Would you replace cam belts after 4 years and only 3,800 miles?

[73JPS]

What is it with replacing exotic car cam belts on a schedule 5 times the rate of "normal car" cam belts? Are they made out of sugar? Are they that much more highly stressed? I can understand a more vigorous schedule to be sure, but not at the rate suggested. The only problem I ever had with my cam belts were when the Lotus dealer replaced them, and wrecked the head on the right bank of cylinders. Now I just wish I had left them alone, since the subsequent head rebuild left me with a valve stem oil seal issue.

I was just speaking with a dealer regarding a 1996 Ferrari 355 with 11,000KM on the clock: cam belts have never been done. The dealer is going to do them just to make the car more saleable: but his opinion is that the belts (which are visually perfect) should just be left alone.

Edited June 7, 2012 by 73JPS

[Günter]

Patrik, personally I wouldn't fear any Ferrary without those 'freshly changed belt' ..as it is right that the risk is the same for most cars with belt driven valve system, seen on potential mileage until a belt snaps over/fails

-the point is: lets call it 'customer expectation' of a fault and costs, compared with a 'daily driver' car worth a cupple of bucks (as you say in US..) . If a car is meant to 'use it and dispose it' noone would care about a rebuild in case of, but with a 32valve system engine and exotic (but in reality not any higher quality..) parts there is a cost difference. Lotus tried to compeed with other manufactures on the US marked, but needed to stay within the mass production warranty announcements of the big players (Toyota,GM and so on) -and as such there was the only way to be a little mental on frequently beltchanges (for free).

In the same production period of the 1996ff Esprit V8 series other passenger cars & light truck/light duty vehicles with belt driven valves had a maintenance/renewal frequency of around 90.000km over here in Europe (have professionally worked in this period of time) -some have failed earlier, most of them I had to work on were just regular changes. So that's why I tried to run as much as possible with the previous belt-set on the V8 .. and you can see the result in the *caught by murphys law* story -tooth profile sheared, and therefore cam stopped to run, valve to piston contact caused overtension and the belt snapped ..simple thing

[Iconic Ride]

One aspect that sometimes gets overlooked in this debate (if that's what it is), is the fact that the Lotus V8 is one of the few belt driven cam(s) engines that doesn't have an automatic tensioner (except for the accessory drive belt). Any tendancy for the cam belts to stretch over time is thus not compensated for, hence the recommended tension check interval being three times more frequent than the belt change itself. To a point, one would think less tension would actually make for less wear and tear, but at the risk of becoming so loose as to skip a tooth eventually. I've been told (by Dave Simkin, the Lotus USA "go to guy") that you would begin to hear some sort of "slapping" sound if they got loose enough, but that to rely on that cue would be foolhardy.

[fmxa]

It's the $12k bill you get when the Esprit belts let go!

[Iconic Ride]

Ahhh......now I see. Apparently, it's the sound of one's self-slapping of the face!

[Günter]

John, the thing with the 'not enough tension' on a valve belt is nearly the same as on this chart (OK -it's for engineering, mainly in terms of steel/metall ..but the principles are the same)

http://www.bs-wiki.d......3-11.JPG����

(main mechanical tension/load situations)

..if the tension is to loose -you will see the instable loads in the valve drive even more, caused by the valve springs, which try to hold the cam on the different lobes in a constant position ..you can see this load if the belt gets changed and is undone -the cams trie to move in a defined position as long as no spanner is holding them. So as every belt system does have a 'tension side' and a 'slack side' you will see instable load peaks on the slack side, if the belt is not tight enoug -those loadpeak effects are even multiplied if the belt is going loose more and more. The shematics in II b) would match this situation , I a) would be ideal for a long lasting system ..and the worst situation [in teerms of longlife/ durability] III c) is luckily impossible (as a rope/belt can not transport negative orientated loads..)

Edited June 13, 2012 by Günter

[Iconic Ride]

Interesting stuff, Gunter. And just when I was beginning to get back on a normal sleep schedule.

What I'd really like to see is a description of the manufacturing process and design "ingredients" of the cam belt(s) themselves, and a cross section diagram of whatever layers are involved and how they are bonded together (if that is how they're made). A "testing to destruction" video would be enlightening as well, and since I'm once more consigned to lying awake at night feverish with worry anyway, I may as well wallow in the quagmire of disturbing possibilities.

Sleep is for wimps! Show me what you got!

[lotus4s]

[Günter]

that's the simplest pictures I can offer

..think even you will understand the basic shematics late in the night (should be daylight now for you ..as it is dark outside here?)

http://www.atu.de/pages/werkstatt/unsere-werkstatt/technik-wissen-motor.html

to make the proces even clearer for you all..

[Iconic Ride]

Ooohh! Ooohh! I love it when you talk like that. I'll be awake for weeks now. Just think of all the late night B grade movies I can catch up on. And this is so much healthier than methamphetamine. Gunter, you're a prince. Many thanks.

[V8 FOU]

How does this check condition / check for cracks work? Gates will tell you that it is almost impossible to assess the condition whilst fitted.

Struth! People will next be advocating checking the tension by twisting the belt thru 90 deg!!

