I understand that when a timing belt breaks your engine is toast, but what happens if that occurs when your driving at 100kph? Does the engine lock up resulting in the front wheels locking up as well? Could you lose control and end up in a ditch?

Not going to toast your engine, but it would be costly to repair.

The belt may loop itself somewhere in the timing case, and do no damage. It might thrash about, and damage the plastic, crank angle sensor, water pump, etc.
Needless to say the engine would stop, but in doing so any number of the 24 valves will be bent, the heads of the valves will skew at an angle and that cylinder will have no compression. Unlikely to happen, but a valve head may snap off and crunch the piston top and cylinder head.
As for locking up . . . not on an auto, in a manual probably not either, but the moving wheels will keep turning the engine over until you push in the clutch, and metal bits will shred the belt wherever it jams.
Won't be a pretty sight when you open the engine, probably easier/cheaper to find a S/H engine to replace it. Before you put a S/H engine in, do the timing belt, to avoid a replay of the disaster. lol

In theory, a timing belt will break at the moment of greatest stress, which is when you start the car.

Google "cam belt break damage" and look at the images.

if you want (and have somewhere SAFE to try it) shut off your engine while your driving, to acc, not off, dont want to risk the key barrel locking.
Leave it in gear and feel how quickly it slows the car down.
If the belt snapped it'd probably be about 2-3 times faster at bringing you to a stop (and a lot more internally violent)
I would doubt that the wheels would lock up unless you managed to snap the crankshaft in the process.

Fyi, do this at your own risk, however in theory it should pose no danger of damage to the engine, the oil pump will maintain pressure while the engine is turning over, water pump will keep pumping ect, it just wont have any fuel injected or spark ignition.

Does the automatic transmission not "disconnect" when the engine stops?

Does the automatic transmission not "disconnect" when the engine stops?

Yes. Same effect if you lift your foot off the accelerator at speed.
In a manual, a sudden engine lockup would be more severe and potentially damage a lot of other bits - and even ditch-park the car.

The engine stopping while moving will have flow on effects, you instantly loose power steering and brake boost is good for maybe a couple of pushes on the pedal.

what happens when a timing belt breaks?

Forgot to mention . . . one of the things that happens is that you suddenly start to use a lot of swear words, some your mother would be very upset about!

(But I'm not worried - I change them when they are due.)

Engine shuts down and ffs dont shut down your motor while driving as is both stupid and dangerous plus can do damage to your motor and trans

What would you do in this scenario...

I know of someone who recently asked me about his TS Magna (V6 Manual).
It's done almost 500,000kms
The timing belt etc was done at around the 300K & 400K mark, so it's almost due again.
The engine is still going strong(ish) but with the high K's, he's wondering how much longer will it survive and if it's worth doing again?
If he chooses to do the Timing Belt he's up for $800+ and still has an aging engine (even though she's okay at the moment).
If he chooses not to do it, it could go for another 50,000+ or could break tomorrow - but if/when it does he can put in a low(er) km engine, for say $1500?
Which should he do?

Depends on how much he likes the car, how much money he has. It's not a ? anyone can answer.

yeah agree, pretty much what I said. I asked him, if the engine did go, if he'd just junk or part the car out. He intends to keep the car but that poses the same question... Maintain the existing engine or run it into the ground and pick up a lower KM engine later. hmmm :think:

Needless to say, it certainly will not be a cheap job too repair! Always keep up to date in regards to these belts!

Why not just run it untill the belt breaks then fit another engine.

He intends to keep the car but that poses the same question... Maintain the existing engine or run it into the ground and pick up a lower KM engine later. hmmm :think:

If he is still thinking about it, it means he is doing nothing about it at the moment. So currently he has effectively decided to run it into the ground. lol

The easy way through this is to keep driving, and when it lets go buy another car.

Why not just run it untill the belt breaks then fit another engine.

This is what I'm doing.
Got the car with 500,000kms on the engine and 400,000 on the belt. It's pot luck as to when the belt lets go.

