m6 bolt with a shoulder and drilled a hole down the middle (with my lathe) then cut the head off and cut a screwdriver slot to thread it in with some epoxy.
On the strut that drawing will probably help but I was thinking going up at a 45 degree to tie into the diagonal frame member near where it joins the horizontal piece under the seat. That should help quell some of the vertical harmonics too.
 
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Use these to keep the bolts from backing out, work 10x better than Loctite.

I had a hard time keeping bolts on mine too before these:

 

fgauvin7

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Oct 14, 2012
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Use these to keep the bolts from backing out, work 10x better than Loctite.

I had a hard time keeping bolts on mine too before these:


Thanks for the tips, I have seen them in the past and we have some at work! I will certainly use some on the most problematic area.

My ktm reed walls are pretty thin too. I couldn't find any really small npt at the hardware store and I didn't want a big hole so I just used a m6 bolt with a shoulder and drilled a hole down the middle (with my lathe) then cut the head off and cut a screwdriver slot to thread it in with some epoxy.
On the strut that drawing will probably help but I was thinking going up at a 45 degree to tie into the diagonal frame member near where it joins the horizontal piece under the seat. That should help quell some of the vertical harmonics too.

I will do somewhat the same for the fitting, after thinking about it you are right that a small M6 hole is easier to pass in my mind haha I have turned a brass nipple on my lathe at M6 and I will secure it in JB weld... Pump is ordered too, I should have it this week. In the mean time I installed an electric pump and I carry a battery from my Milwaukee cordless drill to activate the pump and do refills.

For the swing arm hole mount I will fid a way to brace it but the under seat subframe is not very strong, at least not enough to dampen any sort of vibration. I have few Idea, I just need to find the easier one to build.

But ha have a done a small ride this afternoon and it vibrate a lot less in actual riding condition since I'm not always pinned in high gear. The lower seat is so nice to have and create a lot of confidence for a new rider like me! I'm not very tall and I have tried a real conversion kit to and it is pretty hard to ride if you are not used to. So overall It is a big win with the ride today, nothing broke and nothing loose that I have noticed so far. Coolant temps is spot on all the time to! There is still place for a lot of improvement but there is now something to ride with maybe a decent amount of reliability. I will know soon enough!
131996622_389281855656540_5563338234732103445_n.jpg
 

Sheetmetalfab

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Thanks for the tips, I have seen them in the past and we have some at work! I will certainly use some on the most problematic area.



I will do somewhat the same for the fitting, after thinking about it you are right that a small M6 hole is easier to pass in my mind haha I have turned a brass nipple on my lathe at M6 and I will secure it in JB weld... Pump is ordered too, I should have it this week. In the mean time I installed an electric pump and I carry a battery from my Milwaukee cordless drill to activate the pump and do refills.

For the swing arm hole mount I will fid a way to brace it but the under seat subframe is not very strong, at least not enough to dampen any sort of vibration. I have few Idea, I just need to find the easier one to build.

But ha have a done a small ride this afternoon and it vibrate a lot less in actual riding condition since I'm not always pinned in high gear. The lower seat is so nice to have and create a lot of confidence for a new rider like me! I'm not very tall and I have tried a real conversion kit to and it is pretty hard to ride if you are not used to. So overall It is a big win with the ride today, nothing broke and nothing loose that I have noticed so far. Coolant temps is spot on all the time to! There is still place for a lot of improvement but there is now something to ride with maybe a decent amount of reliability. I will know soon enough!
View attachment 363675
Video????? :)
 
Feb 4, 2011
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@fgauvin7 Good work man. I've been following this. You've done a really good job with "outside the box" thinking. Here is what I like:
  • Unconventional front suspension allowing for a lighter weight chassis frame.
  • Getting the rider position back onto the track behind the jackshaft.
  • Narrow style rear suspension rails. I'm guessing that is really nice in firmer conditions.
My current project is a large and powerful beast built for big mountains and deep snow but I'm thinking about a light a nimble machine to add to the quiver. I'm entertaining using your chassis/front suspension design for a light weight build. I'm currently a big fan of sled engines and CV clutches so I'd probably use some sort of small sled engine.

One of my questions for you is, did you mimic the rake and trail of the front suspension from any particular bike?

Do you have any photos of the chassis/suspension before the engine was installed?
 

fgauvin7

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@fgauvin7 Good work man. I've been following this. You've done a really good job with "outside the box" thinking. Here is what I like:
  • Unconventional front suspension allowing for a lighter weight chassis frame.
  • Getting the rider position back onto the track behind the jackshaft.
  • Narrow style rear suspension rails. I'm guessing that is really nice in firmer conditions.
My current project is a large and powerful beast built for big mountains and deep snow but I'm thinking about a light a nimble machine to add to the quiver. I'm entertaining using your chassis/front suspension design for a light weight build. I'm currently a big fan of sled engines and CV clutches so I'd probably use some sort of small sled engine.

