so far the poulan has the echo beat in the weight department, I believe it was about 2lb 4oz including prop, I just acquired a 16cc echo (this one ran before I tore it apart, so that's a better start than the 18cc was), the engine was like 5lb 6oz with EVERYTHING on it including gas tank, once I stripped it down to magneto conversion specs it lost 2 pounds and was 3lb 6oz, but I hadn't removed the starter pawl off of the rear of the crank, once you remove the flywheel and coil/module and spark plug you are down to 2lb 6oz (5oz of that is the muffler), this is without a prop adapter or prop, haven't trimmed the case or made a prop adapter yet.

as for a prop adapter, I'm thinking of running this thing on gas/glow to keep the weight down, not to mention the magneto is mounted on the fan schroud, and the ignition system is bulky with the two separate parts. This engine has the straight cut output shaft with a keyway, I was going to make a short round spacer with a key slot to act as the flywheel did on the magneto and top that off with a standard simple threaded all the way through prop adapter with a prop bolt, this sounds a lot simpler than making an adapter that is held on by the nut, then the prop held on by say 4 smaller bolts. I suppose I could make a super short adapter and hold the prop on with the nut, or chuck the crank up in the lathe and tap the end to accept a bolt... I think I'll stick with the original plan...

I'll try to get some pics up tomorrow and as I make progress

the plans for this engine are to mount it up to either the .40 size US Aircore biplane I have sitting around, or get a .40 or .60 size Stick, heck, maybe put it on the tower trainer across the room...

Heres a pic of my 20 or 21cc echo.As you can see i did one of the ways you mentioned.Mine is a straight shaft also.I didnt put a keyway in yet and not sure if i will.I put a taper on bottom of hub to match taper on crank.When tightned down it shoudnt move.Not sure if im going gas/glow or not yet.The weight on mine in pic is 2lb,7ozs.The shroud around engine was the stock cooling shroud and i left it on there and bent the edges out a little to promote good airflow around the cylinder.This has domed piston top.Dont know if its better or not.As you can see it has the 4 bolt case with large bearings and seals.Doesnt the poulan have the cantlever crank and no rear bearing.

ok, so I'm a couple days late...

like I said, the crank is straight cut, not tapered, I could probably go without using the keyway and just loctiting it down, I guess that would be about the same as the normal method...

This engine seems to have a flat top piston, I haven't stuck a compression gage to it, but it started right up so I assume it's in pretty good shape. It's a 2 bolt jug, I haven't taken it apart any further than in the pics other than taking the muffler and carb off, looked good through the exhaust port, bit of blow by, but not serious.

yep, the poulan is a cantilever crank, I think that's why it's lighter, less "stuff", it can be seen in the last pic, the thing was less than 2.5 pounds as pictured, once converted to 24cc was still under 2.5 pounds... a friend needed a piston and jug for his actual weedeater, so that 24cc got donated, will probably get a bowman ring for the piston/jug I got from him since it just had a stuck ring, piston and cylinder are fine, it was a victim of being ran partially choked (so much for running lean and clean, it was even a two needle carb, I did him a favor and removed the limiters) and ran rich to death...

Buck, looks like you neglected to attach the pic

Yup,got carried away with the keys and forgot the pic.Mine has the 4 bolts for cylinder,but this is the 20cc but i was posting because my crank is straight like yours and weight.Just wanted to show the hub.I used my new boring bar to do the recess on top of the hub with the allen head bolt.

been there, done that

I have one of those engines, odd setup, the fan is way different than any others I have, I think that's the only engine with that spark plug setup, or at least the only I've seen

is the crank threaded for a bolt, or did you thread it? that's not a bad idea, but I don't have the tooling to pull it off accurately, might attempt something, we'll see

The crank was already threaded.As a coincidence,it used the same bolt as you see in the pic.But,as you stated the easier way would be to use an all thread,slide everything over it,and just use a washer and nut to tighten.Or if somone didnt like using all thread just use a stud.Ace has a very large selection.Thats where i go.Im going to makea header and use a tuned pipe[muffler] that i made for it already[the muffler].

I haven't forgotten about this thing, life just keeps getting in the way of fun... working 60 hours at work doesn't help anything, especially when it's 60 hours being stressed out the whole time...

would a 40 size ultimate biplane be too much for the 16cc echo? if it is, there's always the magnum .46 on the shelf...

I had a 16cc Echo that I slightly modified once. Light porting, free flowing muffler, larger carb, and electronic ignition. I can't remember props and rpms, but it flew a .60 size Big Stik. It was adequate for basic aerobatics at sea level, but was slightly underpowered when I later moved to a field elevation of 4000' with high temps.

Try a 14 or 15 x 6 prop, and I recommend APC.

AV8TOR