aj0nr

The troy also has the cast-in mag shield.
Another # would be TB65SS

combatpilot

4 prots? Do you mean 4 intake ports? does it have the 2 runners per side on the intake? If it does then I have found that this cylinder really is pretty poor as far as combustion chamber design and has a much smaller compression ratio


Av8tor1977 I have a hard time beliving that this gapless ring could have an 800 RPM gain. Im not saying it couldnt happen im just saying its hard to belive. I think now im gona have to get ona and try it lol. It would be nice to see someone else get one and try it to to see what they get in gains also.

How does this ring achiev a zero gap? does it have segments on the ends that overlap or do you adjust it to a zero end gap. If you adjust it ususally with a file till it has a zero end gap then this is a really bad thing to do. the ring will grow in length as it gets hot and expand. if there is no end gap to take this up then it will grow in the bore and bind up. Ever ring that I have ever seen that was zero gap had segments at the gap part of the ring that would overlap the other side of the ring gap creating a zero gap.

av8tor1977

My Feedback: (6)

Yes, Frank makes the ring with notches that go over the pin in the piston. Frank recommends zero end gap with his rings. I have used many of his rings set up with zero end gap and have had no problems whatsoever with ring butting. The aluminum cylinder grows as it heats up, and Frank uses a top quality cast iron in his rings. It works with zero gap just fine. As I mentioned, in other engines in this size range the factory specified gap is .003". Measure a stock Ryobi ring gap and you will find that it is around 10 times that.

Other than an 11mm venturi carb and a good muffler, the very next thing I would recommend for a Ryobi would be a Frank Bowman ring. (Don't forget that you have to either tap the pin in the piston down halfway into the ring land, or grind it halfway down.)

AV8TOR

Racinrc14

My Feedback: (7)

Combat and AV8TOR. You guys are the shizzo.

My engine came from a Ryobi 720r, 31cc marked on the label. It has single, wide transfer ports, with no slits. The exhaust port has a center divider. Single ring piston, ZAMA P11 54P carb, 7.5mm venturi. Looking at the exhaust port from the back of the engine, there are two casting lugs, one on either side of the muffler mounting bosses. There is a "5" cast onto the left one, and a "95" cast onto the right. There is also a letter "D" cast onto the jug, just above the left jug mounting flange. My crankcase has the separate, bolt-on mag shield. Just to the left of the bottom lug, a "24" can be found, with a cast-in circle with the number "5" in the center with some other hash marks. To the right of the same lug is a cast-in horseshoe shape with the letters "ST" in the center. These are the only distinguishing features I can find on it, and the serial number has been lost long ago, sorry.

Do you guys have any part or model numbers for the larger carb? I'm going shopping on Ebay tonight.

Bought my magnet(s) last night. Radio Shack had exactly what I was looking for. 3/16" x 1/8", 2 in a package for $2.99, no shipping!

Combat, I have some very thin stainless steel. I have .008", and a smaller amount of .012". I can send you some if you like.

av8tor1977

My Feedback: (6)

At one time not too long ago someone posted a comprehensive list here in the forum of 11mm venturi carbs. Do a search and you should be able to find it.

If you find a number of a carb on e-bay that you want to research, you can do so here: http://wem.walbro.com/walbro/family.asp

You want an 11mm carb with both high and a low adjusment needles.

AV8TOR

Racinrc14

My Feedback: (7)

Thanks, the website is helpful, but it'd be nice to know the number so I could just do a search.

I took my engine apart and measured a few things. This is what I found:

The reed thickness is exacty .006" on my engine. And it is the later, non-recessed type.
Took the ring off the piston, and shoved it in the cylinder with the head of the piston and measured the ring gap. No kidding, it's .071". I couldn't believe it either. So I checked again and measured the feeler guages with a micrometer, .073". I think I'll be ordering a piston ass'y. Does Frank Bowman do rings for the two-ring setup? Would that be necessary? I need a new piston anyway, mine is scored up pretty good, so I may as well get the two-ringer.

