400ex Stalls Tight Spot Engine Help!!!

[440EXRACER#10]

Alright, I've been having so much troubles with my 440EX. So, one day I was out riding it and it just acted like it locked up. Tires siezed and it shut off. So I got it started up and it almost sounded like it was missing. Luckily I got it home and it was making some odd noise. Took the head off and realized the cam chain was unbelievably stretched. So I figured I would tear it down to the bottom end without splitting the cases. The rod had no play up or down and a little left to right, but it was in spec. So I decided to order a Cometic Top End gasket kit, Wiesco HD cam chain, a Hotcams stage 3 cam(used to have a Curtis Sparks X1) and a Cometic clutch cover gasket. Also the cylinder looked great, the piston looked great and the oil had no metal shavings. When putting together we got the timing dead on. And adjusted the valves to spec for that cam as well. And adjusted the cam chain. Started it up ran for a little bit and then bam, shut off again and "locked" up. We had to spin the engine a tiny but clockwise and then I would turn over counter clockwise. But it would run and then do the exact same thing. It runs super strong and doesn't smoke at all. No knocking or any engine noise at all. The engine has only about 15 hours on it.

Please help me out.
Thanks

[CJM]

Obviously somethings binding up. Sounds like the crank might be seized.

Remove the plug and turn it over by hand, does it turn over nicely then your good-if its tough your cranks shot.

Id also check the timing chain tensioner, You are supposed to replace it when you do the chain. But usually the engine spins freely but wont start if its bad.

Another idea: Whats your jetting, in the least should be a 180 main. Less, your frying the topend more than likely

[440EXRACER#10]

With the spark plug out, sometimes it will crank and crank before it locks up. But then you have to pack the engine clockwise just a hair and then it will crank and crank without spark plug. Jetting has nothing to do. Valves go up and down fine. But it will run and then all the sudden bam. Lock up.

[440EXRACER#10]

I have a manual cam chain tensioner as well. So I know it is not that.

[CJM]

Id say your crank is seized. Friend of mines ktm is exactly like that, you can move it a bit but then it gets stuck, move it back and it moves again and then gets stuck.

[JOHNDOE83]

Originally posted by 440EXRACER#10
Jetting has nothing to do.

Maybe not with the current issue but out of curiosity what is the jetting at now?


Once I had the same issue, it turned out in my case to be chain related, probally not in your case tho, sounds like crank issues.

[440EXRACER#10]

Do you think it's just my bearings or my whole crank. I swear this 400 is nothing but headaches. I maintain it like crazy. And it just had a rebuild.

[on the rocks]

Poor rebuilds will make them a head ach. Don't get on a 400 forum and talk crap about them to the people who like them and expect help from them.

But on tipic a friends 400 would run fine and then lock up all of a suddent and it was because the bearings for the crank balancer was hitting the connection rod and locking the motor up.

[440EXRACER#10]

Thank you all for the input, an sorry about putting 400's down. I have some thing that may help some one give me a definite answer. When the engine locks up all the valves shoot up. No matter where they were, when they engine stops the valves shoot up. After this hurricane passes, I am going to drain the gas and clean carb, to make sure it is not hydrolock. And then I will go from there. It does not smoke or knock or tick or anything.

Please continue with the feedback I really, really, really need it and appreciate it. Thanks guys

[riotact]

I'd say its jumping time then.Did you put the key in the shaft on the timing gear in the bottom end when you rebuilt it?

[440EXRACER#10]

Does anyone else have any ideas what it could be? Please, please let me know.

[440EXRACER#10]

Does anyone else have any ideas what it could be? Please, please let me know.

[CJM]

yes, you need to take it to a qualified mechanic.

[440EXRACER#10]

Well I'm trying not to pay a mechanic. That's what I thought this site was for lol. But thanks for the help. I just wish someone could tell me. As many 400s there are and how long they've been out someone should be able to tell me.

[CJM]

The problem is I and the others cant see and check it to properly diagnose it.

Like I said earlier-it sounds like your crank is seized.

[440EXRACER#10]

But if it was crank wouldn't it smoke or knock? It doesn't do either

[JOHNDOE83]

I have had this problem but was found that other issues caused it.

I asked what your jetting was and you never responded, it "COULD" be a possibility.

A slack chain could cause it, but you said it does it at idle or without even running?

bad valve gaping could cause it, bad timing could, bad valves can.

It could be a number of things working in conjunction.

My best guess from the info given is that your crank bearings are going bad and throwing the piston and timing off allignment just enough to mildly lock your motor.

get some video, get some pictures, maybe we can help more.

until then, it needs a qualified mechanic.

sorry for your loss, good luck.

[440EXRACER#10]

Thanks man. My main jet is a 185. Also I just gotta brand new cam chain and tensioner. Timing is perfect. So it definently has to be bearings.

[Rivet]

Sounds like a starter sprag, only backwards.

[400EXRAY]

I agree with CJM, your crank is the issue. its most likely warped which happens right before a full on engine seize. the warped crank is pinching your rod most likely. if you tear it down, you should be able to see where the crank is rubbing the rod.

[440EXRACER#10]

Thanks man. Alright guys thanks for all the support. I am going to start tearing it down. So now I have a few questions. Why did this happen? I always changed my oil and checked it. Could it just be from a lot of hours on crank or what? Thanks guys so much. And also do I need to buy a whole crank or just bearings? And what brand should I go with. Hot rods, wiesco, or oem. Thanks guys. You guys have helped me soo much. :) thanks

[JOHNDOE83]

Wear and manufacturer defect's cause these issue's and sometime's rider error.

The same reason why one 400ex need's a crank in 2 year's and the other 400ex under same condition's will last a lifetime. That's just how it is for some vehicle's and how the parts were manufactured. Even if they were manufactured at the same place at the same time, one will have more defects then the other.

[440EXRACER#10]

So from all the posts obviously I'm going to replace my bottom end. What brand should I go with?

[CJM]

You do realize if you dont press the crank bearings on right it can and will fail...right? Its not all that easy to do it btw.

OEM is all I would buy. Infact it would be far easier to buy an entire bottom end and slap it on.