I just got through converting and souping up an Echo 21.2cc engine for my brother. We all look for the better 23.6cc engine, but this 21cc turned out pretty well.

Specs:

Port timings changed to:

Exhaust 150 degrees
Intake 143 degrees
Transfers 100 degrees

Free flowing muffler
9.5 mm carb "massaged" to 9.7 mm
Carb adapter opened up to match carb outlet
Deck clearance set to .020"
Frank Bowman top ring at .001" gap
Stock second ring

Running on Gas/Glow, after only one tank of fuel it turns an APC 14 x 8 at 9600 rpms!

I don't have other props on hand at the moment, but it should turn a 16 x 8 at over 8000 rpms. Not bad for a little 21cc, $10.00 engine...

It starts on the first flip nearly every time, and curiously, after about 20 starts it has never once started up backwards. My other Gas/Glow engines do occasionally start backwards if I'm a little lazy flipping the prop.

AV8TOR

I know,my ECHO 21.2cc -1.3 clone-runs real nice-I am running an apc 16x4w prop on it though.Have'nt flown it yet but it pulls my engine stand real hard.I have a post up "FPE clone" I'm sure you have read it.Mine is stock too,.......Hmm maybe I'll do some mods on it or send it to you av8tor1977! If yer interested.Mines full gasoline though.I'd like to keep it that way.

ECHO 21 is the original, FPE is the clone...........

Here's some pics of the little guy. Fun project. It weighs 2 lbs. 8 oz. as shown, ready to fly.

AV8TOR

how are you doing the prop adaptor?

Hi AV8TOR,

Nice conversion! Did your Echo 21.2cc come from the blower?
Thanks...Brian

You know, I've had so many of these little guys I can't remember which is which now... I think it came out of a blower.

AV8TOR

how were you attaching the prop drive?

The prop hub screws on, and has a set screw that goes against the crankshaft for extra security.

AV8TOR

dont seem precise enough for hall sensor

Echo 21 is a great engine. i have an ancient one with the factory points to mag conversion , the cranks at that time still came through with the cam ground into the crank for the points.

Oh the prop adapter doesn't move once installed. I use Loctite on the threads, and then with the set screw besides, it doesn't budge. Often times when I take them off I have to heat them to get them to come loose.

This particular engine was set up to run Gas/Glow, and it doesn't use a Hall sensor. When I use electronic ignition, I make up an adjustable collar that goes around the small diameter of the prop adapter. The magnet goes in the collar, and the timing adjustment is made there. Works fine, and has done so for many years.

AV8TOR

cool im here in az as well do you have any pics?

Sorry man, I am visiting my brother in Tucson and don't have access to my computer files and pictures at home. Probably be here another couple of weeks...

AV8TOR

Here is a link to a thread with a pic of one of my electronic ignition prop hubs. The picture is a little blurry as at that time I was still learning to take close ups with my new digital camera, but I think you can get the idea from the pic anyway.

http://www.rcuniverse.com/forum/m_81...tm.htm#8139075

AV8TOR

I have one that I want to try gas/glow on. What fuel mix and oil mix have you had good luck with. Of course, what plug, and start only or full time glow? Thank you very much. Do you make prop adapters for other people, I need one?

Regards,

Richard

If you want even more power, you could put a g260rc head kit on it. It ran well until the flywheel came loose and destroyed the keyway [:@]

my 21 looks way different

The G26 cylinder and piston fit on the Echo 21cc crankcase??? Any modifications needed?

AV8TOR

Sorry Spaceworm, didn't notice your question as the G26 cylinder apparently on an Echo crankcase caught my eye.

Here is all the detailed info on Gas/Glow: http://www.rcuniverse.com/forum/m_80..._1/key_/tm.htm

AV8TOR

Well, kind of.
Since the two cylinder bolts are on opposite sides to the echo's cylinder, I had to drill and tap two new cylinder mounting holes. Before this I also had to strengthen the case halves using jb-weld, to give the screws some more material to bite into. The hardest part was getting the cylinder correctly seated onto the case.
The G26 piston and pin went onto the 21's connecting rod without any modification. The only thing I got a bit worried about was the fact that the piston skirt comes very close to touching the counterweights at BDC. But this never gave me any problems. The transfers also need to be matched to the case...but I never got around to doing this. Also, the stroke of the 21 is about 1mm shorter than the zenoah's, but once again this never really caused any problems other than a slight loss of compression.
I think a G23 piston and cylinder would have probably been better, but I already had the spare 26 head kit laying around.

Interesting. Thanks for the info. If I remember correctly, the 25cc crank has approximately 1.5mm longer stroke. Might make a better match?

AV8TOR

Yeah that would be perfect. I didn't realise there were so many variations of this engine [&:] Do you know if the 25cc crank would fit into the 21's case?

Yes, it will fit. I have made hot rod "stroker" Echos using a 25cc crank in a 23.6cc engine. The 21.2cc and 23.6cc engines are identical except for bore size, while the 25cc engine has a longer stroke and a physically bigger cylinder. It's been a while since I did it; I think you need a couple of spacer washers on the crank to center it in the crankcase and take up some excessive end play when swapping the cranks. You also have to make a cylinder spacer, but you size it to get the deck height exactly how you want it.

AV8TOR

I just found this thread. I have an Echo 21 which had some sort of custom ignition system added. This has a throttle adjustable advance system, but the wires to the hall sensor cracked. I believe C&H (out of business) sold an ignition system with no auto-advance. The only systems I can now find are auto advance such as RCexel. I did test the engine on gas-glow and I may continue to do that. But I am wondering if there are any non-advance ignitions available these days, so I can use the original thottle advance. I may also remove the throttle advance and use an RCexel.
Anyway it's a cute small engine which will find a home on a plane sometime.[X(]

Rod S