Timing belt change

[bcossa2001]

97 Avalon--205K. Timing belt is 60K old.

Why does the manual tell me to put the #1 cylinder at TDC prior to changing the belt? It seems to me that as long as I don't turn the engine or camshaft when the belt is off (which would seem obvious any way not to do) that the position of the cylinders is immaterial.

 

[Chris142]

Because w/o a belt the cams tend to spin on their own. Putting on on tdc makes it easy to get back in time when this happens.

 

[oggb]

That part of the manual should include reference to the fact that the cams tend to want to change position with the belt removed and say "YOU HAVE BEEN WARNED" in big bold letters.

Unless you have one of those fancy tools to hold the cam gear in place.

 

[Jim_Truett]

Setting the engine to TDC starts you off from a known position at the timing marks. Not doing so can result in the cam timing being off from the cam rotating under valve spring pressure. I have also seen bent valves from individuals deciding to set it at TDC after removing the belt, and turning the crank by hand burying a piston into the valves on an interference engine.

 

[Colt45ws]

As stated above, the cam will want to rotate on its own without the belt. This is due to the valve springs pressing on the lobes. It will move until it finds a "Neutral" position to sit in.

 

[user52165]

FWIW - I have not seen that engine specifically, but it is normal to have some sort of marking system for the cam and crank sprockets to indicate TDC. May need a manual but usually they are self evident with some looking.

 

[kschachn]

Yes to all of this. If the cams are in some arbitrary position they will never stay there once you pull that belt off. Even with the #1 cylinder in TDC this means that one cam is stable and the other one is on the points and unstable. But at least it is metastable in this position. That back cam is going to flip off the points at least once while you are messing with it and you’re going to have to put it back.

The other thing that was mentioned is that the timing belt comes with marks that have to align. And it is all too easy to think that the proper installation position is one tooth off. If you aren’t absolutely sure where things are aligned I think you will get it wrong.

If you haven’t bought your belt yet let me suggest an OEM Mitsuboshi belt. I have tried the rest and I did not like them. The Gates belt had the marks off ever so slightly and was a bit thicker than the OEM belt. Thicker meant that it kept flipping off the crankshaft pulley (or jumping a tooth) while I was trying to position it on the camshaft pulleys. It made it so difficult I returned the belt and bought one at the dealer, which went on no problems and the marks lined up perfectly.

 

[kschachn]

BTW I am assuming you have a 1MZ-FE engine in your Avalon. You will find conflicting information on the web about whether this engine is an interference type or not. Most people say that it is. In my experience it is not at the speed where you will be turning the crankshaft and/or camshafts by hand. The manual makes no note or warning about turning anything with the belt removed and I have done it many times to align everything. I read once where someone described the 1MZ-FE as a semi-interference engine where at high speed things can come in contact but not at slow rotation. This makes sense as the squish zone in the cylinders is very, very small.

It is so small that a weird thing can happen. The back bank of cylinders is almost vertical and the squish zone slant is pointing downwards. While you are doing a timing belt change you will probably have the back bank flip off the camshaft points more than once. This is somewhat violent and goes with a clang of sorts (not enough to damage anything) but it can knock carbon loose from the valves. This carbon will fall into the tiny squish zone and then as you try and turn the crankshaft it will appear to hit a resistance or stop. Trust me it happened to me. I found an old post somewhere about this happening to another guy who ended up tearing down his engine only to find some carbon flakes in the cylinder. If this carbon would fall down during normal engine operation it would just power through the resistance and move on. But when you are trying to turn the crankshaft by hand it feels more substantial than it is.

 

[bcossa2001]

Yes, 1MZ-FE engine. It was my understanding that it is non-interference.

Thanks to everyone for the information....now all I need is a little courage to attempt the belt change...

 

[artbuc]

Originally Posted By: kschachn
If you haven’t bought your belt yet let me suggest an OEM Mitsuboshi belt. I have tried the rest and I did not like them. The Gates belt had the marks off ever so slightly and was a bit thicker than the OEM belt.


