help.. cam lobes vs timing?

[Westro]

With "T" in the timing window off the flywheel and the cam timing marks are straight accross and one point straight up, the cam lobes should be DOWN, right?

I just want to make sure that I don't have the cam 180 degrees out.

Thanks

[400exrider707]

Originally posted by Westro
With "T" in the timing window off the flywheel and the cam timing marks are straight accross and one point straight up, the cam lobes should be DOWN, right?

I just want to make sure that I don't have the cam 180 degrees out.

Thanks

yes

[Westro]

Thanks... after the rebuild, it will only pop and not run. good spark but will only backfire at about 3/4 throttle.

Any idea? I just replaced the valve seals and re-rung it. Is there an automatic decompression that I messed up?


Thanks again

[MIKE400EX]

Make sure they are still lined up after you install the cam chain tensioner. Also double check that you used the T mark not the F, and re-check valve lash.

[Westro]

yes, the marks line up after the tensioned is installed. I hand rotate the engine over a couple of times and they still line up.

Now at the risk of sounding stupid, what is valve lash? Remember I'm a 250R guy so the only valve I have is a REED valve.
:D

[MIKE400EX]

.004" on the intake and .005" on the exhaust side. I believe it's printed on a sticker up by the front top shock mounts.

[TC426EX]

Unless he has an aftermarket cam, where sometimes the manufacturer reccomends a different valve setting...

[wilkin250r]

I don't think it's possible to have the camshaft 180 degrees out. If I'm not mistaken, the 400EX has a phantom spark on the exhaust stroke as well, so you actually get a spark every single revolution.

If the cam was 180 degrees out, the phantom spark would become your new spark, and the engine would run just fine.

Somebody feel free to correct me if I'm wrong.

[Westro]

I think I figured it out, I had the decompression spring wrong. Would this cause my no run situation? The motor only pops at about 3/4 throttle and has not ran after I got into the motor.

[skinful]

how did you figure out the decompression spring was wrong???

[GPracer2500]

Originally posted by Westro
I think I figured it out, I had the decompression spring wrong. Would this cause my no run situation? ....

Yes. If the decomp spring and plunger are not right (no way to really mess that up besides having them backwards or missing) it will never start.

[jonboysnegy]

im having same problem, after rebuild ive adjusted tappets/lobes and no run plenty spark
i have lined up the t in crankcase and piston is top dead centre and valves are closed, at this process i thought timing may have been out 180 degrees but still the same any info

[rideracelivemx7]

Originally posted by Westro
With "T" in the timing window off the flywheel and the cam timing marks are straight accross and one point straight up, the cam lobes should be DOWN, right?

I just want to make sure that I don't have the cam 180 degrees out.

Thanks

.... when i had my t in the window tdc my cam lobes were in the 12 o'clock position and everything lined up and hadnt had a problem? why are yours down? lmao and ive put in several cams, rebuilt the top end of my quad several times also, and same results every time? runs at half a click of the start

[NacsMXer]

Originally posted by rideracelivemx7
.... when i had my t in the window tdc my cam lobes were in the 12 o'clock position and everything lined up and hadnt had a problem? why are yours down? lmao and ive put in several cams, rebuilt the top end of my quad several times also, and same results every time? runs at half a click of the start

Maybe it doesn't matter which they they are facing. I've always put the lobes down myself.

[soonerdude77]

I know the aftermarket cams don't use the decompression stuff so does it matter if a stock cam doesn't have that stuff installed? I just went from a white bros. cam to a stocker after a rebuild and now it won't run and I can't remember if we bothered putting the spring and ball back in.

[NacsMXer]

Originally posted by soonerdude77
I know the aftermarket cams don't use the decompression stuff so does it matter if a stock cam doesn't have that stuff installed? I just went from a white bros. cam to a stocker after a rebuild and now it won't run and I can't remember if we bothered putting the spring and ball back in.

As far as I know the stock cam requires the decompression assembly to run properly.