OOPS! ..more 400ex woa's

[bugler30]

I'm going to sell the effin thing... I'm going to take a loss but oh well

Got it back together for the second time last night and after some minor fuel delivery issues tried to start it. wouldn't start, coffed a couple times but wasn't wanting to start. Tried to pull start it and when I dumped the clutch I heard this really bad clacking noise coming from the top end of the motor followed by the rear wheels locking up. Knew right away the engine was seized, got it back to the garage and took it apart AGAIN. Got the top end off and sure as one of the intake valves had broken off and fell into the cylinder chewed up the head and piston.





I must have done SOMETHING wrong on reassembly but I have no clue what. I made sure the timing was correct, the only thing I can think of is somehow that valve decided to stick open when I pull started it and the piston hit it and broke it off. It was making no unusual noises when I tried to e-start it immediately before that.

So now I have to buy at minimum a new piston and head, cylinder seems ok upon first inspection. At any rate nothing will be happening until probably April unless I can get some stuff sold.

[Chazz of Blades]

I think I found your problem, you see that extra wheel up front?

[falloutboy]

I think I found your problem, you see that extra wheel up front?

very funny... :P this was SUPPOSED to make me some money so I could rebuild my 350x, now I have to spend another 500 bucks to get it fixed. Talked to my dad who says that the valve seats may be able to be replaced and then buff out the gouges the best that can be done then replace all valves and springs. I'm going to take it up to my grandpa's who has the know how and equipment to repair it if possible and see what he thinks.

EDIT: this is bugler30... lol, on my brothers computer, forgot it was logged in under his account. oh well

[Chazz of Blades]

I was offered a 400ex in trade recently, I'm kinda glad I didn't trade, I rode it and it just didn't......feel right.

[bugler30]

SWEET! guy called me today in response to a CL ad I posted looking for a stock cam, he's selling me a complete motor, yellow plastics, and a CDI for $200 total. I don't need the plastics or CDI but I can sell them and offset the cost of the engine. I may use the plastics though depending on what kind of shape they are in.

[younganreckless]

i have a verfy very built 440ex as u can see in my sig, but do u have a over sized oil tank?

[ejam]

You might want to check the stator and make sure that the key on the shaft hasnt broken and allowed the stator to move on the shaft. That will cause timing to be off. I had that happen on a honda xr350r . I was lucky enuff to catch that before I got the engine back together and tried to run it.

[bugler30]

I got the motor I mentioned and got it together and it ended up having a bad 2nd gear so I tore it apart AGAIN and used the top end of it on my old bottom end, it has been together and working perfectly for a few weeks now. I had bought a complete parts tranny so I have the gear to replace 2nd in the other bottom end and I found out that my old head is salvageable and I have a stage 2 hotcam so I might put some money into new valves and springs and do a big bore kit with a higher comp piston (11.25:1 or so) and put that in the bike and sell the stock motor thats in it now.

[jensenracing77]

i know tons about building a 400EX engine. i strongly recommend not going over 10:1 on the piston. you can but there are things you need to do and consider for reliability. i love this engine but does have a major weak spot with the head studs and design. as for big bore, steer clear of the 440. you can get more out of it and have more reliability with a 416 (.80 over). you will find more info on how to build one wrong than you will building one right. i ben there done that when it comes to 400EXs. it makes me sick to see all the bad info on atvriders about this.

[younganreckless]

^I highly disagree I have NEVER been touched by a 416ex and mine has run for 3 yrs no probs

[jensenracing77]

lol, you are only in central il, come on over and we can make it a first time.

[bugler30]

I have the stage 2 hot cam that is not currently in use, with the longer duration it lowers the actual compression (the reason I didn't like it in an otherwise stock engine). I will keep a 10:1 in mind though as I do want to be able to run it on pump gas, I will need to do some more research but I've got nothing but time because I don't have the $$ any time soon to do it.