ESE's works engine tuner

[Nath88]

Pretty hard - in a two-stroke. Saab did quite some spark plug ionisation monitoring research with good results, but that was in a four-stroke.
In a two-stroke the squish action is much more violent and the concentration of ionized gas at the plug gap depends more on squish velocity than on pressure.
Here is some reading on the subject.
Attachment 331522

Good light reading material there thanks Frits, looks like trying to correlate the ion current to the cylinder pressure for the two-stroke would be flawed, hopefully the presence of flame can still be detected.

It isn't difficult to do electrically, I've run a model of the circuit to ensure I don't fry the CDI, will need to isolate the coil from the frame, then add the sensing circuit in between.

[wobbly]

Yes I would think that the small diameter plug body, in the longer 19mm size would for sure pull less heat out of the chamber
and be easier to cool.
But you would need to do the calculation of exposed body area in the chamber divided by the threaded contact area in the insert to see if any inherent advantage is present.
But the nose configuration is the same trick fine wire electrodes, so no combustion performance issues to be concerned with.

[Jannem]

We want to keep the squish area boundary layer and thus the trapped end gases cool - you work it out, I have but aint telling.

I appreciate the hard earned experience you are sharing and don't expect getting all the answers laid out.

I'll resort to a shadetree solution of putting unpleasant looking burr finish to the squish surface. Adds surface area for cooling and helps wet flow.
Whether it would be a good idea to do that to the piston outer perimeter, I can't weigh the pros and cons. Similar rough finish could help the squish wet flow, but would add surface area to the piston to absorb more heat to the sides. On the other hand, polished surface might leave it somewhat wet and charge could be burning on the surface longer. Or evaporate, compress and detonate. I'll try a matte scotchsbrite surface there as a compromise with polish in the center.

Coatings are out for us anyway, but this is just an elbow grease kinda thing.

[Jannem]

We had to go with a compromised piston, which has higher than desirable dome. Piston top thickness is however 3.5mm. Thinking about machining a flat on top to lower the dome for improved flow and reduced combistion surface area. 44mm piston.

What would be a safe amount to take off? Are there reasons why this would be simply a bad idea?

If I can make it flat all the way to the squish pad, would you round off the corner at the piston top or leave it sharp?

[Frits Overmars]

Piston top thickness is 3.5mm. Thinking about machining a flat on top. 44mm piston.
Are there reasons why this would be simply a bad idea?

Yep, 3,5 mm is already too thin for a 44 mm diameter piston.

[Jannem]

Yep, 3,5 mm is already too thin for a 44 mm diameter piston.

That's it then. Thanks!

[chrisc]

A shout out of thanks to Guy Hockley from the UK for helping me get my hands on some Vinamold to get a proper look at these SX50 ports. What a good dude. I've found it hard to get information on the SX50 online so I thought I'd post some up for those interested.


I just used a small pot and my camping cooker to melt it down. I held it about 250mm above the flame because even at the lowest heat, the vinamold melted quickly. I didn't want to burn it.
I stuffed up my first attempt by not putting a screw into the vinamold so I could get it out easily. I also left it overnight before trying to get it out. Took a while to evacuate the failed attempt I found it easiest to get out when still a little warm, maybe 15 minutes after pouring (it was 4 degrees in the shed too).





I started to get the hang of it though not as good as this other white version I found on the internet:


My first (very unprofessional) impressions are that the B transfer ducts could move further around to the C port to square up the inner wall. The C transfer duct is super duper skinny in the bend. The B port roof angle is quite flat. The B transfer inner duct radius is very square and unlike the teacup shape which has been recommended. The A transfer duct inner radius is comparatively much better although has a flat in the middle of the 2 radius. The aux ex port entry is quite flat unlike the big hook of the RSA125. There are weird bumps in the A port wall which can't be good for flow direction.

Also found this port rubbing online here: link . I took some cord width measurements of the ports
Ex port: 28mm, Ex aux ports: 10mm, A port 16mm, B port 16mm, C port 12mm. I measured the transfer port height at 9mm also, not the 10.5mm of the rubbing. The 10.5 doesn't make sense to me. If you add the height of the aux port and port top to deck height (9+22=31mm) is the same as the transfer port top (31mm) meaning practically no clearance between ex aux port and A port according to the rubbing.

