guess I never actually showed why I am doing this.......

 

does that fit in to any sort of failure of the month category or anything?? LOL

 

Be sure to use air scoops if you choose to go big bore kit.

 

So have any of you guys successfully tore down a bottom end by yourself? and got it back together no issues?

 

Took the clutch cover off, just got my fly wheel tool in the mail, going to split it and flush it out. Read through the manual doesn't seem to rough. One of my buddies has all the tools to measure the rod and bearings so we can check the wear on it. Seems like it is something I can handle.

 

Wow. I just picked up a 400EX, for a similar song and dance. I got it home and noticed the same exact issue. Zero compression, then removed the head to investigate and noticed the same problem you posted here. Intake side of the piston was GONE. The piston fell off the connecting rod into my hand when I pulled the cylinder.

Luckily, my brother has the identical bike, and is wanting to put on a big bore kit. He will hand over his stock jug, piston, and rings if I will just do the work.

Have you completed this build? Since the piston is shattered, did you have to split the case to remove any chunks that may have fallen in? I have a case splitter, but not really to excited about having to split this case and would rather not if possible.

 

Ahh.. read the last comment AFTER posting that. Run into any issues with the split?

 

Haven't had time to split it yet. I took the clutch cover off and was using a pick to pull some chunks out so far. I removed the screen from the bottom of the case and seems like most of the metal from the piston was in there. I think I am going to try and tackle splitting it and cleaning it up tomorrow. New gasket set is in the mail so I can put it back together when it arrives.

 

Well I got the case split, much easier than I thought it would be. I left as much of it together as I could, all I am trying to do is get the metal chunks out of the case.



When I split it I was looking at the crank and saw a heat pattern that had me concerned. I showed the picture to my local quad service shop and they said not to be concerned that that was from original assembly of the engine. This is what I had seen.....


I dropped off the cylinder at the shop to have it bored. They said it will take a .5mm bore to get it cleaned up to new again. So that is the route I am going, and stepping up to a forged piston 11:1 compression. Since I have it apart, I think I am also going to slide in a Stage 2 cam for kicks and go up a couple numbers on the jets. Should help to bring it to life once I get it all done. I hope to have the bottom end back together by the end of the weekend and put back in the quad. Then will just be waiting on the top!!

 

Quick update,

Got the bottom end all cleaned out, everything still feels tight so I think the bearings are ok. Flushed out all the internals, put it all back together with new gaskets. Now just waiting on getting the top end back from the shop. Still no word from them so I am a little frustrated. Hopefully I can have that back first part of the week so I can have it together and running by next weekend. I did order the stage 2 cam, also waiting for that to arrive. The thing should be a brand new beast when I get it all back together!!

Any suggestions on where to start as far as rejetting? I when I had the carb apart I couldn't even read the numbers on the stock jets that were in it so I have no clue where to start.

I still want to wash out from under where the engine sits, flush the oil cooler, maybe even upgrade to a larger cooler. Any suggestions for just a larger one? maybe even one with a fan? I am also looking in to doing the reverse cooling mod. This bike will probably end up mainly riding trails and I am a bigger guy so I want to make sure it stays cool.