ESE's works engine tuner

[Flettner]

Wobbly, what down angle on exhausts? I wrote it down somewhere, probably on a peice of wood, then promptly used it for pattern making somewhere.
27 degees rings a bell.
The square bore and stroke twin port, water cooled, powervalve cylinder emerges. Straight ports this time not curved like the air cooled cylinder. Hold down studs come up from underneath so free hand in where the exhausts go, no need to compromise for nut fitment or room for a spanner.

[husaberg]

Just how closely do you want the expansion rates of piston material and cylinder material to match? The ideal would be 1 to 1 if piston temperature and cylinder temperature were equal.
But they're not. The piston gets a lot hotter than the cylinder, so its expansion rate should be lower, like a steel piston in an aluminium cylinder.
It does work on foulstrokes. The problem is that the dome surface temperature of the steel piston would be sky-high, and two-strokes do not like that.
Foulstroke manufacturers get away with it by cooling the piston from below with multiple oil jets. In crankcase-scavenged two-strokes we cannot have that luxury.
Attachment 355131

To deal with this we build in taper ,ovality, cam grinds and cut outs even splits and in old ones wire winds and also expansion strips or fillets as in your pic
As well as the oil jets they use more rings, oil on the cylinders and a cooling stroke with much less output per area.
then you throw in the slippery coating and the groves for oil.
I am not sure on a 2t how much heat is transmitted from the rings but on a 4t from what I have read on its far more than most people appreciate.
In an ideal world the 4t skirt will expand just enough to increase the surface area to again be able to transfer the heat when needed.
I was trying to find the clearance on a modern 4T big twin that was mentioned the other day but it was tiny, but then again so was its output/liter.
(edit)Victory air-cooled engine 2nd gen was 25 micron or 1.5 thou. On a 850 cc cylinder 101mm bore.

The piston in your pic
A late model MX bike is now very similar. just with more aluminium to bake up for the 1/3rd strength
My son races YZ450f Supermoto, even with its GYTr twin oil jets the fully synthetic oil changed at about 30 minutes, the piston is good for 8 hours the camchain less then 4.
no big deal other than how bloody much harder it is to do than a 2t is.
3x the cc of a RSA and only a few more hp.

the cutouts below the bottom ring land are to get the pin in and out

[wobbly]

Neil , 25* is optimum.
And the other posts mentioned point is that the majority of heat dissipation from the piston ,out to the bore in a 2T occurs on the bottom ring seal face.
The very first sign of deto starts at this surface - resulting in the term " power deto " coined by Franco Drudi of TM Championship winning fame ( my boss ).
As this process creates free radicles that start eating away at the hottest surfaces trying to recombine the single free electrons that are a result of the detonation phenomenon.
Creating deto uses up a huge amount of the available fuel energy , and this is what we use when data logging the EGT , as it initially flat lines with the first over lean jet change
then drops with the next.

[Flettner]

Best I write it on the shed wall, so I can't lose it in the future. ��
Thankyou.

[katinas]

Steel pistons with iron cylinders were used in Anzani radial engines from 1909.
Later British Anzani produce very interesting two stroke boat racing engines, with combined piston port and rotary intake through the center of crank webs.

[Niels Abildgaard]

Steel pistons with iron cylinders were used in Anzani radial engines from 1909.
Later British Anzani produce very interesting two stroke boat racing engines, with combined piston port and rotary intake through the center of crank webs.

Where have You found these pictures or engines?
The boat engine is interesting and looks like a Trabant but with much fewer parts.

[katinas]

Where have You found these pictures or engines?
The boat engine is interesting and looks like a Trabant but with much fewer parts.

