RE: yes another poulan, a 33cc
Shaun, I think you answered your own question. A 18x6 is about the right size. I have been working with 32cc MacCullochs and I am getting around 7500 RPM. I would suspect that it would do well with a 19 inch prop, but they are not too common. I ran a 20x6 and got 6000 RPM and it seemed to be a bit large, but the engine wasn't really broken in. I open the intake ports, use a bigger carb and open up the exhaust also to get the over 7000 RPM readings. I also am using CDI. I would guess you should be able to get about the same RPMs or there abouts. If you want to go bigger that 18 inch props, I would suspect you do need more cc's.
Posted on: 1/24/2008 5:16 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=6963541

RE: Mcculloch 28cc
Tap the end of the shaft with a hammer while holding the flywheel, with the engine a half inch above your workbench of course so the engine doesn't have far to fall, and the flywheel usually pops right off. You can't twist them off becaue there is a Woodruff key which you have probably already seen at the back of the flywheel. Nothing to it, this works with most engine, just be careful with any threads on the shaft. Engine shafts are not really that hard, you can smash the end and the threads if not careful. There are other posts that can help with converting Macs. I have worked on a few myself.
Posted on: 11/26/2007 7:37 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=6677719

RE: Carb Question
spiffy, That is neat that you figured on adding the brass tube and line to the inside of the fuselage to keep the prop blast from affecting the carburetor, but there might be a simpler solution. The instructions, I read somewhere, say to turn the diaphragm cover so that the hole is facing away from the cooling airflow of the flywheel. I stumbled on this myself, realized how obvious it was, and started changing the covers around on my engines. Hope this helps.
Posted on: 11/26/2007 7:03 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=6677510

RE: mcculloch 28 vs homie 25
I have a photo of my Mac intake port revision, the photo came out good enough that it should be better than a sketch. You will recognize the tonsil layout of the original port with the "tonsil" on the top of the port. What I did was use my rat tailed files to carefully create another "tonsil effect on the bottom of the port as shown. (Top of the port, meaning in reference to the top of the cylinder.) I leave the top of the port alone. Most of the material removed from the port is on the bottom and backside of the port, so that the port flows down into the crankcase. I blended the sides of the port a bit also down to the bottom as shown. The height on both sides now, from the depth of both the bottom and top "curvatures" of the port is .390", plus or minus a bit as judged by the file holder. This port modification along with opening up the muffler, not the exhaust port which seems to be decently sized, awakened the response of the Macs I have tried so far. Even using a larger than original carburetor didn't do as much as expected, so that made me suspect the intake port being too small. (Remember to use a piece of Aluminum flashing (or tin can?) to protect the far side of the cylinder wall in case you bang it with the files.)
Posted on: 11/26/2007 6:48 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=6677415

RE: mcculloch 28 vs homie 25
foamcut, sorry about the slow resonse again, as you all know things come up. I got a new Mac 28cc, never run, engine off **** real cheap and decided to experiment with it. I found that the cylinder material held up well while welding. No tendency to soften or melt and not difficult to weld either. I clean all welding surfaces as though I was going to eat off of them, then wire brush them with a stainless steel brush for good measure. The stainless steel is suppose to react somehow. The Mapp gas allows you to do the welding process rather quickly compared to Propane. (Propane will work for smaller parts, but is definitely not hot enough for a cylinder.) I have been using these rods for a few years now, it does require a learning period. I leave the weld material high enough so that I can grind it flush after cooling, on my belt sander. I have done two cylinders so far and will do a few more. I am real happy with how they turned out myself. The 28cc is a short shaft engine, (it had a long blower shaft with no threads on the end). I also tried my intake port on it first. I ran this cylinder on a 32cc crancase and it ran great, it has good response and sounds like a big glo engine at wide open throttle. I will sketch the port enlargement also for those that wish to see it. As I said before, the intake port seemed small compared to the exhaust port and the cylinder transfers. I suggest welding Aluminum scrap metal before tackling parts of your engines. Note that different alloys of Aluminum will act differently when using these rods, probably some will be harder to work with than a cylinder. Burned up and scored cylinders if you can find them would be excellent practice.
Posted on: 11/1/2007 7:58 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=6568988

