Details of performance two-stroke engines.

[Owen_N]

This is intended for discussion of odd features of performance two-stroke engines.
The one that I am interested is the "wobbly exhaust passage".
this seems to be very long, with a semi-elliptical outlet.
I would have thought the outer exhaust ports could merge at about 30 degrees into the first exhaust chamber, which can be oval or round, and about a cm out from the centre of the main port.
The full port depth in the middle isn't used for the blowdown process, so a chamber of the area of the centre port would be sufficient.
the outer edge of the merged tubes could be radiused.
the wobbly sec is outlet of 75% of the port area.

I am not sure how the inlet to the exhaust is normally proportioned.

Is it about 30 diameter for a 50cc, 36mm diameter for a 125cc, or more?
by area-radius proportion, if 125 is 36, then 50cc = 22.
22mm is the size for a low-rev 60cc, 6-7500 rpm range.

I would expect it to be bigger for a 17500 rpm 50cc engine= or 17850rpm , as suggested by Jan Thiel in one of his articles.
if the 50 goes to 30mm, then the 125 x sqrt (2.25) (1.5) = 45mm. Is this too large??

A normal YZ125 carb is 38mm, but do the disc valve 125s go any bigger? - they both run around the 13,000 rpm mark.
I was thinking 35mm flat slide for a 50 with a fully open resonant intake, but 28mm may be better.
I have a sizing formula for 2-strok3es here- I will study it.
Back to the "Wobbly" exhaust channel. Its very long side channels could be intended to help channel the reflected pulse into the secondary exhaust ports.
This reflection may not like a rounded 30 degree intersection, with side pipes around 18mm in diameter?
<edit>
Here is the image of the "wobbly" exhaust duct.
It doesn't seem to show the transition to the actual exhaust. - the view here looks like about 2/3 of the bore , or 36mm for a 54 mm bore.
This actually sounds not to bad for a 125 cc.

For the exhaust header, an inside bend radius about 3x the bore, seems to be common.

The "wobbly" exhaust duct was designed by Wayne Wright, an associate of Frits Overmar and Jan Thiel,
and the image is an extract from the JanBros pdf.

Another feature of the Aprilia is the wide, rounded main port.
I think that the main port should be more square and narrower, and move the extra port width to the secondary exhaust ports.
The Aprilia could be like this to make better use of the exhaust power valve.

These are not required for pure speed engines, as long as you can make the transitions between gears.
A streamliner really needs an expensive side-loader 6 speed box, with plenty of different ratio choice.

I will just be going for "engine numbers" only , and leave out the actual streamliner stage.
I will also work with 95 RON fuel, as a benchmark.

I will see if I can combine a pipe engine with 8.0:1 effective CR, and this fuel.

Building power high in the rev range seems to reduce knock sensitivity a bit, and I am sure there are a few other tricks.
Instrumentation to detect onset of detonation, or seizure, sounds useful.

Seizure usually occurs in my experience when the piston skirt gets too hot for good lubrication, and can occur even when the piston
clearance has not been fully used up by heat expansion.

It is a risk when retaining heat in the expansion chamber, or using the full restrictor as with the FOS style pipe.
This carries heat back with the supercharge reverse pulse, and makes for more chamber heat.

Some engines are especially touchy in the overrev part of the rev range. Less efficient chamber evacuation could be part of this.

Some other engines add extra holes in the piston sides to assist with piston cooling, but you cannot do this with a full-circle skirt.
I see some pistons have an indent on the "cold side", but no actual hole.

Making the skirt longer , and/or moving the piston pin further away from the piston crown, are possible solutions.
This means the con-rod should be longer, too, around 1.9 to 2:1 x the stroke.
Are any more than this?

 

[Owen_N]

Doesn't seem that anyone here is interested in these things.
This seems to be a common thing.
I will look on Kiwibiker and see if they have a semi-speculative forum, for the more enthusiastic engine designer and builder.

 

[lohring]

I've been interested for over 60 years. My first design and build was a 10 cc race engine in high school shop. More recently I've been involved with developing 26 cc engines to set model boating records. The information for these efforts involved studying all the information available and actually building and testing engines. The internet has made studying easier, but day long trips to university libraries were involved earlier. There are lots of books and research papers. My favorite is Sir Harry Ricardo's The High Speed Internal Combustion Engine. The basic modern research was done by Gordon Blair at Queens University in Belfast. This resulted in computer based engine simulation programs described in his book, Design and Simulation of Two Stroke Engines. EngMod2T is a development from this research. Careful work with this simulation will help reduce a lot of variables, but there is no substitute for dynamometer testing. I've written lots of articles. Some are posted on this forum.

