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Timing belt tension


esprit s2

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Evening all.

Got my car back form the factory on Friday afternoon, all is well but the timing belt sounds way too tight to me. I can't hear the exhaust over the whirring sound!

Can I slacken it off easily or is this something best left to experts with gauges? The guys at the factory said it was tensioned correctly (which I do not doubt) but it is doing my head in. Sounds like an electric motor!

Edited by esprit s2
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  • Gold FFM

If the factory did it, then I wouldn't dream of playing with it without a gauge. Maybe it's not the timing belt?

British Fart to Florida, Nude to New York, Dunce to Denmark, Numpty to Newfoundland.  And Shitfaced Silly Sod to Sweden.

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if it is too tight it will sound as you described...phone the factory up or take it back..

fri afternoon??? we all know what that can be like and just cos it was done at the factory doesnt mean they dont cock things up

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This is the story:

Got up there at 1100 on Friday as I knew they knock off at 1215 on a Friday. Got there, met by Rowland (top bloke) and he said that they had had a problem with my car that morning. When they went to adjust the belt the locknut or adjuster bolt thing (can't remember which) sheared and they did not have one in stock. The machine shop said they'd make one and that took around an hour and a bit. They finished the job around 1330 and then after a quick test drive the guy handed me my keys. Both Rowland and the guy who tested the car said it sounded too tight.

I drove home.

Problem is if I do take the car back I'll have to take another day off work plus money is tight!

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If you want a quick check of the belt tension which is unlikely to cost you anything (assuming you've got a laptop & microphone), try downloading some guitar tuning software (I used an evaluation copy of "enable guitar tuner"), take your laptop out the car, plug in an external mic and hold the mic close to the belt, mid way between the inlet and auxillary pulleys. Tap the belt with a spanner (or something similar) a few times and see what reading it tends to settle at, it should be around 110hz, any higher and the belt is too tight.

Tony.

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It might cost you a day off work, but it'll cost you more if you try to do it yourself and f**k it up. Also cost you more to go to a local specialist garage as they won't cover Lotus's error for free. I'd call Rowley, explain your issues and see if the factory will cover you taking it into a local main Lotus agent. That way you've still got a lotus warranty if something goes wrong, and hopefully a little more local to you. With a main dealer Rowley may have some leverage to get the job done as opposed to an independent specialist.

It's not good if a mistake has occurred, but at the end of the day, anyone can make an error. From what you've said in your prev thread they've looked after you very well, and you've had a track freebie too? If they would do what I suggest and it was me, I'd be inclined to live with the hassle.

Regards

Mat

post-1-0302470001278592957.jpg

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  • Gold FFM

Whereabouts are you, Paul? Want to pop to Watford in an evening and I can check the tension?

British Fart to Florida, Nude to New York, Dunce to Denmark, Numpty to Newfoundland.  And Shitfaced Silly Sod to Sweden.

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You can check the tension with a DIY clavis gauge, which means there is no need to disturb anything Lotus have done. Download 'TuneIt' from the internet, rotate the crank to 30 degress BTDC, using a microphone conected to your laptop you can check the Hz by tapping the belt with a spanner or similar. I set mine at 112 Hz

cheers Steve

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Sparky - PM sent.

Others - I haven't got a laptop and I'm no singer so no microphone!

I'll speak with Rowland tomorrow, I'm sure we'll sort it out.

Let me just make this clear - I'm more than happy with everything else they did with my car and service is second to none. Will be using them again for sure.

Paul

Edited by esprit s2
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  • 2 weeks later...

Steve...what's magic about 30 deg BTDC? And thanks for the TuneIt tip...

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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At certain points in the rotation the belt is under more tension or less in given areas as cams are at the point of opening valves, so it could be set at many different values relative to TDC and at the relevant tension (resonant frequency) for that value, but 30 is then simply a reference point.

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Hi John

30% is specified by lotus for the 4 cylinder models, as Andy says, it will allow a consistent reading. One other thing, the belt must be struck on the run between inlet cam and auxilliary pully.

There was an interesting thread about this if you can find it. 100-110 Hz is specified for the HTD belt, however, as the trapeziod version is lighter, it was determined that it should be slightly higher Hz. (I use 112).

http://www.lotusespritworld.com/EGuides/ET...l/Cambelts.html

cheers Steve

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There was an interesting thread about this if you can find it.

It's here...

http://www.belchamber.org/techtiming.html

and there's some general info here...

http://www.espritfactfile.com/timingbelt2.html

Paul.

Edited by Paul Coleman

Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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Thanks, troops...I can see how the belt tension from the cam pulleys to the crankshaft pulley can vary, as the crankshaft pulley is, er, pulling (!) the belt and the load is coming from the cam pulleys, and it will vary depending on the load imposed by the valve train...but how would that affect the tension where you measure it, between the inlet and auxiliary pulley? Surely that would be set by the tensioner only, the auxiliary pulley having little or no change in load? Or am I opening a can of worms.....

Thinking about the frequencies; the open A string on a guitar is 110 Hz...so apart from all the other clever stuff on computers and Burroughs gauges, seems I could use my electronic guitar tuner, with its' built-in microphone and set it to the A string position, and that ought to give 110 Hz..then set the frequency from the belt slightly sharp using the meter on the tuner, and that ought to work!! Will have to try that next time I'm in the workshop..

Edited by molemot

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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The tensioner is (semi-automatic) variable, as the belt slackens as the rotational force necessary to turn the cam varies, then the tensioner moves to take up some of that slack, but it is achieved by the spring lengthening, so the force it is applying is less than when it is more compressed. So the tension on the belt is less, but less than with a fixed tensioning system.

On the later cars, the tensioner is fixed, so the variation in belt tension as it cycles is greater.

If you mean why is it not constant tension in this particular area of the system, as the belt is pulled by the crank, and so pulls the exhaust and inlet first and the axillary one is more constant in its requirements. The belt is fixed in length (excluding stretching etc), so when it is more tense in one area (between the exhaust cam and the crank) it means there is fractionally more material in the other areas, so less tension.

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John

At any point in the cycle the inlet and/or exhaust cam will be trying to open /close the valves on any of the cylinders. This means the valves affected are applying a load to the cam lobe which in turn is applying a torque to the pulley/pullies. if the crank is considered as locked (not enough force applied to it to overcome friction, compression etc depending on the cylinder, the the torque applied to the pulley/pullies applies a load to the belt making it tight between the crank and pullies.

On the other side of the pullies, you are correct in assuming the auxilliary shaft has a negligible load when the engine isn't running. As previously discussed, this side of the drive is slacker because it is not under tension applied by the engine. It is not desireable for the belt to go into negative tension, eg slack, because the torsionals applied by the cams and crank when the engine is running have the same effect on the belt as it would on your tow rope if you were towing a novice driver. To overcome this the autotensioner is designed to provide a tension to the belt ensuring that the belt can never go slack under the worst torsional loading. What you are measuring on the slack side is the required tension specified to ensure the belt is always in positive tension.

While most people like the simplicity of the fixed tensioner, it is only ever correct on the day it was set and that is why the service manual suggests regular inspection. This system assumes some belt tolerance to increased/reduced belt loads occuring as the engine loading changes and as the engine grows/ shrinks as it gets hotter/ colder. The reality is the fixed tensioner increases belt wear due to this increased loading causing the belt to appear to stretch and the tension applied to fall. If this goes negative, then the risk of greater belt damage increases in addition to the normal ageing process.

A good autotensioner is always the best option

Regards

Ralph

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