Bog's Paddleduck Engine

[bogstandard]

Kirk,

By the sounds of it, as long as your spools were made to the measured dimensions shown in the article, your trouble just might be timing. Even if things are rather badly made, once the timing is something near, it should run.

When I did my very first runs, the timing was later found to be about 10 degs out, and even at that setting, it ran very well.

It can be a little tricky at first just how to figure it out, as Roy (Shred) found out, but once you can get the grasp of how the timing works, it becomes a lot easier.


John

[shred]

If it 'kicks', but doesn't run, when turned by hand I'd say it's most likely timing.  Especially if you have to rotate it quite a bit to get it to 'kick' again.  That's exactly what mine does when the timing is out.

[kvom]

After I found a 1/8" NPT x 3/16 hose barb that I could fasten with a hose clamp, I hooked up the engine to the air supply.  Although my compressor is set at 125 PSI, my regulator will register a maximum of 45 psi, which I assume is a result of back pressure from the engine itself.

The engine didn't self-start, but when I manually set piston #2 just past TDC and turned on the air, the engine started up and ran for several seconds before stopping suddenly.  I repeated this and got another couple of seconds.  Since the first two tries, it hasn't repeated.  If I do the same thing I get 3/4 of a revolution.  Setting piston #1 just past TDC and apply air gets 1/2 of a revolution.

At the point of stoppage there does seem to be more friction (i.e., resistance to turning the crank by hand), but I don't know if it's friction/binding that's stopping it or something else.

A few questions come to mind:

1) Should this engine run on only one cylinder?  If so, I could tune one cylinder at a time by removing air supply to the other.

2) Does it sound as if it's the cylinder 1 timing is an issue?   Visually, it still looks to me as if the eccentrics are at the top positions when the cranks are horizontal.  How sensitive is the vertical setting of the valve?  Would it make sense to adjust that before trying different  timings of the eccentric (since I have no real idea which way to adjust them)?

3) Does it make sense to try to run in the engine some with the drill at this point?

[bogstandard]

DO NOT TURN THE ENGINE OVER BY ANYTHING OTHER THAN HAND OR AIR UNTIL YOU HAVE IT TIMED IN CORRECTLY

If it isn't in correct time, there will be internal pressures built up that are liable to destroy your engine by bending shafts and knocking the crap out of bearing surfaces.

There is only one way you can go, and that is to sit down, study the instructions and the engine, and time it in. It might be a frustrating time for you, but that is the only way to do it. It might take a dozen goes before you get it spot on, but it will be worth it in the end.


John

[shred]

A few full rotations is great progress!  When mine runs-and-then-stops, what's happened is something (typically the valve spools, but sometimes the crank parts or packnuts or joint pins or crosshead rods or whatever) has moved, rotated, or come loose and either thrown it out of time and/or caused binding.  Check on your crosshead rods, valve and crank timing to be sure they're still where you left them.

I don't think perfect timing is critical-- mine is 'sort of' timed at the moment and works ok, but it's got to be close.

You probably don't want to be putting 125 PSI straight into it. I'd start about 60 and lower it as soon as it gets going.  A little oil in the airline is good to keep the pistons and valves happy.

[NickG]

I will just echo what John said, if you've got resistance of any sort it would be crazy to turn it over with a drill. It will just break or bend something and even if not, it won't help at all. I've never used a drill on any engine I've made yet and probably never will.

Try to understand the principle of the valves and the timing they need first, it will be ten times easier to adjust once that becomes apparent.

Nick

[kvom]

Since it "did" run for at least a few secs, I think my timing might be OK.  However, I have taken it all apart and mostly reassembled, taking some of the advice given in prior posts.  A few changes:

1) I followed shred's example and degreased the crankshaft pieces and the crank webs.  That should allow the webs to clamp more strongly to the crank.

2) Today I bought a set of T-handle allen wrenches at Sears.  The numerous 5-40 SHCS are much easier to tighten with the 3/32" T-handle rather than the simple, shorter 90-degree version I used previously.  Same goes for the 6-32 screws.

3) Previously the threaded rod was not fixed in the eccentric fork, so I put a drop of loctite there to keep it from turning.  I also found that, while the pistons will move easily no matter how they're turned, the valves are vwery sticky in some orientations.  When the loctite sets on the forks, I will try to ensure that the valves are oriented in a postion where they slide freely; I will then adjust the valve tuning by turning the fork rather than the valve stem.

Keeping my fingers crossed.   

[ozzie46]

   kvom
   

     Keep at it. You will prevail.

   Know this all you trials are not in vain and will aid others in diagnosing their engine problems. I for one will probably benefit a great deal from your post and I humbly thank you  "Shred", "Bogs" and all the other posters for the info posted.     


   Ron

[DeereGuy]

Kvom it sure will be nice to see that running once your all tweaked in.

