Another Atkinson Differential build

[Ken Brunskill]

Ken:
I've been experiencing compression issues as well, first tried the 1 ring per grove at 0.035 thickness, at start compression was over 20-25 psi before breakin-in, then it went down to less than 5 psi.

Cleaned and re honed cylinder, made new pistons with very close fitting and rings, this time 1 per grove at recommended 0.062 in thickness. Compression was above 20 psi but quickly went down to around 10 psi, seems like the challenge here is balancing friction vs compression.

Have made rings using Trimble method ( heated to 1100 F), forming and machining (turning on a mandrel to final size after parting ) as described by Tom Schwartz in Model engine builder, as well as a combination of both methods.
So far the best rings I think I have been able to make are using BOTH methods. Trimble heat treatment to 1100 F with final sizing using methods and machining as described in Schwartz approach. While compression is low arlound 10-12 psi, engine kind of start, sputters but refuse to run for considerable time, close inspection of rings shows they have not seated all the way around, some more time on assisted cranking may be needed hoping the rings will eventually seat all the way around.

Start attempts are better when engine is cold (i.e. overnight) and when the spark is closer to TDC..

Best regards.
Jaime

Jaime,
Are you building the Perrault design as well? If so please post some pictures.

 

[Ken Brunskill]

Just comments for interest? => When engine testing at the NIS### factory where I worked, the oil consumption had periodic spikes where the 3 rings on any piston aligned during long term testing. And on 4 cylinder engines this happens 4 times more often than a single cylinder. It was monitored on 200 hour durability tests, as on "your car" you don't want to be topping-up the oil every week!
But the rotating ring syndrom is necessary for the "perfect circle" of a ring to fit the same circle of the bore. As the ring pressure is constant for most of the ring, but changes close to the cut ends, the radial variation of pressure (hence wear) needs the rotation to maintain longevity of the ring to bore seal by the rotation causing uniform wear around the bore.
2-strokes with pegged rings have much shorter lives....
K

K, thank you for the very informative treatise on ring performance. While an experienced tool maker and engineer, this is my 1st internal combustion engine build proving that 'old dog can learn (want to anyway) new tricks. Wished may father and brothers were still with us, all good mechanics they would have enjoyed all this enormously.

 

[jquevedo]

Ken:

I have built the Mini A from Dav Perrault design, it is such a nice engine that it was a pleasure building the pieces and assembling the engine, running it, another story, ring making and ring setting is a challenge, that is the main reason I built this engine, difficulty to get something this precise to run.
The issues are mainly related to having two pistons with 2 rings each running in a single cylinder and that cylinder happens to have open ports for fuel intake, exhaust as well as spark plug.
So all the things learned in the past building engines, radial, V8, 4 flat 4 aero engines etc have proven to be very helpful.

I managed to get some decent runs yesterday, but today engine will barely kick a couple of sparks, who knows, maybe rings have rotated and aligned again causing lose of compression..

here are some pictures from the engine as built, flywheel is a new one built to see if I can increase momentum to keep the engine running for a bit longer.

 

[Ken Brunskill]

Ken:

I have built the Mini A from Dav Perrault design, it is such a nice engine that it was a pleasure building the pieces and assembling the engine, running it, another story, ring making and ring setting is a challenge, that is the main reason I built this engine, difficulty to get something this precise to run.
The issues are mainly related to having two pistons with 2 rings each running in a single cylinder and that cylinder happens to have open ports for fuel intake, exhaust as well as spark plug.
So all the things learned in the past building engines, radial, V8, 4 flat 4 aero engines etc have proven to be very helpful.

I managed to get some decent runs yesterday, but today engine will barely kick a couple of sparks, who knows, maybe rings have rotated and aligned again causing lose of compression..

here are some pictures from the engine as built, flywheel is a new one built to see if I can increase momentum to keep the engine running for a bit longer.

View attachment 118999View attachment 119000View attachment 119001View attachment 119002View attachment 119003View attachment 119004

Very nice indeed! See you too went with the one piece Arm's. Good idea in my opinion.

