ESE's works engine tuner

[peewee]

some of this stuff seems to be way over my head. whats the advantages of screw on piston tops ?

[Michael Moore]

When you torch a piston you whip off the head and get your big screwdriver, remove the holed piston top and screw a fresh one on and you are back in action a short time.



cheers,
Michael

[Flettner]

You guys are so last year, (15 years ago)
Copper screw in top, built for my uniflow engine but never run. Clearly for the exhaust piston. Well finned underneath as to cool it best. These pistons were to run in the exhaust crankcases, fuel (petrol) air was at 6 to 1 ratio. Opposite crankcase were air only, subsequent mixing in the cylinder made the ratio out to approx 12 to one.

[F5 Dave]

some of this stuff seems to be way over my head. whats the advantages of screw on piston tops ?

Look back at old pics, I first saw on my phone and couldn't see the reverse dyke ring ledge. Ring can be limited in bulge and pin holes covered. I don't understand how they can be lighter.

[ken seeber]

Rings.
With the Adegnes’s proposal for a full 180 deg circumference exhaust port and the mutually complimentary 2 piece piston construction (eg Mark and others), it is timely to think about the rings & its matching piston design.
If we consider a series of rings with the same radial depth, there are subtle differences. In all cases, the primary sealing force is activated by the dimension X. Secondary sealing force is the same, given the same radial depth.

1. Rail ring. Simple, allows the top land to contact the bore and dissipate heat, does provide an opportunity to radius the crown edge for say the A & B ports and leave the edge sharp for the C port. It can be argued that it does not provide super sharp timing due to the leakage path due to the radial clearance of the top land to the bore.

2. Conventional Dykes ring. Generally positioned so that its top edge aligns with the curvature of the crown. Has more primary sealing force due to the increase in X, has no top land for heat dissipation, but also “sharper” timing. No opportunity for selectively radiussing the “crown” edge. Seemingly a feature for fixed ratio karts; virtually all Italian engines use Dykes rings. I’m sure they have been thoroughly “back to back” tested many times over the years and they are still being used. The well known exception to this is the Rotax Max, but it is to be noted that this has a plated bore, whereas the Italian motors use a CI liner.

3. Inverted Dykes. Maybe a better name would be a reversed or inside out Dyke. Te reality is that it is really just a rail ring with an inner shoulder to act as a retaining feature. Slightly heavier than a rail ring. Does offer the posssibility to selectively radius the crown edge in various locations and does allow top land contact with the bore. Does require a 2 piece piston to allow it to be installed. Also obvious is the fact that there must be some tight clearance control between the inner shoulder and the piston recess to provide adequate control of the ring expanding to a minimim degree; ie to prevent it expanding outwards and snagging into the super wide exhaust port with the resultant sadness. This requirement also means that any ring wear might prevent the ring contacting the bore, but I guess we are only talking about high performance engines here.

However, it’s all good stuff and gets the brains ticking.

[adegnes]

It just occurred to me, why stop at the exhaust port? I think I'm going to delete a couple of transfer bridges too, have the duct walls end 1mm or so outside the bore. Really hope this ring works.
In a rush to become friends with fusion360 and get this cylinder drawn up.

[OopsClunkThud]

I would think the inverted dykes would have the lip pointed down, otherwise the pressure on both sides of the lip cancel each other.

Also, does this offer the same resistance to flutter? Seems that if it lifts to the top of the slot it no longer has any area in X pushing it out, so same case as a standard ring.

[Flettner]

I miss the 'Ryger days' when it was none stop speculation and truly off the wall stuff here.
Ring design, interesting, keep it going, there has to be a better way.
I still like my ring in the cylinder idea but have zero proof of it's workability. I guess I should just try it. But it does revolve around a guided piston, like the epicyloid bottom end I have made would provide.

[SwePatrick]

I wouldn´t acually trust that new mumbo jumbo ring too much.

