timing belt slipped a tooth ?

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POE
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timing belt slipped a tooth ?

Post by POE » Mon Aug 03, 2015 6:25 pm

Checking timing as wont start at all not even a cough ' lined the cam pulley up with the cover marking ' removed bolt in block and inserted bolt to line tdc but had to jiggle to get it in and now cam pulley says a notch out ' belt mark still line up with cam pulley but crank marking on belt is off set meaning the line never lined up with tooth and was either one side of tooth or other ' any help would be appreciated to whether I have a slipped tooth

Oh yes and when I removed cover there was quite a bit of plastic dust debris which I'm assuming the belt has rubbed on the plastic and maybe the cause of the tooth out ??
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Ade
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Re: timing belt slipped a tooth ?

Post by Ade » Tue Aug 04, 2015 11:57 am

Hi,

I've done many Cambelts in my time and hence have had experience of ending up with one or two a tooth or two out first time around. Normally I've noticed it and put right before reassembly but there was an instance on an Astra with VVT where it wasn't apparent until the engine was started and the EML illuminated. Once it was put right and driven again, the EML disappeared.

My point is, the only sign that it wasn't right was the EML, the engine ran fine. Perhaps with hindsight, a slight hiccough on idle but overall if it weren't for the EML, it would have likely gone unnoticed. Therefore a tooth out on the belt shouldn't stop it starting I wouldn't think. Unless its more than 1 or 2 teeth.......
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Re: timing belt slipped a tooth ?

Post by POE » Tue Aug 04, 2015 12:03 pm

Thinking maybe been a tooth out a while and just a coincidence that not starting' only just realised how to set tdc up with bolt in block near flywheel and always used belt marking to align ' was slighty misfiring at idle with a few revs ' never drove car for a few years so don't really notice if not as powerful as should ' think I've disturbed something with doing crankoil seal but think I need to sort timing out first
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doingitsideways
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Re: timing belt slipped a tooth ?

Post by doingitsideways » Tue Aug 04, 2015 1:48 pm

Most likely the crank sensor then?

Agree with Ade, it should still run if the belt was out by a tooth or two.
"If you can't fix it with a hammer, it's an electrical fault!"
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Re: timing belt slipped a tooth ?

Post by POE » Tue Aug 04, 2015 2:04 pm

Tested flywheel sensor and resistance is fine as is temp sensor Something ive not connected properly maybe ' even swapped ecu's over with same result Doesn't even attempt to start
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Re: timing belt slipped a tooth ?

Post by travelman » Tue Aug 04, 2015 4:25 pm

If it will not start check the thin earth wire from the engine to the coil.If this is not good at both ends then it will be as dead as a Dodo! It happened to me quite suddenly due to a build up of gunk beneath the terminal at the coil end. Nothing to do with timing belts,but easy to check.

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Re: timing belt slipped a tooth ?

Post by POE » Tue Aug 04, 2015 4:46 pm

Thanks for the help, ordered a timing belt kit today so hopefully get that fitted by weekend and start the process of elimination 'ruled out the obvious things but need a check list and results etc
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Re: timing belt slipped a tooth ?

Post by Robou » Tue Aug 04, 2015 10:27 pm

Indeed a few teeth, or better degrees, do not harm. It even can be used to give the car more power at either low revs or high revs. But what is won at one end is lost at the other.
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Re: timing belt slipped a tooth ?

Post by POE » Tue Aug 04, 2015 10:34 pm

Very interesting robou ' would I have lost power with a tooth out ' looking at cam mark it needs to be one tooth to the left haha If that makes sense drive Honda jazz so driving Volvo to my home less than a mile away felt very powerful as haven't had the pleasure of driving on a regular basis
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Re: timing belt slipped a tooth ?

Post by Ade » Tue Aug 04, 2015 10:49 pm

Depends which way the cam is out of phase with the crank. Advanced will give more torque and power at higher engine speeds and retarded will produce better torque at low speeds whilst sacrificing top end.

Fixed valve timing is always a compromise, there will only be one particular engine speed that any given setup is perfectly suited to. Most production road car engines find a happy medium. Theoretically the valve timing is optimal when the engine is producing peak torque. Race engines will have timing advanced as they are not required to run in lower speed ranges. A lot of bike engines have quite well advanced valve timing too, again because they normally run at higher speeds. You may have noticed how rough the tickover is on a lot of big sport bikes. This is because of the advanced timing and quite possibly increased valve overlap. (The time that both inlet and exhaust valves remain open simultaneously).

Given a DOHC setup one can alter valve overlap too because you are able to set inlet and exhaust cams separately. Unfortunately this cannot be done on the 480's as they are all SOHC therefore the angular offset between the inlet and exhaust cam lobes cannot be varied. One would need to have a custom camshaft made to vary overlap on a 480.

I'm not going to go into detail, the physics and dynamics of the otto cycle in a spark ignition engine are hugely complex and have many variables and factors to consider. If you ever have a few hours/days/years to kill, do some googling! (Or better still go to a library and get some books on the subject, I find books can be a far superior source on information if one is willing to devote the time!)
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Re: timing belt slipped a tooth ?

