timming ?????

[ltl666devil]

when i do my timing on my 350x which way are my lobes of the cam supposed to be when im at tdc. im having trouble timing this thing. one time the timing is on and then i spin a couple of times and check it again the rockers are to tight or to loose. anyone kno what this could be. i just put a new cam, rockers and piston kit in it. can someone please help me
thanks

well when the motor is at tdc the lobes should be down

[GPracer2500]

There are two Top Dead Centers. One is on the exhaust stroke (lobes facing up), the other is on the compresssion stroke (lobes facing down).

[ltl666devil]

theres only one mark on it for top dead center. when i built it, it was at tdc and the lobes are down. now that its all together when i go to tdc the lobes are up. i dont understand it.

[GPracer2500]

Like I said, there are TWO top dead centers. There is a compression stroke TDC and an exhaust stroke TDC. The only difference between the two is the postioning of the cam/valves. Remember that the cam spins at 1/2 the speed of the crank. So, if you spin the crank 360 degrees the cam will only go 180 deg.

Just spin your crank around another 360 degrees to the other TDC and the cam will be oriented the way you are expecting it to be.

ETA: The mark on the flywheel that indicates TDC won't tell you which TDC you are on--only that you are on one of them.

[ltl666devil]

ok ill try it again thanks alot

[swva400ex]

it has to be on the comp. stroke to set the timing.

[GPracer2500]

Originally posted by swva400ex
it has to be on the comp. stroke to set the timing.

Not really. It's advisable but you don't have to. You can install/time the cam on either the compression or exhuast stroke for the same reason that it is impossible to be 180 degrees out of time. The only reason that it makes more sense to install/time the cam with the lobes facing down (the compression stroke) is so you don't have to spin the crank around 360 degrees before intalling valve cover and setting the valve lash. That just creates an unnecessary extra step...

[swva400ex]

Originally posted by swva400ex
it has to be on the comp. stroke to set the timing.






i am sorry. i meant to adjust valves.

[ltl666devil]

so ure saying that the tdc has to be on the compression stroke to set the valve lash.

[GPracer2500]

Originally posted by ltl666devil
so ure saying that the tdc has to be on the compression stroke to set the valve lash.

yes

[wilkin250r]

It might be easier to understand if you also understand WHY you are setting the valve lash.

In an ideal world, you would want your cam lobes, rockers, and valves all to be touching each other, with no space in between. But that's not possible, the world isn't ideal.

The problem is heat. When things get hot, they expand. Your valves will actually get longer. If everything is touching when your engine is cold, then what happens when the valves expand and get longer? They wouldn't be able to expand upwards, they would have to expand downwards. Now, they're not fully closed and seated, they're partially open. This would obviously be a problem.

So, you put a small, carefully measured space in between the valves and rockers. When the valve expands due to heat, it closes this gap.

Obviously you have to set this gap while the valves are closed. If the rockers are pushing against the valves and holding them open, you CAN'T have a gap. It's impossible. That is why you want your cam lobes facing downwards, so they aren't pushing against the rockers. It's also why you ALWAYS set your valve lash while the engine is cold. If you set the lash when your engine is hot, you'll have too much gap. You should end up with almost zero gap when the engine is hot.

[ltl666devil]

if my timming chain is stretched would it make it do this. like maybe its shipping teeth. i think that would make it get out of time . ive tried everything and replaced almost everything but that.
thanks

[GPracer2500]

Originally posted by ltl666devil
if my timming chain is stretched would it make it do this. like maybe its shipping teeth. i think that would make it get out of time . ive tried everything and replaced almost everything but that.
thanks

I'm confused on what you're trying to do and what the problem is. In your original post you say "...im having trouble timing this thing. one time the timing is on and then i spin a couple of times and check it again the rockers are to tight or to loose...". Are you trying to set the cam timing or are you trying to adjust the valve lash? If the 350X valvetrain design is the same as the 250X/300EX/400EX (and I think it is--but maybe not) then when you're setting the cam timing the valve cover and rocker arms shouldn't even be installed.

I'd like to help but I'm not sure what the issue is, exactly.

[ltl666devil]

sorry
i get my timing on but wen i do the valve lash it changes everytime i start it. ill put it all back together, set it to what its supposed to be, and start it and it will tick low then it seems like it gets worse so i take the vavle covers off and check the valve lash again and its off. thanks