Fan belt damage

[rococco]

A friend's car (non-Scirocco) broke down the other day when her fan belt broke. The AA guy said it had ruined the engine, getting tangled into the timing belt and damaging the timing belt, fan belt, water pump, valves, and the head gasket. Altogether about €2k worth of repairs.

Is it even possible for a fan belt to cause such extensive damage? From my limited understanding I thought that the timing belt was isolated from the fan belt and other engine parts by a protective casing, and that a fan belt failure was generally not catastrophic in any case?

The car is a 2001 Renault Megane 1.4L.

Any budding mechanics got an opinion on this? What signs should I look for to tell if such damage has been incurred?

[RW1]

Is it even possible for a fan belt to cause such extensive damage? ?

Yes it is.

My Mk2 Scirocco did this. Initially the fan belt snapped on the motorway. Replaced it. Called in at a petrol station shortly afterwards. When I came to restart it, it wouldn't.

Got towed home. On looking at the engine, the cams were out of position. Lucky for me, the valves hadn't hit the pistons.

Why did this happen? ... The outer cover strip of the alternator belt had flown off and been dragged/sucked into the cam belt casing. The engine crank sprocket drive wheel on the Mk2 Scirooco has a narrow gap behind the alternator belt crankshaft drive pulley. The strip had entered via the timing belt cover/casing clearance gap around the crankshaft end part. About 6 inches had managed to get in.

Fine on the first restart as the belt cover strip was in a certain "other" position. But at the second petrol station stop, the engine had stopped with the belt strip wrapped over the top of the camshaft sprocket wheel. This stopped the cam belt fully engaging with the camshaft sprocket wheel. So when the engine was restarted, the "stiffness" of turning the cams/valves forced the timing belt to slip and so the bottom of the engine (crank shaft) was not aligned any longer with the top (camshaft). The belt in fact continuously slipped whenever the engine was turned without the camshaft turning.

If it is possible, the plugs can be taken out and without turning the engine, look in with a bright torch and see if the piston crowns have brand new "kiss" marks anywhere for each cylinder. If not, there is a good chance the valves have not met the pistons and been bent. Also ask the garage if the engine touches piston to valves in such a case to be on the safe side. Some engine's pistons don't touch the valves, some do. Otherwise it is head off, new valves, and refit as a summary.

C.

[rococco]

Thanks RW1, that's very useful. So it seems it can happen then, and it has happened to my friend's car.

I had a look at the car earlier. The only visible damage is to the fan belt which had come apart in an unusual way, splitting into stands. Those strands had wrapped around the pulleys and must have also entered the timing belt casing. The engine wouldn't turn over and had no compression so the valves must already be damaged. I didn't inspect the ignition chamber behind the spark plugs.

Am I right in expecting that such valve repairs would roughly cost upwards of €1500 (£1300)? As such it would likely exceed the replacement cost of the car (also ~€1500).

Probably the best course now is to see what value can be extracted from the car and put that towards a replacement vehicle. Any suggestions on where to sell a car with a broken engine (otherwise fine! )?