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  1. #1
    combatpilot's Avatar
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    another darn ryobi post (ryobi performance modification, analysis and comparison)

    Ok there is so much fragmented information on the improvement of ryobi performance it makes my head spin. The descriptions of what was done to improve the performance are usually vague and leaves allot of questions. My intent of this thread is to discuss in detail the building of and hopping up my ryobi engine part by part piece by piece and how the improvements affect engine power one modification at a time so we can tell what works and what doesn’t. I intend to post pics of all the processes I go through and hope that others will post some pics of their engines and parts so we can all see some of the differences in the ryobi parts and what works best. There are so many differences in parts it is mind numbing as is seen in the ryobi differences posting.

    Ok so here we go. This is my engine. I am not going to cover the conversion of these engines as there is already so much info on this process already. I am only interested in covering performance modifications in this post. My engine was purchased at harbor freight a few years back for 50 bucks. I wanted this engine cause it had the two rings set up. The first engine I had converted was off of a weed eater of unknown manufacture I had picked up out of the trash. I still have the parts and will use them for comparison in some parts. I had used some of the parts from the first engine to build the harbor freight engine. Mainly the carburetor back plate. The flywheel I had modified for the first engine would not fit on the harbor freight engine as the key ways were different. Also the harbor freight flywheel had the key cast into the wheel. Anyhow modifying this part is not that big of a job and I did it on a friends lathe.

    Here is my engine in pretty much stock form with only the conversion modifications. It has the back plate off of the first engine as it was already modified and I didn’t want to take the time to modify the new one. You can see that this engine had the mounting cast on to the case and needed to be removed with a hack saw and cleaned up with a die grinder. It’s not too hard to do. The first engine you could unbolt the mount and did not need this modification. I actually like the cleaner look of this case as it cleans up nice and I’m sure weighs less.

    Running this engine in this configuration the best it would do is 6450 rpm. This is with a Dynathrust 18-8 prop. All my conversion parts are from paragon aeronautics as I liked their set up the best.



    As you can see I have the short shaft version.



    With the engine all disassembled you can see when the keyway is straight up the rod journal is just slightly right of center. It would be nice to see some pics of others and see how this compares to others so we might get an understanding of the timing and interchangability of the stock ignition system. I plan on going electronic but that is at a later time.



    My rod is a stamped type with a flat top piston. It looks to me like there is tons of room for a domed piston to up compression. Again post some comparisons on the rod and pistons please.



    Here is my exhaust port. It doesn’t have the middle bar and the rings are already pinned on the piston. I think there is room for improvement here as it seems kind of small.



    Here is a view of my intake transfer ports. It is very interesting how different they are from the ones that were posted on the ryobi comparison thread. Notice how they have a piece in the middle of the port. I think there is lots of room here for improvement but in a way I hate to grind any out of this as it will lower low end compression. It may be worth it in gains of flow. It would be interesting to see if they have the same volume as the ones that do not have this middle piece. I don’t know why they did this other than to de tune it to meet EPA regs. Again let’s see some pics for comparison.

    I will at a later time degree this out and figure out what the port timing is.



    Here is my back plate. It is stock other than being cut down. I did bend the reed valve stop out to 1/8" as I read somewhere this was the thing to do.


    On closer inspection of my back plate I made what I consider to be two important discoveries. The first being that this back plate off of the first engine is of a smaller diameter than the harbor freight engine. This allows for a loose fit and increase in the low end volume which is bad. It looks like the same difference in diameters that avi8to77 discovered in the differences post.

    The second discovery is that when I bent the reed valve stop it bent close to the screws which relieved the stop out towards the intake hole. If you look at it from the side it does not allow the reed valve to completely sit flat with the back plate and you can see a small gap between the valve and back plate. The back plate has kind of a swoop up cast into it where the reed valves sits. It is impossible to get a picture of this as I have tried lol. I don’t know how I didn’t catch these problems to begin with. Just not paying attention I guess.

    Ok so where do I go from here. I think my first step is to modify the back plate that goes with this engine without any performance mods. This will give a stock and correct crankcase volume. I then need to bend and modify my reed valve stop to where it holds the valve flush with the back plate and has the 1/8" gap. I think if you’re going to bend this reed valve stop the best thing to do is to put it in a vice as close to the bend as possible and bend it there not up close to the screws. Check your reed valve when you do this to make sure it still sets flush. I will then test run this engine again in this configuration and get a good starting point. From here I can begin to modify.


