Hello,
My son gave me his old digital camera.(my first)
I thought I try to show the beginings of a lathe/mill project
I’m starting on. An Echo 23.6cc. for bicycle pedal
Assist.(If this is too out of place here,say so, and I’ll
remove it.)

I'm interested.

So what's the plan?

It looks very interesting.

Yeah, what have you got going there??

AV8TOR

Hi,
The 3”aluminum round stock will be the new finned cooling jacket for the
cylinder in the third pic, that one had it’s fins turned off.The plan is just a real light press fit for good heat transfer. Basically this is just for fun. Plus I wanted to get away from the "fancooled" look of the cylinder.

I’ll make up a head button like are used in R/C cars for a little CM-6 NGK
plug I picked up.Not sure how many cc’s to set the head up for yet.

I’ve picked up the exhaust port location on that stock, and will mill a flat and port to mount an exhaust stub tomorrow.

This is a pic (if it loads)of the head button style I have in mind. (not mine)

There is no practical reason for doing this I’m afraid…

So your going to simply put different fins on the cylinder.
And it is still going to be air cooled by a fan?

Are you going to change the port timing?

On a project like this, you can make any timing you want, even lower the ports for nice puttering along
Watercooled or aircooled?

Hello,
I have no plans to change the port timing on this particular sleave.
There is no transmission to deal with a higher timing/less low end.
Since the plan is for a very light press fit ,It could be changed out I guess.Yes lower timing might be good for this thing.

The pic shows the urethane skateboard wheel drive parts collected so far.

The cylinder jacket thingy is what the go-kart guy’s call “free air cooling”
like a little motor bike engine might have, no external fan. There will also be no prop wash over the cylinder on this little guy.

In a book I’ve have here by Cesare Bossaglia ,he talks a little about cooling Fin spacing. I’m going to try .080 thickness with a .160 space between them. The plan is to cut them to depth of a bit over .500” at the top half of the cyl. The lower half have is going to be fun…have to work around the ports,w/no real Rotary table.(I have a 90 degree gearbox I can stick a chuck on for rough work Holding/turning.)

Your book looks very well used
Indeed, for free air cooling a little looser fin spacing is better, though I would see 0.1" open air spacing and 0.05" fin thicknes as a better solution. You need to get all the cooling area you can get on that little engine.

(Behind a prop, controlled flow and jacketed cylinder, fin spacing of 0.04" (1mm) works best according to NACA studies)

Pe reivers
Thanks for the insight on fin design.
I’ll try to attach a couple pictures of three I did quick measurements of.

First- Echo 23.6cc Thickness .050 (spacing .175)
Second- Tartan 1.3 ci? Thickness ..040 (spacing ..075)
Third- O&R implement 1.3ci? Thickness .035 (spacing .065)

Second pic. I’ll try to shoot the book page of Mr. Bossaglia’s Ideas on this.

Please guy’s,this has little to do with your plane engines. I’ll take this stuff
down if I’m not following RCU policy, or mudding up your forum.



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Hi,Please continue. This is interesting, I've thought about this as a way to save weight and inproving cooling. I've been reading about what heat can do to rings and seeing the results on engines I've torn down. On your engine will you use stock rings? What will the tolerances be?

What will your squash be on the head you made?

Hello, I happened upon some used,and nos parts. So.yes std.rings.std. gaps.
There is also an aftermarket ring guy that many here use.

From post#4
"This is a pic (if it loads)of the head button style I have in mind. (not mine)"

Hi, no head made just yet. Squish will likely be ~.025" for 50% of the chamber.
Just have to decide what ball mill to use and how deep to go.
I would like recommendations on the compession ratio, if you have ideas.

Back in the day on a 2 stroke the rule was no more than 9.5 to 1.
8.5 is pretty common on high performance motorcycles.

I read on the doropower site on a couple engines the compression ratio was about 7.4:1.Low,but a starting place maybe.Also if ya havent been there already go check out this website and click on the bicycle power.[just for ideas maybe].
www.carrprecision.com

Hello,Guys
Thanks for the compression ratio tips.
I'm thinking a geometric ratio a little low
to be safe. (to start out anyway.)

Yes, I’ve been to the Carr site, have some of his
Photo’s on the hard drive.

Where I live this will not be “exactly” legal to
ride on the street. All the motor kits I’ve seen
are either like Carr’s or mount in the frame
like the old Harley Whizzer’s.

The little "Free air cooled" Echo will nestle just in front
of the rear wheel on the seat tube of my old Raleigh 10
speed.It should be very slight of build, and hopefully mostly
out of sight, much less obvious and much lighter than the
mainsteam kits.

This thread has my blessing.

Though the engine is not actually intended for a model, this project will endure all the design pressures involved if you were in fact making an engine for a model airplane or car.

Enjoy

Jim - Moderator

In two stroke engines, two types of compression ratio are mentioned. Geometric, and trapped. Geometric is where the displacement is the base value. Trapped is where didplacement after the exhaust port closes is base value.
Neither are of much use, since compression end pressure/temperature is very much dependent on how the muffler system handles the pressure waves.
So a trapped CR of 7.5 is quite common.
My 50cc racer had a geometric CR of 13, combined with 180 degree exhaust porting and tuned pipe, so effective CR (from the moment cylinder pressure equals outside air pressure) was about 8.5, which is the max for dependable engine operation on 98 research octane fuel.

Hello,
I made a little more progress.
I believe the aluminum stock is
starting to look like a cooling jacket now.

Next is to final size the jacket bore and
part off the extra stock.

Looks very good. You are making good progress.