I am working on my first engine conversion it`s a 31cc Ryobi. I am installing a new ring to freshen the engine seal. My question is what other performance mods can I make to this engine to improve it`s power output. The engine came with a WT 340 Walbro carb and has the desirable cylinder, no porting slots. I have read on the forum about guys milling the bottom of the cylinder to up the compression ratio. Is this an advisable mod ? If so , how much is acceptable? Any information will be appreciated.

where you getting the new ring and how much?

See My Ryobi hopup and results at http://home.wanadoo.nl/pereivers/ryobimods.htm

I got 2 questions. Will the stock rod stay in one piece? How is the vibes on this engine? Thanks Capt,n

The engine is sweet running. I think the rod will last long enough if you don't push the engine too hard or run it too hot. The needle bearing is quite large, so can take the load.

Pe reivers: In what state of tune is it sweet running? In other words...how much can you "hop it up" and still have a sweet runner? Thanks Capt,n

I originally purchased an OEM ring from AES Lawn parts in Olathe Ks. for $7.03. I have since been enlightened by this forum to a superior product made by a gentleman named Frank Bowman. I intend to purchase a ring from him at a cost yet to be determined.

In any state of tune. The engine is well balanced internally. My engine was modified with EI for easier hand starting, so ran without the flywheel. However, vibration levels with and without flywheel were low, probably due to the quite moderate compression ratio. My last mod was with rotary inlet. To this end, I used the rotor from a Moki 30cc gas engine, and made a bronze bushed rear cover to fit. Compression ratio was very slightly increased by fitting a thinner cylinder foot gasket.
Improvements should be directed toward better gas flow. Higher compression is a last resort, and will generate more cyle-torque-change vibration and harsher running.
As a side remark: Idle should be kept a little on the high side. At low idle the engine tended to cut out without warning.

pe reivers ; I checked out your website regarding the Ryobi hop-up, it is just what I was looking for to get me started. You have definitely sped up the learning curve. I intend to utilize the modified carb with the large reed design as exampled on your site, but have a few questions. The large reed that is displayed, was it pirated from another type engine or is it something you constructed. If you made it , where would I look to find suitable material for making a reed. Please remember I`m just getting started in this 2cycle world and this is all new to me. Sadly I was unable to access the cad download dealing with compression and porting changes. My Microsoft program keeps telling me that the file was coded wrong upon entry. But I tend to think it may be my ineptness with the computer rather than a wrong code. Nonetheless I was able to find a couple of websites that briefly dealt with the subject. I have access to a mill and a lathe which will allow me to make many of the changes desired. My intention is to mill 30/thou. off the crankcase to increase compression . Could you please outline the modifications necessary to the piston to retain port timing? I also measured the reed retainer to crank pin distance and can mill 80 thou. from the crankcase to decrease the case volume ( stuffing I believe it`s called). Do you have any tips or words of caution regarding my intended actions before I start cutting things up. Thanks for your help the information that you have made available is enlightening.

Don't be too concerned about the timing. We run our engines at around 7000 rpm, so timing can be quite tame. However, the reduction of piston deck height is more damaging, so do not mill the case down, unless you are prepared to mill out the combustion chamber and restore squish space. This squish space can be checked with solder wire. It needs to be more than 0.5mm if you want your engine to survive.
Your ignition may limit rpm to 7000. Check that first. The flywheel has a patent number, can be checked at USPTO.org or .gov, or .com (forgot!). Anyway, the patent gives complete disclosure of how the ignition rpm cutoff (if present) works.

Thanks for the heads up on the ignition cut out and the squish area check. The solder method has been around for a long time. Simple but effective! Can you give me any help with the reed replacement issue ? Thanks again ; John O`Neal

hey, what about your own grey cells?

Slap !!!!! Wow !!!! I didn`t see that one coming. I guess I set myself up for it though. But before we close this dialog box for good let`s do a little review. Being new to the 2-cycle /engine conversion hobby, I was acutely aware of my lack of knowledge regarding parts and material availability, and procedures designed to improve upon the various manufactures offerings. I joined this forum in an attempt to expand this knowledge as well as to accelerate the process. I submitted a thread requesting ideas and information on Ryobi engine modifications. You had every opportunity to pass on this post if you felt your knowledge was proprietary. Instead you posted up and directed me to a web page of your design containing a lot of neat stuff dealing with this subject. Many of the procedures you outlined in the tutorial were well beyond my capabilities and experience level at this time, but I felt a few were within my reach. You were very detail orientated in several of the procedures presented, giving up both material composition as well as the donor source, ie (the rotor came from a Noki 30cc gas engine). With that in mind I held no concerns regarding how altruistic your motives might be. I naively thought that you genuinely wanted to help some one just getting started in this hobby but all that has happened here is that I have given you a forum to flaunt your superior knowledge. I am positive that you didn`t invent the reed valve concept or develop the metallurgy needed to build these springy little objects. You learned of their existence and application somewhere, just as I am trying to do. The grey matter shot was a cheap one, not normally associated with someone of your capabilities and intelligence.

I have used Feeler Gauges as reed replacement Material.

They don't have the correct dimentions for all reeds but they are strong and I have never lost a reed that I have made.

No grey matter needed, I was told about this by a friend.

please cool down. All in good humour, and I did not mean to knock anybody off his feet. Just a slight nudge to keep you thinking for yourself.
You were born under scorpion eh?
I indeed started out like you, and and all I know was taught by others. What I make of my knowledge is mine though. That's where grey cells come in handy. If I conveyed that message to you, I am happy.

John o Neal: I think P. Reivers was kinda in a hurry and just gave you a quick answer that did have a lot of neat tricks. I do think Mr Reviers reply with the "gray matter" does not fit in good at all. I hope Pe R. Gives you more of a apology. We all must try and remember there are all types of people just learning kinda as you go. We do not all start out with high perform ace engines. Mainly we use what is available easy with not too much expense involved. Best Regards, Capt,n

The Ryobi is ok, and it's a neat engine for a narrow cowled airplane like a Tiger Moth or perhaps a Mustang. But it's a lot easier to get more power out of something like a Homelite or an Echo engine for example, in my experience.

Once you get a Ryobi really tweaked, you have to wonder how long that stamped steel rod is going to keep the piston hooked to the crank. Every time I see a Ryobi rod it gives me pause. I'm surprised they hold up as well as they do. But hey, I've got one flying on one of my planes, and my brother as well as many others do too.

The bottom line though, is you are probably best to just add a free flowing muffler, a 9 or 10mm venturi carb, electronic ignition, and go fly it. That's the extent of hopping up I would personally recommend, unless you got one with really low exhaust port timing. If your exhaust port timing is down around 120 degrees, you will see nice gains if you carefully raise the exhaust port up until you get about 140 to 150 degrees. (No more than 150 for sure.) Prop the engine for no more than 7500 rpms on the ground, and go fly!!

Just my two cents worth....

AV8TOR

I am going to try and make a custom connecting rod for one of my Ryobi engines. It shoud be as good or better than original. I also got 4 con-rods I have to machine for my Holt 4 cylinder engine. Capt,n

Shouldn't be too tough to make a rod. Man, I need to buy a mill.... []

AV8TOR