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View Full Version : Setting Timing Chain Properly on 400ex



domijam
02-05-2007, 07:53 PM
When i tried starting my 400ex it spun and felt like there was no compression. I thought it was the head and valves, so i took it apart. Turns out there fine, but i soon found out the problem was the timing chain. I was off and thats why it would not start. Now that I put the motor back together, the timing is worse than ever and it still will not start. How do i properly set the timing chain, to get things back in order??????

mad440
02-05-2007, 09:47 PM
Alrighty im going to take a crack at this, if anyone else has anything to add be my guest.

First: after you have all the plastic and basic bs out of the way. take the spark plug out and find top dead center with the T on the flywheel, dosent matter about what stroke the motor is on right now because your basically going to be resetting the timeing anyway, so just get the piston to the top of the cyclinder, if you need to take a screwdriver and stick it in the plug hole and feel if it is there.

Second: take the valve cover off making sure the pistion stays at TDC (top dead center). Once you have the valve cover off check out the position of you cam looves/loobs (yeah whatever) they should be facing straight down and the indicator lines on the cam sprocket should be horizontal with respect to your engines head, if not (probly your case) undo you cam chain tensioner, you can either remove the whole tensioner or have someone twist it out with a little screw driver and hold it there while you reset the cam, ( a little bro comes in handy when ya dont wanna take the whole tensioner out...lol).

Third: with the tensioner loose or out and making sure the pistion is still at TDC there should be enough play in the cam chain for you to rotate your cam until the indicator lines on the cam sprocket are horizontal with respect to the cylinder head and that the cam loobs/looves are pointing straight down also with respect to the cylinder head.

Fourth: once you have the cam sprocket lines perfectly horizontal and the loobs/looves pointing down. if you opted to leave the tensioner in release it slowly keeping an eye on the cam making sure you settings don't move. likewise for replaceing the whole tensioner if you chose to remove the whole thing.

Fifth: if everything is cool once your tensioner is replaced, then clean up your gasket surface and replace your valve cover. your going to want to leave your setting for TDC because once you have the valve cover back on your going to need to adjust the valves to there proper tolerance.

Sixth: once your done with the valve adjustment, its all a matter of puttin the bike back together

that was my crack at it, i did this same procedure to my bros 250x and it worked fine. Hope this helps

400exrider707
02-06-2007, 06:50 AM
Yeah follow that, except make sure your LOBES are pointing down not your Loobs, haha;)

mad440
02-06-2007, 11:41 AM
Originally posted by 400exrider707
Yeah follow that, except make sure your LOBES are pointing down not your Loobs, haha;)

lol...good lookin out

dariusld
02-07-2007, 02:45 PM
Maybe I missed it(too much reading) ,but did you say if the timing is wrong, when he checks it, that he is going to have to remove the cam chain from the cam to change it. It sounded like you said to move the cam without saying remove the chain(that would just keep the timing the same). Maybe you could clarify that important part.

mad440
02-07-2007, 08:59 PM
Actually I put it as simple as i could while trying to hit the main points, I could have went into more detail, but i was counting on his common sense to extrapolate my basic description and go from there handling the minor details. I did say under the third step that with the cam chain tensioner loose you can rotate the cam and sprocket without moving the cam chain thus changing the valve timing, you dont have to take the chain completely off, only I said it in less words so maybe i should have written more, but that would have ment more reading for you.

mgraff400ex
02-09-2007, 10:22 AM
the only thing i would do different is somtimes you have to walk the chain a couple teeth one way or another on the cam gear to get the timing right. it sounds like he had the cam 180 degrees off so just rotating the cam a little with the tensioner loose probably ain't gonna be enough to get it back in time. of course it might be in time already it's just the valves are adjusted so tight they are staying open on compression stroke thus no compression. Not trying to sound like a know it all just my thoughts is all.

400exrider707
02-09-2007, 10:40 AM
Originally posted by mgraff400ex
the only thing i would do different is somtimes you have to walk the chain a couple teeth one way or another on the cam gear to get the timing right. it sounds like he had the cam 180 degrees off so just rotating the cam a little with the tensioner loose probably ain't gonna be enough to get it back in time. of course it might be in time already it's just the valves are adjusted so tight they are staying open on compression stroke thus no compression. Not trying to sound like a know it all just my thoughts is all.

If it is 180 out all you have to do is unbolt the cam from the sprocket turn it over and bolt it back up, no need to even remove the sprocket from the chain!!!

Also I think we already established that the 400ex can not be 180 out of time due to the ghost spark that honda incorporates into its ignitions, meaning it fires even on exhaust stroke.

400exrider707
02-09-2007, 10:44 AM
Heres a little info for you taken from GPracer2500

"It is impossible for a cam to be exactly 180 degrees out of time. This is because the cam spins at exactly half the speed of the crankshaft. The crank spins around twice for every one revolution of the cam.

What you've got to remember is that there are TWO top dead centers (TDC). One is on the compression stroke and one is on the exhuast stroke. It takes 720 (360 x 2) degrees of crank rotation to complete all 4 strokes. The only thing that distinguishes one TDC from the other is the position of the valves (which, obviously, is controlled by the cam). Look at it this way, with no cam installed in the engine, which stroke is the exhaust stroke and which is compression? Answer--> it's undetermined until the cam is installed. Install the cams with the lobes facing up and you've just set that TDC as the exhaust stroke. Install with the lobes facing down and you've just set that same TDC as the compression stroke. It's all the same as far as the engine is concerned because the plug fires on every up-stroke (even the exhaust stroke).

Lets say the piston is at TDC on the compression stroke. That means the cam lobes are facing down (on a rocker arm equipped head like the 400EX) and the valves are all closed. Now we spin the crank around 360 degrees to the set the piston to the other TDC, the exhaust TDC. The cam only spun around 180 degrees and now the lobes are facing up. We could remove the cam and reinstall it 180 degrees from where we started. What's happened? All we've done is flip-flopped the compression stroke with the exhuast stroke. The engine doesn't care or even know that anything has changed. We're right back to where we started--TDC on the compression stroke and everything is still perfectly in time even though we've flipped the cam 180deg.

Make sense?"

Very informative guy right there!

roman96
05-09-2011, 09:11 PM
im doing this too and if its not too much of a hassle, the next person to set there timing can you PLEASE take a video. im not the pro at quads, this is my 1st quad that i had to even play with the engine.

CJM
05-09-2011, 10:18 PM
http://www.exriders.com/vbb/showthread.php?s=&threadid=466724

That will explain it in detail. its very easy to do actually.

It would help if you got a 400ex factory manual, you can find them all over the net.

roman96
05-24-2011, 06:56 PM
when mad440 said that if you take off your tensioner you have to buy a new one, but i didn't want to pay 50 buks for a new tensioner so i found a way to fix it.

1-once you have the tensioner off, unscrew the Phipps screw on top.

2-then in the hole, youll see a little indented das. get a flathead and twist the dash left and right.

3-this should pull in/out the tensioner.

4-screw the tensioner all the way in and it should get stuck.

5- then put the tensioner back in the motor and evenly screw in the bolts on both sides.

6- then make sure the chain isn't too tight, but the tensioner should do they for you,

hope you understood, if you have any questions just ask. ill be glad to answer them for you