RE: mcculloch 28 vs homie 25
KI8FR, Sorry about the slow response. The prop hub is actually two pieces. Scott Baldridge made the front part of the Prop Hub assembly, the part that has the 7/16 shaft matching rear threads and the Knurling to drive the prop. I made the rear part to fill the space the Flywheel vacated. Of course you need a Lathe to make this piece. I just have a Taig Lathe with patience and perserverance. Cutting the slot for the Woodruff key is a challenge without a Mill or ?, but I do have a drill press. As I stated, I located the Magnet, from Radio Shack, a small 1/8" diameter Earth Magnet, 180 degrees from the Woodruff slot in a drilled hole in the rear, close to the outside diameter of the Magnet hub (rear Part). I rest of the hole has a plastic plug to keep the magnet in place. There is a center punch mark on the magnet hub so you know where the magnet is to set up the timing. Scott Baldridge probably has the dimensions I gave him to make the prop hubs. I might be the first to set up a long shaft Mac like this. I'll see if I can sketch these parts and post them in this thread. By the way, the P-47 prop nut is made from Fortal, an Aluminum alloy about equal to 7075, (good strength for internal threads) and the rear is drilled out to save weight. It looks like a revolver cylinder from the rear.
Posted on: 11/1/2007 7:33 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=6568889

RE: mcculloch 28 vs homie 25
Foamcut, you are welcome. Thats why I posted the pictures. I found that welding a flange onto the exhaust cylinder was possible. Fitting a Aluminum flange does take time. I made a 1/8" steel plate drilling template. I use the Aluminum welding rods and a Mapp gas torch. Mapp gas is much better than Propane. I am going to use the same idea on a few 25cc Poulans. The reason I decided to try welding a flange on the Macs is bercause the Mac muffler is heavy and big and it is very tough to get a seal at the exhaust port on the cylinder, so oil leaks out and makes a mess. The flywheels are also pretty heavy on a Mac, eliminating it helped me get down to 4 pounds.
Posted on: 10/23/2007 1:52 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=6528281

RE: mcculloch 28 vs homie 25
You can get right around 7500 RPMs from a Mac 28/32 with a M/A classic 18x6 or 18x8 prop. For reference, you can get a bit over 6000 from a 20x6 M/A classic but it runs hotter so I think that 20 inches is a bit too much for a 32cc engine. This is what I am getting and the engines are not yet broken in completely. I do mine somewhat different that most. I don't cut the long shafts. The threads on the end of the shaft are used for a P-47 style prop hub to hold the prop on. Then I have a 1/2" long s/s hex head, 10-32 screw in the end of the shaft to safty the Aluminum hub on, (just in case.) I weld on a 2" square flange around the exhaust port to bolt a homebrew Aluminum muffler on. Getting rid of the big steel muffler alows thinning of the front and back of the cylinder and allows a flat plate firewall mount. I also increase the size of the intake port. I made new carb spacers to rotate the carb so you don't need to reach "through the prop" to adjust the idle screws. My Macs look a lot different now. I tried to post photos but I am not having much luck (and I have posted before). I got the weight down to 4 pounds even, complete with CDI and battery and I am pleased about that. I knocked off about a pound. Macs intrigued me so they became another segment of the hobby. I will still try for photos to show what can be done with these engines. Here is a few photos. I have the magnet 180 degrees from the Woodruff key slot so that the CDI sensor can be on top of an inverted engine. CDI is not included in photo and the sensor is what you see on the bottom of the crankcase. One of the crakcase holes provides a strain relief for the sensor cable, a bolt, a piece of wire, and a tywrap are used.
Posted on: 10/22/2007 3:50 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=6523764

