ATC350SX Build Thread - Shaft drive 350x concept

[ps2fixer]

Well I've started collecting parts for this project, so figured I'd get a thread going. I have some crazy ideas for this build, but I'll have to see how things work out. It's a budget built so probably won't end up too pretty, but it's a functional build to get a little more out of the 250sx and more tuned for my riding style and terrian (sand, swamps, mud, tight wooded trails, etc).

Here's what I'm starting with. Also missed the trashed fenders in the photo. 85 250sx frame, grab bar, tank, and some ITP steel rims I got off the guy. I'll have to get a photo of the 350D, it's ride-able but pretty trashed and the engine noise has stopped me from enjoying it as is. Since I fear the worse and the crank needs fixed/replaced I have some interesting mix up of parts I want to try, if they work, I'll have a very unique shaft drive machine, if not, then just at typical 350D shoe horned into the 250sx frame. I'm unclear, but some people say the engine bolts right in, more people say it's nothing the same. I'll find out once I get the engine pulled. Engine mounts shouldn't be a big deal to build but making it so the engine can go in/out of the frame might be a challenge lol.

Anyway, few photos of where I'm at. I'm keeping an eye out for a parts 250sx since I have a feeling I'll need some misc parts but most will be from the 350D. If all goes to plan, I'm converting the engine to kick start only, no battery, I'll keep the voltage regulator/rectifier for lights (maybe LED). Name of the game is to make this thing pretty light since shaft drive naturally is heavier than chain drive. End goal is effectively an atc350x except it's shaft drive which is why I'm targeting the 350D engine which has more or less the 350x top end design.

https://i.gyazo.com/81442ae0ffde5ee5e1a71aa7415a8c19.jpg


Frame looks pretty straight, I haven't looked over it for broken bolts and such, foot pegs bent up a bit but should be easy enough to fix later.
https://i.gyazo.com/f47c436c233f8daa9037f7bd0cfae0c9.jpg


Tank clearly was repaired at some point in time, hopefully it is usable, not too worried about it being ugly. Guy put a bunch of oil inside of the tank to prevent rust.... used engine oil. Couldn't see how bad the rust was, should have asked for some gas and flushed it out. I'm not sure on what tire and tire size I'll be running, he had the rims for pretty cheap so figured I'd grab them encase I needed an extra set, I don't have much for SX parts on hand.
https://i.gyazo.com/ad7b703ec3ac66fdf5ef669bd0055dd8.jpg

I do plan on building a custom harness for this machine once I get everything else figured out.

Always open to ideas and suggestions or other people's experience. I have the 350D on hand, I know the 300/300fw engine is easier and done more often, but that's a 2 valve engine, I want the 4 valve 350x style =). I'm currently not planning anything like big bore kits or anything like that. Wouldn't mind running a bit higher compression piston than factory, I'll be running ethanol free 90 octane in it.

I've heard the XR400 exhaust header works on the 350x engine, anyone have more details on that setup? I heard there's some slight head mods needed to make it work.

I like a quite/stock sounding exhaust, thinking about a TRX400EX exhaust, good or bad idea? Mounting and bending a little is no big deal. The other option is a DG for a 350x, but not really into the super loud exhaust.

Planning to use the TRX400EX carb and will try to use the stock air box (I think I have one around). I don't normally go in super deep mud, but I want to connect the carb up to the frame rail "snorkel" that's factory to keep atleast stock levels of ability for water.

Clearly the 350D engine is full time 4x4. I'm not sure how the offset compares to the 250sx, but maybe I can swap the output shaft over from a 250sx into the 350d engine? If not I should be able to figure out something to "delete" the front drive shaft one way or another.

Any suggestions on cheap but pretty good rear shock? I'm pretty sure I have a spare one from a 350x and should have one from a trx250x. Probably not going to be jumping this thing too much, maybe that will evolve later though.

Hopefully this is a fun thread and the build should be pretty interesting.

[MrConcdid]

:popcorn:

Interesting, I haven't ventured that far out, into mixing and matching that much.
Cant wait to see it come together.
MrC.

[ps2fixer]

I did a little poking around ebay, output shaft is a completely different design, so if the output shaft offset isn't right, I'll have to move the whole engine mounting to align it even if the engine is a "bolt in" swap. From what I can find, no other machine has a similar output shaft design like this one, so I'll have to deal with making the 4x4 setup work with out driving anything in the front.

