OUCH!!!Sore Head

Trevor Harvey · Post by **Trevor Harvey** » Sun Oct 30, 2011 10:56 pm

And the reason it gives a duff indication is because the piston is at TDC for a very short time & inertia (gas) has a say in how quickly the pressure leaks. I think?? Think of the brakes needing to be bled, they still work as long as the foot is moving.

Bill McCarthy · Post by **Bill McCarthy** » Mon Oct 31, 2011 7:29 am

That, hysteresis maybe, and the heat of compression will give the higher pressure indication.

Sandy Hutton LAA372 · Post by **Sandy Hutton LAA372** » Mon Oct 31, 2011 12:42 pm

Sorry Bill, those spin over compression testers have a schrader type valve in them so hysteresis won't come into it. (at least, mine does)

What it will tell you is IF there's wear-taper-ovality-scores, further down the bore because there will be a leakdown on the compression stroke. Leaking at this point will show up in the form of less compression by the time it gets to the top of the stroke. If the reading is low in comparison with the other pots, then you know you have a problem to investigate further.

A differential test can only indicate whether the valves and rings are good at a single point, ie, the top of the stroke. You have to be careful though or you'll get hitted on da head..

I'm happy to use either tool.

Sandy
ps, how's the Sluka?

Bill McCarthy · Post by **Bill McCarthy** » Mon Oct 31, 2011 6:10 pm

An ultrasonic leak detector is good for finding small leaks - I used one regularly to check for tiny steam leaks when ploughing under the oceans. A simple soapy bubble check is also very good for finding head gasket leaks.

The Sluka is down for extensive maintenance and for the installation of the boom tube reinforcement mod (hopefully) - which is getting machined at the moment. Wick has been NOTAMed for out of hours flying for months now (replacement of runway lights I think) but is nearing completion, so I must get my skates on and get tidied up.