[peewee]

you can put a light coat of oil on the passage walls for easier removal of the vina

[dark art]

[QUOTE=chrisc;1131053519]

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The cylinder "port-map" in the pic can be from a older version of the ktm50 or is probably modified, I can´t remember all the dimentions of the stock cylinder but the main exhaust port width is around 28mm, definitely not 32mm.

The 31mm may not refer to "deck height" but to top dead center (TDC), wich may not be the same.

[adegnes]

A shout out of thanks to Guy Hockley from the UK for helping me get my hands on some Vinamold to get a proper look at these SX50 ports. What a good dude. I've found it hard to get information on the SX50 online so I thought I'd post some up for those interested.


I just used a small pot and my camping cooker to melt it down. I held it about 250mm above the flame because even at the lowest heat, the vinamold melted quickly. I didn't want to burn it.
I stuffed up my first attempt by not putting a screw into the vinamold so I could get it out easily. I also left it overnight before trying to get it out. Took a while to evacuate the failed attempt I found it easiest to get out when still a little warm, maybe 15 minutes after pouring (it was 4 degrees in the shed too).





I started to get the hang of it though not as good as this other white version I found on the internet:


My first (very unprofessional) impressions are that the B transfer ducts could move further around to the C port to square up the inner wall. The C transfer duct is super duper skinny in the bend. The B port roof angle is quite flat. The B transfer inner duct radius is very square and unlike the teacup shape which has been recommended. The A transfer duct inner radius is comparatively much better although has a flat in the middle of the 2 radius. The aux ex port entry is quite flat unlike the big hook of the RSA125. There are weird bumps in the A port wall which can't be good for flow direction.

Also found this port rubbing online here: link . I took some cord width measurements of the ports
Ex port: 28mm, Ex aux ports: 10mm, A port 16mm, B port 16mm, C port 12mm. I measured the transfer port height at 9mm also, not the 10.5mm of the rubbing. The 10.5 doesn't make sense to me. If you add the height of the aux port and port top to deck height (9+22=31mm) is the same as the transfer port top (31mm) meaning practically no clearance between ex aux port and A port according to the rubbing.

Great stuff! Much appreciated!

[F5 Dave]

I put the tape on the port faces of a clean bore then a light spray of silicon spray. Overpour a little so you have something to hold onto and ties them together at the right spacing. Easy peasy to wiggle out.

[katinas]

Hi,

Sorry for so long time without info, but just want to test as more as I can before say something.

Now just current results without details :

Done about 500 km.

Testing three different types of cylinders ( two from Honda NS, and last from Honda Cr 125 86") and three different types of pistons.

Very interesting, so different type, but result was the same. The power feels like 20-25 Hp, no more. Power band 8600-11500 rpm. ( harmonizes with pipe dimensions). It revs, but feels that engine want to overcome something.

First piston heavily seized in second gear at 100 km/h, but luckily left hand remember old habit ( absolutely my fault, cold engine, so small clearance ( 0.3 mm- top piston ) for 2618 aluminum, oil fuel ratio 1 to 200) So with Ns cylinder all ended just starting the tests.

Made new piston 58 mm.- 1 mm bigger than NS ( 133 cc) and rygerised Honda Cr 125 1986 cylinder ( very different from NS - Good thing is bigger reed cage with six petals, wrong things two exhaust windows and iron sleeve) Again the power no more than 20-25 Hp

Then made plate to close central intake window, just left side intakes to transfers. Power up to around 30 hp but no more and very clean carburation at top.

Then exhaust stinger increased from 23 to 29 mm. and again power little bit up, but with more retarded ignition. Take of intake window plate, power drops insignificantly.

Then decided to lower compression from 13.8 to 12.5 and results feels immediately, is like 10 hp added. Added 23 mm sleeve to 29 mm stinger but no big difference just feels more tension . Of course this is only my sensations, but in comparison with other motorcycles now I think power is 35-40 Hp. I feel sorry that not lowering compression on the first NS cylinder (compression was 14) before seize, and just left only consideration.

From mechanical side no issues (most surprises for me after seize ), steel tube and small aluminum cylinder good pair ( just small scratches from some sand particles or something) and the PTFE seal amazingly in good shape.

There is so much other things left to try its very complex and so much different combination exists. Now I think that Ryger type engine with clever people can achieve 60-65 Hp


I'll post pictures later and more detail info.

[F5 Dave]

Thank you for reporting very interesting.

[adegnes]

Thank you for reporting very interesting.

+1

.................

[TZ350]

Yes, very interesting.