One of my questions for you is, did you mimic the rake and trail of the front suspension from any particular bike?

Do you have any photos of the chassis/suspension before the engine was installed?
Hi Brett, thanks for the comment! Outside of the box was certainly a goal here and I had many crazy idea that I was curious about.

The front suspension really allow for a light chassis since everything that need to be structural is mounted close together. But If we compare my suspension and steering assembly, I don't think there is much to save vs a traditional fork setup... The only gain I think is in chassis weight. On the other side the A-arm setup is not perfect, it require a lot of valuable space (space that is low) and with it you have to mount the engine a bit higher and lift the CG. Also it is a lot of design and fab work and achieving minimal bump steer is not that simple! Solidwroks modelling has helped a lot!

The rider position sure feels more balanced but with more torque from the engine it would feel even better, the small two stroke don't have the low end torque to make the front end feel light. Since I have coupled the suspension it is a lot better in deeper snow but it feels a bit nose heavy due to the ski pressure from the coupled setup. All of this could be improved with a more conventional rear suspension that allow transfer but in a limited way.

The monorail is everything that I hoped for! Only draw back is the timbersled traverse ski is very wide and give a special feeling on hardpack. Maybe a deeper center keel would give me more roll before hitting the side runner. Oh I guess that this thing can not sit vertical by itself on the shop floor in an inconvenient too hahaha

For the front suspension geometry I used A conventional rake and trail value. Most of the dirt bike I have checked use more or less 26deg of rake and the new Arctic cat ascender front suspension use 27deg of trail. So I figured 25deg would be a good start for my design. For the trail value I analyzed the timber sled ski leg and it turn out tou have about 4in of trail. I used this value but after some testing I feel the steering quite heavy on hard pack and since it is not a speed machine I would like to reduce the amount of trail to give a lighter feeling and it will also benefit in a quicker steering feeling.

I have followed your Yamalaris project too, nice job on it! At the end I'm not a huge fan of the gear shifting thing, I'm not a motorcycle rider at all so I better like the ease or the cvt. I really think that a mix of what I have done and what you have done on yours could create what most people is looking for! But getting a snowmobile power plant in a small and light frame while keeping it narrow is an ambitious project! I have started to work on something with a sled engine too... it will take a lot of time and custom work mo make it happen.

I don't have any photo at the moment but is you have any question feel free to ask!
 

Sheetmetalfab

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Hi Brett, thanks for the comment! Outside of the box was certainly a goal here and I had many crazy idea that I was curious about.

The front suspension really allow for a light chassis since everything that need to be structural is mounted close together. But If we compare my suspension and steering assembly, I don't think there is much to save vs a traditional fork setup... The only gain I think is in chassis weight. On the other side the A-arm setup is not perfect, it require a lot of valuable space (space that is low) and with it you have to mount the engine a bit higher and lift the CG. Also it is a lot of design and fab work and achieving minimal bump steer is not that simple! Solidwroks modelling has helped a lot!

The rider position sure feels more balanced but with more torque from the engine it would feel even better, the small two stroke don't have the low end torque to make the front end feel light. Since I have coupled the suspension it is a lot better in deeper snow but it feels a bit nose heavy due to the ski pressure from the coupled setup. All of this could be improved with a more conventional rear suspension that allow transfer but in a limited way.

The monorail is everything that I hoped for! Only draw back is the timbersled traverse ski is very wide and give a special feeling on hardpack. Maybe a deeper center keel would give me more roll before hitting the side runner. Oh I guess that this thing can not sit vertical by itself on the shop floor in an inconvenient too hahaha

For the front suspension geometry I used A conventional rake and trail value. Most of the dirt bike I have checked use more or less 26deg of rake and the new Arctic cat ascender front suspension use 27deg of trail. So I figured 25deg would be a good start for my design. For the trail value I analyzed the timber sled ski leg and it turn out tou have about 4in of trail. I used this value but after some testing I feel the steering quite heavy on hard pack and since it is not a speed machine I would like to reduce the amount of trail to give a lighter feeling and it will also benefit in a quicker steering feeling.

I have followed your Yamalaris project too, nice job on it! At the end I'm not a huge fan of the gear shifting thing, I'm not a motorcycle rider at all so I better like the ease or the cvt. I really think that a mix of what I have done and what you have done on yours could create what most people is looking for! But getting a snowmobile power plant in a small and light frame while keeping it narrow is an ambitious project! I have started to work on something with a sled engine too... it will take a lot of time and custom work mo make it happen.

