Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Next oddity that I noticed on this engine is on the underside of the cylinder casting, at about 7 o'clock if looking from the rear, and right up near the packing gland end. It is a rather large diameter plug with a lot of exposed thread, but must logically be drilled and tapped into the inner cylinder as well.

As seen here:

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What the purpose for this plug could possibly be, totally escapes me, unless if functions in some way to hold an end plate into that end of the cylinder bore, which would be a very strange setup if you ask me?

Certainly having a valve in this position would make some sense, for draining off condensate from in front of the piston to prevent hydraulic lock situations from occurring at startup, until the cylinder gets warm enough to obviate this issue. But this plug can in no way be used in this manner!

Weird ...

From this point, I started "feeling" the engine to see how it turned through its full revolutions and instantly found that it had a noticeable bind/drag when the crank pin was near 12:00 o'clock, continuing around to almost 9:00, and my first though was ... Oh No, a bent crankshaft.

But the crankshaft on this beast is truly substantial, so I didn't quite buy into that being the issue just yet.

Thus I started to take down the various motion parts on the engine, starting with the valve linkage, and immediately found some rather discouraging evidence of bad/sloppy machining ... as seen here:

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Note that the valve linkage toggle arm bearing shaft hole in both the fixed mount bracket and the boss of the toggle arm itself, are noticeably off center in roughly opposite directions, and the hole in the latter has been wallowed out oversize to facilitate a fit. Also note that the hole in the valve cam linkage arm head is also nowhere near centered as any good machinist would have striven to make it!

Interestingly, this is only true of the holes on the mating surfaces of the toggle arm and mount bracket, while the axle bolt head and nut, or opposite ends of those same bores (outside exposures) are both reasonably well centered.

This all leads me to believe that this engine was bought as a set of castings, probably pre-machined for the most critical work, and then finished up by an amateur likely using hand tools rather than machine tools.

These issues could be remedied with a lot of work, but it is actually a fairly non-critical situation, such that as long as these parts are all free to move through the required range of motion, they should do their job just fine as is. But it does look shabby, so maybe someday I'll get around to over-boring more centrally, and then sleeving those bores to obtain a proper fit.