RE: QUESTION FOR WELDERS...
I am still checking on welding machines. I found a company that I did not previously know about. Their equipment looks impressive in their catalog. I found this company in Kitplanes magazine and the link to their wesite is: www.usaweld.com This company makes one machine that can do MIG, TIG, and STICK welding, its all in the same welding machine. It is a 220 volt, 160 amp output welder. Oh yes, the company name is HTP America Inc. They have several models, 110 volt models and Plasma cutters also plus a lot of welding accessories. Anyone know about this companys products?
Posted on: 6/13/2006 5:51 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4386664

RE: QUESTION FOR WELDERS...
Mitty, I have seen a guy weld Aluminum Pop cans together with the Aluminum propane gas welding rods that I now use. Its a trick, but he did it, you need to be quick and in this case most of the heat goes to melt the rod and then you very quickly sort of smear it on the cans with the rod, its nuts to see, because the propane flame will burn through the thin Aluminum cans as fast as you can blink. I make mufflers with these rods, but I use .060" thick Aluminum as a Minimum, because as you know a muffler will have the manifold section that bolts on to the engine and the main body will be thinner and you need to account for this, as you know, when spreading the heat of the flame around to get the various thicknesses of material up to the necessary temperature of these crazy rods. Different Aluminum alloys act differently as you can guess with these rods as in all welding. Sometimes, only sometimes, the rod metal will flow like solder, but don't expect it to. What amazes me sometimes is that you can melt this rod metal on To Aluminum and then brush it off with a stainless brush or a rag or whatever and there will be no residue, it all comes off. With lead solder you will always see a thin coating of the solder remain. These rods can test your patience, but it can be done, but again, you are working with something that is pretty hot and you sure don't want to get careless, distracted, etc. I keep the necessary welding of my muffler designs to a minimum and I have the hang of fusing the Aluminum and the rod metal alltogether into very stong joints. A drawback is that the rod metal is heavy, so I grind any excess off for looks and to remove the weight. It seems that the process is not always exactly the same as the last time you did it, because of differences of the Aluminum that we scrounge up. One trick I picked up is small but useful at times. If you weld on one section of a muffler and then let it cool down before doing a later weld, it seems as though the first part will need to be brought up to a higer temperature than when welded, before it will melt again, and I use this to get a second weld done without melting the first. This is where the persistance and the observation of a modeler comes in handy. I also use a Stainless welding rod with the coating removed to poke and push the molten rod metal around where I want it, it gets crazy at times, but I get determined to get my mufflers made. I just made two Pitts style mufflers, one for an OS .20 and an Enya .19, you can't buy this size in a Pitts muffler. Yes I have screwed up a couple in the learning process. If anyone wants to seriously try doing this, I'll try to help. I have another post in the Lumiweld post that might help to explain this welding process.
Posted on: 5/10/2006 7:44 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4260438

