Which one is better for conversion?

I have 3 Ryobis and 1 McCulloch. I plan to use an electronic ignition from CH on either one I choose. I've been told that the Ryobi will not develope the same HP as the McCulloch, but the Ryobi is lighter.

I can get a muffler and ignition for each of these from CH. I've read some of the things that you can do to the Ryobi to Hop it up. I haven't read anything about doing hop ups on the McCulloch.

I'm really wanting to do a conversion on the easiest one. I might be all wet here, but the Mc looks like it would be harder to convert.

What do you guys think?

Talk to Terry at CH..I got a Mc in a trade the had been worked on by them..
Kept the ignition and sold the motor...
To tell the truth, a Ryoby31 with a 18-6 woodie and a CH ignition is a real dependable and fun engine..
Whacker sells a great motor mount with all the goodies for about $18.00
Guage the reed stop to 1/8 inch and go with a bigger carb and weld a 1/2" peice of electrical conduit to the back of the stock muffler to open it up for flow and that should be good enough.

Their's no one around here that wants to work on a Mc if anything goes wrong..

Just my 2 cents...
BB1

I figured that the Ryobi would be less of a hassle. If the Mc was to have problems, and i couldn't get help- it wouldn't be too much fun.

Since I've got 3 of the Ryobis, then I guess I'm off and running in that direction. Thanks for the suggestion.

Much of it depends on what type of aircraft you plan to install the engine in. The RIRE Ryobi lends itself very well to planes with long narrow noses like the PT-19 and J-3 Cubs. But the drawback is that the firewall-to-prop-hub distance is very long with most of the commercially available mounts for the Ryobi ( typically >7-1/4"). This means you'll either have to move the firewall back a couple of inches (easy to do with a kit, not quite so easy with an ARF) or mount the engine with the carb sticking back through the firewall.

Not sure which Mac you have, but I think it's either SISE or SIRE, so the firewall-to-prophub distance will be more reasonable, but it will need a wider cowl to conceal everything.

Powerwise, if your Ryobis are the newer dual ring versions, then they will probably be comparable to the Mac. Otherwise, the Mac will be a substantially more powerful, albeit heavier, engine.

If this is your first conversion, and you plan to do most of the work yourself, I would recommend the Ryobi. It is a more popular choice for conversion, so both sources for parts and the experience knowledge base will be more plentiful.

[quote]ORIGINAL: Rcpilet

I figured that the Ryobi would be less of a hassle. If the Mc was to have problems, and i couldn't get help- it wouldn't be too much fun.
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I really meant that parts in my area are almost nonexistent...no one likes to work on them because their's no real parts supplier here..

I figure that if I can have it haul around a 15# bird that will do everything but hold a hover for a $40.00 to $50.00 motor, I'm staying well within my plane budget.

Even though I buried my "Son of Weedwhacker" two weeks ago...and had to stop by the local handyman store on the way home and buy a new motor...Wooopie..

4 cents..

These are the older single ring pistons. I've done a Poulan 54cc conversion. It runs great with ignition from RCIGN. I've got another 54cc Poulan that I've already cut up. I just need the ign. hub, carb adaptor, and mount.

I sent a 34cc Craftsman to Ralph. He's working on it now.

I feel pretty confident that I can do the Ryobi myself. I've already ordered an engine mount from a guy on Ebay. I'm going with the CH on this one. I talked to them yesterday. Really nice guys and very informative.

I'll try to move the reed valve limiter out a bit to improve performance. I've got a friend who is willing to deck the cylinder a little for me. I read somewhere that you can go up to .025" on the cylinder. I'll probably go a bit conservative there and only deck it about .015" I'm going to get ahold of Frank Bowman and get a new ring from him. CH sells a bigger carb for it, but I've read conflicting reports on the carb modification. One report says that if you want to swing a big power prop--like an 18-8; the you should stick with the stock carb and plan on running the engine at lower RPMs. The other report says that if you want to swing a smaller prop-- like a 16-8---then you should get the larger carb and let the engine run up to 8000RPMs or thereabouts.

I'll just run it with the stock 9mm carb for now and see how it likes a few different props. It will just depend on where I can get the most thrust and still have enough clearence to swing that particular prop.

Has anyone done anything with the exhaust port on these? I would think that if you were to shave .015" off the cylinder that you'd be loosing something on the exhaust port. The compression would go up- but you'd be changing the exhaust duration and timing by lowering the cylinder. I guess you'd just grind the top of the exhaust port out the same amount that you took off the cylinder?? Maybe a bit more

CH told me not to try and run it too hard. He told me that it would probably fly apart if I run it too hard and try to hop it up too much. After looking at the crank and connecting rod----I'd venture a guess that CH is right.

