Awhile back I converted a Ryobi 31cc motor over to prop and it has been doing pretty well on the airboat that I built for it but I have been embarking on getting the horse power up on it. My latest mod has been to ditch the stock back plate and mill one out of aluminum that uses 4 custom reed valves mounted in a V shape like on a motor cycle. This worked well but I need to combine it with some port work. Those of you who have had the cylinder off of their Ryobi have seen the 2 slots that extend upwards from the intake ports. They allow the intake ports to open quite a while before the exhaust ports. My best guss is that this is some kind of makeshift compression release for easier starting. Anybody out there know for sure???? Obviously with an electric starter this is not needed. I have found away to almost completly plug off these slots but am wondering if the compression will go to high without this designed in compression bleed off. What I am going to do is locate the slots position on the outside of the cylinder, then drill and ream a whole into the cylinder at 90 degrees in the center of the slot and press in a pin that will essentially plug the slot. Of course the pin must not hang up on the piston or ring. Any other ideas????? Should boost the power output a fair amount especially on the low RPM end of things. Not an easy mod but for someone with a mill and lathe at home it is pretty easy.

Fastball.

Hi,


I am also curious about working on the inside of the converted engines also, I hope you get some good info...



Weskel

Ever consider just picking up an older version wacker 'pre-slots' and changing out the head?

I switched heads on a new 2-ring piston engine and my wimpy elec starter would not turn it over... so there is compression difference.

Fastball,

I would love to see your modification, eager to do that myself.

-ZooMie

I would probably swap in an older head but the one I have has just enough hours on it to break it in properly. I am going to work out the details of blocking the slots this weekend. I already know how I am going to do the setup in my mill but I just need to work out the particulars. I even came up with a good way to determine the location of the slots and position the head correctly so I can cross drill into them from the outside of the case. If successful I will post how I did it so others can follow.

Will keep you updated.

Fastball.

As long as you have it open and can see, possibly measure, with the old back plate screwed on what amount of clearance is there between the reed limiter strap and the rotating crank parts(counterweight). Have wondered since setting 1/8" reed/limiter clearance.

How much, if any, did you open the hole diameter in the back plate for your "V" modification?

I will measure the clearance for you when I get home this afternoon and return post. I totally machined a new backplate out of aluminum and kept the intake hole the same dia for the time being. I am going to possibly experiment making it larger and maby carving some swirls into it to try and get a better fuel/air mix. The trick in the whole thing was keeping the crank case volume the same so the tune of the motor did not change. My current intake port arrangement is rough at the moment, it was more of an experiment at the start so I am probably going to remachine a nice one after I do some more tinkering. Once I am done though I plan to post a set of plans for everybody to follow. So far the motor seems to turn higher rpm with the v cage arangment but I think that I won't see really big changes until I block off the compression bleed slots. Will keep you all updated.

Fastball.

Fastball:
If your using metal reeds, you might try experimenting with carbon fibre and fibre glass ones if your not allready. Lighter, open and close faster and don't destroy the engine if they break. will need reed stops to stop reed flutter.

Mikenlapz, I checked my engine with the stock backplate and with a 1/8" gap to the reed stop there is about .045" clerance to the crankpin.

Flypaper, I have thought about some more flexable reed material made of a composite but I have yet to find anything that I think would work. Right now I am using some stainless material from a large feeler guage for my 4 reeds and it seems to be working. But yes I have been thinking that if I get the motor to put out a respectable amount of HP then breakage might be a problem. Logic dictates that my V arrangment would put less stress on the reeds themselves while allowing for more direct airflow. Let me know if you know of any composite reed material that people are using.

Fastball.

Friend of mine was into racing gocarts and he got the meterial from the place that sell the carbon fibre rods and tubes ( space Age Tchnologies) or something like that. I'll find out and let you know. He gave me some to experiment with so i'll measure the thickness to give you something to go by.

Hey,

Can you guys post some pictures of what your talking about....


I am folling the thread, but I'm like a 1st grader, I need pictures!!!LOL

Weskel

everything that is old is new again........
I think the absolutely best combo is the twin ring piston in the non-slitted head.
There was talk of seeing a Ryobi hover a while ago. My Stinger 1.20/Ryobi has the nuts to climb up from a hover at full power, but just barely. I'm gonna switch 18x8 APC to a 18x6 and I'm hoping it get good enough for better performance.
[link]http://www.rcuniverse.com/forum/m_865281/anchors_865281/mpage_1/key_/anchor/tm.htm#865281[/link]

Hi Fastball:

I filled the compression bleed ports with JB Weld, and it seems to be working fine. I made some test stand runs first, and when I pulled the cylinder the JB Weld looked fine. I've made several flights too, but I haven't pulled the cylinder again, so I really can't say much about durability. I undercut the slots first with a burr type bit in a Dremel to get a bit of a mechanical grip, overfilled the slots a little, and carefully shaved the extra off with a sharp large radius wood gouge without scratching the walls.

This is a worthwhile modification. Filling the slots gave me as much of an increase in power as when I fitted a larger carb, or when I gutted the stock muffler.

I was wondering the same thing Sportflier. The only thing that I was curious about was whether or not it would stand up to the heat. I am sure there are some hi temp compounds out there but I have not started looking for them yet. I have 3 heads to play with so I have been thinking about trying several methods. I will definatly look into a JB weld type of fix along with my idea of pinning the slots. Possibly a combination of the two. Can't do anything about it for about a week though, I am leaving on a business trip in about 15 min. Lets keep the good ideas coming and maby we all can come up with a slot solution for all! Keep us updated on how the JB weld holds up in your slots Sportflier!

Fastball.

Sportflier

This method of filling with JB Weld was discussed before but believe JB Weld cannot stand the combustion temperatures. However please do let us know when you inspect the repair after some running.

-ZM

I don't think the stuff would last at all at a real hot spot, such as near the exhaust port, but the transfer port area gets cooled by the incoming charge each stroke.

Sportflier,

Quite a good logic but lets see the practical results before I jump into it.

-ZM