rollmyown

Hi Dave, I understand what you are saying. I realize it could actually help the engine run smoother. It also might not be necessary to remove as much material as you did, only running will tell. It doesn't look as you you have really weakened the piston. I don't quite have the nerve yet to repeat what you did, but I am working on a 2 bbl engine right now. I cut .020 from the bottom of the cylinder as I planned and while doing that I used your basic idea about reducing the restriction to the transfers by filing half circles in the bottom of the cylinder skirt that protrudes into the crankcase. I wanted to lower the directional intake ports with the .020 cylinder cut and while I was at it the "half circles" didn't seem like much of a risk. This engine is close to be done and usuable. I also cleaned up the carb port to suit a 1/2" bore in a carb spacer I intend to make for a Zama. Here is the photos.

Note: Removing .020" from the bottom of the cylinder turned out to be a bad idea. One thing I overlooked is a sort of a "cornice" because I don't really know what they call it around the top of the cylinder. This might be part of "squish band" idea for pollution or something at the top ring, but anyway after the .020" cut, the piston hit this rascal in the corner. I thought about trying to machine/remove it but this is just about out of the limits of my small Lathe. I am still adjusting the compression with two .010" and .005 paper gaskets. I increased the compression all right, but this is not the way. The stock gasket is about .020" thick (check it), so a thinner gasket is about what is practical, unless the top corner of the cylinder is machined away. Got you curious?, did you really take notice of it?, -- I didn't until the first bump. (I have thought about cutting a matching "L " cut in the top of the piston, and I might.)

Scott Ellingson

My Feedback: (146)

I do ballance all my flywheels. The older 33 may be a better engine. McCullogh saws are made by MTD now. Not known for quality I would bet the older Mac saws from before MTD bought them out were much better.

davewallace

My Feedback: (29)

Hi Scott,
That could be the case as this saw has machined mating surfaces for the carb and shaft. It has a very light piston, unlike the other MTD stuff that I have seen. It has a bolt togather rod like a Homelite XL saw. I guess I'll see how it does. I give my garabageman three bucks for it.

Dave

Scott Ellingson

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I just got done test running my first 1bbl Toro. I did no porting except the exahust. I did nothing to the piston or the bottom of the cylender. I just wanted to see how they did like that. It did well. As well as my 2bbl engines. I got 8100 on an APC 16x8. 7500 on a Pro Zinger 18x6. And 6500 on a Zinger 20x6 (not a Pro). That is very good. For the hell of it I tried a 12x12 APC I had here. It turned it at 9800 ! I thought that was pretty funny. I had to lean it way out on the top end. No load. Not much for thrust but a top speed of 110+ MPH Oh I forgot. These numbers were with a Pitts muffler I make and a 12.7mm carb. Same size carb as a G26.

davewallace

My Feedback: (29)

Wow, that's real good. I was thinking about the smaller transfer cross section of the 1bbl. The 1 bbl is more directional for better scavenging and chamber fill. The smaller cross section causes an increase in volocity which helps scavenging. How much did did you rise the exhust port? I think it is safe to rise it aout 1/16" (75 degrees BBDC). The intake is the same as a stock Homey 25cc at 60 degrees BTDC. It could go to 70 degrees BTDC with out problems by trimming the piston. I need to order a hub so I can test this thing. Scott, where do you get your baldridge hubs?

Dave

Scott Ellingson

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I actually don't go up at all. I just square off the port. If you look inside the port is V shaped on the bottom. I just square it off so it is even on the bottom. It is not much but it doies help. I am going to do some more mods on the nevt one. This one runs so good and has lightning fast responce so I am going to leave it as is.

rollmyown

I have to buy some APC props, I have to see what the difference is compared to the props I am using. Those are good numbers for a 1 bbl engine you are getting. This first engine of yours is basically what I did to mine, except I have a Zama carb. I"ll try the APC prop next, but I also think I can make a low profile carb spacer to fit this Zama and I'll make a muffler also. By the way what is the altitude of your location, I think you are higher than Pennsylvania and you are still getting better numbers.

Scott Ellingson

My Feedback: (146)

I am only around 1000ft or so. The barometric pressure today was 30.11. APC props are far more efficient than most so the RPM will be higher with them. I ran a 18x6 Dynathrust and it was 400 RPM less than a Pro Zinger. It also turned a APC 17x6 at 8500 or so.

Ralphbf

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What is the ready to fly weight of these engines?

That's everything including the prop and the mount.

