Well CONVERTS I can't beleive that 3 years have gone by since I started this tread; I just want to thank everybody thas has partcipated and contributed with this subject to make it have the succes that has been so far, It has help us to understand a little bit more on this field of our hobby and save ourselfs some money on the way; I hope we all keep up the interest that we have shown so far as well as the brotherhood that we enjoy.
So for the third year in a row I want to WISH all of you CONVERTS as well as you loved ones a:
MERRY CHRISTMAS AND A HAPPY NEW YEAR.
Sincerelly:
William R. Pomplun (A.K.A. Aero Nut) and familly

aero nut: I am sure glad you started this thread. It has been very interesting right from the start. I went back and read many of the postings in 2003 2004 and 2005. We came a long way. But we still got further to go. I want to see a exhaust throttle made and fine tuned and would like to hear more about using 2 glow plugs for better idle? i want to wish you and your,s a wonderful holiday season too. Also to all our other friends online. Take Care & God Bless Capt,n

aero nut, Thanks for starting this thread and thanks to all who have shared so much information, a lot of it over my head! I've been playing around with a 25cc poulan with the stock mag. ignition...A 28/32 venturi wabro carb is the only mod... I get 7,000 RPM on gas using an 18x6 APC prop, didn't think that was too bad considering the small ports and low compression this engine has... Today I put the glow adaptor in and ran it on straight 93 octane 40 to 1 gas oil mix and it ran same RPM with glow power on... Just for grins I had some 30% heli fuel I use in my Saito's and added that when gas was down about 1/3 of the tank... I know I had wayyyyy too much oil but this engine ran great after getting the carb set correctly, only needed glow power to start engine, idle real nice at 1900 and was turning 7300... Next thing I did was remove flywheel and got 7500 RPM with way quicker spool-up... This engine has very little vibration and no detination even with a lot of nitro, probably do to a little less compression than some engines... Tomorrow I will remix and get rid of some of the oil and see if that helps a little more...This engine weighs a little less than 40oz with muffler and mount ready to fly, should work good on a Funtanna or something like that... Thanks again for all this great info here!!! Hamman

Bill,

Let me third that emotion. Although I'm a late comer, I am tickled with delight with this entire experiment. Many might have said, no way. Not so,,, way to anything if you just give it a go and see what happens.

Feliz Navidad from the frozen, white north.

Hi guys,

Yep, it's been fun. Happy Holidays to all of you as well. As always, it will be interesting to see what we all come up with in the next year. Lot's of good experiments going on here. Good luck and thanks to everyone, and above all, have fun!

Take care all,
AV8TOR

Hi, I have seen the glow plug adaptor pics. but how far does the glow plug protrude from the bottom of the adaptor? Does anyone have a pic of this. Just woundering how far the plug goes down into the cyl. Thanks

Here is photo of adaptor in a Poulan Feather Lite 25cc. This one is from Wacker Engines.

Thanks for the pics. It looks like it is flush with the adaptor end, and the spark plug was protruding further into the cyl. Has anyone tried to do the same with the glow plug, thinking this may help with the running problems.

Yes it is flush, but compression seems about the same as the spark plug. I don't know a lot about this subject but I do know that you don't want sharp edges such as exposed threads in a combustion chamber that could cause detination. The one I'm using works great.

I was thinking that moving the plug into the cly more would keep the heat closer to the piston and help with the low idle problem of a flame out.
I have not tried this conv. on my motors but I am gooing to soon. I had this work on some old v8 chevys that without the extended tip on the plug the motor ran poorly. This was on a 11.5 to 1 compression ratio

I think this subject was discussed earlier in this thread, its been awhile since I read the whole thing, There just is so much info here to recall. If you look at my adapter it is cut concave, it could be milled straight where the plug protrudes in the chamber, that would get the plug a little closer to the piston. Some of the guys make adaptors out of spark plugs. I think that was somewhere around page 18 or so. I just got a new chuck for my lathe so I will be making my own parts, may try something differant on the adaptor. I ran the poulan this afternoon and idle was very reliable at 1800 RPM with no power to the plug.

I"ll try to make one at this week with a longer reach from a old plug. I have read some of the post but there is just to many.