I don't have any photo at the moment but is you have any question feel free to ask!
Are you looking at an Arctic cat blast yet. 😁
 

fgauvin7

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Are you looking at an Arctic cat blast yet. 😁
hahaha I looked at one at the dealer a couple day ago! But I'm more on the small twin at the moment... I have an arctic cat 2014 500efi engine on the shelf... a small lay down twin like this would keep the CG pretty low and leave a lot of space for the expansion chamber. Only thing at the moment that need a lot of reflexion is to find a way to not have all the clutch setup hanging out on one side... I think I'm on something but it is not an easy one! More detail later when I receive the parts missing for a rough estimate of the machine layout.

In the meantime I will be building a motorcycle frame jig! A good setup to build those project will be really nice to have.

By the way I think I have something a lot stronger for the rear engine mount on the actual project! I hope it will reduce the vibration, I will post a photo when the part is done.
 
Dec 19, 2007
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Ive been chasing the balance between light ski pressure and coupling for years and it's really tricky and highly dependent on where your cg is. Since you can't slide your forks up and down or adjust a strut rod, Would there be an easy way to shorten your rear arm so it pulls up the back of the rails up a bit in the static position? Then you can keep the coupling shock stiff so it won't rock back but it won't force the ski down in its neutral position.
Also if you are intent on keeping the traverse ski for hardpack conditions you might want to try building a spindle with a steeper rake and slightly less trail. I always hated the traverse ski in harder snow but when I welded the fork on my raptor I made it super steep so when I turn the traverse on hard pack the side runners don't hit until the forks hit the stops. It makes the traverse much more tolerable but the best solution is to have a backcountry ski also and only use the traverse if the soft layer is over a foot deep.
Also to help with a high cg and too much ski pressure, ditch the main tank completely and put all the fuel in the back. You can make a nice goggle warmer compartment where the tank was.
If you ever scrap the frame to build a cvt based machine, put me on the notification list to buy the scrap parts! I might try an forkless a-arm build some day.
 

Sheetmetalfab

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hahaha I looked at one at the dealer a couple day ago! But I'm more on the small twin at the moment... I have an arctic cat 2014 500efi engine on the shelf... a small lay down twin like this would keep the CG pretty low and leave a lot of space for the expansion chamber. Only thing at the moment that need a lot of reflexion is to find a way to not have all the clutch setup hanging out on one side... I think I'm on something but it is not an easy one! More detail later when I receive the parts missing for a rough estimate of the machine layout.

In the meantime I will be building a motorcycle frame jig! A good setup to build those project will be really nice to have.

By the way I think I have something a lot stronger for the rear engine mount on the actual project! I hope it will reduce the vibration, I will post a photo when the part is done.
Look at what union bay racing/ fastrax did with the small motor on the timbersled kit.
 
Dec 19, 2007
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I just had a lightweight engineering Epiphany. The reason the frame is heavier with a fork is because the force from the long fork tubes is focused in a small area at the top. The fork tubes only need to be long because on a bike there needs to be room for the tire plus 12"travel. We don't have a tire so the bottom t-clamp can be moved all the way down to the bottom of the upper tubes. and the tubes them selves can be turned down to paper thin. Then the Frame can be made much weaker and lighter but the whole system is stronger. I'm going to try it in the raptor this summer. Might work well to lighten the yamalaris too!
 

Sheetmetalfab

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That really looks nice.

I have thought so much about a similar project. Yes, the headset becomes a significant stress point and you may be on the right track trying to go with A-arms. I really want a ride report, with the different front ski travel as you hit abrupt/steep snow surfaces, will the more straight up and down travel make the ski less likely to want to pop up and over stiff hits?

In my head if keeping a motorcycle style front, alot of changes could be made as there would never be a front tire. Spindle assembly could be much smaller as the entire suspension could be lowered. Headset could also be made significantly longer/taller to reduce the stress concentrations on it... but remember, I'm just thinking, I haven't built anything!

Hats off to you for putting this together. That's a ton of work and it really came out nice. Can't wait to see it on the snow and hear how it works.

I don't think there will be any hard spot in my A arm design. The way the suspension geometry is designed make the spindle go up and back just like a fork would do even with a pointed down A arm like I have at ride height. There is more than just to A-arm there to make this happen...

Sure a fork set could be made to minimize the load on the headset, I explored this Idea but the fork I had were a lot thiner in the area above the seals... the actual triple clamp area is quite beefy and I did not trust the fork structure to lower the bottom clamp and make the header like 16in long.... But in the end I'm sure there is a way to make that work and it could be the simplest solution and as light as my setup. Plus a fork set would clear a lot of space for the exhaust.... Let see what the future reserve!



it is a 12.5in x 120in for the moment, I could easily go longer if needed. The preload on the rear arm slider in the rear suspension will control the ski pressure just like a snowmobile, so it can be tuned and I can also make the rear suspension coupled by just locking the rear MTB fox float.

