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NEW TIMING BELT


lostu

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Hi again, had a new Lotus timing belt fitted at my local garage 5 months ago on my 1984 S3 N/A Esprit.

running great and idling spot on,my reason for this topic is about everytime i work on the engine or too inspect etc

i check over the belt.As it stops at different positions i always have a look,after being out on sat i checked the belt

and there is a small like nick at the outside edge.I ran the engine and watched it looks fine and there is no other defects

anywhere else.Do you think it was done when fitting or am i being too concerned as if there was a cover it would be out of sight.

it normally stops where the lettering is and would never notice,what would be your advice thanks stu.

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hi mike,i had another good look over the belt i think it might have had the nick when fitted as the belt looks still good,

it a wide belt and asking aronnd the belt could run half the width thanks stu.

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My concern would be the shape of the nick. If it has any unevenness in that nick it could cause a stress point and thus tear. Think of it like this, pull a sheet of paper that is (defect free) at the ends, it will possibly hold, or take a lot of force to shear, repeat with a sheet only half as wide, similar, just not as much force to shear. Bow do it with a full size piece, but put a small nick in one side of the paper, it will probably shear from that point at less strain than the smaller sheet, and way less than the large defect free piece.

So, we go on about changing belts regularly, if those are the full sheet with no defects, how long do you want to run with a belt with damage?

It may be worth talking to the people who fitted the belt, the belt shouldn't catch (but yes they can rub on the snubber sometimes), so it shouldn't be damaged this early in its life. If it was damaged during fitting they may replace it FOC, or perhaps (if they don't believe they damaged it but want to keep your custom) fit it at a reduced price.

Andy

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hi andy,it is on the outside edge on the top side only running the same way as the belt about a millimetre inwards.i asked the garage and they said i it was their car he would not change it only if it got worse as the belt is made up of strands and could run half the width.he if concerned bring it in too have a look.i turned the engine again now the belt still has all the lettering and yellow part numbers etc.could it have been a stone ,but i think a little nick when fitting as if it stopped more or less where it normally stops i would have not seen it for maybe a long time.am i right in saying a good timing belt it very tough,also the tooth underneath is not affected and all good thanks stu.

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STU

if you can get me a picture from the back of the belt (opposite side to teeth), the side where the nick is and if poss the front of the belt ( the side the teeth are on) I will give you a thought on the state of the damage. The garage is right that the belt could run on half the width, but not for very long. The belt degrades over time. It starts with a load capability way in excess of the demands and as it degrades over time the load capacity degrades.

If for example the belt must be capable of transmitting 5000N and any level lower than this it will break, then if it starts with a load capacity of 15000N and has been designed to have a service life of say 5 years and degrades at 2000N per year, in 5 years it will be at 5000N and it will be time to replace it. If you have 50% of the belt, it now has a load capacity of 7500N (50% of 15000N). If you assume the same rate of degradation of 2000N per year to make things simple, then it it will now have a life of 1.25 years. If you stick to the normal service interval then things have the potential to become expensive.

Regards

Ralph

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hi ralph,no photos at moment ok the back of the belt flatside the nick is there,the bottom side toothed or as we say inside /out there is no damage at all.i`ll try too explain better.if you looked at the belt side on from the bottom up all the tooth is ok and untouched only near the top edge is the nick.also i have the belt changed every 18 months and at present its been on 5 months doing only about 200 miles wear so far,does this make sence thanks stu.

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With out a doubt I agree with above get the belt changed, not sure how much you payed to get the belt changed but I feel that to get a garage to refit a belt under warranty may be a little hard after five months, But as others have suggested you may be lucky for 50/50 from the firm that did it.

Will be intrested to see how this one pans out with the workshop, best of luck

Regards danny

A

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Stu

Cant really comment about the damage without seeing it in some form but with it being 5 months old and 200 miles I would say you have little to no chance of the garage replacing it. If you change every 18 months regardless then the risk of failure will be less than if you go longer. Obviously the cost of getting it done again is quite an expense, so you have to make that call. It is the cord that is doing the work on the belt, the teeth just stop it slipping so you must be sure that the cord is not damaged. Furthermore, check the cord is not frayed as I have seen a frayed end catch on another part of the engine and unravel like a knitted jumper. Engine doesnt last too long when that happens and cleaning the mess up is a pain as well.

Make sure that when you fit your next belt that you check the tensioner condition. I would also check it now for damage to the pulley incase that is where the nick come from. It may have got damaged during fitting.

Cheers

Ralph

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Hi again,thanks for all your coments,firstly i have ordered a new belt which came today.Next week its getting fitted ye its costing me again,but the guy is fair and giving me a reduced price.i told him i couldn`t drive the lotus with the belt on my mind.my out look on this issue at the nature and condition of the belt as there is no other damage anywhere else.it will always be a wonder how that happened,will reply next week too see if any thing was spotted cheers stu. ps regarding Buddsy its interesting what the other guys would say but my timing belt clock starts ticking when newly fitted good question.

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Buddsy

Technically the belt starts to degrade immediately. The rate of degradation depends on many things, eg tempature, exposure to sunlight and with the older rubbers eg chloroprine, the environmental conditions such as moisure can have an impact. The rate of degradation on a shelf or on a non running engine will be much less almost insignificant than a running engine because it is unaffected by heat. Heat is one of the major aging elements for rubber. Most belt comapnies build an element of storage into their calculations because their product could sit on a shelf for a couple of years before it is used in a vehicle, however I would suggest that providing it is not going to be sitting around for another few years, it should be OK for another 2. I would however make the point that it also depends on how you will drive the engine once it has been run in eg hard use = high temps = reduced life. Talk with me about it next time we see each other.

Cheers

Ralph

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