cam belts...do they really go ping

[RichardK850]

Originally Posted by Crispy-d

Out of interest, why is it that we use belts instead of chains or gears? My brother's Landy V8 uses a dirty great chain that wouldn't break if you suspended the entire Landrover from it, and I believe my father's Rover 75 diesel runs a chain as well. Surely there would then be little concern for bashing in the valves. Is it simply because they're noisy, or a power drain?? Can't see it that way myself, but I suppose there must be some reason - anyone know?

Surely the Landy V8 uses a tiny little chain, since they're OHV, not OHC?

I can shed a little light on chains from the POV of the Mitsubishi 2.8TD.

Say most imported Pajeros/Delicas have done about 70,000 miles, or the typical belt change interval.

Most of them have stretched/worn chains. They also may have suffered failed tensioners.

Replacing the chain "by the book" takes 10 hours. Admittedly it's a bugger of a design where the sump, timing case, top all have to come off the engine, plus access is needed so off come the radiator/fan/water pump (drain fluids), and the engine needs to be lifted a tad.

10 hours.

And about £250 in parts; from a pattern part reseller. You can probably triple that from Mitusbishi UK.

Chains do wear out, they need complex lubrication in more modern engines, and they can be harder to replace.

If you want to see a really silly design, look at an MX5. Thankfully claimed not to be an interference engine, the little 1.8 16v is designed (really) to look like a Ford BDA TwinCam, as you'd find in a Lotus Elan IIRC. Which had a chain. And a rocker cover to match.

So... to change the belt, which has a 45,000 service interval - you need to take the rocker cover off. Even then, the MX5 specialist that serviced ours before we got it only charged £199 for a timing belt service!

[Crispy-d]

Hello RichardK850,

So even though the MX-5 has a chain, the service interval is in fact lower than most belt-driven cars? Interesting. On my bike, and most likey on most others, the chain ran through the centre of the block down into the sump, so most likely got its lubrication from the engine oil.

When my brother restored his Landrover, he fitted it with the engine that he'd built in our shed, so it wasn't standard - Rhoads Hi-Rev lifters, fancy cam, bored out to 4.0, etc. The cam is now driven by a 'Duplex' timing chain set. Think it has fancy nylon bits all over it, and it's double width, very tough and pretty quiet. It's not very long, if that's what you meant, but it's certainly very thick and very tough and is meant to last the lifetime of the engine.

Obviously some manufacturers will be difficult, and design a silly system that requires lots of work to service. But what I meant is on a simple design, where the cover pops off and the belt can be whipped off in minutes, intead of using a belt one could use a chain. It would be no harder to replace, perhaps more expensive, but would provide a certain safety factor against total destruction of the engine! Even if it does not increase service life, it would at least be more robust.

I presume the chain on the MX-5 was inside the rocker cover for lubrication purposes?

[RichardK850]

Originally Posted by Crispy-d

Hello RichardK850,

So even though the MX-5 has a chain, the service interval is in fact lower than most belt-driven cars?

When my brother restored his Landrover, he fitted it with the engine that he'd built in our shed, so it wasn't standard - Rhoads Hi-Rev lifters, fancy cam, bored out to 4.0, etc. The cam is now driven by a 'Duplex' timing chain set.

Nono, the MX-5 has a belt, but is housed in a manner more suitable for a chain, with enclosed rocker cover/belt area rather than "external" to the engine under a plastic cover.

Duplex just means it has two chains A lot of cars use that arrangement as standard; I'd pay for the upgrade to duplex chain/sprockets on the Delica if someone makes it.

(Edit: Had a thought, and went and looked. It IS a duplex chain. Still fails quite often on them though)...

You've answered your own question though - the belts need no lubrication, are "external" (usually) and therefore easy to repair (you still need to seal camshafts/crankshafts somewhere, so you don't have to add seals). A chain mounted in this manner would need lubrication from somewhere, and then you get into oil being all over the place, crankcase pressure issues, venting...

No doubt somewhere there is an OHC engine with an external chain lubricated by a dropper off the head, but basically the easiest way to do it is to enclose the chain between sump and rocker/head cover.

