ESE's works engine tuner

[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 54,5 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

Sent from my RMX1911 using Tapatalk

[Jan Van Hamme]

Re: Wos,
Have you checked on DT125E piston

Sent from my RMX1911 using Tapatalk

A DT125 has a 16mm piston pin diameter.

My VHM connecting rod has a small-end bore for a 19x15 needle bearing.

19x16 doesn't exist. I briefly considered filling the space with loose needles or using adapter bushings, but I opted for a commonly available silver-caged needle bearing measuring 19x15x19,5.

Groeten Jan

[Wos]

125 lc is without ypvs system?

All parts for are still available... ��

Yz 125 1983 had powervalve too...

https://mxlocker.com/product/1983-ya...m-bore-y-ITDol

[Jan Van Hamme]

125 lc is without ypvs system?

All parts for are still available... ��

Yz 125 1983 had powervalve too...

https://mxlocker.com/product/1983-ya...m-bore-y-ITDol

It's an RD125LC-10W. They don't have a power valve.

Because of the higher power I'm aiming for, I wanted a stronger, yet lightweight connecting rod.
I ended up with a VHM connecting rod. So the standard piston parts from a DT or RD won't fit.
The footprint of a YZ125 cylinder doesn't fit on my crankcase.
I also want the cylinder to look like the original on the outside.

I've already bought the VHM connecting rod, three Wössner pistons, and needle bearings.
Thanks for the input, but my main concern is the distance to avoid an exhaust shortcut.

[Wos]

Chance to adapt the ypvs to your print 😉

[wobbly]

JVH, as your engine will be developing a low bmep, the pipe diffuser will be nowhere near SOTA, and thus will not be generating a huge depression around BDC.
Honestly I dont think you need to be worrying about short circuiting, as long as the A port front wall is radially pointing sufficiently back toward the boost port.

[Jan Van Hamme]

Honestly I dont think you need to be worrying about short circuiting, as long as the A port front wall is radially pointing sufficiently back toward the boost port.

That's the answer I needed to clear up my doubts and concerns and move forward with my Solidworks design.
This is the exhaust I'll be using. It's not the same as the one I uploaded in my Pack file to the Engmod2Tgroup.
Thanks again

[wobbly]

JVH, there is alot of residual Blowdown pressure, shown by the bump at TPO - this will be reversing flow down the transfers.
I assume this is a function of the single Exhaust port and conservative timing to help front side.

[JanBros]

a question about carb's. I have 4 engines for my MX-mopets, and now I've bought a whole lot of used incomplete Dell Orto PHVA and PHBN carb's very cheaply- over 20 of them, enough to make spare carb's so I have for each engine at least 2 identical carb's so I can quickly swap them when we are having carb troubles during races.

Since I had to put everything together myself, I had to figure out all the settings myself, and the ones I've selected are working fine, except one thing gives me some troubles : when closing the throttle after full open and the engine needs to come back to idle, they keep idling at arround 2700rpm , allthough after starting and warming up they idle fine at arround 1600. stop the engine and restart immediatly and they idle fine again. I've tried idle jet's from 30 to 40, throttle slide cuts from 10 to 50, different needles, but on some carb's the problem stays . but they work fine when the mopeds are racing.

anyone have an idea of what exactly is the cause of this and how to fix it ?

[wobbly]

A carb " hanging up " above idle after reving is always one of four things.
First is the idle circuit is too lean, where is the idle air screw set ? It should idle and instantly transition best between 1 1/4 and 1 3/4 of a turn - outside this range the pilot needs changing.
Second is the throttle cable has insufficient free play - I like at least a couple of mm of movement on the cable end inside the adjuster screw.
Next is that when reving it, the fuel level is dropping due to the float valve being too small, thus leaning out the fuel ratio. Once the bowl fills again at idle with no load, it returns to a normal A/F.
Lastly is the possibility that once the engine is warm, it has a case leak thru a gasket or seal.

[JanBros]

A carb " hanging up " above idle after reving is always one of four things.
First is the idle circuit is too lean, where is the idle air screw set ?
depends on the idle jet : small ones almost full in, big ones full out. the 30 was too small, the 40 way too big.


Second is the throttle cable has insufficient free play - I like at least a couple of mm of movement on the cable end inside the adjuster screw.
I'll check
Next is that when reving it, the fuel level is dropping due to the float valve being too small, thus leaning out the fuel ratio. Once the bowl fills again at idle with no load, it returns to a normal A/F.
I'll check the fuel flow, but I'm just over 9BHP with the 70's (at +/- 8500), so they are not exactly in need of gallon's of fuel.
Lastly is the possibility that once the engine is warm, it has a case leak thru a gasket or seal.
I don't thinck this is the problem, as it's on more than 1 engine, even on engines that have raced a couple of 4-6h races without any problem's.

It should idle and instantly transition best between 1 1/4 and 1 3/4 of a turn - outside this range the pilot needs changing.
it responses to the air screw, but it might be (so not sure) that the problem is I do not find settings that allow the slide to go down enough and somehow the needlejet is also influencing the idle mixture. could the problem be the mixture tubes ? as I have many different ones and selected the ones that were most common (so swapping them out) so I could have carb's with everything exactly the same for each engine. mostly I'm using the 209GN mixture tubes.

[wobbly]

My instant response is that is a 4 stoke emulsion tube.
With hardly any exception ( a couple of RD Yamaha's ) NO 2T has air corrector holes in the tube - they use a shroud in the bore.
So now we are off on a whole new tangent, especially as you have the issue of the needle/tube combination affecting idle - a major pointer, that should not happen right there.