PDA

View Full Version : Putting motor back together - cam timing question


Mitch400EX
08-08-2003, 04:56 PM
I'll re assembling my top end this weekend and installing the new piston and cam. Since the idiots at Amazon.com decided not to send me my shop manual until today (I ordered it 2 days ago and paid extra for fast shipping), I won't get it until next week. How do you know the cam timing is correct when you reinstall the cam? From what I hear there is supposed to be a T in the timing window and the line on the cam sprocket and the cam lobes pointing straight up. Is this correct? I don't want to bend the valves when I restart the motor.
Castor-426ex
08-08-2003, 05:09 PM
ok there are index marks on the sprocket....but the lobes should be facing down and one index mark should point straight up and the ones on the left and right should be flush or even with the top of the head
BigThumper33
08-08-2003, 05:41 PM
castor is right. cam lobes DOWN
Mitch400EX
08-08-2003, 05:52 PM
Thanks for the info everyone
3x440ex
08-09-2003, 01:55 AM
Cam lobes UP!!!
08-09-2003, 02:12 AM
Originally posted by BigThumper33
cam lobes DOWN


Originally posted by 3x440ex
Cam lobes UP!!!

:confused2 :uhoh: :eek: Which is it? :confused:
3x440ex
08-09-2003, 02:14 AM
Up........i've done my own about seven times now.
nakomis0
08-09-2003, 02:27 AM
Dont forget to have the motor at TDC.
MIKE400EX
08-09-2003, 03:48 AM
It really doesn't matter if the cam lobes are up or down. Just makes it a LOT easier to get the head cover back on with the lobes down.
BigThumper33
08-09-2003, 06:58 AM
YES IT DOES MATTER!! YOU are going to have it completely out of wack. CAM LOBES DOWN DOWN DOWN.

Read the manual, CAM LOBES DOWN. cam lobes up will reverse your timing 180 degrees!!! CAM LOBES DOWN DOWN DOWN DOWN DOWN DOWN. I've had mine apart atleast 5 times.
3x440ex
08-09-2003, 09:02 AM
You are right , I stand corrected, I just checked the manual.Lobes down. I'm pretty sure i instaled my cam lobes up because that's what my mechanic told me to do.....maybe that would explain the ticking sound or would it even run that way?

Got dang it now i need to tear it down and check it.:mad:
3x440ex
08-09-2003, 09:43 AM
The more i think about this i had to of installed mine lobes down because it wouldn't run lobes up because that would make the plug fire on the TDC of the exhaust stroke and there would be no fuel to ignite........just a little dislexic malfunction.:D
BigThumper33
08-10-2003, 01:32 AM
There is simply no way it would run... At TDC with the cam lobes up, it would be opening either the intake or exhaust vavles when trying to fire... I think we all know thats not going to work ;)
3x440ex
08-10-2003, 02:00 AM
It does seem to me that the plug would only fire once during the four stroke process, and that would be at TDC of the combustion stroke, but if you read page 7-19 on installing the cam it reads......

Rotate the crankshaft counterclockwise while holding the cam chain and align the "T" mark on the flywheel with the index notch in the left crankcase cover.

Install the cam spocket onto the cam chain so that the index lines on the sprocket with upper surface of the cylinder head.

Install the camshaft onto the cylinder head through cam sprocket.
install the cam sprocket onto the camshaft flange securely.

Make sur the index lines on the cam spocket with upper surface of the cylinder head when the "T" mark on the flywheel is aligned with the index notch in the left crankcase cover.


So wher does it say to have the lobes up or down?

On page 7-23 it does say to have them down but that's only for installing the cylinder head cover.
MIKE400EX
08-10-2003, 05:49 AM
Install the cam with the lobes down - like I said it will make installing the head coaver a lot easier - because you won't be torquing down the cover and compressing valve springs at the same time.

Big Thumper:
The crank rotates twice for every 1 revolution of the cam, and the spark plug fires every revolution of the crank. I'll let you figure out the rest.
BigThumper33
08-10-2003, 06:13 AM
okay, I was not aware that the 400ex fires a maverick spark on the exhaust stroke.
Dune Surfer
08-10-2003, 06:30 AM
It is cam lobes down
3x440ex
08-10-2003, 01:53 PM
That explains it.....I knew i installed mine up:p .......I thought it was my dislexia screwing with my head.:D :D
Geoff Thomas
08-11-2003, 03:36 AM
It does not matter what directon the cam lobes are faceing. It WILL work either way. It is jsut easier to get the head cover on when there isn't cam lobes pushing up against the rocker arms. The ignition get's it't signal from the crank so it fires EVERY TIME THE PISTON HITS TDC.