[Crispy-d]

Yes, sorry - I forget what make it is exactly, perhaps Cloyes Duplex - but it's meant to be good whatever it is!

If the chain was mounted at one end of an engine, as usual, then surely the cover that would be required to seal up the assembly to allow for sump oil lubrication would be no different to a rocker cover. A relatively standard rubber gasket would probably do the job, and so taking that off to change the chain would be no more difficult than removing the awful and fiddly plastic covers that are used today. The problem with a lot of OHC engines that use chains is that they use one big long chain, which means it's more prone to stretching problems and general wear and tear. I was reading about chains on a Ford forum, and the only reason why the timing chains ever failed on those was due to the silly plastic rollers on which the chains ran. The newer engines which had a better setup would not see a chain change in 150k and still be running with no problems.

It would appear that there's too much compromise in so many cases, and just a little more thought and effort it could work really well. Well, I've read it already does on some cars!

I wonder if using gears alone would work? Possibly a nightmare to setup though! And using crude cogs may introduce too much tolerance for such a precise task - as timing's obviously important. Perhaps using bevel gears, or even worm gears, running a shaft up through the engine so that it connects directly to the camshaft would mean there would never need to be any maintenance of it at all. Oil pumps seem to be built straight on to the crank, so the only belt one would need would be an auxilary belt to drive the waterpump, alternator and a fwe luxuries.
To do away with belts altogether there could even be one hydraulic pump on the engine, which could be used to drive the other necessary bits and bobs. Admitedly, that might not be very efficient...!

Basically - I wish my car had a chain!

[RichardK850]

Gears are used; a lot of competition engines use them, and I'm fairly sure some Alfa-Romeo "road" sports cars did.

They make a lot of noise, essentially. I remember a picture of a helical-cut timing gear setup for a twincam engine and it didn't look terribly complex.

The real way to make engines reliable is to make them simple - look at a VW Boxer engine from a Beetle. Gear driven cam (with metal gears), only four lobes IIRC, pushrods external in tubes. Maintain it well and it will go for a very long time, and if it breaks it is easy to fix.

Or rotary engines. My other car has no cams, valves, chains or (engine essential) belts. Three moving parts, 192bhp, 1.3l "real" capacity.

[kjkir]

Poor misguided fool me had a 95 Vauxhall Omega 2.0 16v Estate, (clean my mouth out after using the GM swear word!). Bought it at 2 year old with 72,000 on the clock. A year after buying it, one evening on the way over the Barton Bridge on the M60, I heard an almighty crack, total loss of power and the steering instantly went heavy. God knows how I managed to get into the hard shoulder. Called the AA and when the patrol came along, he popped the bonnet and took a quick look. No sooner than he'd put his head under the bonnet, he popped up shking his head with a huge grimace on his face. It appeared that the alternator belt had chewed up, rode over the crank case pulley and took the timing belt out which more or less was in tatters and hanging out below the car after having broke through the timing belt cover. Towed me home ( wasn't too bad as I just lived around the corner back then) and then left me to contemplate the horrors that awaited me.

Result, all 16 valves bent, exhaust cam cracked along its entire length, exhaust cam pulley cracked across it's face, timing belt tensioner disintegrated. Thank god for samll mercies that the head hadn't cracked. Ouch indeed. Out of interest I spoke to my local rip off Vauxhall dealer and low & behold they were going to ask silly money (£2k +) to do the rebuild. Ended up rebuilding the head myself, 16 new valves, two new cam shafts, new cam shaft pulleys, all new hydraulic tappets and the head being skimmed and polished & ported at the same time. Still ended up costing me best part of a grand for the build and then an additional £180 to hire a basic mundaneo from a local hire firm whilst mine was off the road.

Moral of the story is I did not change the belts at the right time and It cost me dear in the long run. Even when the belts are changed at the recommended intervals, these can still go without warning. Not only check the belts but also check the tensioners and the pulleys too. That slight little burr on a pulley can over time weaken or strip the belt. One very expensive lesson to learn. Needless to say I shipped that particular car on soon afterwards. But it did also teach me how cruddy GM engines from a certain era can be.

[RichardK850]

You can hardly call it a cruddy engine if you didn't change the belt for a year on a 72,000 mile (at acquisition) car!