[Günter]

Paul, ..I'm not sure what you may think the Gates company can tell me? -but if I inspect a cam drive/timing belt I used to find the longest sections between the pulleys or wheels, to see as much teeth as possible, and even use a small iluminated mirror (sometimes called 'doctors light' ) on a long telescopic arm to see the opposite side of the teeth. You can get these in every modelcrafting store, or even Autoparts store if you have the time to search & ask.. . As my belt failed '08 on one bank it was no surprise -as I had seen while performing my 'routine tension check by hand' the 'not so fresh anymore' condition of the set fitted in the year 2002. Just one year before in 2007, I had bought the regular parts ..but as a lazy boy just ignored what needs to be done ASAP, and stored all replacements for an other year in the garage and just used the car again and again and so on for local track events and gatherings ..and whhoops, one day on the way home there you have it

By the way, if you see my profile you can maybe imagine that I have seen a lot timing belts in my life ..and yes -the "turn it 90° on longest slope" thing is rubbish -as a professional or lets call it 'skilled mechanic' just uses his 6th sense for verifying the tension (at least on an ordinary family salon car ..an older one..where it doesn't matter how exact his feeling is)

-on my Esprit engine rebuild I've used the frequency calibration method, as within the workshop manual, just to be sure that I will do it right like factory wants to have it done.

..that's such a good picture to illustrate what I mean !

..based on experience I would say on the back this belt will probbably have some of those typical 'shiny, dull, shiny, dull, shiny..' -markings (those came from the changes in material stiffness between the teeth and the sections inbetween ..as the belt runs over those tensioner wheels for years and years and years -and the material on the rear side gets rubbed down a little..

..on the tooth-side you can see where the age/degeneration of the material starts ..as there also is a perpanent change in orientation on the base of every toth from 'bend' to 'straight' to 'bent' and so an, as soon as the tooth passes the cam-pulley wheel and goes back in the line straight ahead on the flat sections between all the pulley-/tensioner wheels.

Edited June 26, 2012 by Günter

[Iconic Ride]

Aaarrrrgggghhhhhh!!! Ayieeeeeee! Make the bad man stop! Tell me there's a chaindrive retrofit kit available. Make the rubber band cambelt nightmares go away. I'll be a good boy, really I will. Sell me a camshaft with shorter lobes. Half scale pistons. Anything! I'll sacrifice a goat to the banana valve gods. Whatever it takes.

[Günter]

rumors say the old fashion, gear & pushrod powered, valve-drive system on the Ford-Granada/Taunus V4 (a smal 4 pot engine, just big enough to power up your fruit-mixer over there in the US..) was like you want to have it .. no valve to piston contact as for the low compression an short valve lift.. maybe that's the car for you

http://explow.com/fo...ranada_(europe)

http://en.wikipedia....aunus_V4_engine

John, use this simple tool to sleep well within the next year http://www.google.de...ved=0CHsQ8wIwAA

or this, much cheaper http://de.farnell.com/jsp/displayProduct.jsp?sku=1361385&CMP=e-2072-00001000&gross_price=true

Edited June 26, 2012 by Günter

[Iconic Ride]

Thanks, Gunter. But I know there's a boogy man that lives inside the cambelt covers, and I'm not about to let him out.

Incidentally, Paul is not the first one to state that some sources say a visual check of the belts is insufficient to make a determination of their true condition, and whether on not snapping is eminent.

[Günter]

that's at least why Lotus tried to be a little early on the changes ..and told us over here with the note in the *owners-book* for the Europe market cars to change the belts so often. And again, within the 90th a ordinary petrol engine 'family salooner' like the VW Passat or Golf was doing 90.000km (plus) until a change was recomendet/ordered following the VW owners manual -but at least it was only a VW family car, without high rpm ..so if there are some who fail earlier VW could easylie compensate that in those years (as long as the car was under warranty)

-the timing belts on the 918 are in some ways 'small' for what they have to do all the time, so maybe this was also a reason to be a litttle scared and put this early mileage-limit into the owners manual

[Iconic Ride]

"-the timing belts on the 918 are in some ways 'small' for what they have to do..."

Indeed they are, Gunter. When I first laid eyes on a set, I was shocked at how tiny they are. And how narrow.

But they looked so cute, in their little Lotus sealed plastic bag. You could almost hear them saying "Take me, take me!"

[Günter]

Hahaa... I on the other hand do not have very often the impression that a *labled* products says 'take me, take me..'

-as most time there is an alternative and cheaper part without a *Lotus* lable on the package.

..but I'm not a retired pilot ..that's for sure

[73JPS]

Incidentally, Paul is not the first one to state that some sources say a visual check of the belts is insufficient to make a determination of their true condition, and whether on not snapping is eminent.

In a way, the snapping of timing belt will always be eminent. 'Tis whether it is imminent is the question

[Iconic Ride]

Caught me fair 'n square on that one, Patrick.

Then, too, in a way, the destruction process will always leave eminent remnants, causing one to engage in self-flagellatory reminiscence of the suggested change interval, producing an imminent discriminent viewpoint.

Apparently.

[73JPS]

Caught me fair 'n square on that one, Patrick.

It's almost unheard of

Nevertheless, I think it's time to get my belts tensioned...