  2. #2
    av8tor1977's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    It would be really cool to see a "before and after" comparison of using a Frank Bowman ring. The Ryobi has a large ring gap because the ring does not overlap the pin in any way. With the Frank Bowman ring, you either tap the pin halfway down into the ring land, or grind it half way down. Then Frank's ring has a notch that fits over the pin, allowing a MUCH smaller ring gap, which helps power a lot. I suspect the benefit would be slightly less on a two ring piston than on a one ring, but there still would be a benefit.

    I just don't have the time and patience to do a one change at a time, comparison test program. This will be interesting.

    AV8TOR
    If it is not SCARY, it is NO WHERE NEAR powerful enough!!
    All R/C planes have expiration dates---> It's just not printed on them anywhere!

  3. #3
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I think thats a great idea. Do you have a link where to get these rings? How much do they cost. Cost is knind of an issue right now as i havent worked much lattley. Stupid economy and housing slow down. Right now I have more time than money lol.
    Jeremy

  4. #4
    av8tor1977's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    He doesn't have a website. His contact info is:


    Frank Bowman
    Email: ringmaster46@msn.com

    Phone
    Home: 505-327-0696

    Address: 1211 N Allen Ave
    Farmington,, NM 87401

    The rings run about 12 bucks shipped.

    AV8TOR
    If it is not SCARY, it is NO WHERE NEAR powerful enough!!
    All R/C planes have expiration dates---> It's just not printed on them anywhere!

  5. #5
    andrew66's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I am going to have to keep an eye on this thread. I have a ryobi which is ready for testing. I went ahead and ground the transfer ports, so they are one big slot instead of 2. I posted this a while ago, and i think the title was: could this be the key to power. I havent ran the engine yet cause i dont have a mount. I should also look into getting a tach so i dont over rev the engine. If i ruin this engine, im not too worried, i have a nice stihl engine waiting to be ran as well.
    I hope they serve beer in hell!

  6. #6
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I was looking at doing the same thing. I am wondering if they did it this. I would really like to see what this does. By chance do you have any performance specs before this mod so you have a comparison?

  7. #7
    andrew66's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    no unfortunately i dont... i dont have a tach, so no numbers. What i could do is get another jug and bolt it on when i get my tach. I was really wanting to see if this mod will even hold up, cause im afraid that the ring doesnt have enough support. I really need to get a mount for this thing. Do you think that making a mount kinda like a glow engine will work? and have it bolted onto the jug. or should i make stand offs. I dont want to use a plate mount, cause i dont have a carb spacer so the throttle will open all the way.
    I hope they serve beer in hell!

  8. #8
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I dont understand the question. This engine dosent have mounting lugs like a regular glow engine has. so then from there you would either have to weld on lugs or fabricate some sort of mount that would bolt to the engine to accomplish this. Where would you attach this mount? the engine that I have dosent have the flywheel shroud mounting lugs on it. I suppose if you have these lugs on your engine as I know many of them do then I dont see why you cant fabricate a mount to mount off of the front of this engine and would have lugs like a regulat glow engine. That being said it seems to me it would be far more easy to fabricate a carb spacer out of a flat piece of aluminum, than it would be to fabricate this elaborite mount. i dont know that mounting it off of the cylinder holddown bolts would work well or not. the thing that would scare me about that method is the fact that there is only two bolts to work with and very small area to bolt to. it may be possible that with only one bolt per side the vibration would be hard to control to where it would not flex the mount and cause it to crack from work hardening. I will have to stare at my parts for a bit to ponder this.

    If you get a tach i would recomend the glowbee tach. I really do like mine.

  9. #9
    andrew66's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    i have been pondering for a while now. lol... i just wanted to do this, cause i can get the mount that uses the jug bolts made for real cheap. Im not sure if this engine will even make it to a plane, i just want to be able to run this engine on a test stand for a couple hours. but if its going to crack the jug where it will be bolted on, then i wont risk it
    I hope they serve beer in hell!

  10. #10
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    If all you want to do is run the engine on a test stand then how hard would it be to fabricate a mount that utilizes the front mounting holes? it could be a really simple piece of angle iron.