 

[Steamchick]

Flywheel inertia is significant in getting engines to start. There needs to be enough "stored energy" (Rotational inertia) from a single firing to get the engine through 3 strokes to the next ignition, with all the valve/cam losses, and compression Adiabatic losses (back-pressure effectively), and still have enough energy to get over the firing compression with enough inertia so there is adequate speed to trigger the combustion before TDC without the pressure rise from combustion "fighting back" and giving a kick-back. Hence also the need to a good ****** mechanism on the ignition for starting. Pre-1960s single motorcycles had ****** mechanisms (not the riders, though I suspect a few?) that gave a spark AT TDC for starting. In fact my 500cc Matchless had a manual Advance ****** lever (and exhaust valve lifter to position the engine for kick-starting) that when set for the correct full advance condition had enough travel that fully ******** was after TDC. Easy to start! Really only you need a TDC starting ignition point, then advance to idle position when running. Modern electric start engines don't start when you "just" crank enough to get over TDC.... Old hand cranked engines would do that. Almost self-start on the ignition when you got over TDC.... but needed some speed for the ignition Magneto (Who remembers them?) Not necessary with battery powered ignition though. However, modern engines need to achieve at least some speed for the hall effect sensor to define the TDC of the crank to be able to determine the next ignition point, usually by rotating at least 80rpm or more. So a duff battery that gives you slow cranking on a modern electronically controlled, fuel injected car can develop a no-start condition with a very slow crank because the Hall effect sensor doesn't trigger.
On top of that, especially when cold, the cranking speed needs to be high enough to warm the fuel-air charge with some rapid (adiabatic) compression to assist the ignition. A very slow speed - also from an "inadequate" rotational inertia (stored energy) from the flywheel after 1 firing can mean that the adiabatic heating doesn't happen enough for the second firing, with the cold metal causing condensation of fuel on the metal walls of the cylinder, etc. Note that as the air-fuel mix is drawn into the cylinder, the air is expanding into a lower pressure chamber of the inlet stroke, so is adiabatically cooling and the fuel mist will form larger droplets that need more ignition energy (spark) to ignite, or maybe they are too big so need a flame from other smaller droplets igniting. These larger droplets will wet the walls of the intake and cylinder so the mixture is weakened form the planned mixture ratio, so again ignition becomes harder to achieve. Hot engines actually give some heat to the intake mixture and when running achieve an equilibrium, thus fuel mix is stabilised. Hot cylinder walls, etc. do the rest, and with normal running the higher speed of compression ensure the adiabatic heating of the mixture during compression - and reduced time for blow-by-leakage - ensure the fuel-air charge is OK for ignition when the spark fires.
So: a more massive (actually a higher rotational inertia) flywheel is a good thing for starting! (It can also help stabilise Idle running, when hot and ignition is more advanced, and fuel-air mix is normalised.).
Hope my waffle isn't too complicated and some are able to understand infernal combustion engines a bit better. Any experts can always correct my knowledge, which isn't perfect..., and I would hate to teach people the wrong information.
Enjoy!
K

 

[stragenmitsuko]

love it when people are willing to share their knowledge

 

[Steamchick]

But I have more rubbish in my brain than knowledge... Too few are interested in the knowledge, well, that applies to the rubbish as well.
Ken

 

[stragenmitsuko]

Still , there will be far more with nothing at all in their brains ...;

 

[Ken Brunskill]

Flywheel inertia is significant in getting engines to start. There needs to be enough "stored energy" (Rotational inertia) from a single firing to get the engine through 3 strokes to the next ignition, with all the valve/cam losses, and compression Adiabatic losses (back-pressure effectively), and still have enough energy to get over the firing compression with enough inertia so there is adequate speed to trigger the combustion before TDC without the pressure rise from combustion "fighting back" and giving a kick-back. Hence also the need to a good ****** mechanism on the ignition for starting. Pre-1960s single motorcycles had ****** mechanisms (not the riders, though I suspect a few?) that gave a spark AT TDC for starting. In fact my 500cc Matchless had a manual Advance ****** lever (and exhaust valve lifter to position the engine for kick-starting) that when set for the correct full advance condition had enough travel that fully ******** was after TDC. Easy to start! Really only you need a TDC starting ignition point, then advance to idle position when running. Modern electric start engines don't start when you "just" crank enough to get over TDC.... Old hand cranked engines would do that. Almost self-start on the ignition when you got over TDC.... but needed some speed for the ignition Magneto (Who remembers them?) Not necessary with battery powered ignition though. However, modern engines need to achieve at least some speed for the hall effect sensor to define the TDC of the crank to be able to determine the next ignition point, usually by rotating at least 80rpm or more. So a duff battery that gives you slow cranking on a modern electronically controlled, fuel injected car can develop a no-start condition with a very slow crank because the Hall effect sensor doesn't trigger.
On top of that, especially when cold, the cranking speed needs to be high enough to warm the fuel-air charge with some rapid (adiabatic) compression to assist the ignition. A very slow speed - also from an "inadequate" rotational inertia (stored energy) from the flywheel after 1 firing can mean that the adiabatic heating doesn't happen enough for the second firing, with the cold metal causing condensation of fuel on the metal walls of the cylinder, etc. Note that as the air-fuel mix is drawn into the cylinder, the air is expanding into a lower pressure chamber of the inlet stroke, so is adiabatically cooling and the fuel mist will form larger droplets that need more ignition energy (spark) to ignite, or maybe they are too big so need a flame from other smaller droplets igniting. These larger droplets will wet the walls of the intake and cylinder so the mixture is weakened form the planned mixture ratio, so again ignition becomes harder to achieve. Hot engines actually give some heat to the intake mixture and when running achieve an equilibrium, thus fuel mix is stabilised. Hot cylinder walls, etc. do the rest, and with normal running the higher speed of compression ensure the adiabatic heating of the mixture during compression - and reduced time for blow-by-leakage - ensure the fuel-air charge is OK for ignition when the spark fires.
So: a more massive (actually a higher rotational inertia) flywheel is a good thing for starting! (It can also help stabilise Idle running, when hot and ignition is more advanced, and fuel-air mix is normalised.).
Hope my waffle isn't too complicated and some are able to understand infernal combustion engines a bit better. Any experts can always correct my knowledge, which isn't perfect..., and I would hate to teach people the wrong information.
Enjoy!
K

