Scrubmonkey

hi there everybody. ive been wanting to get a bigger plane and wanted to try gas but my near non existent budget (too low) wont allow me to go get an os gt33 or similair. i was thinking of trying a conversion and bolting it to the front of a hack trainer style plane. here are a few questions.
1)is it better to use a whipper snipper or chainsaw engine?
2)why? reasons for answer above
3) i dont want to use the fly wheel and i have access to cnc lathes and milling machines etc at school. i believe i need to use an ignition system. i was wondering if this (http://www.hobbyking.com/hobbyking/s...nes.html)would work. if not what would i need to make it work?
4)if that wouldnt work what is a cheap ignition system that would work?

i have experience working with small engines and regularly srip down pumps, push mower motors and carbies relatively easily. also if there is anything i missed can you please let me know. thanks for any help in advance.
bernard

rangerfredbob

My Feedback: (13)

1 and 2)chainsaws are generally ported for more power than a weedeater engine, but most chainsaws are large (30CC+) and most of the small saws have roller main bearings that don't lend themselves to thrust loads as well as ball bearings. For a trainer type plane as long as the power is reasonable it probably won't matter, but if you want to tinker with porting the cylinder you can wake up a weedeater engine.

3) that ignition should work just fine

av8tor1977

My Feedback: (6)

I agree with the above, and would add that most, but not all the chainsaw engines are more difficult to convert because the engine is part of the entire saw body, and must be cut completely out of the housings, then mountings figured out, etc. A notable exception is the Homelite 33cc, which you will find lots more info about here in the forum if you do a search.

As far as the weedeaters, I recommend staying away from the "Weedeater" brand itself, as the engines are cheaply made and don't have much power. Good brands to use are Echo, Stihl, and Ryobi. An older model of any of them is better, as a lot of the newer equipment is converting to a new style of transfer port configuration for smog purposes. These are not desirable. I've also noticed a trend to smaller ports in the later model equipment that also is not what we want.

Leaf blowers often make good candidates too, with the same caveats as above. I will add the Homelite brand to the mix when including leaf blowers, because the Homelite leaf blowers usually have, though not always, a 30cc engine. Externally the 25cc and 30cc Homelites look identical, but if you look into the exhaust port, the 25cc has a bridge, and the 30cc does not. There's nothing wrong with the 25cc engines though, and there is a mod you can do whereby you put a pin in the piston so that the ring cannot rotate, fit a new, special ring made for use with a pin, and then you can grind that exhaust port bridge out for more power.

You can count on it that most all of the weedie engines are going to need a larger carb for best performance, and any engine is going to need the exhaust opened up with a new or modified stock muffler.

AV8TOR

83scamp

I agree with all of the above. One thing I would add is try and find an older Ryobi 31cc engine. They are just about the easiest to convert(I have 5). Once you strip off the stuff you don't need, they even look like an airplane engine. The Hobby King ignition would probably be OK for starters, but if you want a really reliable ignition, go RCexl: http://www.rcextremepower.net/ignitions.html by the time you pay overseas shipping, the RCexl will be about the same cost.You can use the original ignition, but most have a safety built into them so they need to see 300 rpm before firing the plug. You cannot flip it that fast. You will need a starter to get it fast enough to fire.Welcome to the world of gas. Once you try it, you won't want to go back to a slimer....

av8tor1977

My Feedback: (6)

Ryobis have been through some changes. As you say, the older ones you just unbolted everything and there you had an airplane engine; no cutting involved. Then they made a version that had a one piece case that you had to cut the crankcase out of, and then I have seen some lately that actually have a Homelite 30cc in them! I also have at least one that has a completely different engine that I don't recognize at all. Just looking at the exterior it looks like it will be a fairly easy conversion, but I haven't had time to pull it all apart and see how good the ports are, etc.

AV8TOR

Scrubmonkey

alright then. this weekend im hoping to go to the dump and see if i can find something decent. so aim for either a ryobi or homelite engine, preforably a whippersnipper as a first choice and either a chain saw or leaf blower as a second choice. am i right with that so far?

Scota4570

Echo chainsaws with the plastic case are excellent and easy to convert. Look for four bolts in the bottom of the case. The short block will have ears with four mounting holes, like a glow engine. A 50cc Echo chainsaw is the basis for the BME 50. I bought a 30cc echo, on clearance,just because is would be so easy to convert. Unfortunately is also makes a great chainsaw. For now it is a great wood cutter.

If you allowed to pick the dump get whatever you can. Go nuts tearing stuff apart and see what you get. If it was free have fun with it. I have only seen one saw that had needle bearings. It was and old Homelite. Those won't work out. There is a carb in there, grab it too! Most of the dead units at the dump have fuel system problems. That is easy to fix and makes for a quick flip to finance your hobby. Some will have scored pistons/cylinders, those will be carbs for the carb box, not much else unless they are very desirable and buying a new jug and piston are worthwhile. I have a 79cc stihl that fits that category.

For now I agree on old Ryobies. For small planes the weedeater cheapo blowers are good. They are different than the wead wackers They are cheap, but they are long shaft and that is a big help. The muffler is held in place by screws, that is good, as some used a micky-mouse spring setup. These will spin a 15x8 are respectable speeds. They clean up very light. Later on you can mess with the big powerfull stuff.