I have a GMS .47 on an airplane. It runs great, but I can't get the engine to shut down. I pulled the throttle and trim back and even put my finger over the carb and it keeps idling. It is obviously getting air from somewhere. Any ideas on how to stop this? It is obviously not a big problem, I just want to have complete control of it.

I read somewhere that after-run oil should be put directly into the cylinder through the glow plug port. It seems to me that I don't really want to take the glow plug out after every flying day. The thing I read said that the after-run oil would eat away at the carburetor's rubber gaskets.

Thanks!

Herb

Take the carb off, remove the carb tightener, put some silicone in the holes where the tightener came out of and some on the shaft itself. Also put some on the carb sealing 'O' ring.

We have found that they can leak air at this point. It doesn't take allot of silicone, just a thin film. Make sure you let it dry over night before starting it again.

This is the only place and problems we have had with over 100 of these engines sold.

YOu can silicon the carb all day long and this won't fix the problem. The air leakage is occuring through the front bearing. Its a known problem with the GMS and their twin brothers, tower hobby engine, line. I've been told that Boca replacement sealed bearings fix this problem. I'd live with it.

Never had a front bearing cause an air leak, The only GMS engines we have had a problem with are leaking past the carb tightener.

There isn't a common bearing that we use in our engines that is totally sealed; what we call a seal in usually a dust shield. Put oil in an engine and stand it on the propshaft for awhile. The oil will come out.

One way to determine where an air leak is is to spray something like WD40 around all the parts of the engine using the fine tip they give you. You'll hear the change when you hit the leak.


We've sold over 100 and had this happen on 3. No other problems.

Herb,

We have had several Tower engines at our field that wouldn't shut down and silicone at the carb base as described above did fix the problem.

If you use marvel air tool oil or most other oils you do not need to worry about the carb o-ring or other rubber parts. I fill the carb with oil when closed, open the carb and flip it over many times. O.S. says after run oil does little good unless you use a lot of oil. Most fuel manufactures say their fuel has additives and after run oil is not needed. The most important part is at the end of the day. Disconnect the fuel supply with the glow starter on and make sure all raw fuel is burned out by trying to start.

PLEASE!!!!!!!!!!!!!! Do not use that damned WD crap in a perfectly good model engine unless you do it just before you run it. DO NOT use it for after-run oil. In fact, just give it to a neighbor you don't like or use it to loosen up rusty bolts. (It doesn't do much for them either.)

WD-40, if left on ferris metal parts, will cause corrosion since it is chloride based. This comes directly from my local FAA Inspector. It was demonstrated to him when he attended a corrosion seminar a few years ago.

If you want to use some type of spray lube, use something like LPS 1 or Tri-Flow.

Tony

Well they must have changed the formula as it isn't corrosive; I have heard that it was used around food processing machines and your FAA has prohibited its' use but I found out that it was because some of the components in it are poisonous.

I've used it for years, coated engines, put into a plastic bag for storage, in fact I just took one out that was in storage for 5 years; the case looks just like when I put it away, no corrosion.

What I have found out and read is it isn't a very good rust inhibitor as it dries eventually and nothing is left, no residue at all. I tried it, sprayed some on a sheet of glass, after 2 months you couldn't tell where it was sprayed.

Maybe allot of people don't know what it was designed for originally. The military wanted something that would dry and actually remove water from some of their components. This was designed to do just that; in fact the WD part stands for Water Dispersing and the 40 stands for the 40th formulation,

Also if it was corrosive it would have to state that right on the can, the can I have in front of shows - Poison, Flammable & Explosive but no where on the can does it say anything about corrosive but does state it will help protect metal so where is the corrosiveness?

Good luck. Even that relatively unknown company in France, Dassault, found that when chloride based lubricants found there way into hydraulic systems, there were big problems. So costly that they started installing chlorine filters in the Falcon Jet hydraulic tanks. The chlorine was traced to maintenance people using spray cleaners and lubes and WD was spacifically one. It was even a topic at one of our maintenance seminars as I recall.

I agree it displaces water. It has long been out performed by numerous other products however.

Tony

Tony,

What other products are they?

Thanks,

Elwood

wd 40 is a chlorinated solvent...reason it is not allowed for aircraft use.
per FAA..MOT..boeing..
if used in an older eng..with some rust,
it breaks rust loose and???right,it goes through engine.(rust or corrosion is???
metal oxide..good for lapping rings and cylinders) get the MSDS sheets on the products you use and learn.