Sounds like I have a hand full of rear diff options for different gearing too. Here's the list with the rear diff gear ratios. Ironically... I own atleast one of every one of these diffs lol. The numbers are the ratio aka 4:1 means 4 turns of input shaft to 1 turn of the wheels. Lower the number, the higher geared it will be (more top speed, less torque). In my head I think the stock 250sx gearing is a good starting point, but would be interesting to compare it with the 350x since it's somewhat similar power output and speed etc I'm going for.

ATC250ES - 5.684
ATC250SX - 4.969
TRX250 (85-87) - 5.684
TRX350/350D - 3.889

ATC350X - 3.077 - Yea I know, not a direct thing to compare, but interesting to include atleast.

I was not expecting the 350 to be the highest geared... by far, I guess it has the most power so the logic is it should be able to handle the higher gearing and also have a byproduct of having a faster top speed. Top speed isn't my primary focus, but it's something I'd like to be somewhere between the 250sx stock gearing and 350x stock gearing for highest gear. So top gear ratios up next for the related machines.

ATC250SX - 0.848
ATC350X - 0.935
TRX350D - 0.906

This is ignoring the primary gear reduction (crank to clutch basket), so I'll throw these numbers up here just for a reference point. This is part of the parts I might be swapping around.

ATC250SX - 2.407
ATC350X - 2.833
TRX350D - 2.103

Well that throws a monkey wrench in things, the numbers all float around so much so I need a base line single number just to make simple sense of the numbers. Now for the math... a 4:1 ratio going into another thing that's 4:1 means the initial shaft has to turn 16 times for 1 turn of the output, so we need to multiply all the numbers to get crank turns vs rear axle turns.

ATC250SX - 10.142
ATC350X - 8.151
TRX350D - 7.410

ATC250ES - 12.395

Another nice big factor is the tire size differences, have to love comparing machines that are all wildly different. I suspect the best number to compare this all is to give the distance traveled per engine turn in highest gear. Another route is to base line one tire size and add a % change for the difference.

Machine - tire size - circumference (travel distance of 1 turn) [2 * pi * r] - travel distance of 1 engine turn [circumference/gear ratio]

ATC250SX - 22in - 69.12in - 6.815in
ATC350X - 22in - 69.12in - 8.480in
TRX350D - 24in - 75.4in - 10.175in

ATC250ES - 25in - 78.54in - 6.336in

If my math is correct, The 350D is about 17% higher geared than the 350x in stock form. I think there must be a number missing, like another gear ratio to account for like for the trans output to output shaft ratio. When I have the engine apart I could more or less validate the numbers by turning the engine backwards so there's no slip in the clutch and mark the output shaft.

Did a little more digging, counting teeth on gears on ebay listings and such, it appears the "middle" gear ratios are part of the output of the trasmission to output gear so those get to be accounted in all of this too...

*Corrected total gear ratios*
TRX350D - 12.688
ATC250ES - 12.395
ATC250SX - 10.142
ATC350X - 8.151

*Corrected travel distances*
TRX350D - 24in - 75.4in - 5.943in
ATC250ES - 25in - 78.54in - 6.336in
ATC250SX - 22in - 69.12in - 6.815in
ATC350X - 22in - 69.12in - 8.480in

Those numbers seem to make a lot more sense! I ordered lowest gearing at the top, so my target is around 6.8-8.5in per engine rev... Which means even with 25in tires I'm still lower geared using the highest geared rear diff. Those "middle" gears are making the rear diff effectively 6.659:1 ratio almost like a full time low range. Primary reduction gears are generally the easiest to swap out for regearing a shaft drive machine besides a direct bolt in diff, so I'll have to research some options for that. Unlikely I'll find a higher geared set though. worst case, the numbers aren't too bad with 25in tires, just a tiny bit lower geared than the 250es. Throws a monkey wrench into my other ideas/plans too but there's other solutions for the issue if I can make my crazy idea fit/work.

I wonder how interchangeable the transmission gears are. Using the highest 5th gear set from the 250sx with the 350d numbers I get 6.614in/rev which is really close to stock 250sx numbers. I might have to have some fun when I split the case with a parts 250sx engine.


Probably a good point to also mention, this build will not be fast by any means. I'm toying around with ideas in my spare time (like the numbers above) and the physical work I'm waiting on better weather. The building to do the work in wasn't built right like 40 years ago so the dirt floor is effectively mud right now. Just eye balling, it looks lower than the drive next to it, and on the other side is a swamp. It needed to be built up a good 12in or so. Maybe a thing I'll fix down the road, or I might build a small work shop to work in. Hate not having a building to really do work in.

