My leakdown tester is totally home made.

The inlet is sealed using a nylon bung I turned up in the lathe, basically copying the dimensions from the carb spigot that fits in the insulator. I then drilled a hole in the centre and fitted a tyre valve so that I can fill with air.

The exhaust is sealed using a big o ring from the hardware shop (cost about 10p) and an aluminium plate that I hacksawed and filed. This bolts on using the original exhaust mounting studs.

Now, as for the plug hole, this is where I fit my gauge. Some will say (rightly or wrongly) that you're supposed to test the plug as well for leakage, but as I'm usually pulling plugs out faster than I'm throwing fuel in I think that it's more important to check other areas such as seals and gaskets. Anyway, my gauge is a 10 quid low pressure gauge that I fixed into the gutted body of an old spark plug so that it can be screwed into the head.

Procedure for me is to pump in 10psi and then leave it. In the worse case it should probably only drop 0.5psi after a couple of minutes.

I spray soapy water over the engine and look for bubbles if it's leaking.

As far as I'm concerned, piston position will make no difference and is not important as the air will leak past the rings no matter where it is in it's stroke.