  11. #11
    andrew66's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I guess i could probably think something up. Im heading home today, so when im at the old man's shop, i could probably "borrow" some materials, and make something up. Once that is done, I will just need to make a battery pack to make an onboard glow setup. I am going to try and run the engine on gasoline with a glow plug powered all the time. Rysium has done this, with good results, so im going to try it.
    I hope they serve beer in hell!

  12. #12
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    [img][/img]I got a chance to get by the shop and get all the parts from the first older engine I converted. Here is the comparison of all the parts

    to start with the flywheels are made by two diffrent companies. the old one by phelan and the newer one by walbro. For all intensive porposes they are esentially the same part. the only noticible difference is the keyway size. the newer on has the key cast into it eliminating the need for a key. You can see by the tip of the pen there is a little bump that indicates the location of the keyway. you can see that the keyway is in the same spot on both of these flywheel in relation to the magnet casting hump. this is important to note to see something in a later pic.



    the next pic is of the pistons. the newer one has two rings and has a different rod than the older one. other than that they are pretty much the same. same rod length same bearings same piston overal dimensions.



    the next pic is the cylinders. there is a bunch of differenc in these. first off the transfer ports are altogether different. the older one has the single port per side and the newer one has the two smaller ports per side. I really dont know why they went to the two ports per side version. it looks like the ports when all totalled together have the same volume per side. My only guess is that this configuration will deliver the fuel and ait mix into the cylinder with more velocity and speaed it out a little better in the cylinder.

    the next is the exshaust port. the older cylinder has the center bar and newer one dosent. the older cylinder port exits straight out. the newer cylinder the port sweeps up just alittle and flares out twords the end as it exits the cylinder. it also looks like the port timming is different but i havent had a chance to confirm this.

    The last difference that i can see is in the combustion chamber. if you look at the chamber where it forms a lip as it transitions into the cylinder the older cylinder has a wider lip than the newer one. this wider lip makes it look like the dome to creat the combustion chamber is smaller. It is my oppinion that the older cylinder is a higher compression cylinder. I am trying to think about cc ing the combustion chamber to find out what the differenc in combustion chamber size is. I would also like to get compression ratios on these engines. I am wondering if I put an oring on the single grove piston if I can get a seal where i can cc it that way.



    here is a pic of the exhaust ports. it is kind of hard to see the differences in these pics.



    The last and i think the most importtant is the difference in the timming with the stock ignition. We already know that the flywheels are pretty much the same. If you notice in the pics the cranks are turned to where the keyways are straight up. the newer enginge the rod journal is almost straight up or a little to the left. the rod journal in the older engine has the rod jornal noticaby visible to the right. this would advance the timming of this engine when using a stock ignition. again we already know the flywheels are the same soit has to be advanced. The cranks look to be the same other than the keyway. since i already have a flywheel for both cranks I intend to install the old crank in the new engine and see how it affects power on one of my tests. again this wont mean anything if you use an aftermarket electronic ignition but i want to do it so the guys using stock ones will know.



    There is a huge difference in compression between the cyingle ring and the dual ring when pushed into the cylinder and your fing held over the plug hole. the dual ring one darn near cant be puished in unles you give it a little time to let the compression leak out. The single ring one can be pushed in easily. I dont know if it will do any good to test the old engine with the original piston and ring. I think however it would be worth a look with the new piston and ring setup in the old engine. this shoud give me a good idea of the performance charateristics between the cylinders in stock form.

    I also miss spoke on the back plates. as far as i can tell the case sizes are the same and the backplates are the same. the backplate just has a sloppy fit.

    So again from here I am gona fix my reed valve problem and re test to get a good starting point.

  13. #13

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Swap meet/Ebay time.
    Evra 190 was sold by Hobby Lobby for a few years. Its a Ryobi 31 with mounting rails cast in to the crankcase.
    TKG
    Too much power is just about right.

  14. #14

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)


    ORIGINAL: tkg

    Swap meet/Ebay time.
    Evra 190 was sold by Hobby Lobby for a few years. Its a Ryobi 31 with mounting rails cast in to the crankcase.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Information on the Internet is subject to the same rules and regulations as conversation at the corner Pub -Author unknown.