As you need some movement on the ring to let it grow in the piston, due to heat(matrialgrowth) and combustionpressure to seal it to the cylinderwall.
If you just restrict the ring in the piston to a certain limit, it probably would loose it´s seal to the cylinder.
And if letting the ring 'float' a little to follow the cylinderwall in different tempratures and pistonmovement(rocking) it can hook into a port.
It just needs a couple of hundreds of a millimeter to fail.

It will sure revolutionize.....
The speed one scraps the cylinders.

[adegnes]

Here's a variation on my "pinned" ring idea.



The ring is located with the hole in the middle of the 100% exhaust port.
The cylinder could be turned 90° to normal orientation and the pin could be pressed(or threaded) into the piston from the underside through a hole in the wrispin boss.
A conventional piston could be used, and as the exhaust side of the wristpin would never encounter any transfer ports, only that side would need to be blocked, maybe even just plugging the pin with something would suffice.

Watcha think? Mumbo jumbo?

I could happily spend the rest of my days failing trying "stupid" stuff.

[teriks]

Here's a variation on my "pinned" ring idea.



The ring is located with the hole in the middle of the 100% exhaust port.
The cylinder could be turned 90° to normal orientation and the pin could be pressed(or threaded) into the piston from the underside through a hole in the wrispin boss.
A conventional piston could be used, and as the exhaust side of the wristpin would never encounter any transfer ports, only that side would need to be blocked, maybe even just plugging the pin with something would suffice.

Watcha think? Mumbo jumbo?

I could happily spend the rest of my days failing trying "stupid" stuff.

Well, I have no input on ring design, but I have ran very wide wide exhausts, and the exhaust port oriented as you suggest.
Even without rings things got difficult around 90-95%. Better start smaller and work your way up.

[wobbly]

The reversed L ring design that was finally patented by Savice Ltd was tested with 100% bore T port ( no T ) and was reliable.
So the concept is workable.
I have suggested to Makr that combining that idea with no external pin bore holes as well,would be a real advance to the SOTA.
Adegnes - dont go overboard , cutting away the transfer septum's will lose all the directional control.
The streams are supposed to be coherent in shape as they exit the duct , having one big hole will create instant short circuiting and a crap scavenging regime ie the Leaning Tower of Frits
will fall over.

[adegnes]

The reversed L ring design that was finally patented by Savice Ltd was tested with 100% bore T port ( no T ) and was reliable.
So the concept is workable.
I have suggested to Makr that combining that idea with no external pin bore holes as well,would be a real advance to the SOTA.
Adegnes - dont go overboard , cutting away the transfer septum's will lose all the directional control.
The streams are supposed to be coherent in shape as they exit the duct , having one big hole will create instant short circuiting and a crap scavenging regime ie the Leaning Tower of Frits
will fall over.

I have a tendency to jump in.
But if my port walls end just shy of the bore in a sharp point to get that tiny last bit of area, shouldn't that retain the same directional control?
The A/B walls "traditionally" converge a bit into the bore, now they converge a tiny bit before it.

[Makr]

Thanks Mark. Here is that destruction picture I was talking about.
Attachment 339211

Are you going to combine that 'piston skirt that threads on' with Denver Lawson's inside-out L-ring that should make ring-guiding bridges superfluous?
Attachment 339212 Attachment 339213

Yes, although I am not going to use an L ring... that is patented. It will still retain the ring.

I am running at ElMirage this weekend, and then after I can tear the bike down and put the engine back on the dyno. Adegnes asked if I could try running no exhaust bridge, so I have some old sleeves I can put back in to see if it works. I have the piston domes machined. Just need to finish the skirts.

[Makr]

Since I am pondering piston rings and placement on the piston I have this thought that I don't think we have talked about.


Or maybe I just have forgotten.


We set port timing by the edge of the piston crown. Yet the ring is roughly 2mm down and is the real seal surface. Is our port timing off? I ask because if I made a regular dykes style ring that seals at the crown tangent point is the timing going to change? Does this matter? Anyone test this?