[shred]

Since it "did" run for at least a few secs, I think my timing might be OK.  However, I have taken it all apart and mostly reassembled, taking some of the advice given in prior posts.  A few changes:

...
3) Previously the threaded rod was not fixed in the eccentric fork, so I put a drop of loctite there to keep it from turning.  I also found that, while the pistons will move easily no matter how they're turned, the valves are vwery sticky in some orientations.  When the loctite sets on the forks, I will try to ensure that the valves are oriented in a postion where they slide freely; I will then adjust the valve tuning by turning the fork rather than the valve stem.
/quote]
I'd bet while it was running a valve or two rotated just a little into the 'sticky' orientation and stuck there..

[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   

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

[kvom]

 

Run in the video is with 1 guide rod per crosshead at 40 psi.  The engine still needs to have 1 piston just oast TDC to self-start, but once started it will run for minutes on end.  Perhaps I need to do the 10 hr. run in that Bogs did.  The only change I made since last night was adjustting the #2 valve a few degrees.  It then ran for 4-5 minutes until stopping. 

I then discovered that the vibrations had loosened the grub/set screws on the #1 valve allowing the timing to go off.  On the second long run the same thing happened on the #2 valve screw.  I am thinking that the #2 eccentric can be loctited to the shaft without causing any problems.  For the #1 valve I might need a deeper notch in the shaft or else a hile drilled into the notch.

I'm guessing the reason the engine won't self-start in all positions is that there is still a fair amount of static friction to overcome, and that a half-stroke of the piston doesn't generate enough momentum. It might be interesting to mount a heavy metal disc on the end of the shaft.  One area of friction that I'm aware of is between the eccentric clevis and fork.  I think a bit of filing on each will help the next time I do a disassembly.

Another thing to try is moving the air to the lower inlets to see how it runs in reverse.

John, you can relax a bit now.   

[Darren]

Way to go Kirk, that is wonderful news.....looks like it's going like the clappers there....

[Bernd]

                                            All right Kirk

Way to go. You out lasted the engine.      

                          

                     

Bernd

[bogstandard]

Thanks Kirk, I will sleep soundly tonight.

I still think that your timing is slightly out though. But now you have it running, you can tweak until you get it spot on.

Give it a drink of auto engine oil every ten minutes or so, down the airline to the engine, and let it bed itself in for a while.

A real good result. Apart from mine, yours is only the second to be shown being built with a running result at the end. Shred beat you to it, but not by much.

Yours is a bit special though, you made it BIGGER.

Very well done.

 


Bogs

[kvom]

tweak until you get it spot on.

Spot on meaning it starts in any position?

Give it a drink of auto engine oil every ten minutes or so

I have been using air-tool oil.  What's the advantage of auto oil?

Apart from mine, yours is only the second to be shown being built with a running result at the end.

Since you built two, mine is only the 4th.   

you made it BIGGER

I have an idea that bigger is easier, aside from accumulating materials.  Other than the brass for the reversing valve and the legs, plus the drillrod I didn't pay for any of the material.   The scrap bin at school was very handy.  For tools that I didn't have at the start of the project, I had to buy some threading dies, a tap or two, and a 1/2" reamer for the cylinders.  I was able to borrow the slitting saw for the crank webs and lathe dogs for turning the connrods. I also got the gift of the silver solder from you.

[bogstandard]

Kirk,

The engine should stop and start from any position, in either forwards or reverse, there are no dead spots designed on this engine at all. The only time it could fail to start is if running on steam, there might be a hydraulic lock caused by condensing water, or if on air or steam, whilst the engine is bedding in, internal frictions have to be overcome for the engine to start. Both mine tick over and run on 5 psi. But they have had a lot of running time. The last steam show I did, they got about 12 hours each spread over 2 days.

If the cranks are exactly 90 degrees to each other, and the timing is set at exactly 90 degrees lead to each crank, then there is always a power stroke, either up or down that will start the engine in motion.

Auto oil is much thicker, air tool oil is like 3 in 1 oil, and is really too thin for bedding an engine in. It will allow more friction to build up due to it having a much thinner film layer.

You are correct, yours is the fourth, but second if you exclude mine.

You definitely went the hard way, not only were you converting from metric to imperial, but you upped the scale as well.

Unfortunately, it will only have the same power or even less than the smaller one, as you kept the bore sizes the same as the smaller one, but increased the moving masses and friction by going larger.

But, you gained a lot of experience, that is the biggest plus about your build.

John

 

[rleete]

Good job.  Sounds like a real powerful one, too.

[kvom]

The bore is less than 1.5x the scale diameter, but the area of the piston is 1.61x normal scale.  With a 1.5x stroke the displacement is 2.42x the original.  Had I scales the bore proportionally the displacement would be 3.38x.

I will try the motor oil tomorrow.

[shred]

 

[sbwhart]

Well done Kirk

I bet you've got a grin going from ear to ear and so you should.

 

 



Stew