My Cox .049 Marine inboard engine

Reducing runout is part of the reason I make the APC prop hubs. It would be easy enough to check runout with an indicator (with the plug out). Even getting the spinner or in this case the drive dog to run true can be tough.

Is this setup running a lightened piston (a whole new can of worms)? I don't think a Cox has enough counterweight even with a lighter piston, I checked some time ago but can't remember. However, with a single cylinder whether or not this is a real problem depends on the entire installation. Some vibration is inevitable. And mounting setups have resonant frequencies. Something as simple as moving the clamps to a different location or changing the mass or enough mount angle will move the frequency out of range. Vibration is a complicated topic.

roddie wrote:Hi Juan, Congratulations on getting the engine running. In both videos; I noticed some "drift" in the needle-setting when you were actuating the throttle-linkage. It didn't seem to affect the engine-run.. but you might want to make sure that it's staying where you set it.. and that there's no air-leakage around the threads. ... Maybe it's supposed to move with that type carb? If so; disregard my comment. I'm still learning a lot about these things..

Did you use a .125" dia. (1/8") drill for your flywheel's center-hole? The 5-40 machine-screws have a .1225" diameter. My Dumas flywheel's center-hole is .129" which could account for a considerable amount of imbalance when running at high R.P.M.'s. I'm not using the Dumas flywheel.. but if I were to use it; I'd definitely bush the center-hole. I found that the plastic used in mailing envelope "windows" is .001" thick.. and could be wrapped around the screw, to take-up the slop.



If you happen to have used a #30 drill (.1285").. it might be adding to the vibration issue. Interesting info. on the balance-shaft though. I did not know this.

That engine is a SCREAMER!! It will be exciting to see how it works in the little "Half-Pint" boat!! Your progress is helping to keep the fire lit with my project(s)!!

     Hello Roddie
                        As you guessed the needle valve rotates with the carb barrel and as it does reduces fuel flow when the engine is throttled towards idle. The AP Hornet .061 carb is a copy of the Norvel Big Mig .061 carb with the difference that is easier to use in an engine with a round intake. The Norvel carb has an oblong mounting stub that is not easy to duplicate.
                         The flywheels that I have made use a .125 inch hole. After mounting them in the High point balancer I realized that I must have done something wrong as both the steel and aluminum flywheels were wobbly. I made a part to mount the flywheels that has helped correct the problem. After I got the flywheel running true I checked it again and it had a slight imbalance which I corrected by drilling a very shallow hole on the heavy side. I do use 5-40 cap screws that I buy from Micro Fasteners. I don`t  buy from the local screw supply because I bought a few and the heads would wobble I think they were imported from china.
                      I also had a hard time with cox .049 prop driver being out of alignment so I started modifying the prop drivers and making collects for them. Here is a pic. COX .049 are the most fun engines to play with. William Atwood did an outstanding job designing them for Leroy Cox.
                                                                                      Juan


.

gkamysz wrote:Reducing runout is part of the reason I make the APC prop hubs. It would be easy enough to check runout with an indicator (with the plug out). Even getting the spinner or in this case the drive dog to run true can be tough.

Is this setup running a lightened piston (a whole new can of worms)? I don't think a Cox has enough counterweight even with a lighter piston, I checked some time ago but can't remember. However, with a single cylinder whether or not this is a real problem depends on the entire installation. Some vibration is inevitable. And mounting setups have resonant frequencies. Something as simple as moving the clamps to a different location or changing the mass or enough mount angle will move the frequency out of range. Vibration is a complicated topic.

Hello gkamysz
                   The engine is a Cox .049 Black widow and the piston is not lightweight.I have not modified the P/L assembly. Vibration is hard to get rid of. In the old days some guys used to add a counterbalance in the hub behind the prop.
                                                                                       Juan

F4D Phantom II wrote:The engine is a Cox .049 Black widow and the piston is not lightweight.I have not modified the P/L assembly. Vibration is hard to get rid of. In the old days some guys used to add a counterbalance in the hub behind the prop.

Yes, I was going to mention that, however I think this has more to do with the window in the crank. Any balancing beyond that would be trial and error. I've heard that some don't balance props just clock them on the shaft until the engine runs smoothest. I've done this with small, high rpm electrics.

I have a Cox car crankcase assembly if you want to experiment with one. It has a stronger crankshaft with a taper for flywheel mounting. The diameter of the crankshaft is similar to the TD. PM me with your mailing address and I'll send it to you.

I decided to start building the Dumas half pint boat to mount the Cox inboard marine engine. The kit is die cut and it has to be built carefully since the parts have to checked and sanded to get a good fit. I think they should shift to a laser cutter to get a kit with a better fit. I have sort of followed their instruction doing things my way when I felt there was a need to do so. I was not supposed to remove the model from where I had it pinned and glued but the bulkheads need to be sanded to make the bottom fit correctly.  here are pics.
                                                                                          Juan

 

I have continued working on my Dumas Half pint boat. I had to sand the bottom frame to glue the two plywood bottom pieces. Since my eye sight is not as good as it used to be using a magic marker I tinted the area on the chine pieces that needed sanding to form a bevel where the plywood would be making contact. used a wide sanding pad to make sure I would hit the bulkheads,the chine and center of the boat frame to provide good contact everywhere. I glued the bottom pieces and started to sand the sides of the frame to get it ready for the two plywood side pieces. Using 100 grit sand paper I have been working on it. I`m planing to use a one piece 1/32 plywood top in place of the mahogany pieces in the kit. I`m going to need to make an aluminum strut for the propeller since I`m not going to use the drive shaft I got in the accessories kit. here are a few pics.

