Cambelt life.
Having done some evaluation work for a belt manufacturer, I thought it might be interesting to apply some belt life factors to actual applications, as the vehicle manufacturers recommendations seem to be so inconsistent.
My formula works like this:
Take a petrol engine with a belt working under ideal conditions, ie correctly tensioned, no oil, no disintegrating idlers. Take a belt base life of 60,000 miles.
Now apply the following factors as multipliers:
Crank pulley teeth (half cam pulley number) 19t 0.7; 20t 0.9; 21t 1.0; 22t 1.05.
Next, apply the following factors as multipliers:
Fixed tensioner 1.0; Undamped sprung tensioner 0.8; 3/4 wide belt 0.75;
1 wide belt 1.0; Diesel engine 0.85.
As an example, the old Ford CVH 1.4 engine had 19 teeth on its crank pulley (0.7), a fixed tensioner (1.0), and a 3/4 wide belt (0.75).
Change interval becomes 60,000 x 0.7 x 1 x 0.75 = 31,500 miles.
This is necessarily a simplification, because other factors such as wrap angles, peak loads and engine expansion cannot easily be accommodated, but if you try this on a few known engines, the results are interesting.
The quality of aftermarket belts is variable. The worst are made by a well known USA tyre company which may cause you to have a bad year financially. The best are Italian and will give you a good day.
Any comments welcome.
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Very interesting..
Did you produce any league tables as a result of your evaluations on various models?.
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I hope you will collectively produce this. My results are theoretical, I'll wait to see how the practice matches up. Ford CVH engines were certainly cambelt breakers.
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Some hard data.
I ran a 1.6 CVH from new to 115,000 miles over 15 years.
Changed 1st belt and tensioner at 36,000 mls
Changed 2nd belt and tensioner at 72,000 mls, changed Coolant Pump too, as a precaution against seizure.
Changed 3rd belt and tensioner at 108,000 mls
No failures experienced. This is partly attributed to the following:-
Genuine Ford parts always used.
Ford Workshop Manual Procedure always used.
Ford Service Intervals always used.
Car never saw a dealer after the compulsory 1st service.
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Well done, All the rules observed. When the CVH came out the change interval was 48,000 miles, clearly adrift (later changed to 36,000). Apart from obeying the rules, by using "Ford" belts, you actually fitted those from the Italian (preferred) source. Originally, of course, Ford sourced these belts from a US (literally) maker, but when the shortcomings of this design became apparent, they specified the best available belts and swallowed their pride. This made the best of a bad job without a redesign, but a lot of people out there were caught out.
There is no substitute for good engineering.
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Volvo 240 1986 B230A ? engine
First Belt failed at 56k (rec change 48k), but it was winter and I had the spare ready to do it waiting for warm weather. At least I got away with no damage! I then discovered that previous rec interval was 36k and had been increased by Volvo with no change to spec of parts.
Subsequently changed at about 90k. No failures by 125k, saved the trouble of a change at 126k by being written off, the lampost got back beyond the Mcpherson struts/ front suspension but we could still open the doors!
pmh (was peter)
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Citroen C3 HDI 16 valve - cam belt change due at 150000 according to handbook.
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Unbelievable! PSA design their drives well, but I would guess after 150k in a Citroen you would have other things to worry about..
pmh, Can you remember how the Volvo engine fits my formula? I seem to remember this engine was also a renowned belt breaker (19 teeth with a 3/4 wide belt)
All of this has a statistical basis. My formula was to a confidence level of 99.9% which I regard as being just about OK for machinery of this value. Obviously, very many belts will run a lot longer, but you have been warned...
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Pardon my ignorance, but what's a Ford CVH engine, please?
And who's the Italian belt maker?
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what's a Ford CVH engine?
Not sure what the CVH stands for, but it's the engine they put in the early (X Reg to D? Reg) Ford Escort XR3i's and Orion's. Common fault with the CVH engine was that the valve stem oil seals always used to perish, so when you first started up or accelerated, you always left a plume of smoke behind you. Every time you bought a new set, Ford parts dept always used to tell you "these ones won't perish like the previous ones did" How wrong they were!!
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Pardon my ignorance, but what's a Ford CVH engine, please?
Compound Valve angle Hemisperical chamber cylinder head
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L'escargot.
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Blimey L'escargot!
This is an old thread you've dragged up. I've corrected your bold text, btw, as I see you still haven't got the hang of it yet ;0)
DD.
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Blimey L'escargot! This is an old thread you've dragged up.
I dragged it up because 659FBE said it would be beneficial to do so in the current "factors affecting cambelt lifespan" thread, so blame 659FBE. And then I just couldn't resist explaining the CVH nomenclature!
I've corrected yourbold text, btw, as I see you still haven't got the hang of it yet ;0) DD.
Thanks DD. I know where I went wrong and I will endeavour to get it right in future. (Withdraws head into shell in shame!)
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L\'escargot.
