Hey guys, hows it going? Back several months ago I bought a 99 Scrambler 400 4x4 just because I felt it was a pretty good deal. The guy told me it ran not long prior to me buying it. Said it died and wouldn't start back. Im not sure what actually happened to it, but I got home and realized it was seized. With a little fiddling, I got the piston broke loose enough to get the jug off. Basically they had left it sitting outside with the seat off and the airbox open and the engine had filled up with water... So i drained the water out and it has sat in my building with the top end off since then.

So now i've gotten a few other projects out of my way and Im starting to think about building this thing. Originally I thought I may part it out if it wouldnt sell whole. I couldnt get anyone to buy it for what I priced it at as a whole machine so Im thinking I would enjoy riding it around and having a 2 stroke 4x4 semi-fast machine to play one when the wife doesnt come along. This machine is pretty darn solid and straight and not clapped out aside from the engine issues. It isnt perfect but I think it would be well worth bringing back to life.

I've rebuilt several 2 and 4 stroke ATV engines so Im no stranger to how they operate or getting it done. What I have some questions about are the installation of the rod. I've paid to have this done in the past but I have access to a press and Im wanting to give it a go myself to save some money if possible as well as just learning how to do it. I believe basically what needs to be done is to measure the width between the two crank halves before disassembly, press it apart, press the new rod in and then the crank typically goes in a v-block to check for runout and you adjust until it is within spec. I dont have a set of v-blocks but I do have access to a lathe and im wondering if I could chuck it in the lathe and spin it slow to check runout once I press the crank halves back together with the new rod.

The other question I have is about the counter balancer. Im pretty sure Rick Ritter rebuilds these. Do these have a mark with the crank gear that I need to pay attention to? If I mark everything and press the gear off, can I get the new bearing for it myself and press it back together?

Basically Im looking at a pretty stock rebuild as far as the crank, with a slight overbore on the piston so I can clean up the cylinder, then I want to do some dealing with Rick Ritter and do probably a mid range pipe, clutch kit, airbox mods, and then possibly look into reeds, portwork and head machining depending on budget. Also probably just mix my own gas.

Basically just looking for any insight from anyone that has done this before. I've never ridden one of these 400 2-stroke polaris's so im hoping this is something I want to do It would just be a fun toy. Thanks for any help or advice!

- I uploaded a few pictures. Its actually a little better and more complete than it looks. Just needs a good pressure washing to get the green off of some of the parts and plastic from where it has sat.

Eric

 

Easier to just get a rod kit and have it installed. Crank halves needs to be marked with a square to have a point of reference.You need a good U notched plate to set between the crank halves for support as you press the crank pin out. Pin is set flush on one crank half,rod,spacers and bearing installed and other half aligned with mark(s) made before splitting. After flushing pin,the crank has to be on v blocks or roller with a dial indicator on the magneto end of the shaft. Allowable run out is .001 Crank halves have to be smartly tapped with a brass hammer in most cases to get aligned or within .001. Counter balance gear is marked in relation to where it aligns with crank gear and must be marked before you even attempt to press this gear off to replace this bearing. Again this is best left to guys with the proper tools or you will just end up tearing up the c/b shaft. If Rick can't get to it Todd Kirby down in my neck of the woods rebuilds them.Polaris 350 400 Balance 3087042 Repair Service w P Bearing and Seals Included | eBay

 

Thanks for the input. I know it will definitely be easier to just have it installed, but I was just thinking it may be something I would like to learn to do. It may be a while before I start the build, im just trying to gather some info and go from there. Did the 400's seem to last pretty good with a good rebuild?

 

Those are the key words on the 400, GOOD REBUILD.. With a complete rebuild they would usually last for years,but a good rebuilt entails rebuilding one from the bottom end up. People that get a used one complain about the 400 after they patch one area after another and then something else goes wrong. Way too may parts in this engine compared to most 4 strokes and 2 strokes just by their design won't last as long as a 4 stroke. Powerful,lightweight engines,but you have to stay on top of one. Here's a good video on rebuilding a Ktm crank shaft. Makes it nice to have a crank shaft alignment jig but not entirely necessary if you mark the crank halves before hand. Don't do like this one idiot did and keep your hands and eyes away from the crank and wear safety goggles..

 

If you do choose to rebuild your crank I would at least suggest having a shop check for trueness when done and ensure it's within spec...

 

Cheap as some of these tools are getting now you can get one for 30 bucks with a magnetic base.https://www.amazon.com/Indicator-Mag.../dp/B002YPHT76 Plus you can have the satisfaction of rebuilding a crank shaft from scratch.

 

Very cool! I guess I'm lucky to have Nashua Rebuilders close by...they did mine for $5...