I've had the Clio one go - 1.2 DiET engine, 61,000 miles, 10 years old. I knew it needed it, was taking it to get it done, and PING! No noises, just car coasted to a halt. Didn't try and restart it.

Apparently the engine was toast, I gave it to a mate to fix as it had new tyres and long tax, but it's taken him a year to get around to looking at it!

I forgot, of course, to clarify my bit about gear-driven cams applies to OHC - there are a LOT of OHV/sidevalve engines with gear-driven cams. And I'm only talking car engines, since quite a few OHC bike engines have gears.

[Crispy-d]

I didn't realise some OHC engines today use gears. I knew some bikes used gears, as they're generally much more compact than car engines. I also have come across a number of OHV engines that have gear-driven cams, as obviously that's a far simpler setup. Are they that noisey then? It would be nice to have gears in an OHC engine, as I would have thought that'd be a very effective setup, producing reliable yet powerful/efficient engines.

I like the idea of pushrods, and using rocker arms as less a force is required to operate the valves. So theoretically, everything should last longer. The problem is, it's said to be such a crude setup that you never get the efficiency and accuracy you get with OHCs and also running speeds are limited. Although I've seen examples where Rover V8s are revving 'happily' to 8000rpm, the setup is still not as responsive as OHCs.

My old bike had rocker arms and yet it was an OHC engine, so you obviously can get both (I think the Essex V6 in the Capris used rockers too, for example) and that revved right up to 12000rpm without any problems. I suppose they got rid of rocker arms as they take up quite a lot of space, and having 4 per cylinder might be a tad tricky?

Rotary engines are very interesting, although they are said to wear very quickly and burn a lot of oil. If you own one then you'll know best! So do they? Also because of the way they run they're also very inefficient, and although that's made up for by being powerful, I've heard they lack torque at 'normal' revs. Funnily enough, my brother's housemate has an RX-8, although I thought he said it was 223bhp, or something like that, but I may have that wrong! I know it was pretty fast though, but he said he was having to rev it high to really get anywhere. Very clever idea though.

....I have heard of auxilary belts going and taking the timing belt with them. Some people will change the timing belt but leave the 'fan' belt. I don't think that's wise, and I also recommend checking everything that's in contact with both of them. Waterpumps always seem keen to fail, although not so much on the 400s. Also, they're run off the fan belt on that engine, so it's not such an issue.

[kjkir]

Originally Posted by RichardK850

You can hardly call it a cruddy engine if you didn't change the belt for a year on a 72,000 mile (at acquisition) car!

The belt had been changed at 60,000 and was stamped clearly in the service book. In all honesty the car had travelled nearly 20k in the twelve months from me purchasing it before the belt went but even so for the belt to go at 90k ish is still a PITA when it was changed at 60K. But there again it wasn't the root cause, that was the alternator belt chewing itself up which then caused the timing belt to go t*ts up!

Vauxhall washed their hands of the car citing that it had not been serviced in accordance to their recommendations so that's why I ended doing the job my self.

I've driven a whole plethora of different vehicles and IMHO german marques & swedish are far more better engineered and reliable versus lesser marques.

[RichardK850]

Originally Posted by Crispy-d

I didn't realise some OHC engines today use gears. I knew some bikes used gears, as they're generally much more compact than car engines. I also have come across a number of OHV engines that have gear-driven cams, as obviously that's a far simpler setup. Are they that noisey then? It would be nice to have gears in an OHC engine, as I would have thought that'd be a very effective setup, producing reliable yet powerful/efficient engines.

I have read that they're noisy; I tried to find the Alfa engine I was thinking of and can't but I did find an example of an OHC engine with gears - the Panoz-Zytek 4.0 V8 racing engine

I like the idea of pushrods, and using rocker arms as less a force is required to operate the valves. So theoretically, everything should last longer. The problem is, it's said to be such a crude setup that you never get the efficiency and accuracy you get with OHCs and also running speeds are limited. Although I've seen examples where Rover V8s are revving 'happily' to 8000rpm, the setup is still not as responsive as OHCs.

