Chris's Slew-Crowd Engines

[crueby]

Update: turns out sliding the cylinders off was easy, disconnected  the assembly from the frame and the links, and it slid right off. Ran that screw back in with a dab of loctite, smoothed off the burs causing a small leak, and its back together.  Now can get back to timing tweaks!


 

[cnr6400]

  Good news!

[Kim]

The valve construction is pretty ingenious, Chris!  And you're making good progress on getting tuned in.  Can't wait for the first run video! 

Kim

[crueby]

All righty! Its running, well enough to get the camera on!   
<a href="https://www.youtube.com/watch?v=nWC-Mlduj3I" target="_blank">http://www.youtube.com/watch?v=nWC-Mlduj3I</a>
Still not running properly in both directions, and has a slight gallop to it, but its running. Been spending a bunch of time experimenting with the timing of the eccentrics and the centering of the valve to the ports. Its tough to do on this type of valve since the ports are never uncovered past the end of the valve, so you can't do a visual centering like on a normal D valve. What I am thinking of doing is adding cylinder drain valves at both ends of each one - with the drain open its easy to tell when the port opens and air/steam begins to flow into that end of the cylinder. On some engines I'll disconnect one of the piston rods or valve links and judge it that way, but its tough to tell at low pressures when the disconnected valve is truly off, and there is not enough room to get the conrod out of the way of the crank, so neither of those options is working for me. That leaves the drain valve method. Tomorrow I think I'll drill/tap near the ends of the cylinders for a 2-56 screw and use that as the drain 'valve'.
Then I can really tell when things are open/closing. Without being properly centered, the port will stay open too long at one end of travel, and not long enough at the other end, which causes all sorts of issues. Should not take long to add the drains - would do it now but thats enough shop time for one day, time to go watch a movie or read for a while. More tomorrow. Overall, quite happy with the progress and how well its moving!

[Sanjay F]

  - it's a runnah, as you said about mine!

Well, done, what a marathon to get here and more to come 

[crueby]

- it's a runnah, as you said about mine!

Well, done, what a marathon to get here and more to come 

   Its great to have it running after all this work - can't wait to get the whole row spinning at once!   

[cnr6400]

  It turns! Just some tuning now I think Chris. Like the drain valve idea for diagnosis. "Paging Dr Marion..."   

[Kim]

Fantastic!  First signs of life!   

You'll get it dialed in, I have NO doubt!

Yes, after a while, it's time to stop and do something different.  You've got to keep the shop time fun!  If you don't go and do other things when you get tired, the rate of silly things happening goes up dramatically.  And besides, if you just keep pushing, it becomes too much like w*rk, and it's supposed to be FUN! 

Kim

[crueby]

Fantastic!  First signs of life!   

You'll get it dialed in, I have NO doubt!

Yes, after a while, it's time to stop and do something different.  You've got to keep the shop time fun!  If you don't go and do other things when you get tired, the rate of silly things happening goes up dramatically.  And besides, if you just keep pushing, it becomes too much like w*rk, and it's supposed to be FUN! 

Kim

Totally agree on having something else to do for a break/recharge!  And as Jeff said, Dr Marion is on the way! 

[crueby]

This morning I drilled/tapped cylinder drain holes in the Marion - its working out great!  MUCH easier to tell when ports are opening and closing on the valves. Started with the throttle in one direction, and I got it running nicely after centering then timing the valves one at a time, feeling for when the air started coming through each port as I rotated the crankshaft with the barring tool I printed a couple days ago.

Then tried it in the other direction, and ... not so much goodness. A partial rotation then stop. So, I pulled out the cylinder plugs again, and rotated it in the other direction by hand. The centering on the valves is not right for that direction of rotation. Could be one of two things (or both). There might be too much slack in the spacing of the jam nuts on the valve rod where they surround the top of the valve. I don't THINK that would show this issue to such a degree, but its worth taking off the top cover to check. The other possibility is the size/spacing of the chambers on the valve. In this direction the pressure is coming through the opposite port, and maybe that one has a spacing issue. Not sure if it would have this effect, or which one I should be looking at. What I will do is diagram it out and see if I can duplicate the behavior on paper (or in CAD). I know the ports are the same size and spacing, that was measured a number of times. The chamber sizes on the valves themselves are what I am suspecting - I had left the walls between the chambers slightly wide to allow for adjustments, and it could be that one of those needs a little trimming, but I need to diagram it out to see which one.

But, its almost time to meet some friends for lunch, so the analysis will have to wait till this afternoon or tomorrow morning...

[cnr6400]

 

[crueby]

Okay, after the lunch outing, came back for a fresh look. Opened the steam chest, and checked the valve freeplay. They both could move about 1/2 of a thread pitch, on a 3-48 thread. Too much, so moved in the jam nuts to get it just clearing. Better.  Recentered the forward direction, and experimented with eccentric  angle to find optimal spot. Still not running in reverse, so next steps. Marked the best fwd eccentric positions first.


Took out the cylinder plugs, and rotated by hand while making a list of positions relative  to TDC and BDC crank posions where each end of the cylinder got pressure. Moved throttle to reverse, and made another list.


In reverse, the left cylinder is good, but on the right cylinder the opening and closing positions are late by a fair amount. Now I  need to diagram out the right cylinder port and valve positions for fwd and reverse and analyze whats going on...


The brain is overheating  a little and the Check Engine light has come on, so stopping here for a while to let it cool down!     Will diagram it later...

[crueby]

But wait!  New discovery. 

Just went back into the shop to turn the crank over each way to make a note of which direction the valve rods move as they are getting towards TDC/BDC. There is a lever between the eccentric arm and the valve rod, which reverses things, so I wanted to make sure I was diagramming it properly.

Was just finishing that up when I noticed something very important. On the left cylinder, which works fine both directions, the pivot from the top of that lever to the valve rod is nice and tight, transferring motion well. On the right cylinder, having the problems, that connection is NOT tight, so when it reverses direction there is movement on the lever before the rod starts to move - I think THAT is the real issue here!   

So, rather than doing all the diagramming, I will get that connection fixed (new bushing for the pivot screw maybe?), and see how it behaves. The time spent up till now diagnosing it all was well worth it, I have a much better feel for how the system works now, and have things all centered well. With that connection fixed, I may have to adjust the center position on that valve, but thats easy now with the drain ports.

[crueby]

That was it!!      
Got the linkage fitting tightened up properly, and one last tweak to timing, and its running well in both directions!
        
<a href="https://www.youtube.com/watch?v=jwVnwm_YOvY" target="_blank">http://www.youtube.com/watch?v=jwVnwm_YOvY</a>
Such a simple thing, I was looking so close to the timings that I never noticed the linkage was a little loose. The other things done earlier in the day were still needed, one of those cases where there were a stack of small adjustments keeping it from running well, and all had to be fixed before it took off. Very happy that its going now!  I'm going to do the same drain valves for the other engines before timing them, it does make the adjustments for this valve style much simpler. And, I can take what I learned on the geometry from this engine and apply it to the other three - they all have the same port/gap dimensions as each other, but they are slightly less than on this one. I should be able to make the rest in one batch, the only difference between them is the height of the valve rods above the valve plate.

Ending the shop time today on a great note!

[cnr6400]

  She's a runner! and a nice runner at that. Great news Chris. Doesn't take much extra clearance to mess up small control linkages sometimes. Glad you found it.    I could see it was trying to slew itself around on the bench when it was running! Must be instinctive...