Looking for 250 big red, 250sx HD driveshaft U-joint optiions

[kevin]

I figured now a days with all the people lifting their trikes there should be options out there for beefing up the driveshaft U-joint. I just finished mocking up the frontend on my honda 250sx but now tackling the rear so before I stretch the swinger I want to figure out what I'm going to do about the driveshaft. So far I'm going to be running 28" silverback tires since I have a spare set and have a 250 fourtrax swingarm but thinking it's not quite long enough but haven't installed yet so can't confirm. Just building this bike for something different to cruise around with.....I can fab, weld and machine so any information driveshaft options would be greatly appreciated!

[ps2fixer]

I suspect using U-joints from a newer machine and building your own drive shaft could be an option. There might be companies in your area willing to build and balance a custom drive shaft, I know they at least exist for the automotive world.

To get a beefed up version of an ATV drive shaft, I suspect a drive shaft from a side by side would still be fairly small, but built stronger etc and probably longer. Maybe you can use one from like a Honda Big Red side by side, and build the swing arm length based on that.

Pretty sure the 250SX can take something like 25-16in factory, the TRX250 is about +3 in longer so I think 28in might just squeak by. Giving it a lift would probably increase clearance enough I'd think. I've ran 25in on my sx for a while, only on hard bumps does it ever rub and it's a completely factory setup. I went back to 22's of course as it was only a temporary thing.

Also prob worth mentioning that the SX and ES drive shafts are slightly different. If I recall correctly, the 250es is a solid drive shaft, while the SX has a slip yoke in the middle. I'm not sure what style the TRX250 used, but pretty sure the spline count on both ends would match the es/sx machines.

Good luck with the build. Hopefully you're not building a 250es since the swing arm bolts on differently than the SX/TRX250.

[kevin]

Yeah I'm building an SX....it's more so that I'm looking for better U-joint options something that can take more angle for when I lift the back of this thing and yes you're right about the driveshaft differences. I thought I seen somewhere that the fourtrax 300 or 350? used a beefier u-joint and had same spline count but can't find that info now.257723257724257725
Right now it's sitting on old garbage tires and stock swingarm but I should have the 28's mounted soon than I'll know for sure how much if any I'll have to stretch the swinger. Fourtrax swingarm is currently in pieces getting cleaned up

[ps2fixer]

Don't know much about the 300s and 350's but I have a TRX350D that I could grab basic measurements from if needed. Not pulling the drive shaft out though lol. I think the rear diff is similar to the 250es/sx/trx250 but mounts slightly different so might be an option. The TRX350D more or less is a 250es bottom end with a 350x top end. Sadly it doesn't feel like a 350x because the machine is heavy... like a tank, it also has a horrible turning radius, so it steers about like a tank too lol. They made 4x4 work by adding a splined output to the front side of the output shaft. I haven't researched it, but in theory if the bottom end uses the same engine mounts, it should be a near bolt in power upgrade for the 250 machines. I'm tempted to see how different the engines are and throw it in a big red frame, would be nice to have a shaft drive version of the 350x with utility style suspension lol.

Going bigger for the drive shaft shouldn't be too big of a problem, your main limiting factor is space inside the drive shaft tube. In theory you could take a 250es/solid drive shaft and cut it in half and get a thick pipe just a tiny bit larger than the drive shaft metal size and put the two halves in each end of the pipe and weld to length. Pretty sure the OEM drive shafts are solid, the pipe might not be the weak point though since radius being larger increases strength quite a lot and is less weight. Like a drive shaft in a RWD car or 4x4 truck isn't solid. Exception to that is FWD cars, they use a solid CV axle from trans to wheel, but it's only about 2.5-3ft long and space is the limiting factor for them.

Personally, I'd use the pipe trick. If you have a metal lathe, you could go a tiny bit smaller on the pipe size, and machine the inside to match the drive shaft so when assembled it will be easier to make it more true/balanced/straight. If the machine's main usage is mud or going fairly slow, balancing is probably not a concern anyway. For higher speeds it might be worth while trying to find a good way to balance it, something like 4 bearings that spin very freely and set the drive shaft on them and the heaviest part should go down, add weight till balanced. Being such a small diameter, not sure how possible that would be, it works for tires though.

Anyway, I'm following along to see the progress on the sx. I happen to have a TRX250 (85 or 86 can't remember) rear swing arm too, and I have a SX I've debated about trying to extend. It's a lot of fun in stock form too, but I might have a lead on a 2nd SX that's in a bit rougher shape that would be pretty ideal for a swamp/mud machine.

