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GMS- just cant get it right!!!!!!!

Old 11-04-2004, 03:37 AM
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trentos
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Default GMS- just cant get it right!!!!!!!

Hi does anybody use and rely on the engines GMS if u do have u noticed that they can never realy b tuned proply or are always playing up???? i have one and i have had trouble with it from the moment i started it up (word of speech).

does anybody have any souloutions to any of the many probs????
why are they so popular when they play up so much???

does anybody aggree??

-TRENT-
Old 11-04-2004, 07:40 AM
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ksechler
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Default RE: GMS- just cant get it right!!!!!!!

I don't have one, but I have read many posts complaining about air leaks around the carb. I'm sure someone can give more details...
Old 11-04-2004, 09:33 AM
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Gene Chernosky
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Default RE: GMS- just cant get it right!!!!!!!

It is critical with ANY glow engine to be sure the carb/case seal is excellent. The GMS .47 has two o-rings...one on the carb and one in the case at the base of the hole where the carb goes...in effect, a double seal. Another thing that could cause problems would be the standard shielded front bearing on most glow engines...I prefer to use a sealed bearing there to eliminate the 'runny nose' effect. The GMS .47 carb has an aluminum throttle rotor which IMO doesn't fit as tightly as it should...comparable to TT/OS, etc. Leaks around the throttle rotor could cause running problems, too, as ANY air leak can.

With all of that said...I have a GMS .47 that runs like a top so all of this doesn't really bother me. I guess it is the 'luck of the draw' to some extent. Sounds like quality control needs to be a bit better.
Old 11-04-2004, 12:29 PM
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DarZeelon
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Default RE: GMS- just cant get it right!!!!!!!

Gene,


I have said this several times in several threads in this forum.

A leak through the front bear is not a malady. It is only a symptom of excessive crankshaft 'play' in the front crankcase.

There are engines that have an open front bearing, yet don't leak significantly, like the Webra .50GT.
Most other engines have a shielded front bearing - no seal, yet they don't leak much either, like the OS.46FX.

Half sealed front bearings (front seal only), will only stop a part of the leak and have nothing to do with the running qualities of an engine. A leak can also occur between the bearing's outer race and the housing, or between the bearing's inner race and the crankshaft, so the seal is not a solution either.

I am talking about fuel/oil leaking out, not air leaking in.


Trent,


Why don't you do a proper break-in, as described in [link=http://www.rcuniverse.com/forum/Tapered%2DBore_Engine_Break%2Din_%2D_Upgraded/m_1850473/tm.htm]this thread[/link], get a new jug of fresh, low nitro fuel and a proper plug and try to get some help from a more experienced flyer afterword.
Before the break-in is completed, it is pretty hard to adjust any engine for good running qualities.
Old 11-04-2004, 03:41 PM
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Harry Lagman
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Default RE: GMS- just cant get it right!!!!!!!

Trent, in my role as one of the club's instructors, I have helped tune and set up a number of GMSs: two .40s. a .47, two .61s and a .76.

Every one of these has ended up running well, so my faith in the GMS brand is pretty good at the moment.

The other guys have raised good points. Carb seal and the throttle barrel are two areas with potential machining or assembly inconsistency. Correct running-in is also critical.

Another area worth looking at is the muffler backpressure. Check out this thread, where this subject is discussed in detail: http://www.rcuniverse.com/forum/GMS_...2290854/tm.htm

Good luck - based on my experiences, this engine should be worth persevering with.

Edit to correct typos
Old 11-05-2004, 03:09 AM
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XJet
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Default RE: GMS- just cant get it right!!!!!!!

The GMS engine one of our members runs still has good days and bad days -- seemingly at random.

Using exactly the same fuel, same model, same temperature and humidity the damned thing will run like a rocket one day and the next it hardly keeps his Extra 300 in the air.

Tweaking the needle doesn't help -- it won't even peak properly on a bad day.

Checked all the usual cuplrits -- fuel lines, air-leaks, plug, etc.

On a good day it will run strong all day from the first flight to the last -- on a bad day it will run bad all day, from the first flight to the last.

It usually seems to have good power until about a minute into the flight then it turns to custard. It's not overheating though, since running without the cowl doesn't make a scrap of difference (on good days or bad).

Meanwhile, my TT46Pro and 42GP never miss a beat :-)
Old 11-26-2004, 02:38 AM
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Default RE: GMS- just cant get it right!!!!!!!

I bought a 47 last year and it gave me a lot of problems with the carburation, it was unreliable, as it was mentioned above, the problem is within the carburator itself, I did not find any leaks in it but the problem was in the needle valve. The conical shape of the needle´s end is too irregular (machining problem I guess) so no matter how many turns you give it in or out it never keeps the same clerance with the seat. thus carburation changes with temperature and other factors. I solved the problem by installing an O.S. 4B carburator that was sitting around from a damaged engine and now it runs like a jewel, very reliable at the whole RPM range, however, not too powerful.


Remember, The one that keeps trying is the one that acomplishes.

Thanks.
Old 11-26-2004, 09:43 AM
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Wayne Miller
 
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Default RE: GMS- just cant get it right!!!!!!!

Hi Trentos,

The tread mentioned above:
http://www.rcuniverse.com/forum/GMS_...2290854/tm.htm
is one I started due to problems I was having with the the GMS engine.

If you try the "fix", I would really like to know how it worked for you. We have not had any feedback yet from anyone who has tried it.

Any feedback, help, or suggestions you can give, would certainly be appreciated.

Thanks for your help.

Fly4Fun,

Wayne Miller

Edited for a typo.
Old 11-26-2004, 10:57 AM
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1Jimbo
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Default RE: GMS- just cant get it right!!!!!!!

I had two .25's and they were nothing but trouble. In 22 years of flying I have never had such poorly crafted engines. Tower took them back no questions asked.

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