  15. #15

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I took apart a couple of Ryobis that I had last night. One of them has the smaller crankcase with the recessed reed in the backplate. It looks almost brand new. The other one was a little dirtier but has the larger crankcase with the standard backplate. It also has the cylinder with the slits cut up from the exhaust port. Both are long shaft engines. Both have a single piston ring. Both pistons appear to be identical. So I thought I would use the like new piston and cylinder off the small crankcase motor and mount them on the standard crankcase. Once mounted up, I discovered that the connecting rods are of different lengths. The piston from the smaller crankcase hits the crank before reaching bottom. I wonder if I will get a good engine if I use just the cylinder from the smaller crancase mounted on the larger crankcase with the piston and rod from the larger crankcase. I forgot to compare the transfer ports. What do you guys think?

    Jim

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    did you install the piston 180* out? the piston skirt is higher on one side than the other to keep it off of the crank counterweight...

  17. #17
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Thats a very good point on the pistons.. can you switch the pistons on the rods? I am thinking the smaller crankcase may be a better engine if you can get one of the new style backplates to fit it. I dont have a recessed backplate so i cant compare. If the recessesed backplate and smaller crankcase has a smaller crankcase volume it mat be the better choice. What does the timming look like on these engines? it would be interesting to see.

  18. #18

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I did have the piston turned the right way. Still hits the crank. There is no way I can see to put the good backplate on the smaller crankcase. It is just too small. Keep in mind that the crankshaft on the smaller crankcase has a shorter off set therefore the connecting rod has to be longer. Just wondering how this will affect the stroke and compression when swapping the head to a standard crank and connecting rod.

    Jim

  19. #19
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    I think it stands to reason that the engine with the bigger crankcase is gona have a longer stroke. so if the stroke is longer and the bore dia is the same on both engines than the engine with the longer stroke is gona have more displacement. there is two truths i have found over the years when it comes to engines

    1. There is no replacement for displacement

    2. Cubic inches cost cubic dollars.

  20. #20
    andrew66's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    the one with the shorter stroke was probably the 28cc. whereas most of the ones that u will see are the 31.
    I hope they serve beer in hell!

  21. #21

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Long ag and far away Ryobi made 26cc engines. I may still have one laying around I compare it to the pictures and a 31cc we got.
    TKG
    Too much power is just about right.

  22. #22

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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    The one with the smaller crankcase did look like an older engine. It had one of the round mufflers on it. It also was the one that was the cleanest looking. If it is a 28cc, will the cylinder work on one of the 31cc crankcases and piston rod assemblies?

    Jim

  23. #23
    andrew66's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    It should work, cause it think the bores are the same size. U should probably measure to be sure, and do a mock up assembly and make sure everything works properly.
    I hope they serve beer in hell!

  24. #24
    combatpilot's Avatar
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    Tommorow or maybee monday I should get to do some testing. I think this is gona be my test procedures.

    Test #1 Stock engine no performance mods. Using old engine 1 ring piston and new cylinder. record RPM I really want to see the rpm diff in the 1 vs 2 rings. I have a brand new ring for the one ring piston.

    Test #2 Stock engine no performance mods. New 2 ring piston and new cylinder. Record RPM. This should give a good comparisoin between the two rings set ups.

    Test #3 Stock engine no performance mods. New 2 ring piston and older one ring cylinder with higher compression and different ports. Record RPM

    Test #4 Best of 1-3 and no cylinder base gasket to up compression. Record RPM. Should change port timming but no port mods at this time.

    Test #5 Best of 1-4 and check port timming and modify if necassary. Record RPM

    Test #6 Best of 1-5 and old crank from older engine with advanced ignition timming. Record RPM

    Test #7 Best of 1-6 and new 12.8 mm venturi carburetor. Record RPM

    Test #8 Best of 1-7 and moddified reed valve. Record RPM moddification will be discussed later. mostly reprofile valve and thinner reed stock.

    Test #9 Best of 1-8 and rework the manifold and bell shape it at the reed valve end to reduce contact surface area. Record RPM

    Test # 10 Best of 1-9 and and try to reduce crank case volume. Record RPM

    Test # 11 Best of 1-10 and use electronic ignition. Record RPM

    If have money and time I may try to make the y manifold

  25. #25
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    RE: another darn ryobi post (ryobi performance modification, analysis and comparison)

    oh pretty please could u get some video?
    I hope they serve beer in hell!


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