Bog's Paddleduck Engine

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kvom:
With the forks loctited to the threaded rod, I went through the top section tuning again, this time trying to ensure that each valve stem stayed in a position where the valve slides easily. I oiled all the places I could think about and hooled up the air.

The engine runs for varying lengths of time when I start it with piston #1 just past TDC, but not otherwise. Eventually it stops. The longest it ran at one time was about 20 seconds, but mostly it would run around 5 seconds before stopping.

There's quite a bit of vibration, and I notice that it tends to loosed the packing nut on the pistons. I was running without the guide rods for the crosshead, but tomorrow I will try it with the rods in place. I'll also recheck the valve timings again.

sbwhart:
Getting closer and closer :thumbup: :thumbup: :thumbup: :thumbup:

I call this stage training the engine to run.

Stew

shred:
You don't want to be running very long without the crossheads in; I think that will cause some pretty odd behavior, wear on the glands and binding as the piston rod is going to get bent every which way instead of running true in the cylinder.

bogstandard:
Kirk,

This is not only very frustrating for you, it is killing me.

I know that if I had this engine in front of me, I could most probably have it running sweet as a nut within no time.

It is very difficult trying to suggest things over distance.

All we can do is share your frustration, and try to help as much as we can.

John

NickG:
Yes, very difficult to suggest how to solve the problems / diagnose faults.

The only thing I can suggest is to go back to basic sub assemblies, start from scratch which is what I'd do to make sure nothing was missed. I had to do similar with my stirling engine.

Do the pistons slide in and out easily with their crosshead guide rods and nothing else attached? If not, why not? ... sort that before trying any thing else, there should be very little resistance, even if it has rings of some sort, the breaking friction will be a bit higher but it should move easily once it's started moving.

Do the valves slide up and down easily? If not, sort this out.

Does the crank assembly spin over freely in it's main bearings with nothing else attached? Again, if not, something needs re-aligning or the fit is too close. As bogs said, steam engines tend to be very forgiving, even if poorly made and there is loads of slop in bearings and joints they usually run!

Now does it spin over easily with the eccentrics / rods attached? i.e. is there minimal friction between the eccentric strap and sheave? It should be a close fit but there shouldn't be any tight spots.

Now do the same with the big ends / con rods attached, again there should be no binding at all.

The final test is with the small ends attached to the piston rods. Unless something is binding in the small end or the rod is bent / out of line, it should all turn over easily by hand.

You know the engine runs so ports must be all ok, it's just a matter of making sure the eccentric sheaves lock up positively onto the crankshaft and getting the timing right.

Good luck and well done as you aren't far away, which is why it's so frustrating!

Nick

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