Two stroke cylinder casting.

[Tjark]

Jo, the cylinders I am working on will be for a racing moped.
Over here are two moped engines very popular and these are the Minarelli AM6 and the Aprilia.
A friend of me is competing in this class with a Minarelli AM6 for hobby.
He’s not driving all the races, only those close to his home.
He also is 15 years to old and minimal 15Kg to heavy.
But in all the races he drove this year he finest in the top 5.
So for next year we will try to make a new cylinder with a different transferport and exhaust  shape.
The core boxes for the transfers and exhaust are ready and tested, see the pictures
Now the boost ports and water jacket are in progress as the outside.

  Tjark.

[lohring]

Hi Tjark
Have you considered Calvin's method of making cores?  He calls them spider cores and would seem to be better at maintaining the relationship between the transfers and the cylinder bore.

Lohring Miller

[Tjark]

Hello Lohring,

I have considered this way off working.
It shure gives always the good shape off the transfer ports in relation to the bore.
But it’s not as simple as it looks to make this.
I have my self no CNC machinery.
A friend of my has but then you have to draw this in 3D and convert this to a step file.
For me also not easy.
I make them now with some help of some original ports what I fill with melting rubber, then change the shape I think will work better and make some core mold’s by poring the melting rubber port shape’s in a couple of pieces with a polyurethane.
I am not planning to make great series off them so this will do I think.
Maybe I get some better ideas for this problem  in the coming time, whe will see.
Get these days a lot off ideas from professional molds, because  I am casting a lot off parts for a professional engine builder these days to generate  some pocket money for the hobby.

  Tjark.

[lohring]

I'm also working (very slowly) on two stroke cylinders.  I also have only manual machines.  My plan was to build a model of the cylinder with separate sections at the transfer and exhaust port heights.  It could be assembled then the passage shapes could be modeled in clay.  After disassembling the parts again they could be used as the male plug with the passages attached for the core box mold.  I have done a little lost foam and sand casting in my foundry but planned to use lost wax investment casting for my cylinders.  They are only 26 cc, smaller than yours.  My cores would be soluble wax that's dissolved out before investing the cylinder.

Lohring Miller

[Tjark]

I am working also on a water cooled  version of  Zenoah cylinder with a friend of me.
The problems with those cylinders is the base and the transfer port shape.
This is how we look at it at the moment.
I would like to make the transfer passage in the same shape as for the 50cc cylinders.
The bolds to connect the cylinder to the crankcase I would like to put inside the water cooling jacket.
This way the cylinder will not crack at the base, this is what I have often seen with the originals.
The pattern making is an issue where I am struggling with, the outside patterns are no problem but making the pattern  for the core’s are difficult for me.
This year I got some help from a professional  German   pattern maker, and this gives a big relieve.
The only problem is that I do not see him that often so progress is going slow.
But at the end we will getting there.
The casting I do is always in oil bonded   sand with SS core’s.
I think for the small Zenoah cylinders this will also be no trouble.

   Tjark.

[lohring]

I'm very familiar with two investment cast 26 cc engines.  The M&D cast cylinder has passages and porting that's very similar to a standard modified Zenoah.  However, because of the inner wall on the transfers it develops at least 1/4 more horsepower.  I own one and have dyno results.  The other engine I'm familiar with is the Quickdraw.  They recently upgraded their transfer port shapes and added some more power.  We ran their older design in 2004 for an RC world boat speed record that still stands.  Look at the M&D cylinder here:
http://mddracing.net/md-rc-boat-racing-engines--parts.html

The Quickdraw site is here:
http://www.quickdrawengines.com/Page_204.html

I have more pictures and information if that would help.

Look at how these engines solved your problems.  The M&D extended their bolts above the transfer passages for a much tougher cylinder.  I've abused mine seriously and it still runs with a new short block.  The Quickdraw relocated their ignition to allow more curved transfer passages.  Overall, the Quickdraw has the best piston port design I've seen with very large ports.  All these engines are limited by the short Zenoah rod.  Its 50 mm long and needs to be at least 55 mm, especially with a 30 mm stroker crankshaft.  60 mm would be better, but no one makes one that long.

You have encouraged me to consider sand casting, thanks.  It's easier but won't produce as nice a result.  For now, I'm sand casting a replacement handle for a low cost sander.

Lohring Miller

[Tjark]

I will post in short time the exhaust core for the Zenoah type cylinder here for you.
So you can see that core’s  can be made this small.
Here is a picture what shows the way I will try to copy in the Zenoah type cylinder to mount the cylinder to the crankcase.


   Tjark.

[lohring]

Do I see a divided main exhaust  port with ports over tha A transfers?  Also this looks like a 4 transfer design with a boost port.  You can't be running this cylinder on a piston port engine.  It's a really nice design. 

I'm planning a FOS style cylinder on a new crankcase and crankshaft design.  There's no way a Zenoah stock rod and big end bearing will last over 20,000 rpm.  I've thrown a rod on my M&D cast cylinder due to too much high rpm running.  Quickdraw postponed problems by increasing the rod big end clearance and cutting an oil slot.  We helped the big end bearing live with a 55 mm rod on a 30 mm stroke engine.  I think the solution will be a longer rod with a bigger bearing and Jim Allen's big end bearing design. 

