Slack in timing belt?

[TransplantCanuck]

So the guy who ended up installing my snorkel (Roger) called my attention to an unusual sound in the engine bay that he noticed. He thought it might have been a bearing on a pulley going, but it actually turns out (I think) to be the timing belt itself slapping against the timing belt cover. Needless to say, I was rather alarmed at this, and pulled off the timing belt cover to have a look. Everything is tight on the tensioning pulley side, but there was a lot of slack on the opposite side - to the extent that there was probably an inch or two of "wobble" visible on that side when the engine is running with the cover off. I just replaced the timing belt (and tensioner, tensioner puller, and water pump) about 20k kms ago, but nonetheless I pulled the belt off again, took as much tension as I could out of the loose side, and re-installed the tensioner. Everything seemed reasonably taut when I was done, but after running the engine for a few minutes and checking again, the slack was back - albeit I think slightly less than before. From what I've read, you should be able to just twist the belt 90 degrees on the slack side, and this rule of thumb seems about right - yet it still sounds like the belt might be hitting the cover. Other than replacing the belt (again), is there anything else I should try?

(I apologize for all my threads recently - just going over everything with a fine tooth-comb before our Cape York trip)

[Gee]

Mate if the sound is a clack, clack, clack type sound that occurs randomly on cold start ups and you have a 1kz I would say don't worry about it. From what I have researched, plenty of 1kzs make it, including mine, and it's normal. It's gone after a minute or so and has never caused a problem. No real fix either from what I've read.

[RED60]

I'm not familiar with the exact engine you've mentioned but have messed with a fair few belt driven ohc motors.... the slack side of the belt should be the side with the tensioner on it... I would also make sure that you have the correct belt... seems to me it's too long for the motor, to me it obviously shouldnt touch anything in correct adjustment... also are you sure you have the correct idler/tensioner, if it was smaller in diameter it would make the belt too loose as well.... just a few thoughts.... tell us what you find....

[TransplantCanuck]

I'm not familiar with the exact engine you've mentioned but have messed with a fair few belt driven ohc motors.... the slack side of the belt should be the side with the tensioner on it... I would also make sure that you have the correct belt... seems to me it's too long for the motor, to me it obviously shouldnt touch anything in correct adjustment... also are you sure you have the correct idler/tensioner, if it was smaller in diameter it would make the belt too loose as well.... just a few thoughts.... tell us what you find....

There's a diagram of the timing belt setup here: http://toyotadiesel.com/photopost/showp ... photo=1093" onclick="window.open(this.href);return false;

The slack bit I'm talking about is between 2 and 3 on that diagram, on the right side. On the tensioner side, the belt is very snug. I got the replacement belt as part of a kit, so it's not an OEM Toyota belt. I just bought a new Toyota belt today, though, so I can compare lengths.

I think it's less than one tooth of slack, though (i.e. I don't think I could pull the belt even one tooth tighter on the slack slide) - it just translates to a lot of belt movement. The teeth do engage perfectly on the pulleys, though.

[McLarryBob]

If it has as much slack as what you are saying i'm surprised it hasn't skipped a few teeth.

[TransplantCanuck]

If it has as much slack as what you are saying i'm surprised it hasn't skipped a few teeth.

I'm going to have another look at it this weekend, and I might swap the belt with a genuine Toyota one and see how that works out. I'll post some pics later tonight so you guys can see what I'm talking about. Honestly, I don't know how there can be that much slack and yet not be able to get it a single tooth tighter.

[UhhOhh]

I don't see how you would get a slack belt on the non tensioner side unless the belt is shagged. It does have some bend given it's a rubber belt and it travels a long way between pulleys, which is normal.

[TransplantCanuck]

OK, here are the pics:

[McLarryBob]

That's HEAPS! Do the timing marks line up??

There is something not quite right there...

[TransplantCanuck]

That's HEAPS! Do the timing marks line up??

There is something not quite right there...

Yup, the timing marks were/are still aligned.

I'm going to pull the belt this weekend, compare it to the OEM Toyota belt, and try and figure out what's going on.

[RED60]

That's HEAPS! Do the timing marks line up??

There is something not quite right there...

Yup, the timing marks were/are still aligned.

I'm going to pull the belt this weekend, compare it to the OEM Toyota belt, and try and figure out what's going on.

Either you have the wrong belt or the tensioner isn't tensioning, as in it has a broken spring maybe.... please keep us informed...

[TransplantCanuck]

Either you have the wrong belt or the tensioner isn't tensioning, as in it has a broken spring maybe.... please keep us informed...

Tensioner is definitely tensioning - that side of the belt has literally no slack in it, and the tensioner itself is practically new anyway.

The odd thing is that when I (re)installed the belt the first time, there wasn't nearly as much slack as there is now on the non-tensioner side - so it has definitely gotten looser, but without skipping any teeth.

[Dane]

Stop freaking out, it is fine.