[kevin]

Ok finally put tires on and with stock swinger and no lift they rub slightly so I'm hoping when I install the trx swinger and lift a few inches should hopefully be ok but we'll see I'm just waiting for bearings to come in257789257790257791

[floydechoes2000]

Wow kevin, that thing looks mean so far! Just a little more lift in the back and it should be unstoppable.

[Dezlemke]

Is that inverts on a sx? Never seen anyone do that.

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[kevin]

Yep put on a set of inverts that I had sitting in the garage off a yzf450 figured I wanted to lift why not stick them on since I haven't seen any others and they're 7" longer than the stock forks. That's just one of the many upgrades I've done since I first got this pos.
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These are pics of when I first got it, think I've made some progress

[ps2fixer]

Looks like it has an ES engine, or was it repainted? Is the rear diff an ES one too? Hard to tell in the pic, but kind of looks like the rear diff was repainted and the paint's falling off.

What's your plans about off setting the gear ratio for the larger tires? ES engine + ES rear diff would get the engine happy with about 25in tires, probably could handle 28in w\o too much of torque problems I think, but some deep sloppy stuff might really bog you down.

Also, is that front fender for a 350x? looks pretty good on the sx xD.

[kevin]

Hey ps2fixer the fender is off a 350x and thanks the motor is an es and diff is unknown but I'll be putting in the trx diff which is the same ratio as the es along with the trx swinger.
Down the road I am going to look what's involved in a gear reduction as with these bigger tires I'm pretty sure it's going to be sucked out.
One bonus is I had picked up another sx complete for parts a while back not knowing anything about the machine later to find out someone put in a 300 motor with sx angle drive but gave up the project since it had no spark. I would like to swap that 300 into this current bike but know nothing about wiring or electrical components I'd need to make this work is kinda scaring me off as electrial isn't my fortay Wiring harnesses on parts bike is a complete rats nest!

[ps2fixer]

Haha, I foresee another harness project for me to build, at least like adapters or something.

90% of the harness is just single wires running from one location to another. Like 3 wires commonly split, ground, power, and kill wires.

I haven't looked over the wire diagrams, but I think you could probably use the 250sx harness on the 300 engine, you'd just need to either hack off the old connectors and mate them up correctly for the 300 engine, or have me build adapters if I can get all the connectors new.

Both machines should generate power the same which is the main concern for the engine. Spark etc should be the same system too. Electric start is simple, just run the big cable to the starter and the existing harness should work like normal. Safety system on the sx vs trx might be different, could bypass it if needed (ex: no e-start while in gear).

[kevin]

Thanks I'd be a buyer forsure! I thought I saw somewhere that you need to use cdi from the 300 and also there's different amounts of wires coming from the stator?

[ps2fixer]

What's the exact year of your SX? Actually better yet, what's the first like 6 characters of the engine serial number to validate model + year of engine. 85 and 86-87 SX engines were very slightly different, nothing ground breaking, but the pulse generator ground is wired slightly different lol. While you're at it, getting the year and/or the engine serial of the 300 engine would be handy. I'll guess that it's a 95-2000 TRX300FW (4x4, but not sure how the front drive shaft is setup to validate). There's 2 main wire setups on the 300FW, 95-97 and 97+.

The alternators are different designs, can't remember what they are called, SX is the Y shape in the diagrams, and the 300FW is the delta (triangle) shaped one. Pretty sure both are just 3 phase, so regulator and such should work electrically yet. Pulse generator looks like nothing special for both 300FW setups, they internally ground, so only 1 wire goes to the Harness, both SX models have 2, a ground + signal so the ground would possibly have to be ran together with the other grounds (green wire).

The problematic area is the "brain" of the system, CDI for the SX and "ICM" (Ignition Control Module) for the FW. The early version of the FW uses a ICM + Alarm Unit, later model they appear to be combined together. In theory the SX/ES CDI could probably drive the engine, but it might not perform super amazing due to timing differences etc in the spark curve map (I used a ton of different CDI's on my 350x, and most can at least start it). If you end up wanting to use the FW ICM/CDI w\e you want to call it, I'd say you would probably want to buy the old style one to avoid the alarm unit confusion.