Sounds like the 350D is a great engine to start with for an extreme big tire mud bogger build, and the folks doing those types of builds should avoid the 350d rear diff which is the same gearing as stock trx300/300fw. There's about a 32% difference between those diffs and the 250es/trx250 diffs, and even the 250sx diff is lower geared.

There's probably little to no info out there about making the 350D higher geared lol.

I guess really long post made short, with 25in tires, this thing will be a wheelie monster, and top speed will be much lower than the 350x by something like 20-25%, somewhere around 50mph, it will just get there a lot faster lol.

Hopefully the reader's heads aren't hurting from all the numbers/math lol.

[newby200x]

I could be wrong, but I thought someone had achieved this idea at this past trikefest. It had the 350D motor swapped into a big red.

[ps2fixer]

You mean this one? I thought the crank cases of the 250es was bored out and a 350x top end was installed. Both engines use the same base gasket. Don't know what was done for a piston, stroke, etc. Pic is from 2015 Trike Fest.

https://i.gyazo.com/0314ebe0fffb13d7e20857685e552308.jpg

[ctk]

Xr400 and or Xr600 headpipe does fit a 350x

[floydechoes2000]

Interesting build for sure! How about using the front output shaft for a PTO? I'm sure you could come up with some attachments it could run.

[newby200x]

You mean this one? I thought the crank cases of the 250es was bored out and a 350x top end was installed. Both engines use the same base gasket. Don't know what was done for a piston, stroke, etc. Pic is from 2015 Trike Fest.

https://i.gyazo.com/0314ebe0fffb13d7e20857685e552308.jpg

This could well very be. I didn't check out the machine in person, but saw images of it on Facebook the week after Trikefest. I can't seem to track down any of it now...not sure how to search for it.

[ps2fixer]

Yea the front to drive a PTO would be neat, problem is you'd have to jack the rear tires up to use it. Maybe while driving it could drive some sort of pump or something that needs so much done per x speed for the rear tires.

Is there much difference for xr400 vs xr600 head pipe? I figured the 400 would be most logical to target since it's the closest sized engine. I could use the TRX lead pipe, but it's long which probably means it doesn't rev out quite as quick like long tube headers vs short tube.



For the 350 big red, I'm not sure how he built it, but that thing ran pretty good. I swear someone was asking about it before he got up there and he was talking about boring out the crank case and such. Either case, here's a clip of the 2nd pull he did, pic above was from 3rd pull. Finding old info on facebook isn't easy, that's why tech stuff works best on a normal form so there's always a reference down the road.


https://i.gyazo.com/ddd91aeacf28dbdd490e6eb44414a8f7.mp4

[newby200x]

I did find this pic..although I'm not sure who the owner is.

https://www.instagram.com/p/B237fqPlKPS/?utm_source=ig_web_copy_link

[ps2fixer]

Interesting, that top end isn't black like the 350x, the top end is likely from a trx350d unless it was sand blasted. Guessing that must be an XR style exhaust. Seems like the person didn't hook in the right spot for pulling the machine out or they got jerked. I was buried about that much in clay at trike fest, didn't have any problems with anything breaking but I hooked on the rear hitch. I normally hook around the neck of the frame if I'm being pulled forward but the pulling vehicle needs to hook higher too.

[Tri-Z 250]

You really hate having to tighten your chain.

[big specht]

I have pics of the engine on his big red engine but for some reason it will not let me load the pics

[ps2fixer]

You really hate having to tighten your chain.

Yep, it gets annoying lol. The part that is even less fun is replacing rear axle bearings all the time. The rear end design on the 250es/sx/350d/trx250 is much better than a chain drive machine for mud, weeds etc. The mud here has a lot of sand in it, and the types of weeds we have in the swamps like to get under seals, so multi seals really help prolong replacing bearings. There's a reason by vehicles for the road run shaft drive, it's not because they deliver better power to the wheels. Besides that, a 350x, 250r, or 200x roller frame is more expensive to get around here, I don't have a spare engine on hand that's chain drive, so going from what I already have on hand, this build makes the mos sense to me assuming I can pull it off. Besides all of that, there's next to nothing documented about the 350d vs 250sx interchange for the engine, drive shaft offset, if the engine bolt pattern matches at all or not, etc. I'm guessing it probably isn't an easy bolt in thing else someone would have done it and said so like the TRX300 engine.






