205 1.1 Compression problem

First thing would be to ensure that the hydraulic tappets have re-compressed. Either leave it alone for a few days or run it for a short while. I have several times been frightened by an engine that won't run right after putting the head back, only to find that a tappet is holding open ! If the above doesn't help then:

Turn the engine to the compression stroke for that cylinder, lock the crank, pressurise the cylinder and see where the air leaks out.

It doesn't have hydraulic tappets but I have checked and re-set the valve clearances.

If I try the second option, how can I tell where the air's leaking out?

" snipped-for-privacy@googlemail.com" gurgled happily, sounding much like they were saying:

Listen.

It'll be coming out of the inlet port, exhaust port or crank breather.

There should only be a slow bleed of air past the rings so the only place you should be able to hear anything is the oil filler, major stuff like your lack of compression will show up as a real whoosh of air probably through a valve with a problem.

So you listen !!! seriously, you will hear if it comes back through the inlet easily enough, the exhaust will be fairly obvious too, a length of plastic hose makes a very good stethoscope. the trickier one is if it is leaking to the adjacent cylinder or through a cracked liner. Compressed air is a really good diagnostic, toolvans like snap on and mac sell a ready made kit or hose, but you could probably fabricate your own adaptor for a one off.

Incidentally did you test the valve sealing before refitting the head? The simplest way is just to fill each port with something thin and runny like diesel or parafin and leave for a while, any leak at the valve or worse valve seat should show up easily enough, engineering shops have a compressed air gadget that makes a vacuum against the port.

All the valves ground in nicely and I crack-tested the

How did you measure the head face for trueness, did you have the head pressure tested?

By using your eyes ears and touch! If the compression/air is leaking past the inlet valve you'll hear/feel air coming out of the induction manifold area, if the exhaust valve is leaking you'll hear/feel the same but out of the exhaust, if it's leaking into the cooling system you'll see bubbles in coolant, if it's leaking past the piston or otherwise into the crankcase you'll hear feel it via the oil filler or dip-stick tube etc. Remember though, that in the case of the latter example, there will always be some blow-by past the piston rings even on a healthy engine, you would be looking for excessive blow-by.

One thing "Mr Cheerful" didn't tell you though is, one you need the correct kit and a compressor to carry out this test, also you need the piston at TDC on the firing stroke, not just on the compression stroke.

The firing stroke starts at tdc, the same tdc at the end of the compression stroke !!!!

As long as both valves are shut the piston can be anywhere up and down the cylinder, but it is easiest to restrain the movement with the piston at tdc.

Obviously a compressor is needed, but you don't need the kit with a leakdown gauge, just a hose with an air line adaptor on one end and a spark plug thread on the other will do, I would think that many compression tester hoses could easily be modified to suit.

Remember, in this case you are looking for a gross loss of compression, not a slight variation on a running engine.

Mrcheerful

Opposed to TDC between the exhaust and the induction stroke (overlap) you mean, hence the clarification of what TDC I was talking about, whilst pointing out that it's incorrect having the piston (for example) half way up the bore on the compression stroke - there are very good reasons why, when one is doing a *LEAK* test, one is that one doesn't want to introduce bore wear into the equation that might cause a miss-diagnosis, it is not a compression test - the other is (as you said, snipped) that it's easier and safer to 'lock' the crank when the piston and crank are at TDC.