ESE's works engine tuner

[Flettner]

wouldn't you just use a tapered thread?
For example, good old BSPT comes to mind.

[wobbly]

The original patented L ring piston design was lighter than a stock piston , and Makrs ones were as well , but not sure about the new combined design.
In testing the original design the ring was retained by the clearance given to the vertical L land , but this seems not to have worked for Alex.
Maybe excessive clearance allowing too much expansion into the port must have been the issue there.
The original piston was tested for reliability and siezure " proness " , if anything they seemed to be superior.

[Flettner]

Or this one. The lump on the top is only there to hold on to for finish machining. This is lighter than the comparable standard generic piston.
https://youtu.be/MxyTBXiaFQw

[obelsik]

Alex is a inspiration to garage mechanics with limited tools. I got my YZ250 head cut to 1.5mm squish by a friend on his lathe and then wanted to increase the chamber volume back to achieve 22 cc CCV. So I lay my old janky drill press on its side and chucked up the head using an old spark plug. Then then slowly wood lathed the dome into shape using a file with the end ground to a rounded shape. This way I could do it at home and slowly creep up on the cc I wanted. Surface is finish is not great but ti works.

[andreas]

At second glance, those snowmobiles look quite interesting. So if one were to couple for example a polaris 600 to a conventional gearbox (gears/belt/chain) what would be the best way?

[Flettner]

At second glance, those snowmobiles look quite interesting. So if one were to couple for example a polaris 600 to a conventional gearbox (gears/belt/chain) what would be the best way?

Cast new cases.

[andreas]

Cast new cases.

Thanks, I seem to have used the wrong word, it should say easy.

[wobbly]

Thats exactly what the Tularis project did.Without a balance shaft the big twin vibrated so badly it was all but impossible to ride for any length of time.

[andreas]

Yes I remember, was a 800 I think, The heavy crank gt 500 works fine. 4-600 maybe is accepable, not sure.

[Flettner]

Thanks, I seem to have used the wrong word, it should say easy.

In the long run it will be easier, when you consider all the problems with trying to join everything up with belts etc.
Cast new will make a tidy package and you can design in a balance shaft. A necessity with this type of engine. Been there, done that.

The pattern just needs to be wood, glue, bondifill and some paint. Can do it in the most basic of workshops, been there, done that.

Just saying.

[Condyn]

Here is a photo of Shannon Bacons rotax powered Suzuki with cvt still in place. A bit bulky but I think he is just intending on tooling around with it.

[andreas]

In the long run it will be easier, when you consider all the problems with trying to join everything up with belts etc.
Cast new will make a tidy package and you can design in a balance shaft. A necessity with this type of engine. Been there, done that.

The pattern just needs to be wood, glue, bondifill and some paint. Can do it in the most basic of workshops, been there, done that.

Just saying.

I must investigate this option.
Condyn, Yea on the bulky side, probably fun nonetheless.

[wobbly]

The 'easyness " of this type of project depends upon one skill - CAD .
If you are sufficiently up to speed and can model a case on the screen , it is then way easyer to CNC this from billet than it is to make the cores , cast it , then have to machine most of it anyway.
Cylinders are a little different , in that again they are relatively " easy " to solid model , but to then have them 3D laser printed is not a cheap exercise.
This technology is however becoming more mature and cheaper by the day.
The first example of this approach was , I believe , the BSL500,where everything was CAD modelled.
Then the all CNC case was machined from billet , and the cylinders were 3D laser printed , directly off the models that had material added for all the machined surfaces.
A 5 axis CNC machining center could completely finish a case and the cassette cover in 14 Hrs .
And near on 20 years ago the laser printing of 4 cylinders at a time ( the maximum the platten could hold ) cost $5000 usd.

[Flettner]

I dont know about that. This engines patterns were built with no CNC or CAD models, in fact no drawing at all. Including the cylinder.
Just used some wood working equipment, kiln dried pine, cheap as chips. Each case half was in the order $100 to cast.
CAD / CNC is wonderful, but its not your only option.
I own both, but find it way quicker cheaper to just go out to the pattern shop and just make the pattern.
Not entirely true sometimes its easier to machine the pattern on the CNC. I don't machine big things like cases from solid because the cost of material is just soo high.

[mantonakakis]

I think Alex's 50cc cylinder would have cost ~1300GBP to have printed by Protolabs, for what that's worth.

On a different topic, I'm working on getting a RD125B engine created in EngMod2T. I don't have a dyno, so working on correlating to an old power curve published in a magazine in 1981 (14.8hp to the wheel at 9000-9500rpm). Assuming ~10% drivetrain loss, let's say about 16.5hp at the crank. There are a few challenges/aspects I'm not super confident about while modeling up the stock setup, namely the boost port and the stock pipe. The induction is cylinder reed with essentially a 360deg piston port, but also connected up to a single boost port as shown here:


I treated the boost port as a separate, short port. I used the Yam12 scavenging model, as it is exactly like the A ports. B ports are similar but with a very steep roof angle (~60deg from horizontal). Here's a side-on view of the inlet port/boost port - cylinder side is to the right, a small portion of the reed cavity without the reed block included to show the transition:


The exhaust pipes are modeled as T-pipes; in reality they almost perfectly match the "standard pipe" shown in section 7 of the "Types of exhaust systems" help file. I ran into modeling limitations on the silencers for a multi-cylinder engine, so I just modeled the T-pipe atmospheric end with a very steep baffle cone to the appropriate restrictor diameter, with a 100mm stinger pipe. It at least gives the same peak power RPM and overall curve shape as the dyno data from the old magazine. So, close enough I guess.

My power curve is too optimistic below the power peak, it seems. After the power peak, it's almost identical. Not sure how to get it any more accurate, or if I should just say "good enough" and move on with modeling modifications? The only thing that's gotten it to be a lot more similar is reducing the CCR in the model (1.2 vs 1.34 as measured).