I have a 2001 400ex that would not run at all, then i had the valves adjusted and then when it would run there was a little bit of a knocking sound, but someone told me it was normal for 400ex's so i took it out and the timing chain broke instantly. Then i ordered a new timing chain and sprocket cause the sprocket got messed up too. And after replacing the new chain and sprocket it started just fine except it had just a little bit of a ticking noise. So i turned it off and check the timing chain and it looked fine, so i didnt know were exactly the noise was coming from, sounded like it was in the top end. So i took it out again and the timing chain broke again, so somebody told me i should've replaced the tension aswell, and my cam was stripped thats why the sprocket would strip off and brake the chains. So i bought a new cam, with sprocket and chain, put it in time and everything and now it wont start, checked all the simple things, getting plenty of aprk, gas, compression, and when i put it in time its at TDC.
400ex wont start
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Check the cam chain sprocket on the crankshaft - sometimes when the chain breaks it breaks a tooth or two off there also (or damages a tooth to a point that might cause chain failure). If the sprocket is good, there is no foreign material pressed between two teeth of the sprocket, the tensioner slipper is good, the automatic tennsioner mechanism is working properly and was installed properly, the new chain that was installed was a genuine Honda TRX400 chain (part number 14401-KCY-671), then about the only reason left for the cam chain to break is camshaft seizure. Inspect the cam chain guide in the front of the cam chain well also. I have never seen one damaged to the point of causing chain failure, but there is always a first time.
Since you have new parts in it and now it won't start - whenever the cam chain breaks, it is likely the piston hit either the intake or exhaust valves (or both) and bent them. Check the compression. If no or very low compression, rebuild the top end of the motor and pay close attention to the valve guides and rocker arms. The ticking noise may have been a sticky valve or rocker arm. As a word of advice; whenever you replace a camshaft you should replace the rocker arms also. The ticking noise might have been piston slap. Somewhat normal and does not lead to cam chain failure, but if the piston and cylinder have enough wear, it should be bored to the next oversize and new piston, rings, piston pin and piston pin clips installed. If the valves are bent, they have to be replaced, the guides need to be checked and replaced if bad and the new valves at least lapped to the seats. The valve seats may need to be recut for proper seating of the new valves.
Since you have new parts in it and now it won't start - whenever the cam chain breaks, it is likely the piston hit either the intake or exhaust valves (or both) and bent them. Check the compression. If no or very low compression, rebuild the top end of the motor and pay close attention to the valve guides and rocker arms. The ticking noise may have been a sticky valve or rocker arm. As a word of advice; whenever you replace a camshaft you should replace the rocker arms also. The ticking noise might have been piston slap. Somewhat normal and does not lead to cam chain failure, but if the piston and cylinder have enough wear, it should be bored to the next oversize and new piston, rings, piston pin and piston pin clips installed. If the valves are bent, they have to be replaced, the guides need to be checked and replaced if bad and the new valves at least lapped to the seats. The valve seats may need to be recut for proper seating of the new valves.
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If it has good compression it doesn't need the valves adjusted. How much compression does it have? Check with the throttle held wide open - should have about 120psi - need 90 or more just to start.
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Firts guess - bent valves
In the shop, I lock the crankshaft at TDC on the compression stroke using the flywheel bolt. Then I put compressed air in the spark plug hole and see where the air coms out. It usually comes out of one of three places. The exhaust, the air box or the crankcase. Exhaust indicates bent exhaust valves. Air box indicates bent intake valves. Crankcase indicates bad rings, a hole in the piston or a blown head gasket. At any rate it means tearing the motor down to fix the problem.
In the shop, I lock the crankshaft at TDC on the compression stroke using the flywheel bolt. Then I put compressed air in the spark plug hole and see where the air coms out. It usually comes out of one of three places. The exhaust, the air box or the crankcase. Exhaust indicates bent exhaust valves. Air box indicates bent intake valves. Crankcase indicates bad rings, a hole in the piston or a blown head gasket. At any rate it means tearing the motor down to fix the problem.
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