Forget WD 40, Forget expensive after run engine oil sold in little bottles. Have you noticed it is usually red in colour? I buy my after run engine oil by the Qt from the local automotive store for about $4.00. There they call it transmission fluid. Have you noticed it is usually red in colour?

I would have to question air leaking in through a front bearing. The air would have to leak in through the fit between the crankshaft and the crankcase. Crankcase pressure would push the air the other way. Which is why you get fuel coming out of a front bearing when the engine is running.

Ed S

You are correct in that there is crankcase pressure but remember this is a 2 stroke. There is also negative pressure during part of the exhaust stroke which draws fuel/air in from the carb. I could also draw some air in from the front of the case.

WD-40 subs. If you want to loosen a rusty bolt, by all means try WD-40.

Afterrun-air tool oil by Marvel works well. (I can't say anything about trans. fluid. Color doesn't mean it's the same as air tool lube but considering what goes on in an auto. trans., it probably works well.)

Long term engine storage. I use LPS-2. (Short term-LPS-1 works very well.)
Note: LPS1,2 and 3 have the same MIL SPEC. Just different viscosities. Since they are aerosol, you can spray them in and get good coverage.

If leakage through the front bearing is the cause (Which I do not accept) then every RC two stroke engine, ball bearing or plain bearing, would have the same problem.

Ed S

I have to agree. Dub Jett builds his engines with out any seals/dustcovers on the bearings. He wants it to leak some to provide better lubrication. It may sling a little fuel while running but shutting the carb does stop the engine.

I'l' stay out of the GMS/bearing portion of the discusion but I must add to Whyes comment.
I was rebuilding a HB .61 PDP. New piston and ring. (Dykes). After the rebuild I decided to shoot a little WD40 down the carb.
I was holding the engine in my hand at that time and then decided to flip the engine over to work in the WD. Bad Idea.
The engine fired and as it jumped out of my hand, wacked me on the wrist resulting in a nice Goose Egg. Now all you engine guru's know that Dykes ring engines have very little compression, so never ever do this dumb thing like I did!
On the other hand, WD40 is the best thing I have ever found to get an engine started in cold weather. A small squirt will bring an engine to life like its a warm summer day.

Miniair,
Do you coat carb bolt and reassemble before drying, or let it dry overnight before reassembling? I have several TH .46 that have fantastic power, but will not shut down. (Are they manufactured by the same Company as GMS? Thanks!

Coat the bolt and the hole, assemble and let dry over night.

Also put a light film around the 'O' ring on both sides of it.

Has worked for all the engines we had a problem with.

I have one Tower 46 that doesn't want to shut down. It leaks around the carb barrel. I have read the threads on the Tower 46 and GMS 47's for some time and I think that the problem is an air leak. It could be from the carb base, the carb barrel, the fit of the crank in the block (the so called bearing leak), or the back plate. Some of these can be fixed others not.

That you must try another solution if the first one doesn't work.

However new bearings will not have a tremendous effect on air coming by the front seal. Clarence Lee says that the leaky front seal has more to do with the fit of the crank in the front part of the crankcase.

Though the GMS 47 and the Tower 46 have different displacements and different bore and strokes, They are obviously made by the same company and run almost identically (good). Set one of each side by side and you will know what I mean. It's kind of like the Magnum and ASP engines that are made by the same company.


Try them all

Jim

I have a gms 61 that I have been trying to break in but it leaks air through the shaft. this problem has been driving me crazy because I have no clue how to fix it. it has bean running so lean that the needle valve has little efect on the engine. infact I bet the engine is already shot from breaking it in while pulling in so much air. I hope if I send it back they will give me one that works, fast.

ps start a new thread about wd because these engines are a real problem

A GMS does leak air through the bearing and around it.If you have taken a GMS apart you might have noticed the channel dug in the case from the front bearing to the carb.If you fill it with RTV it will fix the air leaking problem.I read about the fix in an article by Dave Gierke,and tried it.It worked good.
One GMS I have the bearing is so loose you could literally shake it off the crank and out of the case.The machining of GMS engines is pretty poor.

A word on the After-Run oil... true, don't use WD-40. It's a solvent.

I've read Clarence Lee's column where he describes a concoction that he makes from 50% ATF (as noted above) and 50% Marvel Mystery Oil AIR TOOL OIL.... it has special chemicals in it to prevent rust....

And, I hope that something works on my Irvine 46, Mk III. It is a beautiful engine, but it also won't shut down. I don't agree with the comment 'Just Live With It" because there are times when you HAVE to shut the engine down , like now.

I'm sure that either of the suggestions (replacing the bearing, or the RTV around the carb screw) will work.. I'll try it in mine...

Just my $.02

Bob