The wire diagram I have for the FW is pretty blurry, but it looks like a yellow/white wire comes off one of the AC stator lines and runs directly to the ICM. Also the kill switch/ignition switch would have to be reworked since this is a short to run system, good news is, I'm pretty sure the ignition switch from one of the FW models is the same setup as the large SX switch, so probably easiest to leave the kill switch unhooked and use the ignition switch to kill the engine. It seems the ICM is DC powered, so would have to have probably 1 wire ran for DC power into the CDI, and also the wire going to the stater yellow/white wire.

I haven't dug into the safety system in the FW, but there's a neutral, and reverse switch, and a temp sensor. Looking like it's just a neutral safety switch (short it to ground = allows spark).


The one wire from the stater to CDI is something that confuses me, I don't get what that's used for, unless it's like a dual powered CDI, like it power off the battery if the battery is good, if not then the engine's AC alternator powers it when kick/pull starting it. I've toyed around a little with another CDI that's somewhat similar and I didn't have luck getting it to spark, but it's a different setup completely.


Long story short, the 4x4 utility models are a bit more complex, and the CDI/ICM is kind of the same way even though most newer machines are probably that way.


Also, looking @ the specs, the 300 is only a 281.7cc engine lol. The 300 alternator is slightly bigger than the EX/SX (220w vs 200w). The ignition timing specs are the same or very similar, so in theory idle and floored it should run ok, but Honda doesn't really publish much info for the ignition timing stuff.

I suspect it's a possible project, I'd personally attempt to use an ES/SX CDI with the TRX300 engine though. Sadly it's not a whole lot of CC's gained, but every little bit counts. I've wondered about the TRX350D engine in the 250es/sx frame, I think I read somewhere long ago that the engine mounts were different. It's not that hard to make mounts, so would probably make a beastly ES/SX machine. I have one of those engines in a frame that's bent, no ES/SX frame to throw it in atm though lol. If you want to give this a shot with the SX/ES CDI, I'd say watch ebay for an affordable harness and maybe if you get lucky a spare CDI. Would suck for you to start cutting your own harness up, then run into a brick wall and can't undo the changes.

[kevin]

Wow that's a lot of info right there!
The engine number of the 250 looks to be TE04E-6042372, the wiring harness on this sx was totally hacked up by prior ower so bad that to kill motor you had to pull off sparkplug cap lol. I have since got one of my buddies that's good with electrical rewire to get everything to work as it should minus having a key as there wasn't a dash when I got it.
The other sx parts bike with the 300 is currently in storage so will have to wait a bit to get motor info. Pretty sure that 300 was from a 2wd unless they changed the side cover. Condition of the 300 is unknown but feels like it has decent compression but don't want to spend much time on it unless I can get spark out of it

[kevin]

Found a pic of the sx with the 300 no sure if this helps at all though 257823

[ps2fixer]

Yea I don't really know anything about the 300 model. The manual I pulled the info from was for 2wd and 4x4, saw that right trailprotrailpro I made the post. FW is just the 4x4 version, TRX300 was the 2wd version. Same wire diagrams per year it seems. Didn't know you was in Canada (we don't really see the reflectors down here). Most models should be the same for wiring though I'd think. Engine looks pretty clean. I see there's a bit of a wire mess in the front, but the main harness looks alright.

The ATC250SX harness is pretty simple. Green is ground, black/white is the kill wire. Keep them separated to run, short together to kill. Kill switch on the handle bars would work fine for the switch. To get lights working, you jump the red & black wires where the ignition switch plugs in (2 or 3 pin connector, pretty sure it's 3).

If you get a dash, I modify Honda switches that are still available for the atc250sx machine using the proper plug etc so it's plug and play. If I recall correctly, the wire is slightly longer than OEM. Also sell the ignition key rubber covers since the only way to get them is by buying the whole switch assembly. I take them off the 2nd/spare key to resell. I have something like 50 or so of those rubber key covers on hand if you know anyone into collecting NOS parts w\o orig packaging.

[kevin]

Made some progress on the sx finally installed trx swinger and am currently coming up with different options for bottom shock mount. I like using up spare parts lying around in the garage so I'm hoping to come up with a use for these.258157

Starting to make up brackets hopefully I can make something come together.

[kevin]

Well just an update have bike back together and riding it for a while now with no real issues seems to still have decent power but haven't gone too crazy in the mud. Also have a spare motor I put a gear reduction into so may swap that over at some point
Now next project will be trying to get 300 motor in my other sx to fire up....it's only been a couple years since I last looked at it lol263184263185263186263187