For Jim's rods see:
http://twostroketech.com/index.php?showtopic=4763&page=2 (invitation to site required)
http://gallery.intlwaters.com/thumbnails.php?album=360 (registration required)
http://www.modelgasboats.com/forum/advanced-model-boating-projects-and-techniques/20648-how-to-make-a-reliable-32-000-rpm-hardened-steel-roller-type-connecting-rod/ 

For FOS cylinders:

[Tjark]

Lohring, I am a member of the two stoke tech forum.
The last question I have placed on the forum is the separation off the A and B transfers.
It seems that no one has experimented this before.
Frits I know in person, how ever we have not  seen each other for a long time.
I know also a person who has made the FOS design and did not get the power he hoped for.
The engine did not run properly also.
I made this year changes to a 50cc engine who delivers 12Kw at the rear wheel and uses a 12mm carb.
This is more then the last 50cc Gp engines with the comparison to the carb diameter.
This is the reason that I am busy with a new design for a 50cc cylinder.
The last picture is a example of a 50cc cylinder.
I have put the picture only to get a idea what I mend with the mounting to the crank case.
Below is a picture off the exhaust core for the Zenoah cylinder.
This core has boost ports who are 5mm thick and a complete exhaust height off 11mm.
   
    Tjark.

[Admiral_dk]

I did a lot of tuning of 50cc. moto-X bikes in my youth and my end result when I stopped in 1977 (age 16) I've reached 12HP on a Tomos/Puch bastard - 5 gear Tomos block with Puch X50 / Monza cylinder + head, a 25mm. Bing carburetor and home made resonance chamber. Not too bad when you consider that this had 1HP in the form we could get our hands on (before any modification) and done with a hand drill with a simple 6mm. multiflute mill bit.

So Tjark, I must say that I'm rather impressed that you can reach 12KW. with a 12mm. carby - even considered that I'm convinced that you aren't doing piston ported inlet + air cooling like I did back then .... 

Lohring - I'm aware that I'm not in your league, but I have followed MotoGP over the years and for that reason (Honda spend a billion dollars over the years on two-stroke development) and since they never did any racing (nor did any other brand after 1965) with a two opposite exhaust ported cylinders (I'm sure they tried it in the lab), I'll be very surprised if you get any improvement. I've only seen small model engines without any external exhaust system getting any reasonable power out of this principle - and that was only compared to the competition back then. That's not saying that you shouldn't try if you believe enough in it yourself.

These forums you're talking about, are there any members doing anything like the current 1200HP/L. (- that's not a typo, they are getting 3HP from 2.5cc racing two-strokes now = 1200 HP per Liter) and showing how ?

[lohring]

I am skeptical about power claims from small glow engine builders.  I run model electric race boats after years of racing glow engine versions.  You can measure the input power very easily on the electric motors.  As an example an 1/8 scale hydroplane that had been powered by an 11 cc glow engine was repowered with an electric power plant.  The input power to the electric motor was 4400 watts.  Allowing for around 85% efficiency that's a little under 6 shaft hp.  The electric motor turned around 23,000 rpm, a little slower than an 11 cc engine.  That means the 11 cc engine would need a brake mean effective pressure (BMEP) of around 150 psi (10 bar) at 23,000 rpm.  That's very good for even racing two strokes.  Reliable tests on model engines usually show BMEPs of around 90 to 100 psi (6 to 7 bar).  I would expect around 4 to 5 hp from an 11 cc engine.

The electric motors usually can turn the same or larger propellers at the same rpm as the glow engines.  The boats are as fast or faster.  The difference is more pronounced with smaller boats.  Their shaft power is around 1.7 hp when powering boats with electric motors that also can be driven by a 3.5 cc glow engine.

Isn't the three port exhaust a little overkill for a piston port Zenoah?  Our testing showed that the main restriction was in the intake side of the stock engine.  Raising the intake timing a lot really helps.  The stock transfers with 188 degree or higher exhaust timing seems to be the state of the art these days.  The stock transfers only need a little eyebrowing over the intake port with no other changes.  Even Quickdraws with a huge intake port only have a divided exhaust.  I would think you would need a Zimmerman intake valve to take full advantage of a better cylinder.  A longer rod would let you get in more intake area as well as save the big end bearing.  Below are a couple of pictures of disk valve modifications to 26 cc engines.  The first was by my partner, Mike Bontoft, years ago. 

I'm still undecided on the direction to go with a 26 cc engine.  I can't see much serious improvement over current engines with bolt on solutions.  Following the Aprilia design is the conservative approach.  The FOS approach requires lots more rpm, maybe over 30,000 to take advantage of better breathing.  My simulations can't get close to Jan Thiel's yardstick of 39 hp in a 50 cc twin.  That would be over 19 hp in a 25 cc engine.  My friend, Jim Allen, is working with a Quickdraw and has 8 hp with lots of detail improvements like a chromed liner.  He plans a longer rod with a better rod bearing and a new piston with a toroidal head button.  He may get 10 hp with his pipe design.  I need to do better.

Lohring Miller

[Tjark]

Isn't the three port exhaust a little overkill for a piston port Zenoah?

I always use port area values.
When you can manage a wider port with the same area you do not have to make the port very high.
This leaves more working space for the compression and combustion cycle.
This way you get more power output at lower RPM’s.

   Tjark.