Quite right - the rule is one hard, the other soft. And contrary to expectations, it's the harder material that wears the most!! This is because particles of the harder material become embedded in the surface of the softer material, turning it into a lap. Look at Cox, who used hardened steel pistons in soft leaded steel cylinders. When the fit became too loose, you just threw in a new piston and happiness was restored!!This isbecause most of the wear was on the hardened piston.

The main issue with using a steel piston is that,unlike cast iron, steel doesn't "grow" over the first few dozen or so heat cycles, thus taking up any break-in wear. So you have to get a really fine finish on the piston surface and also need to get the piston fit pretty near perfect right from the get-go - just very slightly stiff, but not unduly so. It will then wear to a perfect fit and become work-hardened during the process. The Deezil cylinder appears to be common-or-garden mild steel tubing which won't work-harden to any great extent, so you want to make the piston out of a high-tensile steel that will work harden during the initial running period (cast iron does this too). As far as Ican tell, the original Deezil piston was mild steel, which means that the engine wouldn't have lasted too long even if it did run - it was a soft-on-soft combination. By contrast, a properly-fitted work-hardening steel piston in a soft steel cylinder should wear really well.

Speaking of which, I just finished testing my LNIBearly Gotham Deezil with the replacement piston. I seem to have nailed the fit - the engine started second flick (albeit backwards!!), and ran perfectly. It feels superb, with outstanding compression yet no trace of binding. Starting was dead easy throughout. Compression remained just as good when hot, with no tendency to tighten up and sag. I put about 20 minutes on it in 5-minute runs with complete cooling in between - all that I judged the neighbours would tolerate, although it ain't that loud! It held up well - the shaft (which is a one-piece Gotham original) took it in stride, so it must be made of reasonable steel Although I kept the engine undercompressed and rich due to the need to break in the new components, I did do a quick spot-check at the 20 minute mark. It managed 6,700 rpm on the Taipan 10x4 GF prop that I was using- a little down on the 7,300 that my previously-sorted Gotham original manages on the same prop. Still, that's not too bad for an engine of this vintage and specification.And it will do better following some more running, no doubt (not that I plan to run this one much).

So another Gotham original is up and running!! This shows that if you're lucky enough to get one of the early examples with the one-piece crankshaft, bronze main bearing bushing, bronze wrist pinand properly-finished cylinder, all that you need is a new well-fitted high tensile steel piston to get it going. Not hard to make ..................... I'd also recommend making a new rod with awider small end bearing - the stock item is just too skinny to last. Do that, and you'll have a pretty good engine!

The really sad thing about all of this is that we now see the Deezil as a perfectly OKdesign that was let down solely by the appallingly low standards to which it was manufactured. With a better piston fit and retaining the one-piece crankshaft, this would have been a perfectly acceptable engine by 1948 standards.