I took piston pictures in the Italian Air Force Museum at Vigna di Valle, on Lake Bracciano. I went to the museum with my son this year, because he is very interested in military planes and especialy wanted to see the real, fastest red hydroplanes from "Porco Rosso". Apart many interesting things, unfortunately I didn't see a single two-stroke engine.
Later at home checked Anzani and found this https://www.boatracingfacts.com/foru...Engines/page30

[mike schmidt]

Scrolling though Kiwi Bikers this morning and the pictures of the Anzani crankcases caught my eye. First think that came to mind was that someone in Europe was epoxying them up just like the ones in my shop. Then I read further and found out the pictures were off Boat Racing Facts. The pictures were posted by John Taylor. A few years ago he got sick and all the Anzani parts were sold to Jim Hunter, a friend of mine. They are in my shop for restoration.

Small world.

[Mollihead]

At the moment I’m searching for a piston fitting to 50mm cylinder.
14mm wristpin
Piston ring at 6 o‘clock. Max 1mm thickness.
Compression height 28-30mm
Cylinder is Nicasil 50mm stroke

Any suggestions?

The piston belonging to the cylinder is from Mahle.
Big chamfer around wrist pin hole which favours short circuiting between Exhaust and A-transfer

[Wos]

At the moment I’m searching for a piston fitting to 50mm cylinder.
14mm wristpin
Piston ring at 6 o‘clock. Max 1mm thickness.
Compression height 28-30mm
Cylinder is Nicasil 50mm stroke

Any suggestions?

The piston belonging to the cylinder is from Mahle.
Big chamfer around wrist pin hole which favours short circuiting between Exhaust and A-transfer

Have a piston from italkit here with ringgap at oposit to main ex

Measured for a quick look comp hight..25

Its from a big bore kit for minarelli am6

But maybe you should have a look at wössner

https://www.woessner-kolben.de/fileadmin/Downloads/Kataloge/Motorrad_Inhalt2018%20print.pdf

[diesel pig]

At the moment I’m searching for a piston fitting to 50mm cylinder.
14mm wristpin
Piston ring at 6 o‘clock. Max 1mm thickness.
Compression height 28-30mm
Cylinder is Nicasil 50mm stroke

Any suggestions?

The piston belonging to the cylinder is from Mahle.
Big chamfer around wrist pin hole which favours short circuiting between Exhaust and A-transfer

Yeah, Wossner and other aftermarket piston manufactories do over size big bore pistons for 85cc MX's that might be the go.

[Mollihead]

I do have Wössner and Wiseco for Suzuki RM85.
But they both have a compression height of 27mm which is only usable for me in case I mill down the casing by 1mm.
Want to avoid that

[husaberg]

I do have Wössner and Wiseco for Suzuki RM85.
But they both have a compression height of 27mm which is only usable for me in case I mill down the casing by 1mm.
Want to avoid that

Honda cr85/100 have a crown height of 24mm
https://www.mitaka.co.uk/piston.php?id=2

there are old school rm100 as well that were 50mm ish based on the 125cc air cooled rm

or YZ is given as being
26.5
https://www.mitaka.co.uk/piston.php?id=78

or troll through Rolfee
https://www.pvlsverige.se/vrm/kolvar/kolvar.html

[Wos]

This is italkit vertex... look at last picture to clarify Dimensions 😉

Comp hight 25,2

https://www.langtuning.de/Italkit-Ra...m-Kolbenbolzen

Comp hight 28 but 12mm pin
Maybe change needle bearing 😉

https://www.langtuning.de/LT-Performance-1-Ring-Kolben-90-ccm-50-mm

[Mollihead]

This is italkit vertex... look at last picture to clarify Dimensions 😉

Comp hight 25,2

https://www.langtuning.de/Italkit-Ra...m-Kolbenbolzen

Comp hight 28 but 12mm pin
Maybe change needle bearing 😉

https://www.langtuning.de/LT-Perform...n-90-ccm-50-mm

I already ordered this piston and sent it back after I found out that the piston is too short for 50mm stroke. Exhaust port opened at TDC.

The only piston I found is a Polini Evolution P.R.E
Ordered it with 49,935 and received one with 49,915 diameter
Now I don‘t know whether I should give it a try with 8,5 1/100mm clearance…