These things do wear out when you've given your engine a bashing or the wear of the passing years takes its toll. Here's a clue to help you decide if you need a new one; there is steam and water everywhere - the wife tells you to put it away - and it hardly turns over. Either ditch the old engine or get a new piston assembly. Simple.

Length of the fully extended piston from cylinder block to the hole for the crankshaft is: 65mm. This is the longest piston available.