Scott Ellingson

My Feedback: (146)

I don't use a mount. The back of the engine is perfect for mounting. The weight RTF on the engine I just did today (pictured) is 3 lbs 8.5oz. Less than a G26.

rollmyown

Balancing flywheels, now that can be a challenge. I have heard about balancing flywheels for years, but I never saw how anyone does it. (There must be electronic devices for this used by the big companys.) I decided to build my own balancer. I found some very small precision ball bearings with close to 1/8" I.D. (actually a hair less, metric?) and I used these. It actually works, I have balanced a few flywheels, but it is a tedious process where something like a crystal ball would also help. More than once it looked like "remove a little bit more about right here and that should do it", but it does something different than expected. Experience and learning when to leave well enough alone helps with this process. Sound familiar Scott? or do you have a majic wand for this?

rollmyown

Your altitude is close enough to mine. I looked at the picture of the engine you just posted. One thing you are using that I haven't used on a Toro is a velocity stack, that could affect the results? I will check a few other props for operation, mainly as a curiosity, and I will use the Laser Tach when it gets here, it will no doubt give more precise readings than my Tachmaster. The bottom line is that when these engines are running well and producing power, you don't even need a Tach, except for testing like we are doing, because you can hear and feel the power. A stock trimmer engine sounds like a trimmer engine, but when modified and hopped up a bit, they start to sing like a glo engine. I know you have noticed this.

rollmyown

Those are some good numbers for the 1 bbl engine. I have one that I did essentially the same exhaust only clean up to. I will recheck this will the Laser Tach. You mention a 12.7MM carb, is this the venturi diameter or what?. I have noticed that the venturi versus the bore diameter of different numbered carbs varies noticeably. 12.7mm is .50" so I would expect that this is the bore at the throttle plate, is this correct? With the Zama carb that I am using, the bore at the throttle plate is .56" and the venturi looks real close to .375". (I can't actually stick the calipers in there without removing the choke.) Dave thought my carb could actually be too large and I considered what he said, but it runs very well. An identical carb gave me very close to 8000 RPMs with a 25cc weedeater with the same 16-8 prop. Of course I opened the ports on that engine and the throttle response is very good, which is a vote for a good carb match. So, I figured the Toro should be able to handle one of these carbs.

davewallace

My Feedback: (29)

Hi Rollmyown,
It sound as though there is some confusion about carb size. Carbs are sized by the venturi diameter. Walbro carbs have a number cast into the inlet side of the venturi. This number is in 64th's, so 28 equals 7/16ths or 11.11mm. 32 64ths equal 1/2" or 12.7mm and so on. Zama carbs don't have this and must be measured with a drill bit shank or caliper. I have seen the same Zama carb model with two different venturi sizes. The next thing is the throttle bore which I find to be 5/8" on all of my Walbro carbs 11mm and above. I don't have any large Zama carbs since all of mine are off trimmers. The throttle bore varies on the 10mm and below carbs from 7/16ths to 9/16ths depending on what the manufacture wants. When you told me that you were using a 14mm carb, you were talking about the throttle bore and I assumed that you were talking about the venturi size. Your carb is actually a 8,10 or 11mm which is fine for a 25cc engine. I guess the big test is to try the Toro with both 11mm and 12.7 and see if there is a gain. If there is no gain, the 11mm will give better endurance. Another interesting experiment would be to make a manifold in three or four sections to test fly and see if a shorter manifold is OK. This would make cowling easier.

Dave

Ralphbf

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What do these weigh with out the flywheel?

Scott Ellingson

My Feedback: (146)

I use a Dubro prop ballancer. It is pretty acurate but not perfect. I get them close enough that it looks like the magnite is the only thing effecting it and not the weight. It is not perfect but very close. I need to replace the beams that hold up the balancer wheels with stainless or alluminum. That way the magnite will not effect the outcome. The Toro flywheels are pretty close anyway. I usually do not need to remove much.
The velocity stack is a good idea on any gas engine. When I put one on the toro I had to lean it quite a bit because all the gas wasn't being sucked out of the carb by the prop wash. Also it picked up 200 - 300 RPM. It doesn't effect all engines that much. But the toro it did. The muffler also helps alot. I used a 1/2 id single pipe before but now that I switched to a single 9/16 id pipe the RPM's are higher but the noise is the same.

Scott Ellingson

My Feedback: (146)

I would have to check the weight without the flywheel. You are thinking glow or electronic ignition? I think the flywheel is 6oz or so.