Lohring Miller

 

[Owen_N]

I've been interested for over 60 years. My first design and build was a 10 cc race engine in high school shop. More recently I've been involved with developing 26 cc engines to set model boating records. The information for these efforts involved studying all the information available and actually building and testing engines. The internet has made studying easier, but day long trips to university libraries were involved earlier. There are lots of books and research papers. My favorite is Sir Harry Ricardo's The High Speed Internal Combustion Engine. The basic modern research was done by Gordon Blair at Queens University in Belfast. This resulted in computer based engine simulation programs described in his book, Design and Simulation of Two Stroke Engines. EngMod2T is a development from this research. Careful work with this simulation will help reduce a lot of variables, but there is no substitute for dynamometer testing. I've written lots of articles. Some are posted on this forum.

Lohring Miller

here is a modified copy of my post on Kiwibiker. You may have some suggestions:

speculation and building 50cc watercooled two-strokes.
I am getting geared up to modify an ex AliExpress 50cc watercooled twostroke engine.
This is quite cheap, although basic, and I think it will do about 10 hp at 15,000 rpm with a pipe, as standard.

I want to graduate to a watercooled engine, much like the guy who runs "2strokeStuffing" on YouTube.
I need:

1) a better benchtop lathe; My micro-lathe is not very stiff, and has a very poor 3-jaw chuck.

2) a small mill; Possibly handy for facing-off, cutting keyways, accurate boring and tapping, some piston machining.

3) A tig welder and gear suitable for welding aluminium- possibly 250A pulsed??

4) To build a water brake;
I would rather use a water brake, as it has a rising torque curve. Pump and friction types are tricky, and I want sustained running, so inertia types are out.

5) to set up a load-cell dyno...- scales kits are quite cheap, and could be adapted.- it just needs an arduino, software, feed to a laptop??

Before I start on an engine.

I have got the Engmod2T package, but haven't tried it out yet.

What I want to try is clearing out the Nikasil;
welding stiffener bars to the barrel and totally rearranging the porting;
Make my own 360 degree piston;
Reorganising the barrel to a no-cutout design, with barrel lift for the transfers;
reweld, lift the case deck, and space the base studs out more.

Then bore and get the Nikasil coating redone.

I want to avoid having to design the whole thing in 3D CAD; and getting the barrel 3D-printed in aluminium.
Investment casting ends up being quite expensive, with a lot of learning and reject castings.

Possibly I need to start with a fresh liner, and weld the port fittings onto that.
I think the engine I am looking at is a barrel-cutout type.

Arranging for water passage cavities is a bit tricky, and I don't know if I can do a wet liner with part of the existing upper barrel.

Has anyone you know of tried anything similar?
Are there standard barrels available that would need less work to adapt?

I am interested in the two-layer port concept, where exhaust ports go about 240 degrees of the circumference, and a there is a full circle of transfers below the exhausts.
The transfer passages would need to be downsized a little to preserve crankcase compression;
and the exhaust manifold/ collector would look like 2 scroll cases that intersect at the outlet.

I also want to look at combined reed valve, and full 360 degree top end inlet flow driven by the pipe.
This seems to work OK on the 2strokeStuffing engine, with an inlet extension tube, and fairly low crankcase compression.
I would use a butterfly valve as the changeover device, and run off the one carb.
It would be an advantage to get the butterfly as close as possible to the crankcase, and split the reed valve cage into two pieces.
- space to fit all this could be a problem.
I need to get an engine before I can lay this out further, so I can measure everything up.
<edit>
I think I need to go to an Aprilia-style barrel and case arrangement to do any better, though I have heard of KTM 125's doing well with reed valves.

I will search for assembly drawings, to see what lift the barrel has relative to the crank wheels, and how that part of the porting works.

Some versions of the Minarelli AM6 seem to be fairly advanced, but there are other top kits for the same engine which are fairly primitive.

