Changing a timing belt.

[patrick]

Question to the OMG crowd.

I've been trying to change the timing belt on my '97 corolla DX. 

I lined the top gear up as described in all the videos I watched. I went about making a few markings on the belt and gears two on the top gear and three on the bottom gear. I took the new belt and counted out the notches 3x for each marking and transferred the markings, but I did not count all the way round the belt to see if it was the same length.

Last night i put the new belt on oriented in the correct direction. The gears had not moved since i initially set them up with the old belt still on. To make sure the new belt stayed on correctly with notches lining up I clamped the bottom to the gear after I put it on and then did the same to the top. Again the gears did not move while doing this. Then with both gears clamped with the new belt on I installed the idler and spring. Once that was installed I removed the clamps and everything looked good.

According to the videos I watched I needed to rotate the engine so the belt went round twice and check the markings to make sure they lined back up. On the first pass they did not so I did the second pass and they were off by 2 notches for each marking. To be sure I rotated two more belt cycles and now they are off by two more on each marking making it off by 4 now.

Do you think its possible that if I took the new belt off and counted the notches on the other side of the belt from where i made the marking that it would be two notches longer or did I completely screw something else up? When I rotated the engine there was no knocking that i could hear.

Any help is appreciated.

[Ben Hutcheson]

It sure sounds like you have the wrong length of belt.  There were (at least) two different engines offered in the Corolla that year; I'd guess you have the belt for the other engine.  On the plus side, a cursory search suggests both are non-interference, so you won't destroy the engine by being wrong, and won't hear any funny noises.  It just definitely won't run.

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[patrick]

So how would the belt being two teeth longer make it not run? Its still a taught belt once the idler is engaged. And I thought it was an interference engine.

[Ben Hutcheson]

If the belt is two notches longer, the timing will shift by two notches with every rotation of the belt.  For the first rotation or two it might still be close enough to run, but after that the timing will be too far off to run.  From what I can see, the 1.6 liter engine should have 117 teeth and the 1.8 should have 121 teeth, so if you're off by 2 you might even have something else entirely.

As far as interference vs non, I did all of 30 seconds of research on that.  If you think it's an interference engine, don't crank it and be very careful pulling it through by hand until you get the marks to stay lined up - as above, it'll be fine for a handful of rotations before the valves are 180° out of phase and start making friends with the pistons.

[patrick]

I'll have to count the teeth on the old belt and compare it with the new belt. Looks like I'll be biking to work all week.

[Stephen Beck]

The length of belt doesn't matter and the tooth count doesn't matter, as long as the teeth are the same dimension and distance apart and the slack in the belt is able to be properly taken up by the tensioner on the loose side of the engine then you should not have a timing problem. The only thing that matters, with respect to belt teeth, is that the tooth count between the cam gear and the crank along the section that is naturally under tension (from motion of the engine) is correct. The slack length of the belt is tensioned by a separate spring our hydraulic tensioner.

If the engine is off after each rotation the belt is more likely jumping teeth on the gears which means the tension is likely not set properly. If I have to adjust tension I will usually start by adjusting it just tight enough that the belt won't slip, rotate the engine around twice, check timing marks and then reset tension with the other side stretched slightly...

When I say "slack length of belt" you may see this as a misnomer because the whole belt may be "tight" per se when you get it on all the pulleys. Let me know if you are not sure of what I'm referring to.

I've replaced probably 40 or 50 timing belts and chains on the last few years, including both 4 and 6 cyl Toyotas, and don't recall ever having the problem you describe without the belt jumping teeth...

Steve

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[patrick]

Yeah i thought a couple teeth wouldn't matter. I know its not skipping on the top gear I will have to have some one watching the bottom gear to see  if it is skipping down there. 

[patrick]

This is the car in question http://www.vindecoderz.com/EN/check-lookup/1NXBB02E7VZ506027

[Ben Hutcheson]

Crap, you're right about the belt length. Not sure what I was thinking. Gears, maybe.

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[patrick]

So right now the idler tension is just from the spring. Think i need to get a newer spring or just move the idler in farther and tighten it down?

On Tuesday, September 22, 2015 at 10:42:41 AM UTC-5, Nuclear Steve wrote:

[Stephen Beck]

So I just thought of something. You put marks on the belt and the pulley. If you rotate the engine around twice the mark on the belt may not line up with the pulley Mark. The timing marks are between the pulleys and the block. The belt does NOT have to line up for the engine to be in time. Check that the crank and cam pulleys are in the correct position. Rotate the engine around twice. Check again. Ignore the belt position relative to the pulleys...

[Stephen Beck]

The timing marks are as follows: when the home in the cam pulley lines up with the notch/ hole in the case then the notch on the plate over the crank pulley should line up with the pointer on the block.

You rotate the engine twice because the crank goes around twice for each rotation of the cam so don't run around once or three times and freak out because the crank pulley pointer doesn't line up...

Steve

[patrick]

Well in that case I believe I'm good from what I observed last night.

[Stephen Beck]

Errors in my last email:

"home" = "hole"

at the end, it's the cam pulley that doesn't line up after one rotation...

[Stephen Beck]

I'm watching the applicable portion of a two hour youtube video with, what sounds like, a German dude giving the instruction. I can see the possible confusion without skipping ahead to the part where you actually rotate the engine...

Steve

[patrick]

I watched that same video many times but kept dozing off. Must have missed that part.

On Tuesday, September 22, 2015 at 11:25:03 AM UTC-5, Nuclear Steve wrote:

[Stephen Beck]

But yeah. Here's an example. A cam pulley has 100 teeth and the belt has 402 teeth. Every 4 times the pulley has turned over the belt has passed .995 times and the homemade marks don't line up even though the engine is still in time.

FWIW I've never marked the belt like that.

Steve

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[patrick]

Funny all the video I've seen mark the belts. Must be a newb thing.

[patrick]

Thanks for the help guys. I put everything back to gather and have been driving it with no issues for the last week.

On Tuesday, September 22, 2015 at 10:04:47 AM UTC-5, patrick wrote: