So I recently got a 2001 Scrambler 400 2x4. The guy before me claimed these things had been done to it:

Top end bored to 420, jug hot tanked and honed, Weisco piston
Oil injection delete (disconnected?)
FMF pipe
Hard wired fan (thermal switch broke?)

I have discovered a few things on the wheeler and wanted to make a post on here since I really cant find much anywhere else on these wheelers.
-First the rear shock is either blown or lost its nitrogen charge. Are these fox piggyback shocks easy to rebuild? Or should I look for other alternatives? Is there a way to try to recharge it?
-The front ball bushings are worn pretty bad (top of strut) and I think I am missing the rubber spacer for them, Should I just get the spacer and see if it tightens up?
-The tie rods were way worn, came with a new set so I have replaced those already
-Wheeler came without an airbox and a uni filter, as I hope to take this trail riding, I have ordered an OEM airbox to put on it.
-Exhaust pipe mount was broken off, I welded it back already so that shouldnt be an issue anymore.
-I have a small oil leak from somewhere, transmission seems to be culprit (low on oil) what oil do I use to replenish?
-Front wheels have 3 stripped lug nuts (i did not do it) so I cant take them off at the moment

It starts and runs and rides and boy is it wicked fast, really wanting to get this thing ready to trail ride in the spring. I would like to re-enable the oil injection if the pump is still there just for convenience and I never had issues with my blasters injection system. What is the best way to re-enable the oil injection system? And what is the best way to get to it with the engine still in the wheeler?

If anyone has any insight or experience working on this particular wheeler your input would be greatly appreciated!

If I need to post pictures of anything let me know and I will see what I can do.

 

I've owned 3 of them and have lots (maybe too much) experience on them...I'll do my best to answer your queries:

1) Motor work - if your motor was worked on there is almost always a builder's mark on the cylinder...if you're running regular (87 octane) fuel then it's not built...
2) Rear shock - the "Sports" generally came with a non-rebuildable gas shock...if it's a Fox shock it should have a remote reservoir and they are rebuildable...cost will depend on where ya go...expect to pay between $100-150...
3) Front suspension - I'd replace anything that looks worn or missing...the stock struts are "ok", the Fox gas replacements are a notch better...
4) Airbox - so...if your motor is built it's most likely has a larger carb...if your carb is not stock the airbox you ordered may or may not fit...so be prepared to modify it...if you are trail riding and there is the possibility of deep water ya definitely want something other than a pod in there...
5) Transmission - more like a gear selector, it takes a small amount of 10-30 regular motor oil...use synthetic if ya want...
6) Oil Injector - personally I'd leave disconnected and pre-mix...while the Polaris unit has been very reliable to me, it has failed others...the pump is in a terrible place (front of motor, down low near coolant reservoir, square box...can't miss it) and makes the thumb throttle that much harder on a long day's ride...
7) Stripped lug nuts - you're a welder...put your thinking cap on and get those off ASAP!

What you didn't mention is probably the NEXT things you may want to look at...the clutches...If you know sledding you'll know how important these are. Once again, another way to know if your motor is built will be the clutch components in both you primary & secondary...if the helix has stock angles or the clutch springs are a stock color...you motor probably isn't built or whomever built it was clueless on clutching...either way before you head out 50 miles into the woods you'll want to ensure they are in good working order (the buttons are a normal wear item often neglected)...and check your belt!!! No belt...no go!!!

 

See this is why I love these forums, there is always a specialist for every vehicle. Thanks for the help!

1. I will look for a builders mark on the motor, that would be good to fact check the kid I got it from. I run 89 in my bikes so that is what i have been putting in the scrambler (only one tank so far)

2. Mine has the Fox gas shock, it is clearly out of nitrogen because I can push the cap of the accumulator in. I work at kind of a ATV shop so I may be able to poke the brain of one of the older guys for some insight on rebuilding it. I also have looked at making a bracket to swap another 20" shock into there (take-off of a XR600) and see if that works, Im going to design a bracket and 3D print it to see if it will work.