Mitch, If this is the Mitch I am thinking it is bring it in to work and I'll time it for you.
Dune Surfer
08-11-2003, 12:31 PM
Originally posted by Geoff Thomas
It does not matter what directon the cam lobes are faceing. It WILL work either way. It is jsut easier to get the head cover on when there isn't cam lobes pushing up against the rocker arms. The ignition get's it't signal from the crank so it fires EVERY TIME THE PISTON HITS TDC.

Mitch, If this is the Mitch I am thinking it is bring it in to work and I'll time it for you.

Correct me if I'm wrong, but if the lobes face up wouldn't you be 180 degrees out of time?
yellow_ho_01
08-11-2003, 02:17 PM
if you have the lobes up,.. that will put pressure on the rockers,. they will push on the valve stems,.. and you will have NO play,.. you MUST have play to adjust your valves,.. with the "T" mark aligned to the case.... dont know if this makes sense,.. but here goes,.. if it is 180 degs out,... the exhaust valves would open when the intake valves should... and same for the intake for the exhaust,... seems to me that would either cause damage,.. or.... .. well. .. damage! i guess....
3x440ex
08-11-2003, 02:17 PM
The crank rotates twice for every 1 revolution of the cam, and the spark plug fires every revolution of the crank

WHAT HE SAID...

If the spark plug fires twice for every revolution of the cam then it doesn't matter, and if it did matter then it would say so in the manual.
MIKE400EX
08-11-2003, 03:41 PM
Why did I ever open my mouth??????
Duner, If you then turned the crank 1 full revolution the piston would again be at TDC and the cam would have only turned 180 degrees - and now the lobes would face down.
You're right Yellowho01, it would be a pain to get the cover back on, and you'd be lucky not to break some of those peanut butter bolts. But if you did manage to do it successfully, turn the crank 1 full rev. and now you can adjust the valves as usual.

Sorry all, I didn't mean to confuse anyone. Just tried to save 3X440ex, and maybe others, from needlessly taking the top end apart.
BigThumper33
08-11-2003, 04:55 PM
Lets make this easy. It will fire on the compression, and exhaust stroke...there we have it... lol
Geoff Thomas
08-13-2003, 03:51 AM
Dune Serfer, No it won't be 180 out. With the cam out set the crank at TDC. Now it is ready for the cam to go in. Now turn the crank 1 time and it is back at TDC. Now is the cam going to be 180 out? No. There is no reference on wich time the piston hits TDC that the lobes are up or down.

Yello_ho_01, All you have to do is rotate the crank 1 turn and adjust the valves. The crank turns twice for every 1 turn of the cam so the piston won't be comming up and hitting the valves and no engine dammage will be done.
yellow_ho_01
08-13-2003, 05:19 AM
im not says there would be damage from the piston hitting the valves.
adeptex
10-16-2003, 09:50 PM
There would be damage to the valves if you put the cam in lobes up and at tdc. You should install the cam with the piston at tdc .
If the cam lobes are up, when you put on the rocker cover it will open the valves and hit the piston because it is still at tdc!
hotex
10-17-2003, 07:59 AM
Maybee this will help. I know it is for a car, but the principle is the same.

http://www.compcams.com/Base/Images/Technical/800-615-ValveTimingIllustration-002.gif


The piston does not know weather it is on compression stroke, or exhaust stroke. There is only one TDC mark on the crank. It does not matter if you install UP, or Down. The position of where the cam is installed is what determines what stroke it is on. If you took two identicle motors, and installed the cam lobes up on one, and down on the other they would both run the same. Like many of you have said before it is easier to install with the lobes down, that is true, one because there is no pressure against the rockers, and two because then you dont have to rotate the crank 360 degrees to adjust the valves (which would rotate the cam 180). Lets say you install the cam lobes up, then you rotate the crank 360, which would put you back at TDC. At that point the cam lobes would be down, because the cam has only moved 180 degrees. That is the same as installing them down (which is easier) at TDC, rotate the crank back to TDC, and the lobes will be up. Try it. ;)