Atkinson Differential Engine - Making it work?

[dsage]

Banggood has everything
Quality is another issue. But it hasn't blown up yet in about 3 uses.
I hadn't thought of using the kitchen oven. I have one in my shop that I use for powder coating with an exhaust fan going outside. But the shaft is JB welded (seems to be the theme on this engine) to the crank disk. So the JB weld might be weakened by the heat. Even though they rate the slow stuff for 600deg (peak). This joint might be a problem in the future but it's easily tacked with my TIG welder if it lets go. I was just lazy when I stuck it together.

 

[awake]

"Quality is another issue" - I've always thought it interesting that that particular vendor's name starts with "Bang"!

 

[dsage]

It's finally time to make the piston rings so I can do the final assembly. The method I use is a combination of both the Chaddock and Trimble processes. Using the suggested calculations from those guys the rings end up being fairly thin which I like. It makes them easier to install and I think they seal better than fat rings.
Making the rings is pretty quick. I use grey cast iron turned into a tube according to the calculations. And then I part them off and lap them to thickness.
Making the holder to heat treat them is a lot more time consuming. There is a calculation for the diameter of the pin that holds the gap open while heat treating. It's a pretty theoretical dimension. I may have got it slightly wrong as I think the maximum diameter of the pin is supposed to be on the center line of the ring ends. But in the end it really makes little difference (IMHO) as long as they are springy when completed.
I only made the jig to hold 5 rings even though I parted off 10 (minus one off spec).
The rings are stacked in the holder and a cap is installed that keeps them in place and seals the container from air. A bolt holds it all together.
I heat the whole thing carefully with a torch to a dull red colour (no more) barely visible in a dark room and held for several minutes.
There is a whole process you are supposed to follow concerning time and temperature but it works fine (for me) approx as described. After heating they are left to cool until room temperature before opening the container. The rings have no scale. They are just dis-coloured and clean up nicely with some very fine steel wool.

While I had the engine all apart I bead blasted all the pieces. I actually used ground glass because it was already in the cabinet and it's a pain to change. It was a bit too coarse for a final finish in my opinion but it is perfect should I choose to paint it. (I probably won't - I don't want to take it all apart again).
In one picture you can see the installed reed valves. The exhaust valve has what's supposed to be a muffler stacked on top of the valve. The exhaust exits through three holes facing down (not visible).

You'll notice what looks like staining on the metal. That's just oil from assembling it. It is easily removed with some brake cleaner making the whole thing a uniform colour.

Some upcoming parts to make are holders for a magnet and a hall sensor so I can trigger the ignition. The ignition will be easy. I'll be using one of my coil driver modules and a car ignition coil.
A carburetor of some sort - I don't like the one in the book.
And finally a cap to glue on the end of that water jacket that I keep forgetting about,

I'm happy to report that the engine has fairly good compression and the valves seem to be doing their thing.
More on that later.

 

[stragenmitsuko]

So they actually work do they .
Good to know . The induction heater that is

 

[dsage]

So they actually work do they .
Good to know . The induction heater that is

Yes. Seems to work. But I can't compare it to any other. I ran it at it's maximum (spec) voltage of 48volts and, as mentioned I thought it would heat the 1/2" rod hotter. I had hoped for orange or bright orange. Maybe the rest of the rod was sucking up the energy since it was wrapped in a wet rag.
My batteries are marginal too. I didn't check the voltage under load. Might have been some of it.

 

[dsage]

I figured out the ignition pretty quickly. I'm using a hall sensor and magnet to trigger one of my coil driver modules.
I made a thin clamp to go around the crankshaft to hold a 1/8" dia magnet. The magnet will rotate with the crank.
Another disk holds the hall sensor and is mounted and cupped around the crankshaft bearing boss and is held in place by a set screw. The initial timing setting is done by setting the pistons at TDC and rotating the magnet clamp to the trigger point of the ignition. After initial setup the timing can be changed slightly one way or the other by loosening the screw on the sensor disk and rotating the disk slightly. This fine tuning can be done while the engine is running. All things considered IMHO it's a pretty compact solution.
You can see in the pictures how I mounted the ignition driver on the back of the engine behind the flywheel. The cut down Ford COP coil is mounted on the side of the engine. A battery holder with 4-AA NiMh cells plugs into a power connector. I didn't add a power switch because it's safe to leave the module powered up.
The ignition gives a nice hot spark at the 1/4-32 spark plug.

