Here'a a quick way to check if your engine has a bent rod due to Hydrolock. This is credited to Connierider, AKA Ted Adcock, an upstanding member of the COG community.
First, you need to make up a quick depth guage. A long round shank screwdriver or metal rod, app 1/4" diameter works well. It needs to be at least 1 foot long. Slide a 2-3" piece of vacuum hose onto the shaft. Make sure it's tight enough to stay in the position you slide it to. If it's a bit tight, grease the rod and and the piece of hose will slide more easily.
Next, remove all the sparkplugs.
Finally, measure the piston depth of the piston PAIRS, in other words compare the height of 1-4 and then 2-3. Don't compare the 1-4 to 2-3, only compare 1 to 4, and 2 to 3. Simply drop the rod through the plug hole til it rests on the piston, then slide the tubing down til it just touches the valve cover lip. Leave the tubing in that position, go to the other piston of the pair, and drop the rod down the plug hole. The rod should hit the piston at the same time the tubing touches the valve cover lip. If one piston is low, the rubber tube will be lower comparably to the cylinder head.
Many thanks to Connierider for offering this idea a couple years ago, and it has served me well. In light of all the hydrolocks that happen, i'd really like to see this post be a sticky. Grin Steve