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Theory is all very well, but if it looks OK it probably is OK. My wife's Passat has done 210,000 miles - I caught the tension pulley whining stiffly at 160,000 and changed it, but the belt was perfectly OK so I left it alone.
Belts usually only break because they are fried by the seized pulleys they drive, usually tension pulleys or,[in the case of my old Audi 100], a water pump. I suppose starting high compression engines with lots of valves is a bit of a strain, but for basic engines like the above I see no reason why the original belt should not last the life of the engine.
The worst thing an unscrupulous garage can do is to change a belt without at least changing the tension pulley. And if I ever decided to change my Audi belt [144,000 - no problems] - I would change the water pump as well.
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Paul, The Ford CVH engine was the first European OHC unit produced for the early FWD Escorts. It stands for Compound angle Valve Head, and was designed to give both good gasflow and swirl. It did, but the timing drive was lousy. Unfortunately, it was designed for lean burn rather than a catylist, so was never able to achieve its potential. The inlet valve stem seals were a nuisance, but at least non-destructive.
You missed my clue as to the belt maker (Dayco).
John, There is a statistical basis for all of this which you may have missed. If you buy 100 light bulbs from Woolies, they will fail in a normal distribution, centred around 1000 hours. The distribution will always be of the same form, but the centre value can be shifted, in this case either by buying better ones, or lowering the voltage.
You are wrong to leave the VW belt for so long. Although if you do my analysis on an early VW engine, it comes out very well, the belt materials degrade in use, due to heat and oil vapour. Obviously, any stiff components anywhere in the drive will wreck a belt (ask GM). At the mileages you give, you are in the region of unreasonable risk. "Leaving well alone" is OK for components which don't degrade (like a chain) but not here.
A final recommendation: change any belt more than 5 years old.
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For my personal benefit, can you advise the best make of aftermarket cambelts and (in your opinion) the ones that are not quite as good
thanks
Ian
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I think I read somewhere that replacement belts are spec'd higher than original belts to cope with the variable fitting and tensioning techniques used by DIYers and others. Does anyone know whether this is true?
Incidentally, when I first changed a timing belt on my old diesel Montego, I tried in vain to hire a tensioning tool - but no tool hire company had one. I asked a mechanic I knew who has been in the trade for years and he said he'd never used one, just tensions them up "not to loose and never to tight" and he claims never to have had a failure. I followed his advice and did 166K miles without a problem, changing the belt every 40K. After 40K the belts looked in good nick, but for £20 and a morning's work, the peace of mind was work it.
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Without the tensioner, the best way to check the tension is to twist the belt midway between the two furthest pulleys. You shouldn't be able to twist the belt more than 90 degrees. Any less and it's too tight. Any further and it's too slack.
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Dave, This depends on the length of free run. If you must tension belts like this, your rule is sort of OK where the free run is practically the height of the engine, ie. from crank to cam pulley, or where any wheel on the tight side is low down. For a diesel, the free run is short between the fuel pump and the camshaft, and the corresponding angle is 45deg.
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Rover 94M Metro 1.4 8v K series.
Service schedule calls for examination at 48K replace at 96K.
Mine being low mileage only reached 48K this year. In view of age factor I replaced the belt using one supplied by local factor who said it was OEM belt.
Gates Powergrip WAM 280. Sure nuff the one on was same nr and
brand. Examination of old one under high magnification revealed little or no cracking of surface even when belt subject to bending backwards over very small radius.
Happy Motoring Phil I
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Volvo 240. Every 40,000 miles, or 2 years in my case.
The belt only costs £17, and it is an easy and quick DIY job.
The answer to the question of course is "One week before it breaks".
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Cliff
Further up the thread 659FBE asked me a question about whether my belt failure on a 240 fitted his formula.
>>pmh, Can you remember how the Volvo engine fits my formula? I seem to remember this engine was also a renowned belt breaker (19 teeth with a 3/4 wide belt)<<
I omitted to answer at the time (why, cannot explain 3+ years on!). And do not have old belt to hand or the manual to answer the questions. Can you answer the questions please, since we are all still around?
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pmh (was peter)
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It's 19 teeth, 3/4" wide, undamped sprung tensioner, therefore per formula should be 25,200 miles.
This is about half the Volvo recommendation.
In fact the belts on these engines do not have a bad reputation - I know of many instances where they have lasted over 100,000 miles. Maybe we just don't here about the failures - it is not (most models) an interference engine, and belts are cheap and easy to change.
Another factor I don't think taken into account is the tooth profile. Earlier Volvos had square section teeth. This was later changed to a sinoidal wave, which I would guess makes the rubber teeth stronger.
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Cliff, I think you have a 200F 2L engine, are these a non interferance engine. Regards Peter
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That's right. But the belt etc are identical with the B230K in my other car, and with my previous B21A, except that that had the square teeth.
Another factor must be whether the engine breathing is kept clear. Oil blown past the camshaft seal will dribble down onto the belt, which can't do it much good.
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Cliff thanks for doing that calculation, if I had known that at the time I would have changed religously at 48k!
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pmh (was peter)
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