Post by Ade » Wed Aug 05, 2015 12:48 pm

Of course, herein lies the advantage of variable valve timing and why it is becoming so popular in modern engines.

Much like there exists a map for ignition timing in our EZ210K's, there will exist a map for valve timing within the ECU which allows it to vary the cam phase to suit speed and load thus allowing the engine to have a broader range of speeds where the valve timing is what you might consider 'optimised'.

If you look at some torque and power graphs for various engines it will become apparent that the plotted curves are much more linear with VVT than without.

With DOHC setups that have VVT the ECU can vary inlet and exhaust cams separately thus allowing variation in overlap too. A greater amount of overlap is desirable at higher engine speeds as the inertia of the gasses flowing through the cylinder can be advantageous in good scavenging of exhaust gas and thus a good full of fresh charge.

The variation in overlap is similar to basic timing in so far as any given amount of overlap will only be suited to one particular set of conditions. A big overlap will mean poor running at low speeds but explosive power and torque will be available @ 4000+ as the cylinders will be better scavenged and better filled too as not only will the downstroke of the piston create vacuum but also the outward flow of exhaust as along the pipe. Of course all this talk of overlap is purely academic as regards 480's as it is not variable because both inlet and exhaust cam profiles are machined on one shaft so the overlap is what it is.

Anyone who likes more power at higher engine speeds might consider advancing the cam by a tooth or two when changing the cam belt as robou says. Just make sure there's no interference and be prepared for poorer running at lower speeds.

The turbo engine has a pretty awesome top end anyway so this might prove an interesting experiment.......

Vernier cam pulleys are quite widely available for many engines, if you could find one with the correct tooth profile and number of teeth (I think ours are a standard '8M' tooth profile which is also widely used for synchronised drives in industry) then it would be more than possible to fit one with a little machining. I know fords use an 8M belt on the zetecs etc and you can certainly get vernier pulleys for most ford engines.

Santa pod anyone :)
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Re: timing belt slipped a tooth ?

Post by Robou » Wed Aug 05, 2015 2:31 pm

I enjoyed your posts, Ade, just one remark. As I pointed out above one should in general speak degrees, not teeth. Everything concerning this subject is expressed in degrees, like valve timing.

I consider 6° the maximum for safety, concerning pistons hitting the valves. This is why the engine always has to be turned over by hand before starting it.
Let it warm up while idling, then slowly rev up till the maximum revs. If an unexpected ticking sound is heard switch off immediatly and correct the setting one tooth towards normal. This check has to be made because intertia at high revs slows down the closing valve.

But back to degrees.
Count the teeth on the camshaft pulley. One turn of the camshaft, running half the speed of the crankshaft, represents 720°. Divide this by the number of teeth and you know what many degrees is represented bij one tooth. I took the camshaft as reference because it is the easiest to come by.

If you like to change the behaviour of the car this most certainly is worth while.
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Re: timing belt slipped a tooth ?

Post by Ade » Wed Aug 05, 2015 4:34 pm

Yes of course, I know it should be spoken about in terms of angular measurements not simply numbers of teeth, I was just speaking in easy to understand terms.

Turning into quite an interesting thread isn't it? Thinking of degrees, I haven't seen a proper valve timing diagram for a long time.......

Setting up timing without marks/holes etc is quite interesting actually. I work for a company that manufactures racing engines for the WRC, Indy 500 etc and to achieve maximum accuracy there are no premachined marks/holes etc, the engines are first assembled and then timing is done with clocks on special fixtures that pick up the piston crowns and the cam lobes and tappets/rockers. Marks are then hand etched afterwards for service purposes.
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Re: timing belt slipped a tooth ?

Post by POE » Mon Aug 10, 2015 9:35 am

An update on fitting new timing belt and idler etc 'was a little optimistic about whether the timing was out by more than a tooth and not starting when rechecked timing with old belt, Seems belt was rubbing badly on the Idler strangely ' anyhow refitted belt and started first turn of the key ?? Maybe timing was out a lot to stop from starting ?? Or I have disturbed some sensor ?? Seems ok with no idle probs and seems smooth ' how many teeth out could you get away with before damage or have I been lucky
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doingitsideways
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Re: timing belt slipped a tooth ?

Post by doingitsideways » Mon Aug 10, 2015 11:57 am

I suppose IN THEORY it could be half a turn out?
"If you can't fix it with a hammer, it's an electrical fault!"
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Re: timing belt slipped a tooth ?

Post by POE » Mon Aug 10, 2015 6:23 pm

That seems a lot and maybe I'm just lucky 'strange it ran then stopped a few times with no indications of a problem 'just need to build everything up and go from there and thanks

Ps 'havent forgot about speed sensor Mr sideways 'waiting for friend to lift shell out the way of engine as no room at the mo :D
1989 480 turbo ,saffron pearl, half leather with richmod and full custom bodykit

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