A sign of a good version would have a tall piston with a fairly low piston pin, and no or minimal barrel side cutouts.
I have seem one with 3 transfers each side.

Any opinions, tips?

 

[ajoeiam]

here is a modified copy of my post on Kiwibiker. You may have some suggestions:

speculation and building 50cc watercooled two-strokes.
I am getting geared up to modify an ex AliExpress 50cc watercooled twostroke engine.
This is quite cheap, although basic, and I think it will do about 10 hp at 15,000 rpm with a pipe, as standard.

I want to graduate to a watercooled engine, much like the guy who runs "2strokeStuffing" on YouTube.
I need:

1) a better benchtop lathe; My micro-lathe is not very stiff, and has a very poor 3-jaw chuck.

2) a small mill; Possibly handy for facing-off, cutting keyways, accurate boring and tapping, some piston machining.

3) A tig welder and gear suitable for welding aluminium- possibly 250A pulsed??

4) To build a water brake;
I would rather use a water brake, as it has a rising torque curve. Pump and friction types are tricky, and I want sustained running, so inertia types are out.

5) to set up a load-cell dyno...- scales kits are quite cheap, and could be adapted.- it just needs an arduino, software, feed to a laptop??

Before I start on an engine.
snip

Any opinions, tips?

I know just about diddly re: your central question.

Some knowledge re: your desired equipment purchases.
re: TIG welding equipment - - - - 250A pulsed - - - - you've entered some rarefied country with that level of stuff.
Do you have tig welding experience?
If no - - - well - - - you're likely going to be unloading at least 12 if not $15k to get into this range of equipment.
Then setting all the parameters - - - wow - - - lots of hours of either experimentation or enough 'not good' or 'not good enough' parts.
If you leave off the need for pulsed - - - then you drop your costs quite dramatically.
I have (IIRC) a Lincoln 225 (with some other designation) TIG stick machine.
In aluminum one is quite limited - - - welding 1/4" (6mm) thick material meant lots of breaker resets and lots of doing other stuff between a little bit
of welding - - - the duty cycle at the upper amperages is low. Not a problem if you have a lot of time on your hands but if you like to get things done
- - - - well its a right royal pita!
The next level of machine is a LOT more mullah - - - much more flexible too.
A bud of mine who regularly works as a tig weldor in quite a number of exotic materials has used my little (very limited) tig box and tells me that it
is quite capable just needing some care.

Pulsed tig or mig is a real nice option for welding lighter materials not sure its actually 'necessary' to produce good parts.

HTH (even a little bit and hopefully others will chime in with their ideas!!!!)

 

[Owen_N]

I know just about diddly re: your central question.

Some knowledge re: your desired equipment purchases.
re: TIG welding equipment - - - - 250A pulsed - - - - you've entered some rarefied country with that level of stuff.
Do you have tig welding experience?
If no - - - well - - - you're likely going to be unloading at least 12 if not $15k to get into this range of equipment.
Then setting all the parameters - - - wow - - - lots of hours of either experimentation or enough 'not good' or 'not good enough' parts.
If you leave off the need for pulsed - - - then you drop your costs quite dramatically.
I have (IIRC) a Lincoln 225 (with some other designation) TIG stick machine.
In aluminum one is quite limited - - - welding 1/4" (6mm) thick material meant lots of breaker resets and lots of doing other stuff between a little bit
of welding - - - the duty cycle at the upper amperages is low. Not a problem if you have a lot of time on your hands but if you like to get things done
- - - - well its a right royal pita!
The next level of machine is a LOT more mullah - - - much more flexible too.
A bud of mine who regularly works as a tig welder in quite a number of exotic materials has used my little (very limited) tig box and tells me that it
is quite capable just needing some care.

Pulsed tig or mig is a real nice option for welding lighter materials not sure its actually 'necessary' to produce good parts.

HTH (even a little bit and hopefully others will chime in with their ideas!!!!)

I am not familiar with aluminium tig welding, and machines.
I have done some with fairly light stainless steel- about 1.2 mm?
All the heavy stuff I have done is with steel and stick welding.

Do I need a dc machine? can you tig weld with 50 Hz AC ??

I thought pulsed DC was good for clearing the oxide layer on the molten pool.
I was wanting to weld up to 3/8"- to build a new crankcase deck with wider spaced studs.
These seem to be required for lifted barrels and teacup transfer profiles.
For 3/8" , 300A is suggested, but I cannot run that off a single phase 230V 10A 50 hz supply.

