The Bucket Foundry

[Frits Overmars]

These are impressive. Look like investment castings made from a 3D printed sacrificial cores, judging by the witness of the series of lines. Agree, it might be the go for HCCI, but for the fact that it needs a skirt for port sealing. Perhaps one could do a composite design with a very thin skirt (eg 1 mm wall extruded aluminium tube). Easy to say, but quite a few issues to be addressed.

Fletto just reminded me of KISS, so I'd like to avoid a composite. But I did sketch a short closed-skirt piston for my FOS cylinder in a way that I could make it myself out of solid aluminium. Wall thicknesses are still very conservative, but that's all open to discussion.

[ken seeber]

Nice one Frits.

[WilDun]

Flettner, would backlash in the epicyloid gearing cause any problem with the rod if the clearance on the seal is tight?
Wasn't your Crecy' style piston/sleeve made of steel?

Looks like you are almost there Ken, looking good!

[Drew]

KISS, Jam nut, it works for rose joints and tie rods.
Attachment 324054

Vibration and loading on rose joints and rod ends is substantially less than what a piston goes through. But in the name of simplicity, a pin with a circlip just like a gudgeon would work.

[Flettner]

Yep. But there's one problem you'll need to solve: the ring gap can't be just anywhere, not if you wish to keep the piston ring in one piece.
How can you make sure that the piston doesn't unscrew itself, and that after unscrewing the piston and screwing it back on, the ring gap will still be in the same place?

I haven't found a solution yet, but I did think of a way to circumvent the problem: Using a split guidance for the epicycloid con rod will allow you to make the piston and con rod in one piece.

Yes I have thought of that too. But I wanted the rod to be made of 7075 and the piston to be hypereutectic alloy. Might be that this is not necessary but this is how it's going to be for the start anyway.
My plan is simple, attach the piston, then machine the piston, ring groove and then fit the ring pin. Sooner or later there will be no ring on the piston, it will be stationary in the bore running against either nikasil or chrome piston skirt.
We got to start somewhere

[Flettner]

Flettner, would backlash in the epicyloid gearing cause any problem with the rod if the clearance on the seal is tight?
Wasn't your Crecy' style piston/sleeve made of steel?

Looks like you are almost there Ken, looking good!

Yes, that's one issue I'm only too aware of, although Mazda Rotary engines use a similar system with an internal/external gear set to control the movement of their rotor, they seem to last.

[Flettner]

Fletto just reminded me of KISS, so I'd like to avoid a composite. But I did sketch a short closed-skirt piston for my FOS cylinder in a way that I could make it myself out of solid aluminium. Wall thicknesses are still very conservative, but that's all open to discussion.

Why solid? Wouldn't you want to cast one? What alloy would you machine it out of?

[Frits Overmars]

Why solid? Wouldn't you want to cast one? What alloy would you machine it out of?

No, I don't want to cast one and then have everybody here commenting on my knees .
Besides, I fear that casting won't yield as dense a material. Also, I don't think that I could cast the thin walls that would be required for lightness, so I would have to machine it anyway. And finally, the shape I drew can be machined out of solid in less time than you would need to make a mould.
What alloy? That is not my field of expertise; I'd have to ask around.

[Flettner]

No, I don't want to cast one and then have everybody here commenting on my knees .
Besides, I fear that casting won't yield as dense a material. Also, I don't think that I could cast the thin walls that would be required for lightness, so I would have to machine it anyway. And finally, the shape I drew can be machined out of solid in less time than you would need to make a mould.
What alloy? That is not my field of expertise; I'd have to ask around.

Just that I always thought the best alloy for pistons was hypereutectic alloy, low expansion rate, and cast. You could machine one from a hypereutectic block I guess if it were available? But it would only be cast in the first place anyway. Second best would be an alloy that say wossner forge theirs from, I guess you can get that in solid bar form. Looking at my epicycloid crank system, the piston would be that thin anyway expansion would likely not be a problem. No big heavy pin bosses to expand. Ken might know someone that could cast a piston for you. Some pistons I made once, out of large truck piston bosses, I spark eroded the center out. Made and electrode from copper, worked well. That truck piston alloy was I think approx 24% silicon (hypereutectic). Neil lickfold will now about this.

[Grumph]

Best information I have is LM13 for castings (high silicon) and 2618 for forgings.
You could possibly sidestep a little by looking at Rapid Solidification alloys.

Bradley gives RSP Technology in the Netherlands as the experts - already doing a range of pistons.
Worth asking if they sell barstock.

www.rsp-technology.com

[Frits Overmars]

You could possibly sidestep a little by looking at Rapid Solidification alloys. Bradley gives RSP Technology in the Netherlands as the experts - already doing a range of pistons. Worth asking if they sell barstock. www.rsp-technology.com

RSP is delivered as extruded barstock but it doesn't come cheap. We've used RSP with 30% silicon for our 6,5 cc model engine pistons since the year 2000.
RSP even modified the alloy for us, increasing the iron content a little in order to make it harder. Our small pistons are manufactured through electro-erosion.

[ken seeber]

PISTON ALLOYS:
LM13. Basically eutectic alloy, 10-12% Si, 200 MPa UTS (T6)
Meteor and other Italians. Hypereutectic G-AlSi18MgCuNi-P, 17-19%Si, ?? UTS
STRIKE Hypereutectic A390, 16-18% Si, 310 MPa UTS (T6)

[husaberg]

Vibration and loading on rose joints and rod ends is substantially less than what a piston goes through. But in the name of simplicity, a pin with a circlip just like a gudgeon would work.

Drew have a look at a few conrods on foul stroke multis
ps the nut was to go on the conrod.

[Grumph]

PISTON ALLOYS:
LM13. Basically eutectic alloy, 10-12% Si, 200 MPa UTS (T6)
Meteor and other Italians. Hypereutectic G-AlSi18MgCuNi-P, 17-19%Si, ?? UTS
STRIKE Hypereutectic A390, 16-18% Si, 310 MPa UTS (T6)

This graph is relevant. from The Racing Motorcycle Vol 2 with thanks. I suspect if RSP was cheaper, we'd see a lot more of it.

[husaberg]

Nearly all forged car or foul stroke motorbike pistons are either
High silicon is 4032
or
Low silicon is 2618.
The 2618 is stronger.

MTC use or at least used to use, a low silicon alloy that has incredibly small cold clearance I have no idea what it is.
Also interesting to see that the piston technology is heading back to ferrous metals.
You could say, they have turned full circle