I still need a carb to try it out. That may take some time.
Getting close.

 

[awake]

Eager to see & hear it run!

 

[propclock]

Nice Dave , glad to see you are using your own ignition, Now my 1.414 cents worth.
Hall sensors draw several ma of power Reeds draw nothing unless the magnet
happens to stop on it. Also what, if despite your pessimism, this thing really takes off
and dances off the table? Yea I know you have that big beautiful flywheel to stop it
But why mess up that beautiful paint job ? add a switch and a power on LED
Just my opinion. I hope it dances , but not off the table. Good luck Dave.

 

[dsage]

Hmm. Good point on the switch.
I hadn't even thought of how to turn the engine off once it's running . My bad.
I must have been day dreaming and lazy as usual.
Ok. I'll add the switch - and maybe a light. Which I guess means a small panel to mount them. You're making work for me Paul.
To go along with the recurring theme of JB weld, I'll glue it on the side of the engine

I did a compression check this morning.
It has 70lbs of compression. That's good.

I'm working on an adapter so I can use a known good carburetor from my V-twin. It will be ugly (but temporary).
There are enough unknowns with this engine. I don't want to add confusion when it doesn't run.

I still believe there will be problems. The reed valves perhaps one of them. (The exhaust reed for sure).

 

[propclock]

Compression!!!! its all just playing now, congratulations!!

 

[bluejets]

The rings are stacked in the holder and a cap is installed that keeps them in place and seals the container from air. A bolt holds it all together.
I heat the whole thing carefully with a torch to a dull red colour (no more) barely visible in a dark room and held for several minutes.
There is a whole process you are supposed to follow concerning time and temperature but it works fine (for me) approx as described. After heating they are left to cool until room temperature before opening the container. The rings have no scale. They are just dis-coloured and clean up nicely with some very fine steel wool.

There is an additional process the rings should go through to bring them back to true round after the heat treatment otherwise they will leak.
Allowance must be made for this during the initial turning by allowing a few extra thou on the outside diameter.

Involves stacking the now-heat treated rings in a purpose made tube.
Then a fitting , similar to the clamp for heat treatment, clamps the rings together.
Assembly is returned to the lathe and the rings brought to true round and size.

Whether or not you agree or do it is entirely up to you.
I know it works.

Last pic shows a highly inviting path for the spark to jump to the frame from the plug cap.

 

[dsage]

Thanks. I'm aware of that "extra step". The full process if you read the Trimble and Chaddock articles is to make them that thou or two oversized in the first place so you have something to skim off.
I don't subscribe to it because there is more runout in my lathe and especially the mandrel used to hold them that it's next to impossible (for me) to reliably "skim" off" a thou. It probably would do more harm than good.
I make the rings exactly the ID of the cylinder - to within part of a tenth - polished to size if required. Then I use the gap to adjust for a fit. They were round when they were made - they'll be round when they are compressed - again just IMHO.
I've made so many rings I can't count them and have never had an engine that smokes nor required any run-in to seat the rings. If your rings need seating in you screwed something up - again IMHO.

Actually the metal tip of the spark plug is well above (maybe 1/4") any metal. Then you have the insulated cap on top of that. The spark plug gap is only about 10 thou. So I don't think there's any chance of an arc through the cap to the frame when the gap is so inviting.

BTW in a previous post I noted I have 70lbs of compression with no run time on the rings. They don't leak.

Thanks for your concerns.

 

[bluejets]

I don't subscribe to it because there is more runout in my lathe and especially the mandrel used to hold them that it's next to impossible (for me) to reliably "skim" off" a thou. It probably would do more harm than good.

I would say this is a setup problem rather than blaming the lathe.
All machines have some degree of inaccuracy and it is up to the operator to compensate.
Even an old sloppy machine can produce accurate results.

However, as I said initially as I expected a negative reply, up to you.