There is a good example of this type of welding and machining on YouTube, where the poster has joined the case off a 4-stroke scooter to a two-stroke crank, rod, piston, barrel, head. It looks like he was using 125 motocross parts.

I think this guy is in Korea- not sure- he has a lot of good gear, and does interesting things with small motorbikes and engines.

I have just started looking at welder ads on Google. I think my upper limit would be $2500nz, or around $1785 us.

I found a cross-section drawing for a honda rs125, so that gives me some idea on where the barrel sits above the crank wheels.

 

[Steamchick]

One job I did was design and installation of welded aluminium bus bars - big ones for Power stations and aluminium smelters. Plates were from 10mm to 6 inches thick. Welded using MIG machines at 450A or more, with 12mm or 1/2" beads.
No use for model stuff, but gives you an idea of the power needed by aluminium.
K2

 

[ajoeiam]

I am not familiar with aluminium tig welding, and machines.
I have done some with fairly light stainless steel- about 1.2 mm?
All the heavy stuff I have done is with steel and stick welding.

Do I need a dc machine? can you tig weld with 50 Hz AC ??

I thought pulsed DC was good for clearing the oxide layer on the molten pool.
I was wanting to weld up to 3/8"- to build a new crankcase deck with wider spaced studs.
These seem to be required for lifted barrels and teacup transfer profiles.
For 3/8" , 300A is suggested, but I cannot run that off a single phase 230V 10A 50 hz supply.

There is a good example of this type of welding and machining on YouTube, where the poster has joined the case off a 4-stroke scooter to a two-stroke crank, rod, piston, barrel, head. It looks like he was using 125 motocross parts.

I think this guy is in Korea- not sure- he has a lot of good gear, and does interesting things with small motorbikes and engines.

I have just started looking at welder ads on Google. I think my upper limit would be $2500nz, or around $1785 us.

I found a cross-section drawing for a honda rs125, so that gives me some idea on where the barrel sits above the crank wheels.

TIG welding aluminum AC is recommended.
(Now if you're using a small wire mig setup - - - different answer!!!)
I got it - - - Al likes a LOT of heat.

So for maybe a few minutes of welding you going to increase your costs (maybe 5x as much - - - - large tig rigs are pricey!!!!!!)

Why not do multi-pass welding - - - its even recommended for heavy steel work.
And then even if you're using 1/4" welding rods and you're welding 2" thick steel - - - - guess what - - - its called multi-pass welding.
Yes - - - I've used 17/64" 7024 rods welding on material that was 1/4" thick - - - can't remember the heaviest stuff.

I'll see if I can make a bit of a picture - - - have to use words because the site uses html and doesn't preserve formatting

Bottom pass is crucial and MUST seal well and completely and give you the second side appearance needed (flat to fill or slightly convex to that side - - - convex is standard but then you need to grind it flat so if you want flat - - - why not weld to flat - - - if you can - - - its less work.
Next pass is focused on either the right or the left side with the toes (outside) of the weld going to only (at most) the 3/4 point between the left and right side of the gap.
Clean with a good stainless steel brush (she's more important that a great girl friend in aluminum welding!!!!!)
Next pass is the opposite side using the same technique (to 3/4 the distance to the other wall).
If you are almost full (the V that is) then your cap pass is possibly a single wide puddle.
That produces a lot of pull stress (a.k.a warpage tendencies) so if that weld is wider than 3 time the dia of your electrode - - - well use two passes.
In pipe welding (a.k.a pressure welding) the preferred procedure is 'stringers' or these narrow passes.
Important to keep the toes of the weld good AND clean (- - - penetration my friend).
That's how you can weld very heavy items and not increase the weldment stresses more than necessary.

Lots of words for something that's actually quite simple.

Yes tig welding w 50 Hz AC is not just possible - - - grin - - - likely a few thousand tons worth of product is being welding that way as we 'speak' - - - grin!!!
(There are times and ways of cheating in even this but the standard procedure is great when you're not trying to push high volumes through and still want great welds. I've had the occasion when I was asked to do a 1/2" fillet weld in 2 passes - - - joining 5/16" plate to a 1-1/2" wall plate - - - but that's not 'usual' and I wouldn't recommend that kind of procedure without it having been tested (that had - - - - very thoroughly!!!).)

