Cam seems right but the front valves won't open

[Angry Rabbit]

Cams must really hate me... Apologies in advance if this has already been posted and I missed it. I've got a 83 and I just pulled the pistons to check the rings and put new gaskets on the top end. I think I have the cam put in correctly, but when I turn the 17mm bolt on the stator, it "jumps" past the TDC mark. When I don't have the head top on (i.e. the rocker arms aren't in place), it rotates just fine and the TDC seems stable. Upon further inspection, I realize that the rear valves of both cyclinders open and close correctly, but both front valves don't. It appears this is causing the system to "jump" when the cam lobes come around. Any ideas for a newbie?

thanks, CB

 

[retiredgentleman]

Do you have a manual and have you adjusted the valve clearances............0.004" intake and 0.006" exhaust?

 

[Angry Rabbit]

I've got a manual and have read up on how to check the gaps. However, the front valves don't even move, so I haven't bothered to see if I can get a guage in under them. The rear valves appear to move fine. It's almost as if the cam lobs are touching the front rockers but don't have enough force to move the front valves. thanks, CB

 

[cros36]

it will hop past TDC. getting it at TDC takes a wrench at the stator, if you use a socket it will just keep going.

 

[hooktool]

Do you have plugs in it?

John

 

[retiredgentleman]

I've got a manual and have read up on how to check the gaps. However, the front valves don't even move, so I haven't bothered to see if I can get a guage in under them. The rear valves appear to move fine. It's almost as if the cam lobs are touching the front rockers but don't have enough force to move the front valves. thanks, CB

Post a picture of your camshaft installed in the engine, so we can see if its installed correctly. Also a picture of the rocker cover showing the rocker arms would be good to see.

 

[Angry Rabbit]

I don't have the plugs in when I do this. Assuming the kids and wife don't bury me with a "to do" list tonight, I'll attach a photo. thanks for the help. CB

 

[gggGary]

Sounds like you need to at least get the front valves set with in range. TDC is compression on one side but the other cylinder has it's valves open. Can't recall if it's one or both. The exhaust is closing and the intake is opening. the closing ramp on the exhaust will force the cam forward and the crank goes along, that's why the "jump" past TDC.

 

[littlebill31]

You need to adjust the valve lash and adjust one side at a time. If the tappets have too much of a gap, then they are not pushing down on the valves, thus opening them.

Stroke 1, Intake Stroke. Piston goes down, opening the intake (rear) valve, sucking in fuel/air.
Stroke 2, Compression Stroke. Piston goes up, both exhaust and intake valves are closed, compresses mixture, piston hits TDC.
Stroke 3, Power Stroke. Spark plug fires, combustion, throwing piston back down.
Stroke 4, Exhaust Stroke. Piston goes up again, exhaust valve open, forcing exhaust out of the exhaust valve.

Here's avideo of how to adjust them. Post #11 is a written instruction so you can print out.
http://www.xs650.com/forum/showthread.php?t=13083