As for what happens when it snaps... You'll loose power to the wheels - your power steering will keep working until the engine stops turning (when you put the clutch in, or if its auto - when it stalls) and your brakes will have one good stop left in them (engine turning or not, it is no longer making vacuum)
Unless you are massively unlucky, the engine wont lock up - you'll smash a few valves, dent a few pistons - perhaps even snap a valve head off, which will make a nice mess on the combustion chamber.
The only way that the engine will lock up is if you somehow hang a conrod through the block - even then it may not lock up solid.

As for if you should do the belt ... weigh the cost and inconvienience of doing the belt against everything involved in swapping in a reco or second hand engine. That will hold your answer.

Does the 3.8 bolt into the 2nd gen?

Not even a 3.5 bolts into the 2nd gen if you're referring to later model magna.

And the mounting points are different between a 2.6 and 3 liter magna so unless you want to spend a lot of money, find a low kilometer engine like the one in your car

I don't know what the fuss is all about. I'd rather spend the $80 on a TS V6 belt and 3 hours of my labour to avoid the problems associated with breaking down unexpectedly.
I don't believe people who say "Can't be bothered changing the belt" but also say "I'll just drop another motor in." I know which job is less trouble.

Yeah the timing belt change is pretty easy on a magna, I helped a friend with it because of the amount of room on that side.

Workshop guide is your best friend

As a matter of interest, mine broke on my V6 NH 3 litre Pajero. No harm done but its a 'non interference' donk. I believe the 3 litre Magna is not, so the damage could be fatal. Luckily I was about 1 km from home and 'uphill' so I was able to roll all the way home and straight into my carport where the repair was carried out. (Although I had no power the brakes were heavy but worked just fine. Steering was only stiff when the car was stationary).

I've also replaced the timing belt on my Magna. Its a tedious, but not particularly hard, job so it would be a pity to trash an engine over the cost of a timing belt.

I don't know what the fuss is all about. I'd rather spend the $80 on a TS V6 belt and 3 hours of my labour to avoid the problems associated with breaking down unexpectedly.
I don't believe people who say "Can't be bothered changing the belt" but also say "I'll just drop another motor in." I know which job is less trouble.

My thoughts exactly. Just imagine the time it would take to locate a new engine, fit it and finding another car to use in the meantime. It will be cheaper and less time to just replace the belt. If you're not bothered about it, buy another car before it happens.

My thoughts exactly. Just imagine the time it would take to locate a new engine, fit it and finding another car to use in the meantime. It will be cheaper and less time to just replace the belt. If you're not bothered about it, buy another car before it happens.

Exactly. And it won't usually happen somewhere convenient. It could happen in the middle of an intersection or hundreds of ks from home.

The cost of the tow truck would probably exceed the cost of a new belt to start with.

I was driving a 4 cylinder 5 speed manual Nissan Pintara a few years ago that I only paid $100 for, ran well but only had home services for the 6 years prior. 240,000km on it, I was giving it a highway run and all of the sudden at 100km/h I lost all power, no bang or anything, just like all fuel/spark was cut off instantly. I put the clutch in and the engine stopped instantly, released clutch again and the engine engaged but no power once again. I took it out of gear and coasted into a safe spot off the road, tried starting and the starter motor just spun with a high pitch. That's when I realised the belt must have snapped. I took the timing cover off and the belt was completely shredded, I had no idea how it held on so long, it appeared to have been the original belt it was that far perished. I didn't bother taking to it with spanners, just towed it home and called the scrap yard and sold it to them for $200 and they picked it up from the house so I actually made money out of the car lol. But yeah in this instance, no issues with engine lock up, just a short time to find a place to safely pull over with the engine to never fire again.

I have had a TE do a timing belt (AUTOMATIC) came out of a roundabout and gave it what for, belt snapped with a big bang, Actually thought that I had had a Plenum chamber explosion as I was on LPG at the time, slipped it into Neutral rolled to a stop several hundred yards down the road and stopped outside a friends place! A few weeks later put it on his car float and brought it home.

No danger in anyway to any body on the road!

Please note most problems occur because the driver panics, swerves and has an accident! Clutch in and into Neutral!