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Goodness Pete...that is some engine build....congratulations ....& the video link confirmed a few things1. from the image below, it is a twin engine build ...not a twin cylinder engine as there is no interconnecting crankshaft between each engine2. so with respect to timing the engines @ 90 degrees, [and maintaining the timing] does this rely on the mechanical rigidity of the Pullman arms, linkages, the paddle wheel axle and all?
By reading your WEB thread it appears that the vessel hull selection is not yet set in stone ....so from this point it would seem criminal to install such an engine hidden behind a deckhouse superstructureOne alternate here could be to consider a smaller sized vessel with open engine casing walls but build her to a larger scale & hence the same~~~physical model size & displacement
In one of your WEB images we see cotton string lagging on the steam tubes.......these as is will get oily & dirty For my long time engine assembly, I copied a concept from a member of Model Boats Mayhem in UK .......1. Superglue a 1/8" ID white nylon washer at each end of the pipe spool2. wrap with cotton string as you have....& secure at each end with superglue3. apply a Polyfiller [wall & ceiling paste] over the string4. allow to dry & carefully sand the OD to a uniform diameter & straightness5. paint with enamel undercoat & enamel gloss top coatAny oily marks or splashes simply wipe away
I thought items such as water and fuel had to be close to center so as they are consumed the trim of the hull remains steady.Pete