RE: LUMIWELD
I think your thread is from before I joined RCU. I use these rods all the time, they are tricky but they can be made to work. I use just a Propane torch, I have Gas welding equipment but its not necessary. The challenge to using these rods, I will take a chance on being able to explain this for you and others, IS: The temperature at which the rods melt and thoroughly fuse with the Aluminum you are welding, AND the temperature at which the Aluminum will oxidize completly amd just melt away, are pretty close, I have found out the hard way, of course. The "temperature window" in which you are trying to get a thoroughly fused or welded seam between two different parts is pretty narrow. I would suggest a couple of scrap pieces of metal, 060" thick for a minimum to start, and then just go all the way to melting the pieces together using the rod as part of this experiment so you can see all of the stages of what can happen. When trying to build a muffler, you are trying not to screw it up, that is hard at first. Mess up some scrap pieces to find out how it goes. Then try it with Aluminum pieces of different thickness to see how the heat has to be divided among the different thicknesses according to the thickness requirements. You test the temperature of a part by using the Aluminum welding rod to "touch and scratch" the piece to see if the rod starts to melt on to the part being touched. This might sound like doublespeak if you haven't tried these rods, but that is the nature of these Aluminum Rods. It can be done, I saw others do it, so I knew I would eventually be able to use it for our purposes. Hints: Use designs for mufflers that keep needed welding to a minimum. Use .060" Aluminum as a minimum thickness for the main body of the muffler. The "manifold" part will need to be thicker, of course. If you weld one stage of your muffler and then let it cool, it seems that this first weld will melt then at a bit higher temperature than it did initially, so I utilize this small bit of "leeway" to get my second weld done without melting the first one. Yes, it is a bit tricky, because you need to keep an eye on the first weld while you are doing the second! If you learn how to do this, you will be the "Welding Wizard" in your area. My Dad was a great welder, for about 50 years, and he found this to be very tricky, he didn't believe I would be able to do it, but I rember telling him, Dad, I saw the guy do it, you didn't get the chance to see him do it, so I had a small advantage and the determination. If there is any interest in this, or any questions, or hints wanted on muffler designs, or photos of ones I have done, lets resurect this thread. I remembered something else to do, A stainless steel brush helps to brush the parts with, this helps the process and I use about a 1/16" stainless steel welding rod with the coating removed to move the Aluminum rod metal around to where I want it to be. This is not a lot like other flame welding processes, it might be weird, but it can be made to work. I just looked at my joining date, I guess I lied, where did the time go?
Posted on: 5/10/2006 7:40 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4262660

RE: LUMIWELD
So you also have used the stainless steel brush to clean the parts, I just added that to my post and scrolled down to see yours. You have essentially done the same type of welding so I think you could make mufflers with the same technique. Its a challenge, very interesting to be able to do, and satisfying to have a special muffler that you have made for an engine. Lately I made a Pitts style muffler for a Fox .45 and it turned out very well and has a great sound. It wasn't much more trouble to make it than it would be to adapt an existing muffler to fit. I haven't flown it yet, but it is ready to go, maybe tomorrow. I guess I should photograph some of the mufflers I have made. (I also have a post in the Questions for Welders thread.)
Posted on: 5/10/2006 7:35 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4263731

RE: LUMIWELD
duplicate message deleted.
Posted on: 5/10/2006 2:39 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4262618

RE: Who is converting Toro trimmers?
Hi Poco, I opened up the Intake the most, and the exhaust also. I did these after experimenting with 2 -21cc Poulans which I got up to 7k with a 16x8. they would be best with a bit smaller prop. The 25cc Poulan can handle the 16x8 better, I got 8200RPM, and it runs smooth and reliable. The first thing to go was the single needle carb, it was a Kapon. The mag mount is a problem as you say, I ground and blended in the bottom as much as possible for looks, but still kept it rigid, then I added an Aluminul brace to the top and bolted it to the top head cooling fin. Its not bad looking at all. I just got done with a new roof on the house, thank God thats done, so now I am trying to catch up with my hobby projects. Working on 4 aircraft in various stages of design and construction, definitely not bored, will get to testing No. 2 Poulan 25cc next. If the second is as good as the first, I did it right. The Poulans I have HAD very small ports, but not now.
Posted on: 5/10/2006 1:38 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4262468

RE: QUESTION FOR WELDERS...
Thanks Ken, for answering my question about CO2 for welding with a MIG. If you want something to test your patience, try the aluminum welding rods used with a Propane Torch. When you think about it, there is a lot of skills involving technical knowledge that modelers learn to do. I have been in this hobby for many years and have been amazed at what others can do more than once. It all makes for very interesting people, modelers in their particular hobby, and radio control for example has evolved into a technological industry of it's own. I saw and used the very early radios and they were Dinosauers compared to what we have now. I don't really have the desire or the patience for Museum Scale RC models, because no matter what I will fly them, but I have seen models that look as good as the full scale versions, at least. A TIG system is pretty expensive for welding a few mufflers, so I would "test my patience" trying it with a MIG. I once worked in a fabrication plant, they welded all metals. They called one system a "squirt gun welder", I guess it was MIG and they use to roll 1" thick aluminum plate into large diameter pipe, bevel the edges, and then fill the "V" on both sides with Aluminum welds. They also used one of those "Railroad" systems to hold the gun and crawl across the seams. I remember seeing some beautiful welds. Yes, I know this was very heavy metal, much heavier that .060" model engine mufflers. I learned something else lately, the older you get, the more stories you have.
Posted on: 5/10/2006 1:16 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4262398