For turning radius I get as much as a bike, around 45deg each side. Let us see your project in the future!

I just had a lightweight engineering Epiphany. The reason the frame is heavier with a fork is because the force from the long fork tubes is focused in a small area at the top. The fork tubes only need to be long because on a bike there needs to be room for the tire plus 12"travel. We don't have a tire so the bottom t-clamp can be moved all the way down to the bottom of the upper tubes. and the tubes them selves can be turned down to paper thin. Then the Frame can be made much weaker and lighter but the whole system is stronger. I'm going to try it in the raptor this summer. Might work well to lighten the yamalaris too!

You epiphany came from this thread quoted above. 😂😂😂
 

fgauvin7

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Oct 14, 2012
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Ive been chasing the balance between light ski pressure and coupling for years and it's really tricky and highly dependent on where your cg is. Since you can't slide your forks up and down or adjust a strut rod, Would there be an easy way to shorten your rear arm so it pulls up the back of the rails up a bit in the static position? Then you can keep the coupling shock stiff so it won't rock back but it won't force the ski down in its neutral position.
Also if you are intent on keeping the traverse ski for hardpack conditions you might want to try building a spindle with a steeper rake and slightly less trail. I always hated the traverse ski in harder snow but when I welded the fork on my raptor I made it super steep so when I turn the traverse on hard pack the side runners don't hit until the forks hit the stops. It makes the traverse much more tolerable but the best solution is to have a backcountry ski also and only use the traverse if the soft layer is over a foot deep.
Also to help with a high cg and too much ski pressure, ditch the main tank completely and put all the fuel in the back. You can make a nice goggle warmer compartment where the tank was.
If you ever scrap the frame to build a cvt based machine, put me on the notification list to buy the scrap parts! I might try an forkless a-arm build some day.
Yes there is a very easy way for me to ajust the length of the rear arm, I have a slider on it and a rubber bumper to allow the tip of the rail to lift and just climb on snow instead of trenching. To control the transfer I just have a small bushing on the shaft that limit the motion of the skid, I just have to make this bushing thinner to give a bit more transfer (less ski pressure) or make the said bushing in the same rubber as the other bumper that I have on it. This way is would be coupled but with some give to reduce ski pressure when there is enough load.

It is a good advise on the rake to minimize the impact of the traverse ski on hard pack but I'm not that concerned about how it handle on hard pack as long as it is functional to go to the spot. But the trail I may play with it in the next few mods, I hope it would lighten the steering some by removing a bit of trail from around 4in at the moment to something like 2-3in. Changing the rake, well it is an hard one to modify! Like you said I would need to change the A-arm length, but this would mess up the geometry that allow the spindle to move only up and back. Also the steering linkage and bumpster would certainly be messed up too... So le just say it is 1-0 for the fork setup on this one hahaha. A-arm suspension is not really tunable.

For the CG, this one is not a problem. I don't feel it top heavy at all, plus if I combine both tank at the moment I only have around 20L of capacity. Removing the top tank would remove around 5-6L and I don't have room to carry an extra fuel tank... So I will keep it for the moment!
 

fgauvin7

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Oct 14, 2012
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I just had a lightweight engineering Epiphany. The reason the frame is heavier with a fork is because the force from the long fork tubes is focused in a small area at the top. The fork tubes only need to be long because on a bike there needs to be room for the tire plus 12"travel. We don't have a tire so the bottom t-clamp can be moved all the way down to the bottom of the upper tubes. and the tubes them selves can be turned down to paper thin. Then the Frame can be made much weaker and lighter but the whole system is stronger. I'm going to try it in the raptor this summer. Might work well to lighten the yamalaris too!
Like Sheetmetalfab posted, we discussed of this and I still think it is the best way to use for a purpose built machine. I have a set of SSS fork here that I hang on to for the next project and as I analyzed the situation it is the bottom T-clamp that carry all the load of the suspension compression. The top t-clamp only keep the fork inline with the stem and take the load from the ski or wheel pushing back. But unless you can machine a custom set of fork tube the lower t-clamp will have to stay where it is! The top clamp could be transferred above the seals to lower the stem on the frame and having much less force on it since it is closer to the ski.

It is still possible to use stock fork and achieve a 12-16in long stem tube but it is not an easy one as previously discussed. Also a setup that would allow it with the stock fork tube would require some extra parts that would cut down a bit on the weight saving possible.
 
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