                                                                                    Juan

The 1/2 pint is looking good , i see you have taking care in getting the wood to seal good and it shows . carry on !

1/2 Pint is a classic little boat that’s been around a long time…. Nice to see one being built
“live”…. Thanks for sharing

Hello all
                   Thanks for the comments they are appreciated. I have continued working on the boat. I`m slow and take my time doing things and I`m not happy until what I`m doing feels right and looks right. I have added some pieces of wood to the bow to provide for more gluing area for the sides. they were to be glued at the front on 1/16 of the keel and I felt that a small bump could split the bow. I have sanded the bow to end on a sharp edge. I have done more sanding on the chine and the sheer edge.  I have used a sanding block with 100 grit on one side and 180 grit on the other. The sanding block has part of it covered with masking tape that I lean against the sheer when sanding the chine to get the right bevel on the chine without sanding the sheer. If a bulkhead sticks out a bit it gets sanded at the same time to provide a straight line from the sheer to the chine. That way the sides will sit flat when I`m ready to glue them. I also flip it around leaning the masking tape on the chine as I sand the sheer edge. I still need to do more sanding. I took some time and painted the inside of the boat and areas that I would not be able to reach when the sides are glued. I used clear fuel proof paint.
                                                                       Juan

The boat is looking good , you do nice work

Thoughtful and careful work with the sanding block, Good job

Hello
              Thanks for your kind words guys. I have done some more work on the boat. I was planning to glue the sides but before I did that I got the front portion of the plywood sides wet with water and then I clamped the sides in place for them to take the curved shape needed. While I waited for them to dry I thought that It would be a good idea to install the motor on the mounts that came with the kit. I needed to remove 1/2 inch from the bottom of both mounts due to the mounts I made for the engine,it would sit too high on them. After cutting the mounts and bolting the engine in place I decided to add the propeller shaft thru the slot I had made in the bottom of the boat. The shaft would fit at an angle when viewed from the side. To get the shaft to flow smoothly from the engine I had to cut a slot on bulkhead number 4 to raise the shaft and get a smooth transition from the engine to the shaft. Not having the sides on were a plus in doing this job as I could see how everything fit. here are pics.
                                                                               Juan

Hello
           Between yesterday and today I worked on making an aluminum strut for the propeller and also made a brass bushing for the metal rod at the end of the Black Marlin flexshaft I`m using.  I tested my set up hooking the flexshaft to my variable speed Dremel and spun it to 25K rpm. I oiled he bushing and everything worked fine. I placed a steel washer between the brass bushing and the brass prop dog as I didn`t want brass rubbing against brass. some pics.
                                                                                     Juan

Looking Good your getting a lot done in a few days

Hello
             Today I have done some more work. I glued the plywood sides to the boat. I started with the one that was harder to bend and I clamped the side. I started gluing at the back until I got to bulkhead number 4. I used thick CA and glued the bottom portion and then the top. The front portion I had to use clamps to get it to sit flush with the front of the keel. After that I stuffed some foam pieces in the bow to help with flotation in case of a problem. Then I started on the right side starting at the back after lining up the side to make sure I had it in the correct position. I glued again to bulkhead number 4. Then I worked on the bow section. I had trouble bending the plywood to meet the front edge of the keel. I thought I could use a couple of screws and the fill the holes when finished but then I had an idea and using my monokoting iron I decided to use heat to bend the wood. I applied a wet towel to the wood and holding the plywood against the keel I applied the very hot iron and the plywood and I got it to conform to the shape needed. I released the plywood and applied thick CA making sure the plywood was touching the chine and the sheer without gaps. I decided not to use the mahogany included in the kit for the deck . I will be using 1/32 birch plywood. I`m thinking about covering the boat in 1 oz fiberglass Here are the pics.
                                                                                        Juan

Too darn cool Juan. It looks fantastic. This is exactly what I want to do. My son picked up a .049 Babe Bee with marine running gear. I just don't have the stuffing box. I have to ask, do you have a place to run this boat? This would make a terrific video.

Hello Ken
                     I still don`t know where I`m going to run it. I live about 5 minutes from the beach but I don`t want to try it there a friend mentioned a place 30 minutes from where I live and I will go to take a look. I still need to buy a radio,receiver,battery and servos I will be buying them this next monday.
                     
                    I started to sand the top to get the plywood sides to be even with the sheer to then glue the top. I started sanding and realized I needed a third hand. I used a piece of stiff foam I bought at a local upholstery store that I use when building model airplanes and it provided the support I needed. Using a long sanding block I got it done. Pics.
                                                                           Juan

Enjoying your boat build Juan…. Much precision and attention to detail…. Will be a nice end result I know!!