Random questions related to timing belt change

[dandaman]

I'm in the middle of my TB + WP 90k change, just taking a break for dinner. A couple of of nagging questions I thought of while doing the belt:

1. The timing mark on the back cam (RH) was damn impossible to see. The cable loom kept obscuring it and I only have two hands. I eventually think I got it correct, but it got me thinking. The first time I got the belt on it had jumped a tooth at the crank, and then there wasn't enough slack to bolt the tensioner on. So after fixing that I had just enough slack to get the tensioner on. So based on that, I would assume that I had everything lined up correctly.

1a. Similarly, let's assume I didn't have the back cam exactly at the right mark. My doubts here are because I didn't have the mirror at exactly a 45 degree angle so I was seeing a little parallax. Since the belt fit pretty tight with little slack, that means it would've been a little past the timing mark at worse. Since I had the mark on the sprocket matched up with the line on the belt, when you turned the engine the LH cam sprocket would take up any slack before it started turning the RH cam and would resolve any extra tension. Am I thinking about that right?

So with all of that, it seems like getting the sprockets "close enough" to the right spot so that you have enough belt to make the belt marks match up correctly is the ultimate goal. Since those marks are based on the tooth count on the belt, as long as the belt isn't so loose that it skips a tooth when the cams initially turn, you're golden. Once you turn the crank with the belt on it'll resolve any tension issues on the upper end.

2. When you start the removal of the old TB the instructions have you back the crank up to 60 degrees BTDC so that the cams can spin freely without worrying about valve-piston contact. This doesn't make sense to me. With a V6 you should have a piston at TDC every 60 degrees, so backing up 60 degrees would just put a different piston at TDC, right? I'm not sure what this is actually gaining you.

Aside from that the change is going good, took me a bit to get the sprocket bolts off to get to the WP, and no broken bolts. I did strip the 5.5 head on one of the double threaded bolts, unfortunately.

[TrailDust]

FWIW, just throwing this out for you for reference. It's for the Camry, but the procedure is still the same for the Sienna:

Changing V6 Timing Belt Pics and the $270 Coil Connector

[dandaman]

Oh yeah, have that bookmarked, it's been helpful. I'll have everything back together tonight, it's just me trying to verify what I did in multiple ways before I turn that key.

[TrailDust]

I understand. Wish I could have been more direct help. If there's anything you learn in the process by all means post up any observations.

[dandaman]

Well I finally was able to take it on a test drive (finally got plates for it). Bought it on 12/31, 1/1 I already had the engine apart No issues at all, new belt, pulleys, tensioner, and water pump all for $150.

In regards to my question I'm pretty sure I'm right on #1. The TB is pretty much a foolproof operation. If you keep the crank on TDC and the cams anywhere near the mark, as long as the marks on the belt line up with the marks on the crank and cam sprockets you'll be right. With the side-bolt tensioner you don't have much wiggle room, so if the belt is off by one tooth or the sprockets are off by a significant margin you won't be able to get the tensioner on. If you have a slight amount of slack between the two cam sprockets the tensioner and belt will take up that tension when you start turning the crank.

I won't call it an easy job but if you have the right tools, mainly a nice air impact to get the crank bolt off, it's more than doable. It ended up taking me 14 hours or so because I tried to halfass it and do the waterpump without removing the cam sprockets, which wasn't worth the hassle. I could probably do it in 4-6 hours if I had to do it again.

[TrailDust]

Thanks for posting the update....