3. I got the rubber washers for the front end, the plastic ball bushing things looked pretty ok to me. I noticed the cylinder rods are a tad bent but not enough to really worry about for how much they cost to replace.

4. Im pretty sure (from pictures on the interwebs) that I still have the stock carb. So hopefully the airbox mates up ok (it will be here today). Once I get it mated up I will adjust the carb accordingly and hopefully then be safe to go trailriding without getting water into the engine.

5. Since ive gotten it I have read up on the drivetrain. Seems simple enough, wierd the crankcase doesnt use oil but i guess it gets the oil from the gas.

6. Upon further inspection the oil pump is entirely removed and there is a cover over where it was, appears to be an actual delete kit so that makes me feel better. I think I will follow your advice and just premix.

7. Lug nuts should be off soon... going to look at getting one of those little sockets that are for stripped nuts. I have a set of wheel spacers that will fit my front end, would those give any favorable preformance? or should I keep it stock width?

I will dig into the CVT once I get everything else done, I have some experience working on them from my SAE Baja team in college, we used a Gaged CVT. From the look of this thing it sure looks like a quad that was designed by a sled guy.

One other thing I want to look into is getting a rack for carrying stuff while trail riding. any reccomendations for that? OEM racks are really expensive and im having a hard time finding one on craigslist or facebook marketplace.

Thanks again for all the insight.

Pics are of what I am thinking for the shock. I will post the bracket if I get it figured out.

 

If maintained they are, in my opinion, one of the best trail machines out there. 2x4 is no 4x4 so it will have limitations...just remember that momentum is your friend

 

Ok so I have the rear end mostly apart to try to swap the shocks so I haven't gotten to work on the carb at all yet or look into rerouting the oil tank into the fuel tank (still planning to try that).
Got a 2500lb winch from craigslist today, thought it would be a good investment since I only have 2x4
I plan to mount the fairlead rollers to the front bumper by cutting out one of the slots and making a mounting plate.
I will be cutting the lower radiator mount off entirely and am planning to make mounts elsewhere for the rad since that lower mount is right in between where the rollers will be and where I am planning on mounting the winch. I will try attach some pictures if it will let me so you can see what I mean.
I am also going to try to wire a second battery on the same charging circuit as well for more winching power. The stock battery should be enough but more power is always better.
I wired in a voltage meter as well for monitoring purposes. I am also planning to add a coolant temperature sensor since my radiator fan is now manual.
I need to figure out why my LEDs are not very bright when wired to key on power, when wired directly to the battery they are pretty bright but when I have them on a key on wire, they come on but are super dim.

 

 

If you leave the engine running when you use the winch you shouldn't need a second battery. AFAIK no one else does. The winch is only going to draw just so many amps no matter how many batteries you have.

 

Where did you pull that shock from? Looks like it may have been paired up to linkage...if so you might have your work cut out trying to get it set up decently...just a thought...

I have the same front bumper...they hold up well...

 

The shock is off a Dirtbike. It does have linkage but i dont know if there would be a way to fasten the third contact point of the linkage I have with it. I ended up ordering a sportsman rear shock (less than half the price), after some research I discovered that it is the same lengths and should have the same end dimensions as well as a similar spring rate (plus its not a stupid accumulator shock so it doesnt need to be recharged).

My winch mounts should be finished pretty soon. I removed the lower rad mount to make room for it. Looks like everything is going to fit fine. Im not sure if i even need to make another lower mount because it seems the radiator is held pretty well from the top. If anything I may just 3D print something so I can connect the lower posts on the rad to the lower frame tubes and just mount it in with a hose clamp or zip tie or something.

The LEDs I put on Im pretty sure are pulling too much wattage from the battery, when im riding and I turn them on the bike doesnt accelerate too well, losing too many watts to the lights. going to get some 18W lights to put on instead.

 

Those charging systems are pretty hardy and LEDs pull little to nothing (that's why everyone is switch to LED lightbulbs)...I ran an electric lift plow on mine for years and it didn't complain to much running that...maybe dirty ground or something...