When my white Special is being driven with the engine under stress, eg going hard up a hill, there's a noticeable smell that is kind of oily and sweet and fumy - but not really exhaust fumes. Also, there's a kind of rattle that sounds like a sort of slurping noise.

The smell goes when the engine is under less stress, and so does the slurpy noise.

Any 2CV doctors care to give a diagnosis?

Unfortunately, it will be eroded cylinder head seating, allowing combustion gasses to enter the heating system.
Most likely cause is prolonged detonation, caused by incorrect ignition timing, spark plugs with too hot heat range or an air leak in the induction system.

If you're lucky, retorquing the heads may restore the seal or reduce the leakage, but since carbon monoxide is part of the mix entering the cabin, a full strip down and repair would be preferable.

The noise is probably pinging/pinking, but that's usually described as light metallic crackling or rattling, like nails being shaken in a bucket.

ken

p.s. Now Uni Challenge is finished; if you're going to keep using the car, your immediate priority should be to sort out whatever has caused this problem, starting with the ignition timing. Have you got a strobe?

Ooh 'eck!

Are there any threads on here that will show me how to repair my engine?

If you can get it down to Ross, I'll give you a hand with it one weekend.

That's very kind, RT. What would I need to buy in order to do the job, and would it be a one day job, or two?

I've relapped the valves on an old Saab V4, but that's the sum of my engine reconditioning experience.

the cheap quick and easy way would be to fit head gaskets as the 2cv doesn't have them they are a mated surface. The more expensive longer and harder way is to have the head and barrel re skimmed to make a complete seal again.

No Ken, don't have a strobe. Better buy one.

BTW: My sparks are NGK B6HS, using dgnition instead of points. Car goes like a train - 75mph easily. No smoke. Good compression. Starts 1st time every time. But now it's smelly. Better get the plugs out and see if they tell me anything, I guess. Haven't serviced the car for 3000 miles.

BTW, can you recommend a good value-for-money strobe? Nothing pricey, mind!

I bought an Accuspark H8000 for around £18. Haven't used it yet, but the reviews online seem good. If you spend a bit more you'll get one with adjustable advance settings and a tachometer.
Off the top of my head, you'll need a complete gasket set and valve stem seals and (possibly) new manifold nuts, studs and locking washers, but that depends how your old ones look.

well lets hope the "bargain123" hasn't cost you a cylinder head.
unfortunately its as its going like a train at 75mph when all the damage has been done DG has a habit of over advancing the timing and so its been pinking away merrily, this is why it is so important to check the advance on these engines - and you can only do that with a strobe and some white marking paint. The peg in the hole is now relegated to initial bench set up and finding a datum on the flywheel.

if it had been set by strobe the worst that would have happened was a slightly lumpy idle

- bet you've been enjoying the "efficient heater" though?

Idles OK. Are you suggesting that I should dump the DG for the long-term health of my engine? Or am I over-reacting, and should just concentrate on the timing?