RE: GMS Engine Tuning Problem

RE: GMS Engine Tuning Problem
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RE: GMS Engine Tuning Problem - 1/10/2005 11:22:47 PM

Flyer Freq

Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

Save your money on those carb bodies

. I just ran the engine with the "problem" carb with my spray bar. It ran exactly the same as before

. I then put my low speed needle in the carb and ran it again. Same problem

. Then I put my high speed needle in the carb. Same problem. I then put several o-rings on my Perry carb and installed it. The engine ran exactly the same. It could have been leeking around the multiple o-rings, but the engine sounded too much the same. I put the original carb back on and started the engine again. I took penetrating oil and shot it at the backplate when it started to ping. Things happened real quick, but the engine smoothed out and then died. I tried to repeat this, but I was lucky to hit the backplate the the first time, due to all the prop wash

.

The spray bar may have had some to do with the lean high

, but it definately wasn't all the problem

. The backplate gasket may be it

. It is an o-ring also

. I may try adding permatex to test this theory

. Sorry for the wild goose chase

! I really thought I had it solved.

Andy

P.S. Sorry for all the emoticons, just trying to make lite of a dissapointing situation.

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Wayne Miller)

Post #: 126

RE: GMS Engine Tuning Problem - 1/11/2005 1:44:18 PM

Flyer Freq

Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

Now I'm really confused. I talked to the owner of the engine I am "playing" with at our club meeting last night, and one other guy that has an O.S. .46 AX that is the same age as this GMS. The owner of the GMS couldn't believe that I was able to fly the engine at all, based on his experiences with it, before I worked on it, and the AX owner said he was dissappointed too, since his AX would not transition well in the cold, and a vertical transition is out of the question. Do we have the problem figured out or not? Are these two engines just not broken in all the way? Are they designed in such a way that they won't hover well in cold temperatures? I have no answers, and don't know if I can come up with one until the weather warms up considerably. I do want to permatex the backplate on the GMS and see if it transitions better. I at least have to try that.

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Flyer Freq)

Post #: 127

RE: GMS Engine Tuning Problem - 1/11/2005 2:25:23 PM

Wayne Miller

Posts: 978
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline

Hi Andy,

First I should let you know that I fly with 15 percent nitro and always have some castrol in the fuel - what nitro are you running? If its lower, you may have to play with the head gaskets, however, I have never done this.

Whenever we have an exceptional cold day, and the engine is running too cold to be reliable, you can keep the engine running warmer by putting a strip of aluminum cooking foil around the bottom 1/3 or 1/2 (sometimes more) fins of the motor. Hold in place with a twist tie.

I understand that your mid throttle problem first appeared when you tried to hover. Since fuel draw is more difficult in the nose up attitude, we still may have a fuel draw or pressure problem.

I can not remember, and can not seem to find it in this thread, so I need to ask, did you ever drill the intake fuel nipple and exhaust pressure nipple, if so, to what size?

I drilled mine out one drill size larger, then the engine started to work. I may drill the nipples out two drill sizes larger and give it a try, it won't hurt and may be best for a standard fix. The brass insert on mine has already been drilled so the opening is directly below the fuel intake nipple with the insert fully seated, so this does not need to be done.

Again, your doing a lot of work trying to solve this problem. Thanks for your help and keeping everyone up to date.

Fly4Fun,

Wayne

(in reply to Flyer Freq)

Post #: 128

RE: GMS Engine Tuning Problem - 1/11/2005 3:30:00 PM

Flyer Freq

Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

Thanks Wayne!

No I haven't drilled anything out. Sounds like a good tip on the aluminum foil. I run 5% nitro, with castor in all my engines. I know higher nitro is usually run in the winter. I pulled two of the head spacers to match what I have in my own GMS. I thought it would help, but not much change was noted. In analyzing this, in regard to vertical performance, if I was level and at or near full speed, and I pulled straight up, she would climb out of site. If I am vertical, and cut my throttle to halt my climb, and then add throttle to maintain altitude, the engine dies, If I then go back to idle, quickly, the engine remains running. I drop my nose then, and give her the gun in level flight and we are back off to the races, tearing through the sky like its tail is on fire. Weird and frustrating!

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Wayne Miller)

Post #: 129

RE: GMS Engine Tuning Problem - 1/11/2005 7:23:51 PM

Spicoli

Posts: 474
Joined: 1/31/2002
From: TERRACE, BC,
Status: offline

Flyer Freq,

I would try a little RTV in the Fuel-Return groove.
Or try a double sealed bearing
I posted an article by Dave Gierke in the "Obvious Air Leak" thread that helped me.

< Message edited by Spicoli -- 1/11/2005 7:26:53 PM >

(in reply to Flyer Freq)

Post #: 130

RE: GMS Engine Tuning Problem - 1/11/2005 7:55:35 PM

Flyer Freq

Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

Thanks Spicoli!

I'm afraid I have to plead ignorance, though

. What are you referring to as the fuel return groove? I will read your article on the bearing seal. Thanks!