I have pics of the engine on his big red engine but for some reason it will not let me load the pics

You'll probably have to 3rd party host it with another site. The image uploader on here has been having issues. I use Gyazo for screen shots on desktop, not sure what a good app is for cellphones.

[MrConcdid]

Now I'm not one to discourage anyone from doing what they want, by all means carry on.
But.......
What is your main goal? just to do it?
Do you need/want a big inch shaft drive three wheeler?

Why not take a Honda 420 or 500 and put a 200x front end on it? you could do that in a weekend.
or slam a 420 2wd engine, trans ,axle into your sx frame and front suspension.
Either of those options sounds way easier and cheaper.
Just a thought
MrC.

Ps.
There are some real upgrades there also, wider axle, longer swing arm, efi if you wanted, radiator with fans cooling, better spring rates as well.

[ps2fixer]

I haven't found a quad in my area for under $1000 in years. I'll be about $500 into this project if I bought the 200x front end off the guy local to me. Getting the front end geometry right isn't my strongest area, so I'd rather start with a machine that already has that figured out. I'd love to throw a bigger engine in, but I know next to nothing about them, and some of the interchanges I have in mind won't work for those at all. Not sure if the TRX350D engine is any lighter, but trying to keep weight down even though it's shaft drive which is why I'll probably do a starter and battery delete. I could have always gone with a big bore kit on a 250sx engine but I've had this 350d for a while and my original plans for it has changed. I really love how the 350x engine runs, might just be because it's a bigger engine than the 250es/sx. The 450 foreman engine runs nothing like the 350x though, it runs much closer to the 250es/sx engine. Know pretty much nothing about the 420 and 500 machines but I suspect they run similar to the 450.

I think my area is a bit unique, we have a LOT of auto mechanics, there's so many people that the wadges they make is pretty low for the work involved (rust belt etc). There's a lot of people that work on their own machines at home here too. I find some of the most trashed rigged up machines around here even though it happens everywhere I'm sure.

I've been wanting to atleast try this project for a few years, just looking for a cheap 250sx parts machine hasn't worked out so I went after getting the bare min, frame and such.



This reminds me, here's an interchange I found no one even mentioning online. The trx350/350D shift "cage" does function in a 250es/sx machines. You can see in the pic the opening is wider so the shifter travels further for the shifts. There might be an issue down shifting if the shifter hits the foot peg, but it does fit in the engine in either case.

Also the shift shafts interchange, but shifter sticks out from the engine much further though. I'll probably have to put the 250sx shift shaft into the 350d engine to make it have a good shifter location.


350d left, 250sx right
https://i.gyazo.com/c63925dd5d259d9d26a565dc0da68943.jpg


350d top, 250sx bottom
https://i.gyazo.com/30ce1a4ced52205f839b452b46553889.jpg

[Homeless Dave]

I am curious to see how this project comes out. I think that the longer sifter shaft would make it easy to run a heel toe style shifter from a motorcycle, assuming there is not issues with the back part of the shifter hitting the fender.

[ps2fixer]

Well I screwed up the numbers, the older models included the output shaft gearing as part of the final gear ratio. All of the machines use the same gear set except the 250sx. With 25in tires and the 250sx diff I'll be around the 250sx stock gearing, 250sx diff + 5th gear swapped out to the trx300 one would be close to 250sx gearing with 22in tires and close to 350x gearing with 25in tires. I have to split the case, so I'll have to check out where to get the gears. Looks like the 250sx also has the same number of teeth for 5th gear as the trx300 but different part number. Being the 300 and 350 seem to be closer related engines, I suspect the 5th gear from the 300 might work in the 350, but the 250sx I have on hand already. The other interesting thing is the 350's 5th gear is the same teeth count as the 250es.

I'm digging in the service manual, and the measurements given seem to line up for the trx300, trx350, and 250sx transmissions for 5th gear atleast. It kind of sounds like this might be possible to swap the gears around.

[Tri-Z 250]

It’s gonna make a sick mudder, and understand the need to work with what you have.

[MrConcdid]

Ps2fixer;

You mentioned front end geometry not being your strong suit. If I were to do it, I would just weld up a fixture on my table. mount the 200x frame in a jig run a pipe through the neck and weld it to my table (braced of course)
mark and secure the neck and cut off the rest of the frame leaving the neck in place. put the atv frame on to the table establish height and squareness and weld the 200x neck in place to the atv frame. Your smart enough to figure out an even a better way if you wanted, that was just the first way that came to mind. angle finders are fine, I like to use them as a checking tool, not a building tool.


