HJ replied to a query in the paper on Saturday recommending a small Fiat with a FIRE engine because if the cam belt went, the valves wouldn't damage the pistons.
I can't quite visualise how this works and, in any case, I thought cam chains were better than belts as a general rule.
Any enlightenment anyone?
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When the valves are open they do not protrude below the level of the cylinder head into the piston space so if they were to stop moving as when a cam belt breaks the moving piston will not hit them and cause any damage.
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Two litre Ford T88's(usually but wrongly called Pinto) were also safe;there is sufficient clearance in the combustion chamber for the valves to remain open without the piston contacting them-some of the valves will remain in the open position due to the camshaft not rotating.
As to whether belts are better than chains? Belts tend to be better and quieter for long distances between crank and cam drive-chains for shorter-but I only said tend.
Edited by jc2 on 16/06/2008 at 13:46
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CVT belts never seem to get replaced, do they last for a vehicle's lifetime?
If they do then why not make cambelts out of the same material?
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They do Continental manufacture gauranteed for life belts.
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Early CVT belts were rubber and there were two and if one broke you could make it home albeit slowly on one;modern CVT belts are steel and operate in compression not tension(too complicated to explain here-you need to go to a CVT website) so cannot break in that way.
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CVT belts don't have to last the life of the car; only the life of the second gearbox.
The first box is usually covered under warranty and the cost of the second failure at around 30,000 then writes off the car.
Chain cam-drives are not an improvement, or longer lasting, than a well-designed belt. Keyless cam pulleys; gas tensioner; easy access and a chunky belt is all that's needed for 10 years plus of trouble-free life.
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My old 1.6 Sierra suffered a cambelt failure when idling at a set of traffic lights. Had it towed home, timed the engine back up, fitted a new belt, turned the key, and it fired up sweet as anything. I know the 2.0 units were non-interference as jc2 said, so either I was lucky, or the 1.6 was too.
I maintained that car to the letter, but for some reason completely forgot about the timing belt. Have never done it since.
cheers
DP
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1.8 & 2.0 were safe;1.6 could get away with it depending on position of valves when belt broke. 1.3 OHC(not sold in UK) always smashed the valves.
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Thanks. I can follow now. How would you find out if your engine was built with the valves out of the pistons' way? Answers advising breaking the belt or chain will not be seen as helpful!!
Bit surprised to hear what Screwloose has to say about CVT. I thought the Merc A and B class autos were Autotronic CVT's and don't recall negative feedback.
Also hear that the Nissan owned JATCO plant in Mexico is tooling up to produce 800,000 CVT boxes this year.
Where's the problem or weakness?
Cheers.
Edited by Optimist on 16/06/2008 at 14:15
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This is an american site which tells you if an engine is interference or not, it will only cover models sold there though. I can't find one for the UK .
www.theautoshop.com/timing.html
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DP
The 1.6 was - just - a clearance engine. If the belt went at speed, it could lip a valve, but mostly you would get away with it.
CVHs had only two tiny spots where it didn't hit - but when it did hit.....
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I've got an Almera 1.8 2003 model with a double chain and I can sleep soundly (when I'm driving) - knowing that I haven't got a belt ... yeah, yeah, I know there has been some probs with the 1.5 lump but I change the oil twice a year (as advised by HJ)
I 've come across toooooooooooooo many ruined engines due to cambelt failure !
To be quite honest - I have a dread of cambelts - ghastly things !
Obviously I'm an ole duffer & I'm going back a few years but I've seen people fork out £1000 for the want of a £30 belt (BX 1.9 GTI) etc.
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I'm not worried about mine - belt goes, should be OK, a clearance engine.
Now chains - have you ever seen an engine where a chain has broken? I saw the remains of a chain sticking through the block where it had made it's bid for freedom. Bit of a mess.
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Now chains - have you ever seen an engine where a chain has broken? I saw the remains of a chain sticking through the block where it had made it's bid for freedom. Bit of a mess.
Happened to my father's 380 Benz. Nasty mess indeed, and needed a 'new' engine after that.
My 1.8 Astra gets the 75 000km changes as recommended, plus a new tensioner and water pump at the same time.
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Just a general question:
Can't all engines with cambelts be designed to be non-interference?
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Whether or not an engine is interference or non-interference is down to the design of the combustion chamber - both in the cylinder head and in the piston crown. The design constraints here dictate the shape, and whether or not an engine will survive a cambelt breakage unscathed is probably low on the design priorities list.
Think you'll also find that the higher compression ratios necessary for diesel efficiency mean very little space at top dead centre, and that is why, I guess, almost all diesel engines are 'interference'.
Happy for someone who knows more to correct me.
PS: in line with this thread, I've only once had a belt break. It was on a 1982 Cortina MkV 1.6, and like the thread has already said, I got away with it. only 1 mile from home, so even recovery wasn't a problem. Had a new belt on, tools put away, and hands washed within an hour. Mileage? 37,200, and belt should have been changed, IIRC, at 36,000.
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Screwloose / jc2 - thanks for the info on the Ford engines. Thank heavens it was idling then. :-)
I saw a Ford 1.8TD (Endura DE) engine with its cam cover removed after a cambelt failure on the motorway. I've never seen such mechanical carnage.
On these engines, and a lot of other diesels, the valves are vertical, so are hit "square" by the piston if the belt fails. On this engine, it had slammed one of the exhaust valves back up through the head with such force that it had actually broken the camshaft, and one of the cam bearing caps into two pieces.
I changed my Mondeo's belts the next week!
Cheers
DP
Edited by DP on 16/06/2008 at 15:46
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I had a cambelt snap on my last car (Citroen ZX TD) at 97k. I had at the time thought the cambelt had been changed by the last owner at 72k (I know...).
The belt snapped at low speed, 2nd gear - probably 1500 rpm.
Didn't try starting the car as I suspected what was wrong. Towed to the garage and end result: Two bent valves, snapped camshaft (plus a snapped brake vacuum thingy (connects to the cambelt / engine or something for power brakes (a Citroen thing).
A friend at an Escort TD - car was stolen then recovered - found with the cambelt had snapped. Insurance company would only pay £400 for the damage and not write the car off.
Friend gets a recon head fitted. Car ok until fan belt snapped about a year or so later and wrapped itself round the cambelt (don't ask how that happened as cambelt cover was on) and cambelt snaps again....
He sold the car as spares /repairs after that!
Edited by Shaz {p} on 16/06/2008 at 15:57
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DP
My record for blowing up an RF is four cam bridges snapped and the cam in six bits. [It was a new belt and a new guide roller that seized.] Three valves had S-shaped stems and two had snapped the bottom off their guides.
Good job I've got a lot of new ones for spares. [Only one complete new engine left now.]
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The only such accident I had was with the fanbelt of an armoured Jeep. One of my escorts sacrificed a jungle boot lace and this got us to a workshop.
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Screwloose,
Ouch! Not much more to say really. I remember you saying in a previous discussion about your stock of replacements. Very handy.
The shock of seeing the one I looked at was enough to make me do a belt and tensioner change the very next week. Glad I did too, as the water pump bearings were about to give up the ghost, and the first dribbles of coolant were seeping past the seals.
Cheers
DP
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