Mine are flush with the end of the adapter. Off hand I would say the compression ratio is the same or slightly higher, as you don't have the volume a spark plug has around the center insulator.

My engines seem to idle more smoothly, slowly, and reliably on Gas/Glow than on ignition, so I'm not sure which idle problems you might be talking about.

The Gas/Glow setup does require the idle to be a bit richer than one would set it for straight gas and normal ignition.

I hesitate to mention this, but what the hell. Here's a modification to get a better idle and transition on any of these engines, whether they are running Gas/Glow or gas and ignition. Please do not try this if you are not:

A. Comfortable trying the procedure.
B. Willing to possibly trash a carburetor in the name of experimentation.

If your carb has any holes in the throttle butterfly, (Not Choke), solder them shut. Then using a needle file, file a tiny notch in the butterly where the exit holes in the venturi are. These are tiny holes in the venturi where the idle and transition mixtures enter the air stream and a little difficult to see, but you want the notch in the butterfly to line up with those holes when the butterfly closes. Start with a really tiny notch, as if you make the notch too big, you won't be able to get the idle slowed down even with the butterfly shut. Please don't try this unless you are comfortable with the whole idea, and be careful to not get metal shavings into the engine, etc.

AV8TOR

Well I finally was able to test some of the higher-octane fuel mixes. Still do not have the Shindawa ready to go, so I mounted the 35cc Stihl on the test stand. I made several runs on the following mixes:
1/3 ST glow, 2/3 93-octane w/10% ethanol.
1/3 ST glow, 2/3 93 octane w/ 10%ethanol and 10%toluene.
1/3 methanol, 2/3 93 octane w/ 10% ethanol, no nitro.
1/3 ST glow, 2/3 93-octane w/10% ethanol added 3 ml Permatex octane booster.

All of these mixes improved the overall vibration level to an acceptable level at 1500 to 2500rpm and 5000 rpm plus. Vibration in the 3000 to 4000 rpm range was higher than I would like it to be. The only run which significantly reduced the vibration in the 3000 to 4000 rpm range was the run with the Permatex octane booster added. However, as I suspected the MMT, which is an organo metallic (manganese) compound, fouled the glow plug after about 5 minutes run time.

I tried one other mix just to get the maximum octane level which was 1/3 methanol, 1/3 ethanol and 1/3 toluene. If my calculations are correct, this would give an octane number of 113. The engine would only run with the glow plug on. There was virtually no vibration in the 3000 to 4000 rpm range, but WOT rpm dropped from an average of 8200 on a 18 X 8 to about 5200 rpm.

I guess it is back to the drawing board since fuel mixes didn’t get me where I wanted to be.

Merry Christmas and Happy Holidays to all and may you have a great New Year.

Will

wvarn1957: I have a Stihl chainsaw of about that same size. My saw has bad vibes, and I do not think there is much a person can do to smooth them out. I hope you can. I do not think I will ever convert that saw engine. Best Regards Capt,n

Try raising the cylinder. This will lower the compression both due to an increase in combustion chamber volume, and due to increased exhaust timing. If it runs well and to your satisfaction, then you could try increasing the intake timing to regain that lost due to raising the cylinder. Worth a try in all your experimenting.... The only downside would be a reduction in quench, or squish area which can be detrimental in the fight against detonation, but I don't think that is quite so critical in these small bore engines.

AV8TOR

Adding a couple of gaskets under the cylinder was the first thing that I tried. The two gaskets probably raised it about 15 thou and it did improve the situation. I guess the next thing to try is adding another gasket and trim the piston skirt to get the intake timing back. What is really puzzling to me is the fact that on EI the engine behavel great. Too bad there isn't a way to get variable timing running glow/gas.

Will

What glow plug are you running? We are running a four stroke plug in the lower compression engines, but a higher compression engine might like a regular two stroke plug. A cooler plug, if it will stay lit with the gas/glow mix, would retard the timing as well.

Just as an off the wall guess, I was thinking you should raise the cylinder around .045". Once again, that goes against normal engine optimization theory in the area of the squish/quench band, but it's an easy experiment to try and once again, the squish area shouldn't be as critical in these small bore engines.

