Timing belt question

[speedknot]

I'm going to change the belts myself on my M750.  I watched the video tutorial but it seemed like there were a few things I didn't understand.  Why do I have to worry about aligning the marks if I install the new belt with the gears in the same position as when I took the old ones off?  Meaning, the new belt is going on the same way the old one came off and the gears are staying put.  How often do you have to go back and recheck the belt tension?

[Speeddog]

When the marks are lined up per the standard procedure, when you remove the vertical belt, the vertical cam will almost certainly turn, as it has a valve open.

You could check the tension after 1000 miles, wouldn't be a bad idea.
Then check it again after another 5k miles.

[normalcyispasse]

I didn't think there was too much of a need to worry about marking gear position or holding the gears while swapping belts, but I did it anyway (three marks on each gear/case).

That was SUPER useful. Once tension was released on the vertical belt the cam gear immediately spun to a different position.

[needtorque]

Trust me, as someone who has changed many, many timing belts, on cars and motorcycles, use the marks.  Many times when you put the new belts on and apply tension the pulleys turn just one tooth.  Without the marks you will not know this has happened.  Safer to use the built in marks and have no worries.  I just changed the belts on my S4R last night.  Used the marks.

[Slide Panda]

+1 having just done my belts today use the marks. The vertical cam will move and it's super easy to move the horizontal just jockeying the belt off. Like needtorque said it's super easy to loose your reference.

You can just pull the plugs and use the rear wheel to turn the crank

[speedknot]

Thanks for your input guys.  I didn't know that the cam gear has a tendency to spring out of position as described.  I'm enlightened.

[ducpainter]

Thanks for your input guys.  I didn't know that the cam gear has a tendency to spring out of position as described.  I'm enlightened.

Just the vertical because that is the cyl with the open valve when the marks are lined up.