Scott Ellingson

My Feedback: (146)

I usually used a 11.11 mm carb on the Toro. A WA 58. I tried a 12.7 on the last one. There was no increase in top end power but the throttle responce seemed a little faster. I have a bunch of the 12.7mm from new Mac 38cc saws so I figured I would try them since i am now out of the new WA 58 carbs. I should never have sold any of them

davewallace

My Feedback: (29)

Hi Ralph,
I have a 1bbl engine. It weights 55oz. complete with mag ignition,hub,stock muffler and 11mm Walbro carb. Without the coil and flywheel it weights 43oz. Add the electronics and battery and you have close to the same weight as the mag version. The stock muffler weights 6oz. compared to 4oz. for a Wackerengines muffler. The flywheel was not trimmed yet, so thats an extra oz.

Dave

davewallace

My Feedback: (29)

Hi Ralph,
The untrimmed flywheel weights 8.4oz. and the coil weights about 5oz.

Dave

Ralphbf

My Feedback: (27)

There is a thread going that is basically about converting gas to glow.

They are mixing Gas and Alcohol 50/50 adding oil and running a F-4 glow plug powered all the time.

The results seem to be as good as with the standard gas/oil mix with a mag.

It seems to me that taking 16 ounces off this engine for a flying weight of 39 ounces would allow it to be used on

on a whole range of planes.

Now I'm wondering if I should of waited to buy my ST-2300 for my 90 size Groovy.

davewallace

My Feedback: (29)

Hi Ralph,
As I stated in a previous post the engine weights 43oz. without the coil an flywheel. This is with the stock muffler which is 6.4oz. and a 1oz. spark plug. It would make a good choice for gas/glow operation. The untrimmed flywheel and coil weight 13oz.

Dave

Scott Ellingson

My Feedback: (146)

I have converted a few gas engines to glow. One was a Poulan 42cc. It ran perfect. No glow driver needed. That was mounted upright. Mount it inverted and you will need one. FOr my mix I used 1 gallon of car fuel with 20% nitro mixed with 2 gallons of pure methinol. The result was 5% oil and 7% nitro. Approx. Not as cheep as gas but still not bad. I think the Toro would be a great one to convert to nitro. I just hate the thought of onboard glow on an inverted engine. More money and more weight with the big battery you will need to fly for a good period of time. Otherwise it is a great way to go.

rollmyown

Hi Dave, I knew there was a bit of miscommunication about carbs and then we had two brands in the mix. What you state in this post is about right. I have noticed there is more than a few differences between carbs also, because they tailor the models to specific engines, of course.
From the "background paper" in your photos, it looks like you have done a lot of research on engines and carburetors.
I already ran a 1bbl engine with a "big" carb and it seemed too big, I covered this in one of my posts. I made an Aluminum muffler, a pitts style, it is 1" thick x 2" wide x 5" long. I haven't run it yet. You have to Aluminum weld this muffler, but you have already seen the aluminum stock, it is scrap pieces from Aluminum railings and it has a .060 wall thickness, which is about perfect to make a muffler. I tried thinner material and it is a pain to aluminum weld without burning up.

I am talking about the aluminum rods and a propane torch. I have made other rmufflers from this stock. The paint smells when it burns off but that is how it is. I bet that garbage man engine supplier of yours might be able to come up with some of this railing scrap, lol.

It weighs 4 ounces, the stock muffler weighs 7 ounces, and the stock muffler is a lot thicker. I am going to make some 1/2" thick carb spacers. (The two bbl engine is more of a challenge for a carb spacer than a 1 bbl engine. I am going to try and do it without an external pulse line.) I would like to get the total width of the engines minimized. I will post a picture of the complete engine when I get it done. I am now thinking about designing an airplane for one of these and around 7" or so in width is a lot.

rollmyown

I have the ballancer but come to think about it, I was so busy checking other things I didn't think to check the balance on the Toro flywheels, but I will now. I also noticed the velocity stack on the Fuji engines, simple and compact, and should be easy enough to make out of plastic stock. The muffler I just made has two 3/8" I.D. (actually a bit larger, the O.D. is 1/2") pipes on it. I want to finish everything complete before I run them again. I am adding photos to this. A 3/8" carb spacer is shown, there is no gaskets yet, but it is all assembled. The gaskets are easy but getting the carb close to an engine requires doing something to the throttle linkage and the photos show my approach to this. I almost forgot, if you can see the notch on the right of the spacer, that is a new holding spot for the throttle return spring so the throttle servo won't need to fight with a typically tough spring on these carbs, there is still plenty of return pressure. (I try to get the details, it has become a habit.)