RE: QUESTION FOR WELDERS...
Mitty, I have seen a guy weld Aluminum Pop cans together with the Aluminum propane gas welding rods that I now use. Its a trick, but he did it, you need to be quick and in this case most of the heat goes to melt the rod and then you very quickly sort of smear it on the cans with the rod, its nuts to see, because the propane flame will burn through the thin Aluminum cans as fast as you can blink. I make mufflers with these rods, but I use .060" thick Aluminum as a Minimum, because as you know a muffler will have the manifold section that bolts on to the engine and the main body will be thinner and you need to account for this, as you know, when spreading the heat of the flame around to get the various thicknesses of material up to the necessary temperature of these crazy rods. Different Aluminum alloys act differently as you can guess with these rods as in all welding. Sometimes, only sometimes, the rod metal will flow like solder, but don't expect it to. What amazes me sometimes is that you can melt this rod metal on To Aluminum and then brush it off with a stainless brush or a rag or whatever and there will be no residue, it all comes off. With lead solder you will always see a thin coating of the solder remain. These rods can test your patience, but it can be done, but again, you are working with something that is pretty hot and you sure don't want to get careless, distracted, etc. I keep the necessary welding of my muffler designs to a minimum and I have the hang of fusing the Aluminum and the rod metal alltogether into very stong joints. A drawback is that the rod metal is heavy, so I grind any excess off for looks and to remove the weight. It seems that the process is not always exactly the same as the last time you did it, because of differences of the Aluminum that we scrounge up. One trick I picked up is small but useful at times. If you weld on one section of a muffler and then let it cool down before doing a later weld, it seems as though the first part will need to be brought up to a higer temperature than when welded, before it will melt again, and I use this to get a second weld done without melting the first. This is where the persistance and the observation of a modeler comes in handy. I also use a Stainless welding rod with the coating removed to poke and push the molten rod metal around where I want it, it gets crazy at times, but I get determined to get my mufflers made. I just made two Pitts style mufflers, one for an OS .20 and an Enya .19, you can't buy this size in a Pitts muffler. Yes I have screwed up a couple in the learning process. If anyone wants to seriously try doing this, I'll try to help.
Posted on: 5/9/2006 10:58 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4260477

RE: QUESTION FOR WELDERS...
CaptJohn, The rods you saw being used with a Propane torch or a Mapp torch are the ones I talked about earlier in this thread. I have the hang of using them now and can weld up mufflers that stay together. I haven't done Mig or Tig but I have done gas, Actelene, Prestolite, Propane etc., so I watched the guy at a Flea Market myself, and then I knew it wasn't just a promotion to sell something, I just messed with it until I got the hang of it. But, now I have been researching Mig welders myself. I have been looking at a couple of Clarke brand welders a model 130EN 130 Amp wirefeed, which is a 120 volt input for $400 plus s&h and a model 180EN wirefeed and 220 volt input. Both have carts and the conversion kit for gas and the 180EN is $500. I have an electrical background so I took notice of the duty cycles, the 130EN is 30%@90Amps and the 180EN is 25% @ 130 Amps. The 130 Amp model would no doubt be suitable for what I want, mostly thinner metal welding. (I already have a Lincoln 220Amp stick Welder.) I still would prefer a 220 volt input model. I saw these Clarkes in a Northern Tool & Equipment catalog. They aslo have a website. I would think these are a grade up from the Harbor Freight Welders without being too high priced. I watch the Hot Rod and Bike building shows on TV, some of those guys have real talent, using their Mig Welders, and I am beginning to want one. In looking through catalogs, I noticed that with the Flux wire Welders, that don't need gas, the spools of this gasless flux wire is noticeablly more expensive, so the gas would probably be cheaper in the long run. It seems that you get more splatter with the gasless wire also, as some of you might be able to confirm. I would use a Mig for Car body repair and similiar thin steel, but didn't one of you say that a Mig isn't the greatest for welding model mufflers and TIG is better? Anyone have any comments on the Clarke brand of Welders? They have aluminum, mild steel, and stainless steel wire for these in 3 different diameters, and now who knows how useful Mig would be for Aluminum for model use?
Posted on: 5/9/2006 10:06 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4260227

