By the shift lever, there should be a metal tag that is welded to the frame - the numbers are going to start with a "W", then the 2 # Year, 2 # Frame, and 2 # Engine ( ie. W968140). In the 4X4 models, frame # 80 is a Sportsman, #81 is a 400L, and #91 is an Xplorer.

The 400 2 stroke has tons of HP mods - base HP @ 5,700rpm is 35 horses, with potential to produce up to 72 horses with all the mods.

If you are doing the work yourself, take your time and rebuild the whole engine, this way you know you are starting out fresh and new - without having to go back later and replace waterpump bearings, or seals, or whatever.

 

<div class="FTQUOTE"><begin quote>Originally posted by: MECHANIKE

sounds to me like you dropped your timing chain,you said you can turn the engine 3/4,piston goes up+down.you probably have a valve open+the pistons hitting it,preventing complete revolution.</end quote></div>

It's a 2 stroke

 

10/4 ON ITS A 2-STROKE.

 

ok, i haven't got this apart yet, thanks for the info again, and i do know it doesn't have a timing chain lmao!!! UJOINT what parts do i need for durability, and performance. It would be nice to get a lil more speed out of it, and do they make a clutch kit or anything?

 

The possibilities for a 400 polaris 2 stroke are endless. Wiseco piston for sure, then an RCR mid range pipe, good reeds, and then go have some fun. And those are just starters.

 

the pistons, domes or not? I haven't got it apart yet, but my sled had a single ring pistons, is that what's in that 400? btw my tag is gone, no serial number......another question, how do you adjust the chain tension on the front drive? maybe you can't? idk

 

Remove the chain guard, adjust the center chain first. Then move to the front. You roll the eccentric carriers to tighten/loosen the chains.

 

If you decide to go through the whole engine (which is not really that hard since the engine is divorced from the tranny), ALL of your bearings are common US bearings available at the local bearing supply store. Gaskets and a complete seal kit are available thru your local ATV independent repair shop.

Polaris 2 stroke pistons use a 2 ring system.

The 350/400 engine is prone to lose the water pump bearing/seals, and the counter balance shaft bearing (which Polaris wants to sell you a whole assembly) is replaceable ($18 vs. about $400), you just have to mark the gear and shaft prior to pressing the gear off.

As for the performance mods - Dad's been working on ATV's for almost 30 years now, and he has a 95 Scrammy he's done a little work on - it gave an EFI BF 750 and eye opener the other day, out of the box (although the BF did catch up and pass him). He blows my SP 700 away every time.
Like Dr said, pipe and reeds make a good start, jetting the carb - - Wiseco piston? I'm not sure - most people rant over the Wiseco as it reduces the potential for breaking the piston skirt.
Dad uses a Namura piston as he has beef with Wiseco requiring a 0.005" piston to cylinder clearance vs. the others at a 0.002" piston to cylinder clearance. He theorizes the skirt breakage is due to improper warm up before hammering down on the engine - dad always "putts around" for about 5-10 minutes before he showers the throttle, and has yet to lose a piston skirt.

He's running a RCR pipe, V force reeds, polished ports (Dad did himself with a drimmel tool - notice I did not say ported, just polished), shaved head, jetted carb, and I'm not sure what size piston (I do know that it would not be max as he believes in saving the cylinder for future bores). Although clutch kits are available, I don't ever remember him installing one on his Scrammy.

You can visit the Aaen Performance or Ritter Cycle Racing (RCR) websites to "drool" over all the HP mods available.

 

here's the number I got off the tag by the shifter, 2316433 is that the serial number? how do i tell what year it is?

 

The 400 2 stroke polaris motor is also prone to breaking the cylinder skirt. One thing to keep in mind about building a 2 stroke is they should be rebuilt every spring as far as the piston type goes in general we like building our motors a little looser on the tollerances, at high rpms the extra slop will be picked up as far as warm up goes it is strongly reconmended to warm the motor before cracking wide open I prefer to feel the heat from the exhaust it usualy takes a little while for the exhaust gasses to warm up at the tailpipe as far as speed and power goes I have a 1998 400 sport L with a DG exhaust, wiesco piston, Boysen reeds, K&N filter, and rejetted carb My 400 sport will give me a heck of a run on my 2006 Polaris Predator 500 TLD the power of the 2 stroke is defiently good