Very informative, thank you. Your comments give rise to more thoughts to trying butane as a fuel, for this engine. Curious as to what the thoughts are on that.

 

[Ken Brunskill]

K, thank you for the very informative treatise on ring performance. While an experienced tool maker and engineer, this is my 1st internal combustion engine build proving that 'old dog can learn (want to anyway) new tricks. Wished may father and brothers were still with us, all good mechanics they would have enjoyed all this enormously.

Think that will be the last time I post from my phone . (may instead of my) is the kind of dumb errors that creep into the the sentence's.

 

[jquevedo]

Propane gas is cleaner to run so they say, for me it stinks worst than regular gas, does not provide lubrication to engine parts and in engines like this which depend on the gas/oil mix for lubrication, I think it would need an oiling device to work.


Wont work all the theory here but engine lacking of compression will benefit from higher power fuels like MAPP gas /Propane, RC alcohol nitro mix but there are ways to get around the low compression issue.

I removed pistons yesterday to find that rings have indeed rotated to the point where the gap in both rings are aligned.
In the pump piston, the two ring gaps aligned with the spark plug hole, in the case of the power piston the rings have aligned with the intake port..

Did some work yesterday in the rings and cleaning the engine inside, and today I have managed to ge4t three very decent runs using Coleman fuel mixed with a bit of synthetic 2 stroke oil.
I'm using a slightly larger diameter flywheel (0.250 over original design) but with all other dimensions per drawings, therefore increasing the momentum more than the mass.
Will work an idea on a new set of pistons and rings and see if that helps to solve the problem of low compression.
JQ

 

[stragenmitsuko]

Propane/butane will have the advantage that it's already a gas , not an atomised or vaporised liquid .
So all problems of running lean when cold , fuel condensing , wet spark plugs etc will be gone .
A needle valve in the intake from a small torch fi will be all you need to experiment .

No lubrication whatsoever so indeed some oil will have to be added .
After all this is basicly a two stroke engine , altough it has 4 strokes .

Ignition will need abt 1500 volts more compared to regular fuel because an air / propane mixture is
harder to ionise .

Air fuel ratio is 15.5-ish instead of the 14.7 we all know and love

 

[Richard Hed]

But I have more rubbish in my brain than knowledge... Too few are interested in the knowledge, well, that applies to the rubbish as well.
Ken

Tell me the rubbish then.

 

[Cogsy]

However, modern engines need to achieve at least some speed for the hall effect sensor to define the TDC of the crank to be able to determine the next ignition point, usually by rotating at least 80rpm or more. So a duff battery that gives you slow cranking on a modern electronically controlled, fuel injected car can develop a no-start condition with a very slow crank because the Hall effect sensor doesn't trigger.

Hall effect sensors work on magnetic flux magnitude and not the variation of the magnetic flux so they should work even at virtually zero rpm in theory. Anecdotally, I have had hall effect model ignitions fire at very low crank speeds when trying to manually determine ignition timing. At a guess, I would assume a low battery that gives a slow cranking speed is simply not producing enough current to energise the ignition system and simultaneously turn the engine over rather than the hall sensor not triggering.

 

[jquevedo]

Hall effect sensors in practice are as good as contact points, reed switches etc, they sense the magnetic flux and send a signal.
The delayed spark issue surfaces when the ignition system has functions like advanced spark control, the ignition system (not the hall sensor) needs time to determine when the spark needs to occur, been it the first spark and the subsequent ones based on some key factors like engine temperature and engine rpm's.
I have been working ignition systems for full size engines including Bosch systems for Ferrari cars and it is amazing how simple and reliable they are. Have done good progress with Micro/Mega squirt to handle model EFI injectors. Need some work in smaller sensors.

