JCaste

Hi all,

I've been looking at some Ryobis on the net and I'm a bit confused. Well, I searched for Ryobi simply because it's what I hear most, so I figured it was the common choice for conversions (I don't doubt there will be more powerful engines out there).
Probably, the basic design has been around for many time, so it's kind of logic that not all them are the same.
Some places tell you about single or double ringed pistons; improved (stronger) connecting rod, "compression release channels" (something to make it easier to start?) and other marvels of the modern world. I don't know how much of that can be said to "improve performance"; IMO often design variations are made to make construction easier, cheaper, faster, etc. and not necessarily to make a more powerful (and "thirsty" too) power tool.

So what are the main differences between versions? Is there a real difference in performance with those changes? An older model can be "updated" somehow?
Thanks in advance!

davewallace

My Feedback: (29)

J,
Ryobi's come in single and two ring versions. There are two shaft versions, long and short. Many have vertical slots cast into the cylinder wall above the transfer ports. These make the weedie easier to start, but reduce topend power. Some older models have tinnner con rods, which don't hold up to high RPM as well. Some have smaller diameter countwer weighs and crankcase inside diameter. There is some variation in the backplate and reed designs. This effects case volume. The port timing is about the same on all models. Exhust duration is 150 degrees and transfer duration is about 110 degrees. Of course the intake timing is variable, because it is a reed valve. Thats about it.

Dave

JCaste

Thanks Dave. That was very helpful.

I'm worried about this... It can mean a important power decrease. In fact, it's the first time I hear of such thing in a small engine (the kind of "decompressor" I knew was a valve on top of the cylinder in some small bikes, which you pulled with a steel string). Is there a way to find out that without opening the engine?

davewallace

My Feedback: (29)

J,
You can look through the plug hole, if you have enough light. The exhust is the best place to look with the plug removed. Homelite used a small hole above the exhust, half way up the cylinder. It went into the muffler. I tap the hole and plug it with a screw. Not so easy with the slots. There are so many venders and versions of the Ryobi, that it is hard to tell by model number etc.

Dave

JCaste

Thanks again Dave! If you just tell me if those "slotted" engines are worth a try or better avoided, I won't bother you for a while.

davewallace

My Feedback: (29)

J,
If you get some used engines from the local repair shop, you can take them apart and use the best combinations. If you buy new, look out for thoughs that claim real easy pull or easy starts slogons etc.

Dave

Rcpilot

My Feedback: (78)

The 725R is the long shaft.

The 700 is the short shaft.

The ones from Harbor Freight can be had for around $50. They state "factory reconditioned", but my engine looked perfectly new to me. Cost me all of $58 shipped to my front door. I bought the 725R engine in an MTD/Yard Machines weedie. It is a twin ring with NO compression relief slots. Carb is a little small, but anyone who tinkers with conversions is gonna have 5 or 200 carbs lying around.

You can get parts from Peter Faith at www.wackerengines.com I heard he got hit by a hurricane, so his website might be down. Don't have any idea what type of business he's doing after the storm. He's a good guy and will talk your ear off. Full of knowledge.

www.carrprecision.com is another place to get conversion info.

Go to ebay and buy "parts" chainsaws. As long as the cylinder and piston ain't scored--you can pretty much make an airplane engine out of any of them. Try and stay away from the ones with needles on the crank bearings--McCulloch in the smaller sizes. They can be made to tturn a prop--but it's a bit more work. Easy if you have a milling machine and a lathe--not so easy if you ain't got those tools.

Chainsaws are kinda doggy on power untill you get up over 35cc. Get yourself a 40cc or 60cc chainsaw engine and you'll be pooping your shorts when you start it for the first time with a big hunk of lumber bolted to the business end. It's a kick in the pants!!

tstotts

Running a 2 ring Ryobi 31 on a 4 star 120. Any suggestions on prop size?

JCaste

Dave, I just can't go to my local repair shop here. [:@] Most power tools are electric, so the few that exist are property of its respective brand; i.e. you have a stihl repair shop. In some small towns you can be lucky and find one, but their engines are overused and expensive (I tried once and will never again). The price and availability totally defeats any benefit of a conversion.


That's a nice idea! - but it's more than likely that Harbor freight won't ship to me. It's this item, isn't it? http://www.harborfreight.com/cpi/cta...emnumber=55008
A bigger carb and misc. conversion parts (mount, hub, etc.) could probably be ordered from those sites (I think wackerengines is working). I have a lathe, so I could machine the flywheel myself.

Buying a big sized chainsaw and salvage the engine was another option in my "to do" list. A 60cc would be just great! I don't know how much power they have exactly, but from what I've seen and read those engines aren't powerhouses unless you heavily mod them (not my case). Is there any engine like that at harbor freight? Or should I search ebay till I find a used one (which scares me, you have no idea of the health of the engine)? Are there any basic guidelines to follow when looking for such things?

I'm sorry to ask so much, but I live in southern Europe and things here work very differently. Almost everything is electric, except for the biggest and meanest power tools, and a few chainsaws (and they cost at least 50% more, so buying one outside with shipping and taxes still is much cheaper).
Regards!

mikenlapaz

JCaste Loving 3D since 8/6/03! Do not expect to do 3D with a Ryobi 31. Big gas trainer planes and some warbirds are better suited for weight and power output. Plan on a larger carb as well.

JCaste

Mike, in first place, I didn't plan to use the engine for anything more than mildly aerobatic, and that, in the best case. Those engines seem good at swinging a big prop and having a very cheap operating cost (making them good for big scale planes like Pipers, towers and such, perhaps something a bit wilder). In second, I'm going to update my signature.

I've just been searching for chainsaws in ebay and it's been discouraging for several reasons.
To begin with, I don't know what stuff is good to be converted, no idea what brand or model to search for and what is a reasonable price. Yup, if you have a mill and lathe you could convert nearly everything, but that's not my case (some engines may also be a bad choice or have low power).
So I do a search by price range, and realize they are not even close to the 45$ a fellow rcu memeber paid for a 55cc chainsaw (going for 99$ with a couple of days left). But even if I was lucky enough to find a deal, I couldn't bid for it - shipping only to the US.[:@]
It really kills my desires to experiment with gassers.[]

captinjohn

JCaste : Did you call Harbor freight or email them. They may ship to spain. Not usre! Capt,n