Topic: Help i have cam trouble!

[axehole54]

So after taking my topend apart lapping valves, stem seals, head gasket, o-rings, valve cover gasket and putting it all together again i think i have my cam out 180 degrees motor rolls over without resistance and does eventally start but sounds like plug wires are on wrong plugs can i change the order or do i have to 180 the cam. I know back in the day on sohc chevette used to just be able to move wires and it'd run

[scottly]

If the cam was 180 out, you would still have compression, and the motor wouldn't run at all. Before pulling the head, take a compression test, and double check the tappet clearances.

[axehole54]

Shall do when i said run i mean just barely and only if i run choke and near full throttle but like i said it sounds like mixed up wires

[scottly]

I hope it is just something simple!

[axehole54]

Me too leaving for my trip tomorrow morning and i'm still 2 hours away from my bike

[Bodi]

There is no "180 degrees out" on the cam. You could have it with the crank 180 out but I think valves would crash into pistons; you would have to set the crank at T23 when you set the cam on its mark. Don't try this.
If you set the crank at T14 and put the cam in one way, turn the crank 360 degrees and you'll see that the cam is exactly 180 degrees different - you can install the cam either way "up" but it's actually the same way.
With our twin dual fire coils there is no wrong way to set the cam assuming the marks are lined up, car engines with a single coil and distributor are very different. It's fairly common to have the points wires mixed up, and there's no problem with swapping them at either the points or coils to get the plugs firing at the correct time.

[scottly]

I stand corrected. If the cam was timed at the 2-3 mark, it would be 90 out.

[jessezm]

When you put your top end back together, did you 1) back out all your tappets and tie the rockers up out of the way before reinstalling the valve cover, and 2) set your valve clearances before just firing the motor up?

When I did my top-end, I accidentally installed the cam 90 degrees out, like Scottly said, by using the T23 mark instead of the T14 mark.  Luckily, I was able to catch this early because I tried to set the valve clearances and could not get them right.  After some mental re-calculations, I decided to pull off the valve cover and discovered the problem and fixed it.

The reason I asked about backing out the tappets is because you risk bending your valves if you reinstall the cover and just crank it down without making sure the tappets aren't catching on the valve stems unevenly (at least that's what I think does the damage...).

Bent valve stems might cause the problems you described, but it does sound like your cam timing is off.  One is an easy fix, the other is not...

[axehole54]

made sure the cam was dead on last night, rocker clearances too turns out i initallly had everything right.. still doesn't run worth snot.... I also during the course of the head gasket change put in 115 main jets as I have pods and unbaffled drag pipes... now I'm wondering about the carbs... I cleaned what i could get to when they were off and did nothing else but change the jets... today I tried putting the mixture screws to default for a k model (1.5 turns out) and while it ran a little better it still sounds rough... Pulling hair out now if anyone needs me.. oh by the way i rotated the motor over a few times by hand before I put the valve cover on and then again with the caps off and everything is doing what its supposed to be. bike had 110 jets before and ran mostly ok but leaned out when you got into it

[MCRider]

When you put your top end back together, did you 1) back out all your tappets and tie the rockers up out of the way before reinstalling the valve cover, and 2) set your valve clearances before just firing the motor up?

When I did my top-end, I accidentally installed the cam 90 degrees out, like Scottly said, by using the T23 mark instead of the T14 mark.  Luckily, I was able to catch this early because I tried to set the valve clearances and could not get them right.  After some mental re-calculations, I decided to pull off the valve cover and discovered the problem and fixed it.

The reason I asked about backing out the tappets is because you risk bending your valves if you reinstall the cover and just crank it down without making sure the tappets aren't catching on the valve stems unevenly (at least that's what I think does the damage...).

Bent valve stems might cause the problems you described, but it does sound like your cam timing is off.  One is an easy fix, the other is not...

While Mr AH didn't specifically state his model, which I prefer, it does say in his signature its a CB750. The CB750 does not have the same rocker arm architecture as the 500/550 and consequently the whole tieing up of the rocker arms is not only not an issue, its not possible.

The rockers are in stands which are attached to the head. The cover just drops on.

[jessezm]

Oops!  I'm a little CB400f-centric I guess....  I stand corrected, thanks!

[MCRider]

Oops!  I'm a little CB400f-centric I guess....  I stand corrected, thanks!

No prob, I though all SOHCs were like the CB750, learned different here.

[dave500]

the cam can be 180 out per marks and its still ok.its spark timed from the crank,cars can be 180 out as well so long as the dissy is timed accordingly if its a cam driven dizzy,im an old v8 guy.