96 scrambler 400 2 stroke. it had a recent namura top end, disconnected oil pump and I was running mixed gas 30/1, was working great. this thing ripped.
then started to sound funny, like louder, as if the muffler seal was leaking. losing power, then the engine quit all together, wouldn't turn over.
took it apart, the piston came out easy and looks in good shape, but the lower connecting rod bearing is seized solid. I have had 2 strokes all my life and this is the first time I have ever experienced this.
what could cause this?

 

If you're able to salvage the top end,piston and cylinder are in good shape and not damaged consider yourself fortunate.I don't know how many times over the years this has happened to people that had brought in cylinders for me to bore that I've warned about checking and rechecking for any perceivable wear on crank bearings and lower rod bearings before they threw on a new top end assembly.A lot of times when this happens bearings will shoot up into the cylinder and the piston can grab them and score the piston and cylinder, essentially taking out a brand new top end that people have spent good $ on. Any time you do a top end only you just place added pressure on the rod and lower rod bearing.Some can get by with this,a lot of people can't.In the shop I wouldn't guarantee doing just a top end no matter how good the bottom end felt or looked. All it took was for me to get snake bit a couple times early on when I rebuilt top ends for folks until I wised up.Sorry to be brunt on this but again you're very lucky if you can reuse the piston and cylinder. New rod kit and crank bearings for sure now along with new crank seals. Plus believe it not you can have too rich a mixture of oil ratio to gas and it can essentially harm an engine also.30/1 is kinda overkill.On an engine like this the very most I'd run would be 36/1 with good 2 stroke oil. When this happens you loose octane and engines can actually run hotter from too much oil and not enough octane. Malcolm Smith told me this to my face over 20 something years ago when he came to our shop and we had time to talk over a few things as he had Ktm dealerships in California after retiring from racing. Plus who am I to argue with one of the greatest riders in the world that has seen it all? Again check ebay for deals on rod and bearing kits. Here's a couple. http://www.ebay.com/itm/WSM-Polaris-400-Connecting-Rod-Kit-45-305-/201384750720?hash=item2ee3776e80&vxp=mtrhttp://www.ebay.com/itm/NEW-ALL-*****-Main-Crank-Bearing-Crankshaft-Seal-Kit-Polaris-Scrambler-400-400L-/171867806808?hash=item28041e9c58&vxp=mtr

 

as usual thanks for the help and advice opt

 

Don't take it too bad as you ain't the first one that's had this happen to and surely won't be the last.. Good luck and keep us posted.

 

this makes absolute sense OPT.i never really thought about it until just now while reading this post. now i know what happened to my old ski doo citation did a top end job and then the engine froze up on me, however i dont know the extant of the issue as i have yet to tear into her.

 

Going through this myself here's the bearing numbers if it helps it's cheaper to order them separate from the Polaris kit you save about $100 and the bearings are all on eBay. You might not need to order all of them like in my case.
Ntn 6000 water pump I would ordered a sealed bearing for this
Ngk 6004 counter balance
62/32cs all 3 internal crank bearings
Ntn 16008c outer crank bearing
Ngk 16006c3 outer counter balance
This is only for the 91-96 Polaris 350-500 2-stroke engine

 

well i remember when my piston blew apart into piececs and i did the top end luckily i actually bought a brand new crank and rod for like 90$ shipped to my door step( i have 95 scrambler) so i would suggest that you try and find a similar option or at least this was the best thing for me to do because around where i live (rural NW Ohio) there isnt any shops that press the bearings into the rod which i believe is about the only way you can do it someone correct me if i am wrong.
Here is a link to your Part number to ebay although i didnt see any new ones listed http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=3084776&_sop=15
and here is alink to the rebuild kits http://www.ebay.com/sch/i.html?_from...kshaft&_sop=12
GOOD LUCK ON YOUR PROJECT
RUBEN

 

Don't have a sealed bearing for the water pump on the 400! Have had people try that years ago and they didn't last. It has to be open to receive the oil that's in the counter balancer cavity to keep it constantly lubricated. It along with the counter balancer bearing and oil pump driven gear bearing(at the end of the counter balancer shaft) are lubricated by this small amount of oil, 100ccs or so that's in the cavity.This is a high speed small bearing. You can remove the shielding on the inner side of this bearing if you wish and that would probably work ok and it would get enough oil. Several different kits are available on ebay from a small set to a complete engine bearing and gasket kit.http://www.ebay.com/itm/NEW-POLARIS-ATV-350-400-90-03-SPORTSMAN-CRANKSHAFT-MAIN-BEARING-OIL-SEAL-KIT-SET-/321792919408?hash=item4aec5a4770&vxp=mtr http://www.ebay.com/itm/NEW-POLARIS-ATV-400-90-03-SPORT-COMPLETE-ENGINE-BEARINGS-GASKET-REBUILD-KIT-SET-/321793155804?hash=item4aec5de2dc&vxp=mtr

 

If you have a machine shop close by it's cheaper to get the 37 buck rod kit and have it installed and trued up. Plus there are a few places online that can do it reasonable. L.A.SLEEVE - Services - Shop Services
Plus I remember all the ones I had to do like in this video.My hands are glad it's over.

 

thanks for all the info guys. i have a crank from my last engine, now im gonna have to get it rebuilt before i use it, gonna have to get a rod kit
its gonna have to wait a little while though, cuz all my time, money and interest is going into my sportsman 700. (which btw has lots of power and pretty good speed, but doesnt have near the propulsion of the scrambler)