I feel pretty confident that I can do the Ryobi myself. I've already ordered an engine mount from a guy on Ebay. I'm going with the CH on this one. I talked to them yesterday. Really nice guys and very informative.
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Nothing to it...
Just cut the backplate down even with the case sides...make sure the you place a washer between the low spot in the back plate, (You'll see it) as not to distort the motor mount or back plate...with the bolts that come with thre kit, their will be two new gaskets that comes with the kit that you ordered from Whacker Engines, their's a aluminum spacer that goes between the carb and the back plate, a gasket goes on both sides, make sure that the pulse port is not covered by either of the gaskets and the hole drilled in the spacer lines up with the carb...if it's inverted the adjustment needles are straight up...Some times you can get the whole carb through the hole in the motor mount to bolt up the motor sometimes you can't, if you can't the motor has to be bolted up first to the motor mount, then the the carb bolted to the back plate. Don't use two grunts and a grone for tightening the screws...or you are going back to the junk pile for a new backplate. I do recommend a good grade of thread locker be used on the bolts to the case and lock washers under the heads of the bolts..
The throttle arm my give you a fit..I soldered the ball of a ball link set to the arm after it was screwed together..never had a problem with it..
The pickup ring (actually a hose clamp with the chip mounted on it) and the prop adapter have marks on them and you just line them up...the will put you in the ball park..mark the snout of the motor and the hoseclamp with a scratch mark to use as a reference point to tweek the timing...
Here is the good part....SNICKER...I had this problem and called Terry...their will be toooo much clearance between the magnet in the adapter and the pickup...the only way to adjust it is to smack the brass channel with a hammer, (not a big one) and tweek in the clearance to specs...I kinda' fell out of my chair when I talked to him...just spent a lot of $$$$$' and he tells me to smack something with a hammer...But it works..
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I'll try to move the reed valve limiter out a bit to improve performance. I've got a friend who is willing to deck the cylinder a little for me. I read somewhere that you can go up to .025" on the cylinder. I'll probably go a bit conservative there and only deck it about .015" I'm going to get ahold of Frank Bowman and get a new ring from him. CH sells a bigger carb for it, but I've read conflicting reports on the carb modification. One report says that if you want to swing a big power prop--like an 18-8; the you should stick with the stock carb and plan on running the engine at lower RPMs. The other report says that if you want to swing a smaller prop-- like a 16-8---then you should get the larger carb and let the engine run up to 8000RPMs or thereabouts.
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This part here I don't fool with...I ran a 18-6 wood Master Airscrew with the stock carb. and it loved it..

I'll just run it with the stock 9mm carb for now and see how it likes a few different props. It will just depend on where I can get the most thrust and still have enough clearence to swing that particular prop.

Has anyone done anything with the exhaust port on these? I would think that if you were to shave .015" off the cylinder that you'd be loosing something on the exhaust port. The compression would go up- but you'd be changing the exhaust duration and timing by lowering the cylinder. I guess you'd just grind the top of the exhaust port out the same amount that you took off the cylinder?? Maybe a bit more
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I don't fool with this either..Have read about making a base gasket out of a office folder and reducing the cylinder height that way...Haven't tried it...

CH told me not to try and run it too hard. He told me that it would probably fly apart if I run it too hard and try to hop it up too much. After looking at the crank and connecting rod----I'd venture a guess that CH is right.
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The rod is a two piece affair with the bearings in the middle, the back of the crank is plates sandwiched together..ALA...if it goes too fast or tooooooo hard, "somthin' gotta' give."

Moral of the story..."Ya can't make a Silk Purse out of a Sow's Ear..."
You just might be spending enough money to make a "hot motor" that can be purchaced for the same price that you will have in the one you just converted..

Hope this helps...
BB1

Good news[&:]
I tore the engine down and checked things over. Looks pretty straightforward. I found what's left of my first attempt at a conversion; a McCulloch 35cc chainsaw. Too bad it had needles on the crank shaft. But, the carb is still worth a look. I took it off the enfine and checked it against the Ryobi. The Ryobi stock carb is actually SMALLER than the intake port on the backplate. My other carb from the mac 35cc engine was a drop-in replacement------only its the exact same diameter as the backplate port. That ought to pump things up a bit. The pressure holes for the pump line up perfectly and the linkages are all the same. Its about 2 or 3mm bigger than the stock carb. It's a Walbro WT 348 carb. It'll need a gasket kit, but thats no big deal.