 

[propclock]

Rings and Religion, not worth your time discussing. But
I have a cool way of adjusting the end gap. Learned from a master
Dwight Giles. Put 2 ,600 grit circular disks of wet /dry back to back .
~3-4" diameter make a mandrel to mount them on.
Yes you can use scissors to cut them out . Make a slotted
I,use aluminum , shelf for your tool post . In the lathe two disks of W/D sandpaper spin in the groove . Some back up disks are needed
for the W/D mandrel.
Then you squeeze the ring against the rotating W/D. The ring resting on the slotted tool post rest.
Nice square end gap , then put the ring in you test fixture measure the gap and continue until you are happy.
You of course have a test fixture? Just an accurate bore with a nice taper to test the ring end gap. Use you piston to push it in square
I have 2 V8s 48 rings. It took very little time. .
This is just for the end gap. The how to make rings conversation is where it becomes , What software is best?
The answer always is, What works best for you.
Anxious to hear first pops Dave.

 

[dsage]

Sounds like a home-made version of a manual ring gap grinding tool that you can buy. I've used them for full sized rings. Totally manual with a handle you crank to turn (if I remember right) a two sided diamond wheel. Same process. Lay the ring on the little table and squeeze the gap. Test and repeat. I do something a little more crude but more or less the same process with like you say W/D paper.

As for first pops. Don't hold your breath please. In the end there were a lot of things I changed in the mechanism that could throw a wrench into the works.
I won't be re-building it unless the solution is really simple. I'm sort of tired of this engine.

 

[dsage]

OK. It's official !!
IT'S A DUD.
I made an intake manifold adapter for a carburetor from my V-twin engine that is known good (although it's pretty touchy) I put some fuel to it and gave the engine a spin with the drill. I made all kinds of adjustments on the carb and the ignition timing but I couldn't get even one pop from it. I finally hit it with some starting fluid and got one very quick pop. Only one in several tries. It also unloads the starter slightly when you apply the starting fluid as if there is something helping the starter. It may just be the lubrication of the fluid. It also smells a bit like exhaust when it's spinning with fuel. Probably all wishful thoughts.
It has good compression. If you put your finger over the sparkplug hole while cranking it loads the starter down.
The intake and exhaust reed valves "seem" to be doing what their supposed to be doing. If you put a paper towel in front of the carb it will be sucked in with no signs of blowing out. Same sort of thing on the exhaust port.
It shouldn't matter if the valves are leaking because they are not a factor in the compression. As long as the fuel is being picked up by the pistons on intake, the compression and ignition take place at the other end of the cylinder so leaking valves will not be a problem.
The only thing I can think of is the fuel is being sucked in but it's not making it to the other end of the cylinder.
Upon checking the spark plug it was found to be wet. So maybe the fuel is not a vapour any more after traveling along between the pistons. Liquid fuel would not ignite. Although you'd think the starting fluid would remain a vapour.
Food for thought.

It has tons of spark because I'm driving the COP coil directly (without a ballast resistor) from 4-AA NiMh batteries.
SO I'm at a loss. Usually you can get some encouraging pops and it's just a matter of finding the sweet spot in all the adjustments.

Gordon:
Sorry Pal. I did my best to figure it out. At least it does have compression so you can rule that out of the things that ail this engine. Now it exhibits the other problems you described on you post. One of note is that fuel is coming out the exhaust slightly.
For now it seems it is doomed to join yours on the shelf.

Sorry to have strung all of you along on this build.
I'm going to put it aside for a bit while I go on to other things that need to be done around this place.
I may visit it again in the future if I come up with some revelation that doesn't require re-building it.
I'll post more then.


And no I didn't get around to putting the cover over the water jacket or adding the switch to the ignition

 

[propclock]

Bummer, makes no sense?

 

[awake]

How disappointing! Maybe a midnight revelation will occur, and you will realize some simple adjustment that will fix all ...

 

[stragenmitsuko]

A suggestion :
try using propane as a fuel .
Just a small needle valve into the intake circuit .
That would rule out the non vaporising or condensing fuel issue .

 

[dsage]

Tony:
I briefly let the engine breathe in a bit of propane from a torch placed just outside the carburetor intake. It didn't seem to respond at all. But from my Parcell and Weed engine that runs on propane I know it can be VERY finicky as to the ratio of air to propane. The is a very narrow range where propane is combustable.
So there might be some hope there. But Gorden says he tried propane and a vapour carb (and almost everything else ) and didn't have any luck.
It will be worth some more experimentation though.
Thanks

Andy: Yes I'll need to sleep on it.

See the next post.