It's all about compromise - if we wanted the best we'd all have valves operated by air or hydraulics with no mechanical drive at all - solenoids, perhaps. I think some F1 cars have such a setup.

My old bike had rocker arms and yet it was an OHC engine, so you obviously can get both (I think the Essex V6 in the Capris used rockers too, for example) and that revved right up to 12000rpm without any problems. I suppose they got rid of rocker arms as they take up quite a lot of space, and having 4 per cylinder might be a tad tricky?

If you want a lower engine, you use rockers and have the cam sideways (indeed, the Opel Manta and so forth had a "Cam In Head" engine design); single-cam multivalve engines use rockers usually (like the Dolomite Sprint). The Essex is an OHV engine; Ford's OHC V6 engines were the Cosworth version of the Cologne, maybe some North American Cologne variants, and some Mazda derivatives like the Mondeo 2.5. The Renault/Citroen "Douvrin" engines use an OHC and rocker design, too.

The main benefit was easy adjustment of valve clearances, and hydraulic tappets have basically wiped that out.

Rotary engines are very interesting, although they are said to wear very quickly and burn a lot of oil. If you own one then you'll know best! So do they? Also because of the way they run they're also very inefficient, and although that's made up for by being powerful, I've heard they lack torque at 'normal' revs. Funnily enough, my brother's housemate has an RX-8, although I thought he said it was 223bhp, or something like that, but I may have that wrong! I know it was pretty fast though, but he said he was having to rev it high to really get anywhere. Very clever idea though.

Rotary engines made correctly don't wear quickly - the Renesis should be good for 200,000 miles before rebuild (the rest of the RX8 is another matter). The reputation for reliability in Europe was trashed by NSU's units being made of Bavarian cheese, whereas Mazda used proper alloys and materials from launch, so even the little Cosmo engines were lasting into 100,000 mile territory when most cars were considered pretty worn out by then.

They don't burn oil as a concept, however part of Mazda's success with making the engines last is to have an "oil injection" system to lubricate the rotor tips. So they use oil by design rather than just being poorly made - but the amount they use is very small; mine uses a litre every 2,500 miles which compares well with say, VW's 2.0 Golf engine.

They have very little torque at low revs but "you need to rev" implies that you have to make it work hard - you don't. It loves to rev, his should redline at 9,500 rpm (he'll have the 230bhp model which has 6 engine ports, six injectors, and a 6 speed box - mine's the 4-port 7,500 rpm one).

Part of the revving is how the power stroke works. In a conventional four-stroke engine, you need two revolutions for a "power" cycle of intake-compression-ignition-exhaust. In the ****el, you yet all of these in one rotation of the crankshaft, and the crankshaft rotates three times for each rotation of the rotor. The rotor has three faces so as one is performing intake, the other is under compression/ignition and the other one is exhausting. With two rotors, you get a very smooth, balanced engine.

But in terms of frantic activity, whilst 9,000 rpm sounds like a lot - one piston is undergoing 4,500 changes of direction per minute at that speed - the rotor in the RX8 is actually turning over at a leisurely 3,000 rpm. At idle the rotor is spinning at a mere 300 revolutions per minute.

And they do use a lot of fuel, though it's proportional to the power output if not the torque. The European RX8s suffer from Euro emissions mapping which makes them run rich to keep the catalytic convertor cooler and "make it last the required 100,000km" (Works well, not. Mine was replaced at 17K).

It'd like to see a properly mapped RX8 engine hooked up to a CVT gearbox. I think it would be a very good setup, very smooth.

....I have heard of auxilary belts going and taking the timing belt with them. Some people will change the timing belt but leave the 'fan' belt. I don't think that's wise, and I also recommend checking everything that's in contact with both of them. Waterpumps always seem keen to fail, although not so much on the 400s. Also, they're run off the fan belt on that engine, so it's not such an issue.

Whenever I change a timing belt, any water/oil or other devices attached are changed too (which makes it expensive as I don't DIY timing belts). I sold an Audi 90 to someone with the very, very stern warning that the water pump was failing and they should "replace it with the one provided ASAP". I'd bought one, just had no time to change it. They left it, it seized, the car snapped the belt - thankfully the engine wasn't an interference design.