Xs650 valve adjustment

[MaxPete]

Yup - here is the optimal order (or so I’m told):

• Torque the head properly
• Set the timing chain tension
• Set the valve lash
• Set the ignition timing.

 

[aldo5468]

When at TDC, the valves should only be loose on one of the cylinders. That is the one that will be at TDC on it's compression stroke, and the one you can set the valves on. The other cylinder will be at TDC on it's exhaust stroke and it's valves cannot be set. Both should be tight still with no clearance. The exhaust will just be finishing closing and the intake will just be starting to open.

If you had the top off your motor and could observe the cam, you could see this. The rockers ride on top of the cam. In the pic below, the right cylinder would be at TDC on it's compression stroke. The rockers would be riding on the base circles (lowest point) of the cam lobes on that side. The left cylinder's rockers would still be riding on the approach ramps to the lobe high points, which would make the valves tight .....

Just to be clear here, the right cylinder is on the left of this picture and the left cylinder on the right, correct? (Judging from where the kick start lever shows)

 

[5twins]

That would be correct. This pic was shot looking at the motor from the left front.

 

[Brassneck]

A secondary way to know you're on the correct stroke for that piston is if you put your finger over the spark plug hole--when it builds enough pressure to blow your finger off, you know you're on the compression stroke. All other strokes will either be creating vacuum (creating suction on your finger), and/or a valve will be open and not build pressure. You can spin the motor around (CCW) a few times to get a feel for it...for me, it can sometimes be easier to do that rather than trying to look at intake/exhaust valves moving up/down. Or it's a way to double check your self.

 

[mike in idaho]

Or you could do it the way we used to set the valves on a Triumph twin, not using the timing marks: Roll the engine over until you see the right hand exhaust rocker go all the way down(maximum valve opening). With that valve all the way open, the the left side exhaust lifter will be on the base circle of the cam. Adjust the exhaust valve on the left cylinder. Now turn the engine again until the left valve is all the way down and adjust the right hand exhaust rocker. Repeat on the intake side. Works with any engine having a 360° crank. No need to take the timing cover off or to pull a spark plug out to find tdc.

 

[Jacob Canada]

Hey guys just wanted to give you and update. All the advice help out a ton! Got the motor back in the frame and she fired right up and sounds great! Thanks again for all the help!

 

[XSLeo]

A cam lobe has several surfaces. Two are ramps. One ramp lifts the valve open, the other lets the valve close. The rest of the lobe is called the base circle. This area covers about half the rotation of the cam. This base circle, being a circle means this area is the same diameter over its whole surface. You can adjust the valves at any point on this area.
When at TDC one set of valves has no pressure on the cam. The other side both valves have pressure on the cam. These to valves don't have the same pressure on the cam. The valve spring have enough pressure to rotate the engine slightly to even out the difference between the two.
Get the engine to TDC then let it find it's own stopping point. This leaves the valves I want to adjust with in a few degrees of TDC.
If you want to check this turn the engine over by hand watching the valves. As soon as the vale opens, slide in the feeler gauge.
Slide the feeler gauge around a bit while you rotate the engine back a bit, when it gets too tight to move stop and note the engine position, Now rotate forward moving the feeler gauge till it gets tight. Stop note the engine position. How far did you turn from one tight spot to the other? Bet it was close to one full rotation of the crank. Which as previously mentioned 1/2 the rotation of the cam.
As you turn the engine between these two tight spots you will not notice none to vary little variation is the tension on the feeler gauge.
This should prove to you that anywhere on the base circle will be fine to adjust the valves.
On V8 engines we used to set valves by rolling up to TDC on #1 adjust both valves on that cylinder and all the ones that were loose, turn the engine around so the points rotor pointed the exact opposite from the #1 position then adjust all the rest of the valves.
I guess if you had a degree wheel and new at what degrees the cam lobes held the valves fully open you could roll the engine around to these points and adjust each adjuster to a zero clearance. That wouldn't be easy or really needed. I doubt even racers will devote that much time and trouble.
Leo

 

[member28833]

Get the engine to TDC then let it find it's own stopping point. This leaves the valves I want to adjust with in a few degrees of TDC.

I like it