+1. Tried the Gates TB on my 99 Avalon. Didn't like it and bought a factory belt. I believe my original TB was Unitta. Gates and Unitta have a JV. If you can get a Gates belt from the Unitta factory you are good to go, but no way of knowing that until you get the belt in your hand.

 

[lexus114]

VVT-i is interference, non vvt non interference.

 

[kschachn]

Originally Posted By: lexus114
VVT-i is interference, non vvt non interference.


Well there you go then. I thought perhaps that was a difference but I had no way of testing it. Like I said, on the non-vvt version (mine) you can spin everything independently and it has never been a problem.

 

[kschachn]

Originally Posted By: bcossa2001
Thanks to everyone for the information....now all I need is a little courage to attempt the belt change...

I wouldn't do it without the book, but with that in hand it is quite do-able. I've done it five times now, three times on my Sienna and twice on a friend's van.

If you are interested Rock Auto sells an OEM kit for a very good price, about $142 without the tensioner. The kit includes an Aisin water pump, the two idlers and the belt.

 

[mechtech2]

This is NOT recommended over the factory procedure, but you CAN mark the gears and belt (in any stopped position], then count teeth and mark the new belt.
This will get you back to running. It may even be perfect.

Some factory belts cam with those marks, and marks on the gears!

 

[kschachn]

I know what you are saying, but I don't know how you could do that unless you had one of the locking fixtures for the camshafts. Without that as soon as you pull the belt off (or just loosen the tensioner) one or both camshaft pulleys are going to flip. Heck even the crankshaft might move if you are halfway up a compression stroke and the pressure hasn't bled out yet.

And even if you counted teeth, good luck getting the two camshaft pulleys to stay in that position while you wrap the belt around the crank pulley and the water pump and the two idlers.
Originally Posted By: mechtech2
This is NOT recommended over the factory procedure, but you CAN mark the gears and belt (in any stopped position], then count teeth and mark the new belt.
This will get you back to running. It may even be perfect.

 

[stephen9666]

Originally Posted By: kschachn
I know what you are saying, but I don't know how you could do that unless you had one of the locking fixtures for the camshafts. Without that as soon as you pull the belt off (or just loosen the tensioner) one or both camshaft pulleys are going to flip. Heck even the crankshaft might move if you are halfway up a compression stroke and the pressure hasn't bled out yet.

And even if you counted teeth, good luck getting the two camshaft pulleys to stay in that position while you wrap the belt around the crank pulley and the water pump and the two idlers.


These same problems will likely happen with the engine in any position.

Plus, you have the same problem of keeping the timing marks lined up while putting on the belt whether you mark the new belt or not.

I used the mark and match method when changing the belt on my girlfriend's Beetle and it worked fine. I put the engine at TDC, but the camshaft sprocket still moved a little when I took the old belt off.

 

[bcossa2001]

Seems I've read somewhere on BITOG that one way of marking it is to put a dot on the belt and then a dot on the camshaft on either side of the dot on the belt. Do this on the camshafts and the crank while the old belt is on, remove the belt, and transfer the belt marks to the new belt and then install the belt. Is that what you ("ya'll" as we say in Bama) are speaking of??

 

[kschachn]

I'm not sure I can beat this poor dead horse any more but here goes...

What exactly is your worry here? Making marks, counting teeth, holding camshaft pulleys, etc. seems a whole lot more work than just setting the marks as instructed. I mean my goodness this is a very easy engine to set the marks - you don't have to muck around with actually finding out when the #1 piston is at TDC, that is accomplished when you turn the crank pulley so the dot aligns with the mark on the oil pump. It's staring you in the face when you are working with it anyway. The only reason they say to first align the cam pulleys with the marks is that then if they stay there you are all set to go when putting on the new belt. If you don't do that or if they move, then just move them back to the marked positions. It's not rocket science.

Seriously I would be a whole lot more worried that I would make a mistake putting it together any other way, and you won't really know you made a mistake until it is all put back together and you go to start the engine. Maybe I'm weird but I only like to do jobs once so I try my best to make sure it is done the right way the first time.