Timing belt jumped a tooth?

[loply]

Hi folks,

Slightly OT as this relates to a car, but, could someone in the know tell me if it would be obvious if the timing belt had jumped a tooth on a modern 1.3l petrol?

Car runs absolutely perfectly but I've got the garage telling me the timing may have jumped a tooth as I'm getting the MIL light on. My opinion is that the engine would run badly if it was a tooth out.

This is a Toyota VVTi engine though, so maybe the VVTi is compensating for the jumped tooth?

Cheers,
Rich
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[Kickstart]

Hi

It probably would run badly but maybe not that badly, but I would also be surprised if it jumped a tooth (rather than someone fitting a belt one tooth out).

Doubt the variable valve timing will do anything to compensate (although it might well make it harder to set the cam timing when fitting a new belt).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[loply]

Hi Keith,

Thanks for that. The VVTi has the ability to advance or retard the intake cam by quite a bit so could compensate for a tooth being out, I figured? The ECM 'calibrates' the VVTi by advancing the cam until it's in the right spot, and can do so by quite a way, so I figured it may be able to advance it far enough to mostly compensate for a jumped tooth?

The car only has 30k miles and hasn't had the timing belt touched.

My next guess is the crank or cam sensor is playing up but again I would have thought that would cause real bad running (unless it's just intermittently mis-sensing).

Bloody modern cars, this is going to be a wild goose chase!

Cheers,
Rich
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[thomp1983]

you need to take it to someone with a decent diagnostics setup and who can look at and understand the live data it shows, a faulty cam or crank sensor is easy to spot with live data or an oscilloscope. again the one tooth timing theory can be confirmed in an hour, they'll only need to set the engine to it's timing marks and remove the timing covers

chris

[Kickstart]

Hi

I would expect that if the belt was much out and the ecu detected it that it would light up the engine management warning light. A bit surprised that it tries to move the cam to sort out the timing itself.

I would be more suspicious of the timing variator, or the position sensors to be honest, than the cam timing jumping.

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[loply]

[loply]

If I want to check the timing hasn't jumped a tooth is it a simple matter of popping out the airbox and coils, then unbolting the cam cover?

Or will I need a new gasket if I do that?

Cheers,
Rich
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[Kickstart]

Hi

I have seen a car that ran acceptably (just not perfectly) with the cam out one tooth on one bank of cylinders (a flat 4).

To be honest I would expect the variator to manage to move the cam more than one tooth worth, just surprised if self adjusts like that.

As to checking the timing of them, not sure on the Toyota. For example (and from memory) on the variable valve timing Alfas it is far from that easy when putting on a new cam belt to get the cam timing right. Set the engine to TDC, take off 2 cam caps and replace them with ones that lock the cams in position (cutouts shaped like the cam lobes), take out a spark plug and use a dial gauge to check the appropriate piston is at TDC and then put the timing variator in place on the tapered end of the cam shaft.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Bezzer]

Have a look on the very good Toyota Forums https://www.toyotaownersclub.com/forums/index.php?showforum=59 They have loads of the service manuals and bulletins in each of the model sections. Be worth a search as well to see if your warning light is a common problem. Helped me out no end when I had warning lights everywhere and it just turned out to be a duff brake switch
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I used to be indecisive but now I'm not quite so sure.

[thomp1983]

what age and model is it ill have a look on my copy of autodata and see if it has the diagram for the timing marks

chris