One of those what to do questions??

[426ex88]

Well just this past week I bought a 2002 400ex for 500 bucks from a guy. Its a little rough around the edges but it has some aftermarket goodies on it, like works shocks, moose racing bars, nerf bars, new tires on the back. Well the motor has been blown up, well just the top end. I think what happened was the kid ran it with out the air filter or something and sucked some grit down into the cylinder. So the cylinder is shot, piston is too. What I am asking is could a guy of my mechanical knowledge be able to put a new piston in and get the timing and stuff right, after I have the local ATV shop bore the cylinder out to a 426?? Doesn't seem like rocket science, but I also don't want to put it together and then 5 hours later something goes wrong with the motor. The local ATV shop told me it would 450 bucks to have them put it back together, that's including parts and labor. What is a guy to do?

[katch26]

where are you located someone may be able to help you out.....i avoid dealers at all costs JMO

[fauxamish]

Save your money and do it yourself.

If it is just the top end, then it should be fairly easy for you to rebuild it. Is it seized, or is the piston/rings just bad? If you are pretty decent with tools, you should be able to do it.

First, buy a Clymer manual (or get it from the library...). It is an excellent book and is extremely helpful.

Second, take your time doing it. Don't rush because you will probably be taking it back apart after 5 hours if you do.

There are a ton of threads on here about rebuilding. Don't be afraid to ask questions.

What made you go with a 426? What compresion? I'm just asking. You should probably think about a HotCam, HD studs and CRF timing chain.

Hope this helps. I'm getting ready to do this myself, after I finish some other projects...

[Rkangel7]

I guess it would depend on your mechanical knowledge. You may consider picking up a service manual and checking out the sections related to rebuilding the motor. Then you could get a feel for whether or not it is something you're comfortable trying.

If you are comfortable, then you can save the $450, or put it toward more upgrades.

Just a thought...

[426ex88]

katch26-Im out of Mid-Missouri and its a guy who has been racing quads for a long time, so i think i would trust the man.

fauxamish- no its not seized, the back side of the piston is scratched to h***, cylinder wall is the same, scratched. Well the reason why I put the 426 is because the guy at the quad shop said that the cylinder had been bored before and that he would take it out a little more so it would be a 426cc. He also said not to do the 440 Big Bore kit because it would lose all of its reliability of a 400ex, start blown head gaskets. So that's why. And i think it was going to be like 10.5:1, I think thats what he told me, but most everybody I have seen with a 426 has like a 11:1. So if you got any suggestions on that, that would be great.

So far this site has been great to me. A lot of helpful people and threads.

[big95xj]

Where at in Mid MO? I moved to florida about 2 years ago but lived all my life before that in Jeff City. Let me know and i may be able to direct you to someone...

[426ex88]

I live pretty close to Columbia, Missouri.

[fauxamish]

I'm going with a 416 because I read a lot on here and decided that a 416 would be the most reliable for me. A 426 still uses the stock sleeve, but you are a lot thinner. I agree that the 440 would not be as reliable. 11:1 compression should still run on pump gas (93 octane) but I've heard the owners manual calls for at least 91 or 92 anyways.

The compression depends on the piston. If you look on eBay, you can find a 88mm piston (426cc) with 11:1 or lower (or higher)

[426ex88]

If I go with the 426 is a guy gonna have to get the HD studs and CRF timing chain. I mean Im probably going to do the CRF timing chain as it is. And also I think I'm going to do the 11:1 comp. Oh and I think I convinced myself, after a sleepless night, that I'm going to do the motor rebuild myself. And i got a Clymer manual on the way off ebay for 25 bucks plus shipping. Only bad thing is that the kid that had the quad before me tore into the motor, so I don't think I have all the bolts let alone where some of them go. :(