I'd like to hone my cylinder, as it has some scuffing. Would a brake cylinder hone work for this?

av8tor1977

My Feedback: (6)

Frank can make whatever you want for rings. On a two ring piston, I usually use the stock ring in the second groove, and one of Frank's in the top groove.

A hone won't work very well on most of these small engines, as it will hang up in the transfer ports, and ruin not only your hone, but probably the cylinder as well. If your cylinder is so bad it won't clean up with some 400 sandpaper, you should probably just get another cylinder or engine.

AV8TOR

Racinrc14

My Feedback: (7)

Found the thread you were talking about, great information.

I tried some 800 grit, but I'll give the 400 a try also. It's worth noting that the engine ran o.k. as a trimmer, but seemed a little soft. I'm hoping the new piston/ring ass'y will give her new life. Oh, and the mods you and Combat are laying out for us might help too, and maybe the CDI also,.....I'm looking forward to getting it going. Just need to figure out how to mount this thing in an airplane.

ckangaroo70

My Feedback: (51)

Well I am not the swiftest on the Ryobi engines, but I do collect and restore vintage John Deere garden Tractors. So I have rebuilt quite a few cast iron 4 cycle K-Series Kohler engines, and as long you can find the specs on what the cylinder bore should be, and using a micrometer to check the wear. If the wear is within limits then of course an engine cylinder can be honed and a new ring installed. However if the cylinder is out of round or past its spec for wear, then a bore job is needed. Since nobody offers oversize pistons and rings for these...then yes a new cylinder and piston would be needed. I don't know where you would find the specs for these engines though. We need somebody to start making oversized pistons, bored out heads, and then lets talk nitrous injection!LOL Of course that would not be cost economical, but the idea of a hopped up engine being a weedeater one day to aiplane engine the next amuses me, and I find it quite interesting.

av8tor1977

My Feedback: (6)

Jag engines and others make mounting kits. They look heavy however. I just use a flat plate with a hole in it for the carb. It is mounted to the back of the engine, on top of the original plastic backplate. You then use bolts and stand offs to mount the engine. Note that you need to make a spacer about 3/16" thick for the carb so that the linkage will clear the mounting plate.

AV8TOR

combatpilot

Well sounds like im gona have to try one of those rings. or two of them in my case lol. I know there is a serious difference in the one ring and two ring set up as far as compression.

Try this like for the carbs. then click the series and select a carb number you want. it should have the venturi size somewhere.

http://wem.walbro.com/walbro/family2.asp

As far as honing what i use with some success is a sandpaper flapwheel that is just a touch bigger than the bore. Flapwheels can be bought from most any supply but i get mine from mcmaster carr. Its aboutht the only thing your gona be able to hone with and be able to hone over the transfer ports. Try this and look for the dia you want. remeber needs to be a little bit larger.
http://www.mcmaster.com/#flap-wheels/=ufyp1


Thanks for the offer on the shim stock but a stock valve is .006. I was hoping to get some .003 stock.


Here is one with a 12.7mm venturi
http://cgi.ebay.com/Walbro-WT-466-di...d=p4634.c0.m14
here is the parts dia on this one.
http://web.archive.org/web/200504111...rtnum=WT-466-1

this one has the 11.11 mm venturi
http://cgi.ebay.com/Walbro-WT-600-ca...d=p4634.c0.m14
here is the parts beakdown
http://web.archive.org/web/200710030...rtnum=WT-600-1

I got my carb from this guy. his price is the best i have found and his shipping is very fast. I would recomend him at any time.

I bought a 17-8 prop from a club member for 5 bucks. this should give me a good idea if im against a rpm limiter. thanks for the idea diceco

Racinrc14

My Feedback: (7)

Don't the standoffs crush the firewall when you torque them down? Maybe a two plate arrangement similar to what you have, with a plate against the firewall to take the load from the standoffs. Is there much deflection with your mount, AV8TOR?

aj0nr

The Jag backplate mount is 4.2 oz or 119 grams

diceco

Yeah, here's the reference to the RPM limit! [link]http://www.rcuniverse.com/forum/m_8313441/tm.htm[/link] post #14

diceco

combatpilot

yep thats the one I saw also and its why am thinking maybee I am up against an rpm limiter. I should know the answer to that tommorow as the weather is suppsosed to be pretty nice.

av8tor1977

My Feedback: (6)

Just use some large flat washers and your mounting should be fine. Lot's of engines nowadays use stand off mounts; including the high dollar DA engines, etc. I have a couple running like shown with no problems whatsoever.