RE: what is the angle between surfaces on v-tail
For reference, the Beechcraft V-Tail Bonnanza, the famous V-Tailed general aviation aircraft, has a 120 degree tail.
Posted on: 5/9/2006 9:16 PM by Author "rollmyown" in the forum "Scratch Building, Aircraft Design, 3D/CAD"
http://www.rcuniverse.com/forum/fb.asp?m=4259992

RE: QUESTION FOR WELDERS...
since you are an instructor, I have a question. I happen to already have a Carbon Dioxide tank with the regulator, left over from a Pizza Shop and soda pop use. How compatible is CO2 for use with welding and is it a good substitute for Argon. I would like a Mig for occasional use on auto body panels and a Tig would be nice too, but awful expensive for just making small parts like mufflers. I am thinking now only about a Mig system and have looked at the Harbor Freight systema also. (Is Chicago Electric their house brand?) This is more that one question now, maybe we can bring this thread to life again. We have a Harbor Freight in our area now and I am wondering who is buying their welding machines? I don't know anyone that has one to give an opinion, does anyone know someone with one? The people at Harbor Freight only know about selling and that is why I didn't jump at their prices which look pretty good at first glance, but what about service as brought up previously in the thread.
Posted on: 5/5/2006 10:52 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4245307

RE: Featherlite versions
Hi Volture, I have a few of these Poulan engines myself. I have two 21cc engines, 2 FL-25s and an extra jug and piston but no rings for the piston. Someone overheated the engine and cracked the rings but the piston and jug seem to be ok. The only reason to mention this jug and piston is because it has 2 rings and the piston diameter is between the 21s and 25s I have. I was surprised to see a Poulan with 2 rings. I might buy some rings and put them to use. The 21s at first only turned 6k so with nothing to lose I ported them and they now turn a 16x8 right at 7k. I got one of the 25s to turn the same prop 8200RPM. I will soon test the other 25 to see if I can duplicate the RPMs of the first one. I don't intend to mess with many more of these, but they are nice running engines for what they are. On the long shaft, with a Lathe, you can cut and rethread it. Doing it with a hand die set is tough to do accurately, as you can guess. (There is too many engines and not enough time.)
Posted on: 5/5/2006 10:20 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4245190

RE: Who is converting Toro trimmers?
Aeronut, I also have seen 8000+RPM from a modified Poulan weedeater, Model FL-25. I now have a second one and want to see if it duplicates the first. Both were new engines I got off of ---- and both had the plastic snout for the pipe broken off and were never run. I like them being pretty compact and they seem to run pretty smooth. I got the 8k with a M/A 16x8 Classic prop. spring is here and I will be testing the second one. I modified them quite a bit also. I am working on a lighter and hopefully better muffler, when I get back to it. I also used a different 2 needle carb, of course.
Posted on: 5/4/2006 10:59 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4241733

