Hi Guys

There are no timing marks on my flywheel, and the hole has been machined out.

How can I find TDC ....without specialist equipment?

Are there any other marks available, without disassembling the engine.

A long reach spark plug will do the job.
Remove both standard plugs, screw the long reach one into one head than adjust its depth until when the engine is rotated _gently_ clockwise and anti-clockwise, the points at which the piston makes contact with the 'stop' are separated by about 10 teeth on the flywheel.
The precise number of teeth can be fine tuned by altering the depth of the plug.
Split the difference between the pair of marks you've scribed on the edge of the flywheel and that's your TDC mark.

Thanks Ken

Typically, I threw my long reach plugs away, as I no longer needed them!

Worth investing in a new one I think.

In that case, a standard A series plug with the earth electrode bent outwards can be used...

I don't doubt you Ken, but that didnt work! Even though the electrode was at the bottom.

The theory is all correct, but it wont work!

Edit

I cant make it work.

Apologies,
it may have worked on race engines, which have shortened barrels and cc'd heads.
Anyway, it only took me about 15 minutes to put this tool together, using an old plug, an 8.5mm drill bit and an M10 tap, plus a 10mm setscrew and a locknut.
With the first guesstimate for the setting, it produced marks on the flywheel with 5 teeth separation, so that will do for me.
Dyane engine, unmodified so with 9.0:1 pistons.
.
That will be going in one of the toolboxes which I take to the 24 hr race every year...
.
TDC finder for A series engines. by Ken Hanna, on Flickr

I started making something similar, but with just a nut and bolt through the middle.

Don't have the facilities to work your magic Ken.

Thanks for your help

@Ken

Believe I now have TDC.

Ken

Curious about shortened barrels. I'm guessing that's minimal to increase CR. So minimal so that the manifold still lines up with ports.

What is cc'd heads?

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I've got a similar tool to that, its a relic left over from my days as an MZ [motorcycle] owner.
Its a hollow tube, threaded on the outside to thread/screw into the plug-hole ....and a steel rod marked in mm's goes down the centre, touches the piston, and then on winding the piston up, it shows mm's before or after TDC.
I've no idea if its any use on any of my present bikes [a Yam Dragstar, an Armstrong MT500 & a "ZongShen100" {thats a Chinese copy of a Honda 90Cub} ]
I've never seen reason to actually attempt to use it on my 2CV ....I doubt if it would work, because the MZ's had a flat topped piston, where-as the 2CV piston is {IIRC} sorta "domed" and the plug-hole is at an angle.
But a friend borrows it ocassionally because he enjoys messing about with old lawnmowers, rotavators and other obscure machinery.

Obscure machinery, is what life is about!