I’ve been studying how to replace timing belt / water pump and come across the advice of disconnecting the battery cables. Since the service manual doesn’t call for this step, I wonder if this is just precautionary but not necessary, as long as I don't cut any wire or soak any cable in coolant?

The service manual seems to imply it’s possible to set TDC after the timing belt is removed. I just wonder if it’s my misunderstanding. I feel it’s impossible to set TDC once the belt is removed. Piston and valve will collide when any of the crankshaft or camshafts is rotated without moving the other two. Correct?

 

Once you remove the timing belt, there's nothing left holding the camshafts in time in relation to the crankshaft, so the camshafts might spin/rotate from the valve springs on any partially open valves. THIS IS NORMAL. So you'll NEED to manually spin the cam's in their proper direction to get them back in time in relation to the crank. Just remember as you're manually spinning the cam's that you will notice some resistance; this is you fighting the spring tension of the valve springs. All you're doing is putting the valves in their correct open/close sequence in relation to the piston so as long as you haven't manually spun the crank (which there is no need to touch) there should not be any piston/valve contact.

 

Take the crank pulley off and all of the plastic covers. Then put the crank bolt back and set the timing marks. Like twokexlv6coupe wrote, cams might get out of time when belt off (or when you will be putting new belt on) but if everything was in time before it won't hurt anything.
Just don't spin them too much with belt off, or if you encounter some resistance.

When you remove the pulley, make sure that wondruf key on the crankshaft stays on the crankshaft and doesn't come out with they pulley. If it does put it back before you start rotating anything.

Battery cables are precaution - to prevent any chance of engine spinning while you are working on it. I don't disconnect battery.

 

Thank you, @twokexlv6coupe and @peter6, for your guidance.

Would you please let me know if my understanding is correct?

1. Set #1 TDC before taking off timing belt.
2. After removing the timing belt, don't rotate the crankshaft, which is stable and stays in time by itself.
3. The 2 camshafts, on the other hand, are under valve spring load and may spin out of time either spontaneously or when slightly disturbed.
4. When either camshaft goes out of time, gently rotate its pulley either clockwise or counterclockwise so its time mark on the pulley goes back to 12 o'clock in the shortest distance.
5. Do not rotate the camshaft pulley more than a half turn as it's still possible for some valve to hit a piston when it's rotated too much.

 

Removing the spark plugs, before performing step#1, aids in rotating the crankshaft & at keeping the camshafts in place once TDC has been achieved and TB is removed.

 

I slightly rotate the camshafts / crank out of time to aid in the belt installation. It's hard to stretch it by hand and all of the slack must be on the tensioner side. Simply said, rotate cam ccw, put the belt on, bring it back to timing mark. If belt doesn't have much slack it should be correct.
Use flat wrench on the cams if doing so. Also helpful to have some small spring clamps to keep the belt on the camshaft pulleys. You can do the same with crankshaft - rotate it out of time ccw, put belt on, then back to time.

When pulling tensioner pin, you need to do it fast or it will get stuck. I like to put tensioner in the vise, pull the pin out and put tiny amount of grease on it.

When belt installed, pin out, rotate the whole engine by hand. Having spark plugs out will make it much easier. If all marks align after rotating crank twice you're set.

 

This is a GREAT tip!

 

My issue currently is when I have the crank shaft and cams at TDC with belt on.The back cam moves off TdC when pulling the tensioner pin.Any tips to keep TDC marks in place when pulling pin?