HTH

 

[awake]

re: TIG welding equipment - - - - 250A pulsed - - - - you've entered some rarefied country with that level of stuff.
Do you have tig welding experience?
If no - - - well - - - you're likely going to be unloading at least 12 if not $15k to get into this range of equipment.
Then setting all the parameters - - - wow - - - lots of hours of either experimentation or enough 'not good' or 'not good enough' parts.
If you leave off the need for pulsed - - - then you drop your costs quite dramatically.
I have (IIRC) a Lincoln 225 (with some other designation) TIG stick machine.
In aluminum one is quite limited - - - welding 1/4" (6mm) thick material meant lots of breaker resets and lots of doing other stuff between a little bit
of welding - - - the duty cycle at the upper amperages is low. Not a problem if you have a lot of time on your hands but if you like to get things done
- - - - well its a right royal pita!
The next level of machine is a LOT more mullah - - - much more flexible too.
A bud of mine who regularly works as a tig weldor in quite a number of exotic materials has used my little (very limited) tig box and tells me that it
is quite capable just needing some care.

Pulsed tig or mig is a real nice option for welding lighter materials not sure its actually 'necessary' to produce good parts.

HTH (even a little bit and hopefully others will chime in with their ideas!!!!)

As a data point, I bought a 200A Everlast AC/DC TIG/Stick/Plasma unit a year or two ago that has been giving me very good service. As best I recall, I paid around $1500, on a really good sale. I just checked their website (not everlast.com, but everlastgenerators.com), and it looks like you can get a TIG-only (well, TIG and Stick) AC/DC machine up into the 350A range for $2500 or so. These are units with all the bells and whistles as far as pulse, balance, 2T and 4T, and so on.

I have no affiliation other than satisfied customer. To be clear, these are import machines, not in the same class as the Lincolns and Millers. At the same time, this particular brand seems to be among the top-end of the import machines, far better than the typical eBay special that might be only half the cost. This is my second Everlast machine (I sold the first, DC-only unit to step up to AC/DC), and I've been happy with them ... but that should be understood in the context of a hobbyist, who welds an average of two or three hours per month at the most. T'were I a professional, I suspect I'd want to invest in something blue or red ...

 

[Steamchick]

On aluminium weld size: MIG welding busbars (4" thick joints made by overlapping plates to fill a 1 ft wide gap). The 1/2" welds were done in 3 passes. The root pass, 1 side pass, then the final fill pass. These carried current, and the busbars were not cosmetic, so slight "overfill" wasn't a significant problem, but "thin" welds would overheat in service.
For model stuff, I have been assembling bits of aluminium with "aluminium solder". (Chinese source vie E&@y). Works fine for me with a simple gas blowtorch to heat the parent material, when the heat can melt the solder into the joint. I think the solder is 95% Al, 5% silver... or something? - I used to use "Lumiweld" Zinc based rods, but the new Al rods are even easier. Strength seems almost as good as parent Aluminium.
May give a means of joining your bits? - At lower capital cost than a TIG welder.
K2

 

[Owen_N]

Interesting point:
The Dutch efforts have yielded 24 hp at the rear wheel. How much loss is there in a motorcycle transmission? They may be getting up to the 30 crankshaft hp zone?-I got this second-hand from Alex at "2Stroke Stuffing". This may explain his interest in the supercharged engine, as he probably can't beat 24 rw hp.

I see that Alex is using an unusual carb that looks like a PWK body, but has a 33 mm bore, and a very wide, smooth intake trumpet built in.
He doesn't say , but could this be a special Keihin race carb?
Is it valuable to have a carb with a huge flared intake, or would an extension trumpet work as well?

I have selected a 30mm, as the selection formula says this is good.
That may be better for a powervalve engine rather than an all-out power engine, though.

I could add an extension to the PWK bellmouth and reshape it slightly, but the PWK carb has a little air scoop in the entry rather than all recessed holes.
generally, an airbox is desirable for air entry. Does this surround the carb bellmouth, or have some kind of extension tube?
The side-carb racers use a long, flat extension up to the main airbox, but the bellmouth stands out in clear air about 1 throat diameter spacing all round, 1/2 dia spacing at the rear, and about 1.5 diameter spacing at the front of the carb.