If you can't get it to work after you run out of experiments, you could always run FAI mix; straight methanol and oil. It should run well at those compression ratios.

AV8TOR

Will,

After you raised the timing, did you find need to adjust the main needle? If so, in what direction?

Andy,

When I first changed from gas/EI to gas/glow I had to richen the low and high speed needles on both the Stihl and the Shindawa about 1/2 turn. Adding the gaskets to the cylinder base of the Stihl made very little difference in the carb needle settings. Each of the different fuel mixes that I tried required some minor tweaking, but in every case it was less than 1/8 of a turn.

As far as different glow plugs, I have tried OS-F, Hobby People's big bore, OS-8, OS-3, Fox Miracle Plug and some old Mc Coy plugs. There were some differences, but nothing dramatic.

Early in the game, I modified an old Zama Carb to be able to run straight methanol. Using methanol with Klotz @ 36:1 made little difference in the mid range vibration level. Power was up quite a bit in that it was turning a 18 X 8 around 8800.

Next week after I make it through the round of parties,family gatherings and various other pre holiday activities, I am going to raise the deck 45 thou as Av8tor suggested and see what happens.

One thought though, I am trying to set up an engine for a large (142" WS) camera platform which requires a pusher. Most of the tests I have been running have been with the engine turning clockwise. I elected to go this way because the selection of pusher props is very slim. Maybe I have overlooked something, but I can't see how the rotation direction would have any bearing on the vibration. I really wanted to use gas/glow to avoid any interference with the flight controls or the camera-electronic equipment which the plane will carry.

Right now I have substituted a tractor engine module(ST-3000 on EI) for the camera/electronics module just to test out the flight charateristics.

Hi,

Well, that reverse rotation idea is at least worth running a few test runs in the normal rotation to see if it could be causing a problem. Many years ago I remember reading an article about moving the cylinder off center of the crank axis, and supposed gains in power achieved by doing so. I don't know if anyone is doing this in manufacturing, but if so that could perhaps cause a problem when run in reverse. I know often times auto engines have the pin in the piston offset a bit to lessen piston slap. If they are reversed, the engine will gain a touch of power at the expense of more piston slap noise. If your engines happen to have the piston pin thrust offset, this could also be a factor. These things might be difficult to measure, as we are talking thousands of an inch...

Just trying to throw ideas out there to help.... Good work on the extensive testing!

AV8TOR

Av8tor,

I had a chance today to do some more testing on the Stihl while the wife was out shopping. She fusses about the noise when I run engines at home ratha than at the field.

Ran the Stihl first in the normal counter clockwise direction of Glow/gas made with 93 octane. Really couldn't tell any difference in the vibration. I remounted the EI just to go back and verify my original observations. Ran it in both directions. The mid range vibration is higher than it is below 3000 rpm or above 5000 rpm, but acceptable for use on a plane.

I raised the cylinder deck to a total of 45 thou and ran on Glow/gas mix. Some improvement in the 3000-5000 rpm range, but still too high to put on a plane. I didn't try shaving the piston skirt to get the intake timing back because there wasn't enough improvement with the deck raised to justify modifying the piston skirt. I think that the Stihl runs well on EI I will use it on another plane with EI ratha than Glow/gas.

I still need to find an engine that is suitable for the camera plane. The power requirements are not that high since the plane is designed for a flight envelope of 25 to 35 mph. I have a Homelite 25 cc and a McCulloch 28 cc which I have not yet converted. Any comments on which one might be the best candidate?

Will

Hi, I have to coment on your plane. I love that look! Did you buy those plans or make them yourself? Looks like something I'd like to try for a engine testbed platform. Were could I get plans for it? Chris

Chris,

Glad you like it, thanks. The plane is of my own design. I have the plans on AutoCad and would be glad to send you the file. I'll have to warn you though, the plans are not in any kind of finished form. I usually don't try to finish plans for publication so many details are not included. Once I get basic structure and dimensions I do a lot of changing and modifying as I build. Anyway. you are welcome to the file if you want it.

Will

wvarn1957: That is a interesting airplane. Can you post a couple more views. If you can include a view from above it. Thanks Capt,n