Good luck,
AV8TOR

combatpilot

I talked to frank on the rings. I need to measure mine to make sure what i have. I need to do some scrapping so i can get some money to pay for it and i will order them as soon as i can.

Racinrc14

My Feedback: (7)

Combat, if you buy a new piston ass'y as I did (picked it up yesterday, it was actually an in-stock item at our Big R store!) you will NOT need the Frank Bowman ring. My new two-ring piston has rings identical to the ones described from Frank. They both have a shoulder that fits over the pin in the piston's ring land. To be sure, I removed one of the rings and put it in the cylinder and couldn't get a .003 feeler in the gap. It looks really good, too. The part number again is:

MTD 753-04367 and it was $29 at Big R.

Not as cheap as online, but I didn't have to wait for it to come in the mail either.

Racinrc14

My Feedback: (7)

Okay, if it works for you, then I'll try it.

diceco

Here's a photo of those slots. Sorry it's out of focus but you get the idea.

In [link]http://www.rcuniverse.com/forum/m_8313441/tm.htm[/link] post 18 pe reivers talks about filling in the slots with aluminum. Has anyone tried this??? It sounds shaky to me!

I've got this really nice cylinder I'd like to use except it's got those slots.

diceco

combatpilot

Man to bad i dont have a Big r store here. Im sure somebody has one though. Its good to know ya can get the piston rod and all with this style of ring all in one shot. That makes it nice and east to convert an older engine witht he one ring set up and still get the zero gap ring. should be a little cheaper this way to.


Its to bad they did that to the cylinder with them slits. I can see it is the higher compression cylinder head. I dont know about making an aluminum wedge. I just dont see how its gona stay in there. I had a pretty large gouge in a hydraulic cylinder on my track loader. I took it to a hydraulic shop and they filled it full of ca glue and filed it off smooth. its still in there till this day. I dont know how this will hold up to an abrasive ring and the heat factor of the combustion but it may be worth a try. I have since fixed many of cylinders this way myself and no kidding it does work.

I am getting so close to having this thing all wrapped up and on my plane lol. When i get it all done i will have to do a page that list all the conversions i think are the best set up with all the part numbers we have found here.

By the way did you look at those carbs on e-bay? what do ya think?

combatpilot

I just looked and my order just shipped. WHOOO HOOOOO yes i wonder how long its gona take lol.

Racinrc14

My Feedback: (7)

Yeah, mine 'shipped' the day after I ordered it, we'll see. Shouldn't take more than about 7 business days. I do Ebay a lot and stuff from China doesn't usually take too long.

I think I'm gonna go with the Zama 11mm carb. CQ-something. Hopefully I can retrofit the cool looking finned cover off mine!

tkg

My Feedback: (1)

Clean the cylinder with acetone and then use JB Weld to fill the slit. Make sure the JB Weld is just a tad below where the ring runs. This won't be a perfect seal, but it will greatly reduce the flow through the slit.

combatpilot

I tried to run my engine today and see what RPM I would get with the smaller prop. It ran for a few minutes then quit. After some choice words I found it had no spark. Somehow my coil fried as I have no continuity in the secondary coil. I am gona have to switch the crank out to be able to use the new flywheel and ignition coil. Bad thing about that is I wont know if the old coil had a limiter in it. I may have to wait and do my ignition conversion before I go any farther. I was wanting to save that for the last test.

While tearing my engine down a inspecting I realized that I already had the zero gap rings with the notch to fit over the piston pin. My cylinder must be a little worn as i am getting a .019 gap on the top ring and a .017 gap on the bottom ring. I dont know if a new set would have a beter gap or if its my cylinder.

I checked all the parts places here and none have it in stock. I may have to look and see where there is a BIG R farm store closest.

Maybee tommorow I will get a chance to put it all back together with the new crank and do some more testing.