RE: Small Conversion Engines For This Twin?
This is interesting, I always liked this Aircraft, the full scale version, except for the hot running problems with the rear engine. The size of this model aircraft suggests that the wing loading is going to be a big problem. If it was sized for two .45 glo engines and they don't give the wing area or the wing loading, I would email them and ask what these two specifications are. Knowing these two numbers will help a lot in evaluating the possibilities of the project. I would guess that at 13.5 pounds this airplane doesn't have the lowest wing loading to begin with. John
Posted on: 4/8/2006 11:12 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4141966

RE: Who is converting Toro trimmers?
Scott, I have a tip for you about using setscrews on to a threaded shaft area. To use a setscrew without marking the threads, drop a piece of solder into the hole first. About as big a piece as you can get across the diameter of the hole. This holds very well, and doesn't damage the threads on the shaft. It is something that is done with reloading dies for ammunition. I have more than one hobby and sometimes you can transfer ideas. Try this and I think you will be surprised. If you need to take an engine apart later, you won't have to deal with rough spots on the threads. You tap the assembly, after removing the setscrew, to get it loose. There is a thin line between a hobby and mental illness -- Dave Barry.
Posted on: 3/8/2006 12:36 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=4007597

RE: Walbro/Zama 11mm carburetor list
Hi Railridr, I just want to add my thanks for your effort to post the carb specs, I also printed them. John
Posted on: 2/18/2006 9:49 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=3929247

RE: Bargin Carb Buy or Not?
I mentioned these carbs to Dave Wallace and he informed me that they have a 3/4" throttle bore, which you didn't mention. Correct? Most of the carbs we use have a 5/8" or smaller throttle bore. 3/4" is pretty big to match up physcially to most of the intakes on most of our engines, a 25Cc to 38cc or therabouts range. These carbs are no doubt more suited to 45cc (min) and larger engines. Even with a venturi reducer as I mentioned, I wouldn't expect it to work on these 25cc to 38cc engines, I mentioned, as typical of a lot of the ones we use (or are just playing with at this point). I envision a venturi reducer to be useful to bring a 13, 14, or 15(?)mm venturi down a few sizes to maybe 11mm. this should be within a practical range considering there are other components to a carb such as the jets and their sizing to the original venturi size etc. I have a couple of carbs in the 14 or 15 mm range that I hope to get around to trying my idea with and find out if it works. (What do your carbs weigh, weight is always a factor too)
Posted on: 2/17/2006 11:22 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=3884970

RE: Who is converting Toro trimmers?
Hi Subarubrat, From what I have read over the years concerning Briggs and Stratton and other even smaller bore engines, regular grade gasoline has quite a bit more octane than any of these engines need. The volume of these small cylinders is minuscule compared to auto engines and the heat generated inside is a lot less also, and the heat is basically what determines the needed octane. We can raise the compression a bit, by machining a small amount off of the bottom of the cylinder and maybe by sinking the spark plug some also. Of course, the spark plug clearence needs to be checked. It doesn't take much with some engines to have the piston hit the top of the cylinder and by machining the bottom of the cylinder we are messing with the geometry of the crank and connecting rod, but it is usually not a big problem because we usually can't really machine much off the bottom of the cylinder. I recently have thought about sinking the spark plug also. I have heard of guys using Premium gas in these small engines and have wondered if anyone can prove the need. If you want to check out what seems to really be hot engines in the 40 to 50cc range, that are designed to scream, have you ever looked at the engines used on the mini pocket motor bikes? I have seen these engines on the net and they are pretty cheap. I was tempted to buy one, but I have yet to fly a gas engine. I fly glo engines and haven't decided on what to build for a gasser. I won't go over 1/4 scale in size so I probably won't need one of the "screamers" myself. Lets see if we can get some more comments on this. John
Posted on: 2/12/2006 10:37 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=3903610

