ESE's works engine tuner

[Jan Van Hamme]

If you do it from scratch, why dont you take a domed, single ring piston?

Cant remember any advatage of the flat ones...

Then positioning ring gap in the middle of c port...you are more free doing minimum bridges between b and c ports...

Have a look at oler yamaha yz pistons
Or on suzuki rm 125...we use wössner too..

Exhaust t port?...the bridge is a weak point...not as sturdy as triple port layoutļ

Just my two cents ��

Wolfgang

Hi Wolfgang, thanks for your reply.

It's an RD125LC. I've chosen to limit my rpm to 10,000 rpm.
If I cut out the bottom of the skirt (like with the old YZ125H), there's not much support left against piston tilt.
I'm thinking of making my own windows (two or three).
That way, I'll have some surface area left over to provide support against tilting.
That's why I opted for two piston rings, for the engine speed and a bit more resistance to rattle.

It's a VHM connecting rod (110 instead of 105).
I haven't found any 56mm pistons with two rings, a dome, a 15mm pin diameter offset by 1mm, and a lower compression height that I can shorten or drill holes in (cylinder intake reed valve).
Wössner did have them. That's why I was forced to use the flat piston.
The plan is to install a torroid insert.

On this piston, the ring gap of both piston rings is in the center of the C port. One is directly in the center, the other a millimeter off center.

A single exhaust port (70% and safe roof) is sufficient for blowdown and low timing for the intended power and rpm.
Therefore, I would opt for a T-port or triple exhaust port.

I'm not sure if the distance between the exhaust and the A-port is large enough to prevent shortcutting.

Vriendelijke groeten,
Jan

[Wos]

Hi Wolfgang, thanks for your reply.

It's an RD125LC. I've chosen to limit my rpm to 10,000 rpm.
If I cut out the bottom of the skirt (like with the old YZ125H), there's not much support left against piston tilt.
I'm thinking of making my own windows (two or three).
That way, I'll have some surface area left over to provide support against tilting.
That's why I opted for two piston rings, for the engine speed and a bit more resistance to rattle.

It's a VHM connecting rod (110 instead of 105).
I haven't found any 56mm pistons with two rings, a dome, a 15mm pin diameter offset by 1mm, and a lower compression height that I can shorten or drill holes in (cylinder intake reed valve).
Wössner did have them. That's why I was forced to use the flat piston.
The plan is to install a torroid insert.

On this piston, the ring gap of both piston rings is in the center of the C port. One is directly in the center, the other a millimeter off center.

A single exhaust port (70% and safe roof) is sufficient for blowdown and low timing for the intended power and rpm.
Therefore, I would opt for a T-port or triple exhaust port.

I'm not sure if the distance between the exhaust and the A-port is large enough to prevent shortcutting.

Vriendelijke groeten,
Jan

Ok jan

I stuck with bore of 54.5 for a 125cc

But we run a 125 with adaptet reed valve to cilinder that has down skirt a cutout...and 2 Windows to, with only one ring...absolutely no problem...the wössner is stiff enough...35 h no ploblem


...doing a printed cilinder...wow ...dont you think about changing bore and stroke to square?
...every kind of pistons avaiable...and next to best bore stroke ratio...

Some Pages earlier frits gave a rule of thumb, about minimum space between ports...

Formula was bore x 0,044

If this rule is applyable to bridge between Ex and A port...you should be save



Keep us informed about...especially printing your dream cilinder!

Wolfgang

[diesel pig]

Ok jan

Keep us informed about...especially printing your dream cilinder!

Wolfgang

I would like to second that. Please keep us informed about your project. Metal printing is very interesting!

[Jan Van Hamme]

Ok jan

I stuck with bore of 54.5 for a 125cc

But we run a 125 with adaptet reed valve to cilinder that has down skirt a cutout...and 2 Windows to, with only one ring...absolutely no problem...the wössner is stiff enough...35 h no ploblem


...doing a printed cilinder...wow ...dont you think about changing bore and stroke to square?
...every kind of pistons avaiable...and next to best bore stroke ratio...

Some Pages earlier frits gave a rule of thumb, about minimum space between ports...

Formula was bore x 0,044

If this rule is applyable to bridge between Ex and A port...you should be save



Keep us informed about...especially printing your dream cilinder!

Wolfgang

You're absolutely right. I'd read in Frits' columns and OneDrive that oversquare engines aren't good for two-stroke engines (though they are for four-stroke engines).

So I looked into making a crankshaft with a 54-stroke stroke instead of a 50-stroke, which, as you rightly point out, would also allow a wide range of pistons to be used.

The original crankshaft webs are 87,8mm in diameter. The crankcase has a 89.8mm diameter.
I'd have to mill out the crankcase to make room for the increased stroke.
This would put me too close to the holes used to hold the crankshaft halves together. There wouldn't be enough "meat" left there after the milling.
So, there went my hope of making a crankshaft myself to square up the engine.

I'd read on other forums that the auxiliary exhaust ports on the RSA only came very close to the A transfers over a very short distance.
They wrote that it was very critical to make that close-in zone longer. It was also pointed out that the distance between the main exhaust port and the A transfers needed to be much greater.
I looked at photos of an RSA cylinder, and they do indeed stay far away from the main port. How far?
As you rightly mentioned, I also noticed that Frits explained that formula a few pages back.
Because of those earlier photos and the larger distance at the RSA than the formula, I started wondering... would 5.57mm be enough?

By creating a 3D-printed cylinder, I'm trying to combine everything I've read over the years by Jan Thiel, Frits Overmars, Wayne Wright and try to apply it by and with Engmod2T from Neels Van Niekerk to the possibilities and limitations of an RD125LC.
As a hobbyist, I'm sure there will still be many obstacles in my project.

Working on my motorcycle like this makes me realize how incredibly impressive the knowledge and experience these people possess, what they've developed and achieved.
As I once wrote, their combined experience could fill an entire galaxy.
I haven't yet reached the level of the first ridge on their shoe soles (and for some, even their sandals). Nor do I have the ambition to do so.
I'm glad they, and people like you and others, are helping me through this digital means.

Groeten Jan

[bad'rule]

Re: Wos,
Have you checked on DT125E piston

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