As the title says. This has happened to someone else I know.

The timing belt snapped at little above idle speed.

Do these engines have any purpose built weak points in the valve train in case of belt failure?

The first plan is to look inside the bores through the spark plug holes using an endoscope.

I would be interested in other examples of belt failure damage with these engines.

in the old days a few cars could leave a valve fully open and the piston can go over TDC and still miss it

as engine efficiency picked up, we flattened out the cyl head with shallower valve angles meaning all modern stuff smashes even partially open valves in to the pistons

you can not have a safe version of catastrophic failure - if you cared about whats happening even a whole new cycl head and valves is a bodge job - pistons smashing valves can bend rods, damage bores and mark the big end and even main bearings - on the cyl head we don't just get bent valves - we have damage to the seats and combustion chamber, but usually far worse utterly destroyed valve guides - including damaged cams, followers and these days cam phasers too

a simple cheat saving pennies on a cam belt change can lead to total engine failure and then you buy a new belt for the replacement engine anyway

Assuming it's a Ford sigma engine, the valve heads are angled at about 45 degrees.  They will be bent or snapped by hitting the piston even  at 'slow' speed.

Thanks for the replies. It is a Sigma engine in a Mk1 Focus.

Will a Mk2 1.6 Non Ti-VCT bare head fit a Mk1 block?

Their plan is to try to get it running as cheaply as possible depending on what parts can be found.

 

I don't know enough about the Mk1's to confirm that unfortunately.  This engine barely changed over the years so it's certainly possible that a Mk2 head could fit but probably best to carefully study pictures of both online.

i had one go when i had my 1.6 mk1.5 focus

head off and 14 of 16 valves replaced due to bending. new headgasket and belt and she ran another 40k miles

Thanks for the replies. It is a Mk1.5 so uses a coil pack and not a mechanical distributor.

They did have a look inside the cylinders with the endoscope. Some of the pistons are marked as expected, but no visible bore damage so far.

 

On 10/10/2024 at 9:36 PM, AntonovAN12 said:

Thanks for the replies. It is a Sigma engine in a Mk1 Focus.

Will a Mk2 1.6 Non Ti-VCT bare head fit a Mk1 block?

Their plan is to try to get it running as cheaply as possible depending on what parts can be found.

 

Just a few Months after the introduction of the Focus MK2 Ford changed the design of the 1.6 Sigma engine drastically. The bottom end even changed from a closed deck design to an open deck design.

Since virtually all part numbers are different I do not expect that a Focus MK2 Sigma cylinder head will fit to the older focus MK1.5 Sigma engine.