speculation and building 50cc watercooled two-strokes.

[Owen_N]

I am getting geared up to modify an ex AliExpress 50cc watercooled twostroke engine.
At present, I am building a model plane engine partly using chainsaw parts, just for fun, and to see if I can get it to run without blowing up.
I want to graduate to a watercooled engine, much like the guy who runs "2strokeStuffing" on YouTube.
I need:
1) a better benchtop lathe;
2) a small mill;
3) A tig welder and gear suitable for welding aluminium- possibly 250A pulsed??
4) To build a water brake;
5) to set up a load-cell dyno...

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.

Does anyone want to discuss this project idea?
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.

[Grumph]

Most of that is covered in the ESE Engineering thread in the Bucket section.

Speaking from experience, if you wait till you've got everything you think you need, it'll never happen.

Buy one of the aircooled 50cc engines off trademe, convert it to watercooled and start playing.

[Owen_N]

Most of that is covered in the ESE Engineering thread in the Bucket section.

Speaking from experience, if you wait till you've got everything you think you need, it'll never happen.

Buy one of the aircooled 50cc engines off trademe, convert it to watercooled and start playing.

The watercooled engine off AliExpress is really cheap, though pretty basic.

I thought I need to go to teacup-style transfers and full circle piston at least, (conventional, with piston pin holes) plus secondary exhaust ports as per the Aprilia layout, to get anywhere.
I think the engine is good for about 10 hp at 15,000 rpm as standard, with a proper pipe.

I really need an engine brake to load it up, though. The water brake has a rising torque characteristic like a propeller, but is variable.
The pump brake and the friction brake tend to suddenly stall the engine if you don't fiddle with it.

I have seen some watercooled engines on YouTube with more advanced barrels: the Minarelli AM6, but I think they are a bit scarce?
I can Google them, I suppose.

[husaberg]

The watercooled engine off AliExpress is really cheap, though pretty basic.

I thought I need to go to teacup-style transfers and full circle piston at least, (conventional, with piston pin holes) plus secondary exhaust ports as per the Aprilia layout, to get anywhere.
I think the engine is good for about 10 hp at 15,000 rpm as standard, with a proper pipe.

I really need an engine brake to load it up, though. The water brake has a rising torque characteristic like a propeller, but is variable.
The pump brake and the friction brake tend to suddenly stall the engine if you don't fiddle with it.

I have seen some watercooled engines on YouTube with more advanced barrels: the Minarelli AM6, but I think they are a bit scarce?
I can Google them, I suppose.

Is the engine the copy of the old Beta KTM50? 02-08.



The later KTM 50 is better (09 on)

The earlier 50 top ends can go on the KTM65 lower ends not sure with the later stuff but i suspect they will also swap between the similar models.
The 50MX engines are single speed slipper clutches.
they dont even move until 9k

the later cylinders look like this
https://www.kiwibiker.co.nz/forums/a...p?albumid=4920

[Owen_N]

I had a closer look at the details of the 05 ktm50, and it is only half an engine, with no gears, just a centrifugal clutch.
39.5 bore and 40mm stroke sounds about right, though.

How would I go about selecting an existing gearbox engine, and converting it to water cooling?

The Suzuki engines are 41mm bore.
I can possibly buy replacement barrel and piston for some water cooled 50cc bikes?

There doesn't seem to be much of a market for proper 50cc gearbox engines...

Any suggestions?

What is a good engine to start with?

I like some of the layout of the KTM, with the reed valve entry below the barrel.
The barrel is too hard down on the flywheels for a good port layout, though. This could be fixed with a home-made piston.
My current guide drawing is a cross-section for an RS125 Honda, which shows a better barrel bottom edge setup.

I could have a go at a 360 degree removable piston skirt. However, I need to sort out my ring groove and boring tools, and whether I can do this on a micro lathe.
I want to get a proper benchtop mini, with much better bits and stiffness.
I had a go at making a parting-off tool with a cut-down hacksaw blade, but the machining quality was a bit rough.
It parted off OK though. I can't find HSS in 1.5 x 5 mm dimensions, or smaller holders for it.
The toolpost on the micro-lathe is a bit limiting. it suits 1/8 sq hss tools , or up to 10mm height tools, but you have to fiddle the tool height a bit for turning.
The boring tip I have for 1/8" hss has really crappy grubscrews. - I need to find replacement grade 10.1 grubscrews for it- I shall find out what the thread is.

How do I make piston ring locating pins, and how do I make them stay put?- or drill the offset hole?
What style of top ring should I look at? - what can I get? even in chainsaw engines, there is a ring variety in width. Should I use a cast iron ring, or can I get something better?