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Spicoli)

Post #: 131

RE: GMS Engine Tuning Problem - 1/11/2005 8:11:26 PM

Spicoli

Posts: 474
Joined: 1/31/2002
From: TERRACE, BC,
Status: offline

Flyer Freq,

Inside the engine there is a channel that goes from the front of the carb to the front bearing.You have to take out the front bearing to see it.

(in reply to Flyer Freq)

Post #: 132

RE: GMS Engine Tuning Problem - 1/11/2005 8:24:42 PM

Flyer Freq

Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

Thanks Spicoli! I realized that after reading the article. Not sure if that will help this engine or not, as I can shut this engine down easily. Did you put the rtv in, in the carb area, or the bearing area. If it was the bearing area, did you heat the casting to get the bearing out?

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Spicoli)

Post #: 133

RE: GMS Engine Tuning Problem - 1/11/2005 9:00:16 PM

Spicoli

Posts: 474
Joined: 1/31/2002
From: TERRACE, BC,
Status: offline

I put the RTV in the channel through the front.
The bearing didn't need heat to come out.All the bearings I've messed with before that one did need the case heated.
I didn't do this until I checked for leaks at every other spot possible

(in reply to Flyer Freq)

Post #: 134

RE: GMS Engine Tuning Problem - 1/11/2005 9:47:54 PM

XJet

Posts: 3462
Joined: 3/31/2003
From: Tokoroa, NEW ZEALAND
Status: offline

quote:

ORIGINAL: Flyer Freq
In analyzing this, in regard to vertical performance, if I was level and at or near full speed, and I pulled straight up, she would climb out of site. If I am vertical, and cut my throttle to halt my climb, and then add throttle to maintain altitude, the engine dies, If I then go back to idle, quickly, the engine remains running. I drop my nose then, and give her the gun in level flight and we are back off to the races, tearing through the sky like its tail is on fire. Weird and frustrating!

I don't know if you were one of those who drilled out the pressure nipple on your muffler or not but those who do this should be aware that doing so can often have a very negative effect.

What is sometimes forgotten is that there's no check-valve in the pressure line so the bigger the hole in the pressure nipple, the quicker the pressure in the tank can bleed OUT once you cut back to a lower throttle setting.

If the hole is to big, this can produce major transition problems.

Here's the scenario ---

You are running at full throttle so the tank build up a steady pressure.

You cut throttle back to a lower setting and the engine continues to run -- but the pressure in the tank now reduces because the tank-pressure is now higher than the muffler pressure so the flow in the pressure line reverses.

You hit the throttle again and suddenly the engine is trying to run at full-throttle RPMs with just a fraction of the pressure it normally has at those throttle settings -- because the tank has yet to repressurize.

I've had quite a bit of success in "taming" badly behaved engines (which won't transition for ****e) by varying the size of the pressure nipple. Sometimes less is more, especially in 3D stuff where you're more interested in sustaining a constant tank pressure during pretty regular and frequent throttle variations.

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(in reply to Flyer Freq)

Post #: 135

RE: GMS Engine Tuning Problem - 1/12/2005 2:17:58 PM

Flyer Freq

Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

Thanks XJet! Very interesting stuff! If a person wanted to reduce the nipple size, where do you get other nipples? I know Dubro makes some nipples that are brass. Can you just fill them with solder and redrill, or is there a better way or better source ???

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to XJet)

Post #: 136

RE: GMS Engine Tuning Problem - 1/12/2005 2:41:46 PM

Wayne Miller

Posts: 978
Joined: 9/10/2003
From: DrumboOntario, CANADA
Status: offline

Hi Andy,

To reduce the hole size, you can fill with solder and redrill, however, I always like to go with temporary modifications to test with first.

Example: You may want to find a piece of brass tube, or fuel filter, with a smaller size hole - or as an alternative, take a 1 in (2.5 cm) piece of brass tubing, fill it with solder, drill and then insert in the exhaust pressure line (to the tank) to do your testing. This will give you the restriction without modifying the nipple. You can make up several of these with different size holes, and take them to the field to test with. If you find a hole size you like, then modify the exhaust nipple.

Just a suggestion, hope it helps.

Fly4Fun,

Wayne Miller

(in reply to Flyer Freq)

Post #: 137

RE: GMS Engine Tuning Problem - 1/12/2005 5:08:27 PM

Flyer Freq

Posts: 912
Joined: 8/20/2002
From: Appleton, WI, USA
Status: offline

Thanks Wayne!

That is a good idea! I also noticed that the inside diameter of the nipple for several of the GMS engines vary. They are .75 cents each, from Tower, and may not be a bad thing to have in the flight box. Your suggestion, is definately quicker than waiting for an order to come in.

I guess my next course of action is to rtv the back plate, run the engine and see what the results are. If they are not what I am looking for, make some orifices out of brass tubing and play around with varying the sizes. I want to make the orifices very short, however, because the length of the orifice will likely have as much effect as the diameter. I will keep you posted!

Andy

_____________________________

Lose not thy airspeed, lest the ground rise up and smite thee!
If you want to make God laugh, tell Him your plans

(in reply to Wayne Miller)

Post #: 138

RE: GMS Engine Tuning Problem - 1/15/2005 1:32:56 PM