Hello

I recently put my 2cv back on the road after being laid up for about four years, the engine was seized but freed off after being gently rocked back and forth. It ran beautifully with no more smoke than when laid up for about ten miles before overheating quite impressively as the fan bolt had not been done up. Frustratingly stopping jobs at the last moment of day light during the recommissioning led to a couple of things being half reassembled before its first run.

After the overheat it produced a significant amount of smoke at first under high vacuum and then progressively more so under high load. The breather is definitely shot but has been running one of the inline crankcase decompression valves from ecas to good effect for a couple of years before being laid up. As the worst of the smoke was under high vacuum I changed the valve stem seals to no effect.

I then checked the compression, ~100psi each side on warm 9.0:1 nearly new pistons, rings, and cylinders with the throttle wide open. Thinking this would suggest glazed bores I whipped the heads off and surely enough I think the bores could do with deglazing, but would this really produce such a significant amount of smoke? The rings all look as good as the day I fitted them.

The only other options I can think of are dodgy valve stem seals which seems unlikely, or knackered valve guides.

I look forward to hearing any thoughts.

W

Did you change the oil? Overheated oil looses much of it's characteristics.

Compression reading is far too low, it should be nearer to 175 psi with 9.0:1 pistons.
Overheating or partial seizure?
The former may affect the 'springiness' of the piston rings, so that they're not exerting enough pressure on the cylinder walls; the latter may cause the rings to be 'nipped' in the bore, causing the piston ring grooves to be enlarged...

Ken

as above never mind the bores what are the pistons like - the skirts scuff and drag material into the rings, the lands can pickup and nip the rings too

A quick hone will highlight any problems with the barrel - new rings and a proper hone to restore the engine - new barrels and pistons are cheap and probably the best route

It ran throughout, albeit whilst smelling very hot indeed, pinking like a sod, and giving off heat like a nuclear reactor once the bonnet came up.