changing Valve springs with heads on

I am in the middle of swapping valve spring retainers etc. and on Cylinder 5 and 8 when I attatch my compressor to the spark plug hose. I hear a loud high pitch squeal and I have to race to get the spring off and then wait for my compressor to build pressure again because it goes from 140psi down to 60 in maybe about 30-45 sec and when the compressor cuts back on it can't keep up. The other 6 cylinders was a piece of cake and there was no rush at all. I'm guessing this is propably not normal and I will need to pull the head and figure out what the cause is. I do have the oil pan off and the engine is in the car. The air sounds like it's in the engine. Has anyone ever experience this before? And is there any tests that I should do before I pull the head? The tank is also a 30 gallon tank, I just hear a lot more air passing. I'm guessing probably rings?

Thanks

Jeff

First off I take it your on the firing cycle of that cylinder. If the air could only escape through the valves,rings,head gasket. You need to find the air leak. Listen throught the carb (INTAKE VALVE) Valve coverS off it coUld be coing up from the oil pan area (RINGS) And the exhaust (EXHAUST VALVE) last would be the head gasket so with caution remove the radiator cap and see if there any thing coming from there. Caution it could be a fountain when applying air with the cap off.

Ace

Listen to the exhaust primary tubes or ports, the intake ports or carburetor also check for external leaks before removing any parts. If an abundance of air is being heard from the oil pan area it could be rings, pistons or block. Can you induce smoke into the air line and watch for it's trail? Sometimes a light tap with a hammer will seat a valve that is not seated. This may also indicate the problem area!

The air leak you describe sounds .... BIG! Shouldn't be hard to find.

Dave.

Thanks for the tips. I have the intake off and the radiator is out of the car. I just did the number 8 intake valve and with 110psi tank full I could still push the valve down with ease. I had tested this on number 1 and couldnt budge it. I'm going to keep troubleshooting, thanks again for the advice, this is the same engine, that when it was running a couple of weeks ago, I couldnt get it to idle down under 1500 rpm and there was nothing on causing it from the outside. Well time to get at it. haha

Jeff