Think about how the setup works. Whilst I am not familiar with this particular engine, timing belt is driven by lower of the two pulleys (I assume the fuel pump as per the 1H series of Toyota engines?). When it drives, the belt is pulled tight and, in turn, drives the cam pulley. What you are seeing here is over-run of the cam or something similar created by the engine shutting down and the belt no longer being tensioned by the driving pulley.

Try turning the crankshaft (the correct way) by fitting a socket and breaker bar to the harmonic balancer bolt and the slack should disappear. The belt tensioner is only for taking up the slack on the non-driven side.

[TransplantCanuck]

Stop freaking out, it is fine.

Think about how the setup works. Whilst I am not familiar with this particular engine, timing belt is driven by lower of the two pulleys (I assume the fuel pump as per the 1H series of Toyota engines?). When it drives, the belt is pulled tight and, in turn, drives the cam pulley. What you are seeing here is over-run of the cam or something similar created by the engine shutting down and the belt no longer being tensioned by the driving pulley.

Try turning the crankshaft (the correct way) by fitting a socket and breaker bar to the harmonic balancer bolt and the slack should disappear. The belt tensioner is only for taking up the slack on the non-driven side.

I'd be happy with this explanation if it weren't for the fact that:
a) I can hear the belt hitting the timing belt cover when the engine is running, and
b) There's already scads of belt dust lining the inside of the cover.

[RED60]

Stop freaking out, it is fine. Think about how the setup works.

I am thinking about how this settup works. The idea is for the belt to keep the cam/valves doing things at high speed in relation to where the pistons are... having a belt with this much slack/backlash is NOT the way to do that accurately.... in fact it appears bad enough that I think a valve should have tapped a piston by now........ SOMETHING IS WRONG, IF IT DOESN'T GET FIXED, IT WILL CAUSE TERMINAL DAMAGE....

[Dane]

Stop freaking out, it is fine.

Think about how the setup works. Whilst I am not familiar with this particular engine, timing belt is driven by lower of the two pulleys (I assume the fuel pump as per the 1H series of Toyota engines?). When it drives, the belt is pulled tight and, in turn, drives the cam pulley. What you are seeing here is over-run of the cam or something similar created by the engine shutting down and the belt no longer being tensioned by the driving pulley.

Try turning the crankshaft (the correct way) by fitting a socket and breaker bar to the harmonic balancer bolt and the slack should disappear. The belt tensioner is only for taking up the slack on the non-driven side.

I'd be happy with this explanation if it weren't for the fact that:
a) I can hear the belt hitting the timing belt cover when the engine is running, and
b) There's already scads of belt dust lining the inside of the cover.

How do you know the sound you can hear is the belt hitting the cover? Is there a serious wear area on the indside of the cover that you can see? Is all of the outside of the timing belt ground off so you can no longer read the writing or whatever is on the outside of it? Maybe spray some marker paint or something similar around the outside of the belt to prove your theory. Just because someone told you something is so (me included), doesn't mean it is gospel. Dust inside the cover is normal, to some extent.

Have you tried turning the crankshaft yet?

[TransplantCanuck]

How do you know the sound you can hear is the belt hitting the cover?

a. Because if I put my ear to the cover, I can hear the belt slapping it
b. Because if I run the engine without the cover, I can see the belt flapping far enough to where it would contact the cover.

Is there a serious wear area on the indside of the cover that you can see?

No, but it's only been ~20,000 since the belt change.

Is all of the outside of the timing belt ground off so you can no longer read the writing or whatever is on the outside of it?

Yes.

Maybe spray some marker paint or something similar around the outside of the belt to prove your theory. Just because someone told you something is so (me included), doesn't mean it is gospel. Dust inside the cover is normal, to some extent.

Yeah, I might . . . but I think I'll try refitting/replacing the belt first.

Have you tried turning the crankshaft yet?

No.

[Dane]

Hope you get it sorted mate.

[TransplantCanuck]

OK, here's an update.

I pulled the belt and compared it to the genuine Toyota one. They're identical in size and the markings are where they should be. I replaced the belt with the Toyota one anyway.

The camshaft mark was perfectly aligned with its mark, and so was the injection pump mark. The marks on the belt also lined up perfectly with these. There was very little slack in the belt when I installed it.

Here's where things went pear-shaped. Apparently, torquing the tensioner pulley pivot bolt to the specified number (35N-m) actually prevents it from pivoting at all, so the tensioner pulley wasn't snug against the belt. I had actually cranked the engine over a few times before I realized this, and by then the belt had somehow jumped about four teeth. Somehow, the camshaft and injection pump marks were still aligned - but the belt had drifted so that the marks were about 90 degrees (on the camshaft sprocket) ahead of where they were initially. I nearly had a heart attack when I saw this, but no damage done (apparently). The engine starts and runs fine. I backed off the torque on the pivot bolt about half a turn and things seem to be fine.

Once again, however, it looks like there's about as much slack on the non-tensioner side as there was before, although subjectively it looks like the belt isn't flapping as much. I'll have to have a listen again and see if I can hear it hitting the timing belt cover.