If you can be certain your @ TDC (compression) on the cylinder your working on.
Then the only thing I could see happening is (on the rear cylinder), the cam chain falling away from the crankshaft sprocket, which is at the lowest point of the chain and half the diameter of the cam sprocket.
The front cylinder might be safer to try this on.
I wouldn't chance doing it this way, it's too easy to remove a valve cover, find TDC for certain, verify cam timing, handcrank the engine thru, and verify cam timing again.

That way your safe, why not check valve clearances at the same time?

~Jeffers <-- I really wouldn't chance it.

 

Galaxieman,
Yes you do definately need to have each cylinder at TDC before removing the CCT to take the valve spring tension off the chain. There is an easy way to do this without having to even remove the valve covers - if you have a helper in the shop for a few minutes that is.

Remove the timing inspection cap AND crank end cap on the left engine case. (Your shop helper will be turning the crank counter-clockwise and letting you know when the "FT" mark comes up at the timing mark in the site window.)

Remove the front-right bolt on the front cyl valve cover. You'll be looking at the right lobe of the front cylinder exhaust cam as the crank is rotated. You'll need a small (smaller the better) flashlight.

When the crank is rotated CCW and the 'FT' mark comes up in the window the cam will be at one of two possible positions. The position you want is when the peak of the lobe is pointed 'up and forward' (toward the headlight). This is the cam position for the front cyl that is used to check valve clearances and the position you can safely remove the CCT.

Now remove the Honda CCT and install the new front cyl APE CCT and set the tension (read my earlier post in this thread).

Now on to the rear cyl.

Turn the crank 270° counter-clockwise and you'll see the 'RT' mark come up in the site window. That puts the rear cylinder in the correct TDC position. You don't need to visually verify this (by looking at a cam lobe) for the rear cyl since your starting from the correct TDC position on the front cyl.

Again, remove the auto-CCT and install the APE-CCT and set the tension.

You're done.

I outlined why I set the APE-CCT tension as I did earlier in this thread but in a different post Jeffers (caffeineracer) had a method that may be a bit more accurate. My method was simply based on the auto-cct from Honda having the correct tension to start with. In reality the Auto-CCT was probably designed to have a safe margin of tension greater than what would be 'ideal'. Since the Honda-CCT plunger has less pressure on the cam chain when it is more extended and more pressure when more retracted (like a newer - lower mileage engine) it seems that it is likely the Auto-CCT may be putting excessive tension on the chain in the earlier life of the engine. My setting of 5lbs pressure on the plunger was based on what I measured on the removed auto-CCT plungers from my engine that were in about mid-travel.
If you adjust the tension as Jeffers does it seems logical you'd have the ideal setting with minimum tension (and wear).
If I remember his previous post, with the engine running he backs off on the adjustment screw to the point of just hearing some chain noise and then slowly retightens it to quiet the noise. That's it. It might be best to start with both CCTs set as I did to be sure the APE-CCTs are 'in the proper range' before starting the engine.

Good Luck

 

How could we prevent the "cam chain falling away from the crankshaft sprocket" for a CCT change ?
Is there another way to check TDC ? (removing front valve cover is not easy....) unmounting spark plug and check how far the pistons is ?

Beginning with the rear at TDC (taking off rear valve cover to be sure), what is the procedure to place the front at TDC ? (how many turns at the flywheel, clockwise/counter-clockwise) ?

 

roadrun_fr
If for some reason you don't like the method I outlined above ( that doesn't require you to remove any valve covers) then you can do the job by removing just the rear valve cover, which beats the heck out of removing both:

1. remove the rear cyl valve cover and the timing inspection cap AND crank end cap

2. crank the motor counter clockwise until 'RT' shows in the timing window AND the lobes are all pointed 'up and out' (ie: if the lobes are pointed 'down & in" just rotate the crank 360° CCW back to the 'RT' mark)

3. Now that the rear cyl is at TDC you can remove the auto-CCT . You don't need to worry about the chain being forced by any valve spring pressure nor do you need to worry about the chain falling off any sprockets. Just remove the auto-CCT and install the new APE-CCT.

4. set the tension on the APE-cct. You're done with the rear CYL.

5. Turn the crank 450° CCW (1¼ turns) and stop at the 'FT' timing mark.

6. Now the front cyl is at TDC, do the CCT swap on the front .... set tension .... DONE

 

Thanks a lot for the "rear" instructions ! :wink:
I would see the cam just after removing the front right bolt thru the bolt hole ?

Why ?

 

roadrun_fr
If you decide to use the second method (removing the rear valve cover) you do not need to visually verify the front cyl cam. Since you verified the TDC on the rear cyl with the valve cover off all you need to do is turn the crank CCW 1¼ turns and that is TDC on the front