 

[Steamchick]

Conventionally, long bell-mouths have been used on 4-stroke carbs, and much shorter ones on 2-strokes. This is to try and obtain a tuned length of intake, to improve resonant ram effects. 2 strokes often rev much higher than 4 strokes, and by sucking twice as often, tune at shorter intake lengths.
Air boxes, on road vehicles, tend to be resonant but have Helmholtz resonators to stop the intake resonance noise at certain speeds. E.g. The Micra with automatic transmission runs at 4000rpm continuously, until higher speeds in top gear. So a resonator is used to kill the intake resonance noise at 4000rpm. Customer happiness is so important. This resonator is not fitted on M/T cars, as they don't usually live at 4000rpm for prolonged periods.
The air box also (usually) removes the variation from the windage of vehicle speed. And it can contain a large air cleaner.
Hope this is relevant?
K2

 

[Bentwings]

I know just about diddly re: your central question.

Some knowledge re: your desired equipment purchases.
re: TIG welding equipment - - - - 250A pulsed - - - - you've entered some rarefied country with that level of stuff.
Do you have tig welding experience?
If no - - - well - - - you're likely going to be unloading at least 12 if not $15k to get into this range of equipment.
Then setting all the parameters - - - wow - - - lots of hours of either experimentation or enough 'not good' or 'not good enough' parts.
If you leave off the need for pulsed - - - then you drop your costs quite dramatically.
I have (IIRC) a Lincoln 225 (with some other designation) TIG stick machine.
In aluminum one is quite limited - - - welding 1/4" (6mm) thick material meant lots of breaker resets and lots of doing other stuff between a little bit
of welding - - - the duty cycle at the upper amperages is low. Not a problem if you have a lot of time on your hands but if you like to get things done
- - - - well its a right royal pita!
The next level of machine is a LOT more mullah - - - much more flexible too.
A bud of mine who regularly works as a tig weldor in quite a number of exotic materials has used my little (very limited) tig box and tells me that it
is quite capable just needing some care.

Pulsed tig or mig is a real nice option for welding lighter materials not sure its actually 'necessary' to produce good parts.

HTH (even a little bit and hopefully others will chime in with their ideas!!!!)

I have to agree with the TIG welding stuff. . You don’t just plop down and start precision TIG welding . I learned “pulse welding old school with the pedal only no fancy machines . Ironically the fancy stuff was very problematic in its early days. Burned out no replacium boards it still took lots of skill just to define what you wanted to do. Then twisting dials and pushing unknown buttons . Much easier today . There are automatic tungsten grinders now but you still need lots of sizes an hand fulls of them . By the way modern tungsten are not cheap either . There are lots of them so you need to know which to use where. I can’t see worth a darn now so my TIG welding days are more less don . I still practice “ welding sketch lines on graph paper so the few times I get to weld are somewhat useful double vision makes choosing which line is the real one hard you can’t weld both at the same time. interesting my old copper pile can still do an ok job if I get the right seam .Sadly LOL

I’m goingvto have to exit . Doc visit soon

Just selecting welding rods is a class all its own .

 

[Owen_N]

Well, I am back down to more average levels of cash on hand, so no buying tig welders or bigger lathes for me!
However, for my bench engine, it is possible to get quite good power from older style barrels, and it will keep me going for quite a while catching up on all the planned alterations that I want to do.

 

[Bentwings]

Well, I am back down to more average levels of cash on hand, so no buying tig welders or bigger lathes for me!
However, for my bench engine, it is possible to get quite good power from older style barrels, and it will keep me going for quite a while catching up on all the planned alterations that I want to do.

Going back quite a few years the pylon racers pioneered the ABC cylinder liners aluminum bronze chrome . These were taper honed so the piston would stick at TDC untill the engine got hit enough . That was not hard with the big nitro loads they ran . I got to dons little honing for them the chrome was very hard I hd some diamond stones that worked well. This was before the cubic boron stones and grinding wheels. I even used some of their left overs in my pattern planes noise wasn’t an issue yet so thy really screamed I used muffled tuned pipes not for noise but because they were easy to tune I had unlimited nitro too although I didn’t use huge loads I usually used a glow plug per flight and occasionally landed with stuck engines or burned pistons