Vauxhall Astra timing trouble

That engine does have a cam chain.

Regardless of the means of driving the cams, modern OHC engines have such tight piston to valve clearances that if the drive is lost and the engine is turned, significant damage is likely.

The amount of damage is down to luck; in theory, when a chain breaks there is always the chance that more damage will be caused by the broken chain.

Repair costs are usually higher than with a belt-drive engine due to the need for more dismantling.

Fingers crossed is something more trivial...

Chris

Principles are just the same - but a chain should last longer than a belt and give some warning of impending failure by rattling.

In message , "Dave Plowman (News)" writes

Unfortunately car stereos are so outrageously LOUD that many drivers wouldn't even hear the engine blowing up. ;-)

Done a few of these, the chain snaps, they have all bent the valves, so its goiing to need new valves, timing chain kit, timing chain cover gasket,headgasket set, headbolts, modified cam sprockets, these engines are notorious for the timing chain breaking, I bet when they take the oil filter out it has collapsed as well !! you also need the oil pick-up in the sump to be cleaned. I cant remember off the top of my head how much it was, but it wasnt cheap !

And that's assuming the cam bearings haven't come loose &/or snapped the cam :-(

never come across the cam bearings being loose or the cam's snapping, but there is always a 1st. It does tend to be down to the lack of oil service., hence why the oil pick up should be cleaned out as it gunges up.

Every one I've seen with a snapped cam had badly scored cam bearings & had obviously not had the oil changed as often as necessary.

Thanks for the replies.

I hadn't thought to of that before but yes, I can see that a chain would have more momentum than a belt, so could damage something if it flew off. What is in the way for it to hit?

Really? Why is that? I would have thought the chain would be connected to the same things that a belt would be?

Thanks. I had heard that chains were supposed to be longer lasting. What causes the rattling before failure? Is it that it is getting loose?

The recovery man removed the oil cap and looked into the engine and said it looked ok. I'm not quite sure what that means but at least something isn't broken!

The car doesn't/didn't cover many miles a year. I think I changed the oil last summer, so hopefully oil changes are not an issue.

This is what I thought would happen but if the pistons destroyed the valves, wouldn't the engine stop turning when everything was mangled?

From what I can tell, the engine idled ok but misfired under revs. I would have thought if there was permanent damage it would not idle at all?

Its surroundings; belts are pretty much in fresh air. with a few cheap bits of plastic or a sensor to destroy if you are really unlucky.

Chains are internal, and the broken chain may penetrate its housing. It can also tangle with the sprocket(s), and break them, especially if they are plastic ones. There are often chain guides that can also be destroyed.

It's not connected to anything once it's broken!

It depends on each individual design how much dismantling is needed, but it's always more than a belt-drive. If you really want to see a worst- case design (for cam chain replacement), Google VR6.

Retrieving the broken chain might also be an issue.

Chris

If it ran in any way at all, the cam chain isn't broken.

I'm not entirely familiar with that engine, but perhaps a tensioner has failed, allowing the chain to be slack enough to put the timing out enough to just bend a valve or two?

Chris

Internally when the cam stops the valves stop and the pistons hit and they bend. Nothing to do with either belt or chain.

Chains are internal and run in oil. Hence the engine needs more pulling apart.

Belts are external, have a dust cover over them, which is a 2-3hr job to replace.

He would have checked if the cam was rotating.

Not necessarily. Many belts have intervals of 10 years/100K miles; some are 120K miles now.

It's not unknown for cam chains to fail before that mileage. Also, some engines use plastic chain sprockets, and it's not unknown for these to break up.

Well yes. The reasons for it getting loose can include chain wear, but often there are chain guides that also act as tensioners, and wear or failure of those is more usually the cause.

Chris

The pistons clip the valves and only bend them slightly. Buggers up the compression tho.

Start with having a look at the plugs and down the holes, pull the rocker cover off and see if every thing is working.

Usually bigger tolerance than that.