I ordered a ring from Frank Bowman. What a nice guy!!! He talked me through the entire process of this conversion. His ring should help the engine out quite a bit.

I ordered the ignition from CH today. What a bunch of nice guys!!!

I'm going to try and clean up the intake ports a bit on the inside of the case. I just want to radius the edges a bit to smoothe things out. I'm not going to hack a bunch of metal out of the case, just radius the bottom side of the ports near the crank counterweight.

Where can I get a gasket kit for the engine? Or do you just make a new set from gasket material that you find at the auto parts store??

If you want to hotrod a Ryobi, I would strongly suggest you do so on a twin ring version. I have both the old single and the new twin. Even though the conrod in the new engine is still the same stamped steel affair, Ryobi beefed it up quite a bit with wider webbing on it. The counter weight is made of a stack of steel plates riveted together - not exactly confidence inspiring.

I did run a single ring Ryobi with Bowman ring on glow fuel for a while. On 15% nitro, it will spin an 18x8 clear past 8500rpm. I chickened out and never lean the needle all the way - only pinched the fuel line briefly to see the tach jump past 8500rpm. Maybe The Ryobi is strong enough to handle the extra power, then again maybe not. Terry told me the same thing about the Ryobi. When a guy like him gives me advice like that, I take it very seriously.

BTW, I got some gasket material from Tower, and it's quite a bit thinner than the original Ryobi head gasket. I'd imagine any type of automotive gasket material should work fine too. Hi-temp RTV also works good.

All the gaskets you need, except for the cylinder base should be coming with the motor mount kit from Whacker...
If not lawnmower repair shops will be glad to sell you gaskets..

BB1

I got a sweat deal on a Synchro-spark unit from Terry at CH. I believe it was a damaged unit that had been repaired. Works perfectly.

I ordered the gaskets from the local mower shop. They should be here next week. I ordered new gaskets for the carb, backplate, and jug, as well as a carb rebuild kit for the one I am using from the Mac 35cc engine.

I bent the reed valve stop on the backplate to let more gas in. I got the ring from Frank Bowman on Saturday.

I've got a motor mount and muffler coming in the mail.

I have the following props available:
APC 16-10
APC 16-8
Zinger 16-8
Zinger 20-6
Top Flite 18-6
Top Flite 18-8
Top Flite 18-10
MA Schimitar Wood 19-8

I'll probably try them all with the stock ring. Then I'll let it cool off and take it apart and put the Bowman ring on. I'll take tach readings and post them.

Wonder how long it will take the Bowman ring to break in? Should I run it rich for a few tanks with the new ring? I've been running 40:1 mix.

This is so fun!!!

I wouldn't bother with the stock ring, unless you're just curious to find out what the a difference the Bowman ring makes. For a fair comparison, however, you'll have to allow both rings to seat properly, which could take gallons. If you've already got a plane, then sure, fly with the stock ring first. Then after a dozon flights, swap in the Bowman ring. Running it all on the bench will be painful.

Running a rich mixture doesn't do a gasser much good. It just cokes up the engine faster. Better go with either 25:1 or 32:1 instead if you want to give it more oil during break in.

Looks like I'll be installing the Bowman ring right off. I'm not about to spend gallons of good gas running this thing on the bench; just to compare RPM gains.[X(] This is a used engine- so I'll assume that the stock ring is broken in. I'll run it briefly with the stock ring and check RPM with different props. Then I will install the Bowman ring. I'll have to check the RPMs preiodically as the new ring breaks in.

Do you think I should run it at 32:1 for a tank or two when I install the Bowman ring?

I'm not familiar with gas engines. This is only my second one and I've not yet had to break one in. My other gasser is a used chainsaw and it was already broken in when I converted it.

Isn't it?

RCpilet, 32:1 is fine. The differences between 25:1, 32:1 and 40:1 are really only about 1 Oz - roughly 5, 4, and 3 Oz. per gallon respectively. I usually just eyeball it and err on the plus side for brand new engines, but it isn't really that critical unless you start pushing the limit with the 100:1 stuff.

Can some one tell me who Terry at CH is.
What is the web site??
or phone number?

Thanks

www.ch-ignitions.com

Terry is one of the guys who works there. Heck of a nice guy to talk with and he's a straight shooter.

Have you used a 35cc mac on a plane ?I have one and would like to know if it will work, and how to put it on.THANKS