Cant wait to see this come together.
MrC.

[Rajunrick]

Here are the gear ratios for the 350D, the 350X, and the 250SX.

268021268022268023

[ps2fixer]

Haha, have to love my site popping up in my own thread xD

Source is https://atvmanual.com =)

[Rajunrick]

Well, I thank you for that site. I've used it a couple of times now.

[ps2fixer]

Yea, not a problem, the site grew quite a lot since it launched. There's a lot of data on there, but I have soo soo soo much more to add. I'm delaying updating the site till I do a slight redesign to make google more happier, and make the management system more flexible. Like the 83-85 atc200x has all very similar specs, google doesn't like the 3 pages being almost exactly the same, so combining them into 1 page will make google happier.

[LA 3W]

Well I screwed up the numbers, the older models included the output shaft gearing as part of the final gear ratio. All of the machines use the same gear set except the 250sx. With 25in tires and the 250sx diff I'll be around the 250sx stock gearing, 250sx diff + 5th gear swapped out to the trx300 one would be close to 250sx gearing with 22in tires and close to 350x gearing with 25in tires. I have to split the case, so I'll have to check out where to get the gears. Looks like the 250sx also has the same number of teeth for 5th gear as the trx300 but different part number. Being the 300 and 350 seem to be closer related engines, I suspect the 5th gear from the 300 might work in the 350, but the 250sx I have on hand already. The other interesting thing is the 350's 5th gear is the same teeth count as the 250es.

I'm digging in the service manual, and the measurements given seem to line up for the trx300, trx350, and 250sx transmissions for 5th gear atleast. It kind of sounds like this might be possible to swap the gears around.

The 250 ES/SX engine is actually more of a sibling to the 300 than the 350D.

[ps2fixer]

Yea, the 350D has a pretty unique design vs the 250es/sx. The "easy" swap is the trx300 engine, but it's more of a utility engine than a sport engine. More cc still makes more power though.

[350for350]

Since this was brought back up, how's it coming along?

[ps2fixer]

I haven't sourced a front end yet for the build so it's been stalled for a while sadly. I've also been busy trying to expand my business, moved from atv harnesses/pigtails/adapters into automotive parts. Most recent research is a simplified harness for derby cars (the bare min wiring to make the vehicle run/move).

[350for350]

Someday. That's when a lot of my projects are going to be done too.

[ps2fixer]

Haha yea, it's not high on the list, it doesn't put food on the table or pay bills =). I'm sure I'll do it eventually, but everyone knows that means probably years xD.

[MrConcdid]

Hey buddy, glad to see you back in action, I have missed you.
Yes, this will be a great build once completed.

MrC

[Pineymudder]

im very interseted in this project also.. i just happen to have 2 250sx engines on my bench and basket case frame and my friend has a 350d engine that needs work just laying around. i am also very familiar with trx300's (i have 4 of them) and old trx350's. id like to make more power for bigger mud tires. one of my 250sx has trx300 rear diff and axle installed already. i couldnt find a replacement for the sx.

[ps2fixer]

If you're going for mud, 100% 350D will give lower gearing. The primary gear set are high geared, but the output goes through an extra gear reduction gear set vs the other engines. I have to run everything the highest geared I can to get even close to sx/350x gearing, so going low geared should be really easy with gear set swap, rear diff swap (250es for example is lower geared than 250sx), etc. Of what I've read the 250sx frame mounts won't line up to the 350D engine, so if you don't want to build your own motor mounts, throw the TRX300 engine in with the output shaft swapped out, if you don't mind the extra fab work, then throw the 350d in. The trx350 vs trx350d has ac vs dc CDI, so for my case I'd be going AC so I can delete battery, starter, etc for the more "sport" focus, but for utility/mud keeping battery and DC CDI might be the better route. If I remember right the stators can be swapped if you kept the rest of the system matched up right, I think both ran batteries, just the AC stator has an exciter coil that powers the CDI directly while the DC one doesn't.

Any mod that works on the 350x top end should work just fine on the trx350d, so 400ex/450r carb, headers, etc. 100% you'll want to make sure compression release is working correctly for kick start, the kick starter is really short on the 350d's vs the 350x (maybe just swap out?).

Anyway, good luck on the project, some day I'll get this project moving along lol. Really need a garage to work in, would make life so much easier.