Proper Valve Clearance Measurent?

I just watched the Mezzmo Engineering XJ650 build series which was great.

He recommended that cam lobes point upward when measuring valve clearance.

The Yamaha service manual recommends lining up the marks on the timing plate and pickup coils which ends up pointing the cam lobes sideways.

Is the result the same either way? Or is one method wrong?

Thanks in advance!

 

Well, that is an odd way that Yamaha explains (and illustrates) the procedure.......you want the tippy-top of the cam lobe (the pointed end) 180* opposite of the geometric "plane" of the shim.......the ensures that the clearance between the rounded end of the cam lobe and the shim will be at a maximum, and that max clearance is what you want to measure. Note that pointed lobes will not be pointing "straight up" at the sky, but will be canted a few degrees off of vertical, as the valves/shim buckets/shims are not perfectly vertical (relative to the ground) when installed.

I don't know why Yamaha illustrates it the way they do, as visually, it shows the rounded lobe of the camshaft in contact with the shims. Technically, there are a number of degrees of cam rotation where the lobe and the shim ARE at maximum clearance (besides the 180* opposite orientation described above), but it's very hard to see those exact points (where the cam lobe becomes "truly circular" and is not within the "ramp-up" or "ramp-down" portion of the lobe profile)....and hence the advice to just rotate the crank / cams until the lobes point 180* opposite of the shim surface.

 

That illustration was definitely drawn in error. They probably made the technical drawing guy do the funny math and he gave up! 720 degrees of crank with peak valve opening at roughly 180 crank degrees apart, but cam degrees are half of crank degrees so 90, but then you have to subtract the angle between valves so you wind up with intake and exhaust about 30 degrees out of phase with each other so at TDC they are pointing skyward and about 15 degrees toward each other....ehhh close enough, I'll just draw some cam lobes here.

 

Thank you for the clarification guys. At least this may explain why my bike never ran right.

Time to check the valves again

 

I followed the book, the cams should be ground so that they will have the same clearance either way. Notice the drawing matches the description of the procedure, so that is what I did.

 

Well dang, on second thought you have to add the angle between the valves instead of subtract from the cam degrees, so that would be 90 plus about 60 (guessing on the actual valve angle) so about 150. The drawing looks like almost a true 180, but the lobes are splayed out like that so the drawing is more or less correct. This is why they gave up trying to teach me math after the 4th grade.....

 

this is what I expect to the the case so it SHOULD not make a huge difference.
The cam should be a constant radius for around for a certain amount (lets say 120 - 200 ?) degrees centered on the opposite side of the pointy end of the cam) . Every bike model can be different. One never achieves perfection in manufacturing and I don't know the tolerance of the cam. Some bikes I KNOW tell you to measure at TDC.
I can tell you this, if I did not have the disk to put it at a comfortable gap, I'd be checking the gap at a few places just to make sure.
I personally have checked the bikes I've done with the pointy end opposite the disk. I have spot checked a couple times and did not find them to be off from that.

 

This makes sense to me. Some things that can throw you off here - oil film under the followers is one, another is cam bearing wear/clearance (and again oil film). This clearance can be wide if the oilchanges have been neglected, and the cam can "rattle" in the bores as it turns.