RE: Who is converting Toro trimmers?
Hi Scott, The light EI engine is interesting, even though we did have a discussion a few pages back in the thread about the negatives on doing this. A light engine as we all know will allow more airplanes to be used. What did you replace the flywheel with. We know there had to be something to provide a mounting for the prop hub and you probably needed a magnetic pickup or ? for the ignition adjustments etc., but my other question is, how smooth do these engines run without the flywheel? If the engine can still run smooth enough, my concerns about short crankshaft life might not be a concern at all. When you think of it, few of our engines will ever run for hundreds and hundreds or ? number of hours as a full scale aircraft engine does. John
Posted on: 2/8/2006 11:59 AM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=3884896

RE: Bargin Carb Buy or Not?
Hi sides7 I had looked at probably the same carbs and thought about buying them myself. I just had an idea of what we might be able to do with them. The idea is this, why not machine a restrictor and velocity stack combination to reduce the venturi diameter and extend it above the carb for a velocity stack? Right at the moment I can't think why this won't work. A minor problem just occured to me, we might have to eliminate the choke, but that shouldn't be a big problem in most installations. Come to think about it, I have some pretty big carbs, I will look at them and see what I can figure out. I have one huge carb I tried on a 32cc Mac and it wasn't the best running engine with it. I would guess that restricting the venturi would improve the carbs operation. Anyhow, its not that hard to do and we try everything else. Maybe we can get some other comments on this idea. John
Posted on: 1/28/2006 9:07 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=3837453

RE: Who is converting Toro trimmers?
Hi Scott, Another idea I know you and a few others must have thought of, and that is sinking the spark plug further down into the cylinders on engines. It should be easy to do for gasketed spark plugs and it looks as though the bottom thread of the spark plug hole never gets used on some of the engines I see. Of course clearence for the plug needs to be checked. I don't know if this will raise the compression very much, or help at all?, but has anyone tried this? (I would be very surprised to come up with an idea that someone has not tried!) John
Posted on: 1/20/2006 9:24 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=3802890

RE: Weedeater porting question
Hi Dave, I am guessing that you bought one of the two bolt crankcase Poulan engines. I am not familiar with what the intake port looks like on those. I would be a bit conservative on porting at first because, as you no doubt know, you can always enlarge them further after a running test. On my engines as I said before I bored out the carb spacer to 1/2". Then I used a metal scribe to draw a line inside on the aluminum with the spacer installed. After removing the spacer, I could see a point from which to start. I followed the 1/2" outline and filed the intake downward in a internal curved shape. I stayed away from the carb pulse port on the right side. Now the port is 1/2" high and a bit more wide because I sort of brought the left side down and the bottom over to the left to create a squared off lower left corner. I made sure not to kick up any burrs at the cylinder inside surface. From the left corner across the port to the top right of the circle is a bit more that 5/8". This is a large as I could possibly go on the port. I wouldn't suggest being this radical at first with any engine. Then I worked over the exhaust port as much as I thought I could get away with, but it wasn't as radical as what I did with the intake. then you need to open up the muffler to let the engine breathe. As far as a 25cc engine turning a Bolly 18-6, I don't know. To begin with I am not familiar with the prop. A light airplane as you describe could very well be compatible. Next time I run one, I will try an 18-6 and see how it goes. I also need to see for myself if I can duplicate the 8k reading with the two 25cc engines I have now. Oh Yes, You mentioned machining the bottom of the cylinders. I removed about .020 from the 21cc cylinders because they didn't feel as though there was much compression and I wanted to see if they would be easier to start. This seems to have helped the 21s operation all around and they went from 6k to 7k with the same 16-8 MA Classic prop. I didn't do this to the 25cc engines, could be a possibility?? I would suggest trying this on your first engine first. There isn't a whole lot of material thickness to the cylinder mounting flange to begin with so check that and the spark plug clearence before you start cutting. I have also thought about sinking the spark plug a bit, the botttom thread and a half never get used as it is and this might be an idea. Maybe someone can comment on this? You were right, these engine conversions are a hobby unto themselves. John
Posted on: 1/20/2006 9:12 PM by Author "rollmyown" in the forum "Engine Conversions"
http://www.rcuniverse.com/forum/fb.asp?m=3802736