[F5 Dave]

Surely Derbi Euro 3 or Minarelli AM5 or 6 would save some time. Possibly with KTM barrel. I don't surf the Freetech stuff but bound to be a better lead there.

[husaberg]

As i said you use the KTM65 bottom end with the KTM50 top end its a bolt on for the 02-08 and likely the same for the later using the sme years
the 65 have a 6 speed.
okay the 09 on has the same base gaskets 65sx and 50sx so i would say as long as you keep in the same design beta or post beta the should swap.
https://www.bikebandit.com/oem-parts...35&sch=1104040

[Owen_N]

As i said you use the KTM65 bottom end with the KTM50 top end its a bolt on for the 02-08 and likely the same for the later using the sme years
the 65 have a 6 speed.
okay the 09 on has the same base gaskets 65sx and 50sx so i would say as long as you keep in the same design beta or post beta the should swap.
https://www.bikebandit.com/oem-parts...35&sch=1104040

OK I will look for a KTM 65 online.
I was looking at a new Minarelli 50 lc, but getting on to $1000 + freight. I can buy heaps of am6 parts at 40.3 bore and 39mm stroke.

[husaberg]

OK I will look for a KTM 65 online.
I was looking at a new Minarelli 50 lc, but getting on to $1000 + freight. I can buy heaps of am6 parts at 40.3 bore and 39mm stroke.

roll along to the local mx meetings and ask around they will know someone who has an old one or a practice bike.
trust me the std later 08 on are a nice piece of kit.

[Owen_N]

roll along to the local mx meetings and ask around they will know someone who has an old one or a practice bike.
trust me the std later 08 on are a nice piece of kit.

I don't go to mx meetings. There was a 2015 one up for auction on trademe, but I bet it will go for a couple of thou.
The minarelli looks more available, but is too expensive for me. I want cheap, like $600 or so for the basic engine, delivered to me.
Getting one with the correct stroke is the problem, and finding a market where I can buy old engines. there is very little on trademe, and ebay is expensive, with super-costly freight.
the minarelli is pretty good, with a 6-speed box. I can carve an engine up if I have to, but getting the output gear to mesh could be tricky with unrelated parts.
The el-cheapo slipper clutch engine could be the basis for a bench engine, but hard to then drive a gearbox and clutch from if I want to install it in a bike.

[Owen_N]

Is the engine the copy of the old Beta KTM50? 02-08.



The later KTM 50 is better (09 on)

The earlier 50 top ends can go on the KTM65 lower ends not sure with the later stuff but i suspect they will also swap between the similar models.
The 50MX engines are single speed slipper clutches.
they dont even move until 9k

the later cylinders look like this
https://www.kiwibiker.co.nz/forums/a...p?albumid=4920

Ah! I see they have auxiliary exhaust ports- the old one doesn't.
I plan to slice all the lower outer skin off, plus the exhaust port level, and have a go at making my own bottom half.
I see online that nitric acid is needed to remove the Nikasil- I need to know what concentration and volume, and how long it takes.
I would really like to extract the head and the upper outer barrel, and start with my own aluminium sleeve. Then I have complete freedom in arranging ports.

I will investigate the two-layer porting scheme, with a 360 degree piston skirt - bolt together through the crown. I don't think having the hex recesses in the piston crown ,
or the steel inserts, will affect combustion. with 10mm csk heads on the screws, heat transfer out of the screws should be OK. What sealant would work? Maybe exhaust paste
in the screw head seats?- I need to run it throgh Engmod2t to see if it looks good.

Regarding rpms- if I tune for 17,800, the engine will make very little torque below 11,000 or so, I think.
I am looking at various schemes to get a reed valve bypass going, and let the pipe do all the breathing. crank-case compression is not really needed on the pipe.
There is some resonant theory involved. Alex from "2Stroke Stuffing" has about 120mm standoff pipe on his inlet, with about 340ml crankcase volume.
I think I can do a little less than that! his inlet ports volume is huge! area taper of 8% along the ducts should be enough?

I would need to weld to it to keep the water in, I suppose.
I don't know if having one sleeve inside another would be any good for cooling???- no welding needed on the inner sleeve for less distortion.
The welded item would need some heat treatment to relax the weld stresses.
Where would I get good tubes in the eutectic aluminium-silicon. does it have to be this for the sleeve area?. Another alloy would be more ductile, and easier to weld.
The upper barrel has to be strong enough to support the head studs.