For slow running engines, I prefer basic systems with no advance spark control.. for 9 or 8 cylinder radials or any of the high speed engines I use ignitions with advanced spark based on engine RPM's.

 

[Ken Brunskill]

Propane gas is cleaner to run so they say, for me it stinks worst than regular gas, does not provide lubrication to engine parts and in engines like this which depend on the gas/oil mix for lubrication, I think it would need an oiling device to work.


Wont work all the theory here but engine lacking of compression will benefit from higher power fuels like MAPP gas /Propane, RC alcohol nitro mix but there are ways to get around the low compression issue.

I removed pistons yesterday to find that rings have indeed rotated to the point where the gap in both rings are aligned.
In the pump piston, the two ring gaps aligned with the spark plug hole, in the case of the power piston the rings have aligned with the intake port..

Did some work yesterday in the rings and cleaning the engine inside, and today I have managed to ge4t three very decent runs using Coleman fuel mixed with a bit of synthetic 2 stroke oil.
I'm using a slightly larger diameter flywheel (0.250 over original design) but with all other dimensions per drawings, therefore increasing the momentum more than the mass.
Will work an idea on a new set of pistons and rings and see if that helps to solve the problem of low compression.
JQ

Wonderful, congratulations! Very encouraging, my new rings are in the HT furnace as I write this, a new Pump Piston is in the works.

Nice that others are contributing informative commentary. Appreciate the discourse on Propane, Mapp gas, Butane, warrants a trial, possibly some collaboration to speed up revealing the results. Of course 1st having an operating engine.

 

[Ken Brunskill]

Propane gas is cleaner to run so they say, for me it stinks worst than regular gas, does not provide lubrication to engine parts and in engines like this which depend on the gas/oil mix for lubrication, I think it would need an oiling device to work.


Wont work all the theory here but engine lacking of compression will benefit from higher power fuels like MAPP gas /Propane, RC alcohol nitro mix but there are ways to get around the low compression issue.

I removed pistons yesterday to find that rings have indeed rotated to the point where the gap in both rings are aligned.
In the pump piston, the two ring gaps aligned with the spark plug hole, in the case of the power piston the rings have aligned with the intake port..

Did some work yesterday in the rings and cleaning the engine inside, and today I have managed to ge4t three very decent runs using Coleman fuel mixed with a bit of synthetic 2 stroke oil.
I'm using a slightly larger diameter flywheel (0.250 over original design) but with all other dimensions per drawings, therefore increasing the momentum more than the mass.
Will work an idea on a new set of pistons and rings and see if that helps to solve the problem of low compression.
JQ

JQ, curious to know if you measured the 'Ring Gap' at the 'Bore' diameter, if so what was it? As mentioned new rings were in the works, thought I'd share photos 1st is the Fixture - it has a .041" pin to establish the gap.
2nd is the HT Fixture simple Cast Iron Nipple two caps, the wood piece is to consume the oxygen, works splendidly-all that remains is a piece of charcoal.
3rd is the HT Fixture in the oven at 1400 F according to the analog temp meter.
All now cooling off in the oven - remove tomorrow when I finish the Pump Piston.

Regarding the use of some sort of gas, if anyone is interested I can provide the dimension for placing the 'oiler' hole such that it would be between the rings when the piston is at the bottom of the stroke (being that I redrew all the parts in Solidworks, it is not very hard to do a measurement), my thought is to make it a #4-40 at most, therefore able to be plugged with a set screw. Believe an oiler with a very small thru hole to be sufficient, anyone have thoughts on that?

 

[Steamchick]

Thanks for info about Hall effect devices. I got my 80 rpm min info from a company paper when I worked for a car company. So maybe there was some other reason they said 80 rpm min cranking speed so the ignition trigger would fire? Possibly software, for fuel injection? So no point firing sparks before fuel is introduced? I simply don't remember any more. I was dealing with starter motors, not ignition systems.
K

 

[bdolin]

Thanks for info about Hall effect devices. I got my 80 rpm min info from a company paper when I worked for a car company. So maybe there was some other reason they said 80 rpm min cranking speed so the ignition trigger would fire? Possibly software, for fuel injection? So no point firing sparks before fuel is introduced? I simply don't remember any more. I was dealing with starter motors, not ignition systems.
K
[/QUOTE

 

[bdolin]

I still have my Matchless G80 CS witn manual spark advance and magneto. My knee still hurts from trying to kick it over at full advance!