JimRoss

Anyone have any experience with the GMS 47 engines? I just bought two of them and when I installed one on a Pizazz it did not want to turn over past TDC.
After much wailing and gnashing of teeth I discovered the piston was sticking at the top of the cylinder liner, like it was way too tight. It is so tight that it will push the liner right out of the cylinder with the head off. This can't be normal.

I did find that by continuing to rotate the crank with the head off and lots of fuel and oil in the cylinder it appears to be getting looser. It still sticks when I stop it at TDC but at least I can roll it through.
I never saw an engine that did this. Have you?
I am tempted to put the electric starter on it and run it until it either breaks or runs in and loosens up. Opinions?????

Trung

I had a GMS 47 a while back. It was very tight at first so I put some oil in and forced it over TDC litle by litle and finally after like an hour I could turn the prop and tried to start it. The sticking at TDC never seemed to go away but after a few tanks it didnt stick as much. This engine was a powerful engine for the price. I had some rust problems with it later on and it never wanted to start so I brought it back to the hobby shop and got it replaced with an OS 46.

blvdbuzzard

I too had my doubts about a GMS .61. It was so tight I thought it was going to break the crank pin or connecting rod. I poured some fuel down the glow plug hole, turned it over with a starter for maybe 10 seconds, put the plug back in, attached the glow plug clip and she came to life. I could hear the connecting rod, cyclinder, piston screaming for mercy. The loud screams lasted 10 maybe 15 seconds. Once there was some heat in the engine to expand the liner it was way on the tight side.

I have had Super Tigre, Thuinder Tiger, Magnum, Fox, K&B, Webra, Irvine, Rossi engines and they were no where near this tight. The engine I was breaking in for my sisters boy friend is now a good running engine. It is still need more run time but it fires right up and has plenty of power.

Give them some time and you may just find you will really like them.

Dru.

Pilotsmoe

use a heat gun to loosen it up before you fire it up for the first time. you are going to mess it up if you keep turning it over like that, just start it.

robb_h

My Feedback: (1)

I agree, the heat gun does wonders.


Robb H

JimRoss

I may be completely off base but in my 57 years of living I have found that if a cylinder is heated the O.D. expands as well as the I.D. making the fit even tighter.
Besides that, if I heat the cylinder, what happens when it cools down, it shrinks back to its diameter. I'm going to the parts house and get a cylinder hone to polish the inside bore of the sleeve and relieve it somewhat.

JimRoss

Railridr

Jim,
Believe it or not this is normal. I recently broke in an ASP .46 that was so tight that It would stick at TDC. Try the heat gun trick, and then run in the engine. The engine will be much looser after 2-3 tanks. It worked for me.

RR

bobhinze

My Feedback: (2)

Jim,
When you get done honing that cylinder to a "perfect" fit, pick up the phone and call GMS. That way you can order a new piston and cylinder set. Read the threads about "running in" on this forum. The GMS is a tapered bore ABC engine. If it is not Sqeaky tight when new, then it is defective. I'm only 55 but I figured out how to break in ABC tapered engines when they first came on the market 20 years or so ago. I did that by ruining a K&B ducted fan motor by insisting on running it in very rich. Managed to wear it out in 2 or three tanks of fuel.
This post is not meant to be slam on your knowledge, but I hate to see a Very Good engine ruined, when all it needs is 2 or 3 tanks of fuel run through it at WIDE OPEN THROTTLE. The mixtuere should be set at a slightly rich 2 cycle. On this engine with a 10x6 or 11x4 prop we are talking about 14 to 15K Rpm. (with stock muffler)
Use the heat gun if necessary to get it to turn over for the first run. This works because the brass cylinder expands more than the ALU piston. Yes the bore of the cylinder does grow. You can check this out with an inside micrometer. I just checked a Megatech 46 and found an increase of .012 in at 225 degrees F.
Break the GMS in right and it will be a screamer for a long time.

Bob Hinze

AMA 2276

blvdbuzzard

As said above. When you get done honning the cyclinder, just order a new one because you will have ruined it for ever. The tight fiot is because ther is no piston ring to seal the gap between the piston and cyclinder. This engine uses a tapered cyclinder so that the piston and cyclinder are sealed at the top. If you hone it so there is no taper you have removed any chance of the piston sealing with the cyclinder.

This is not ment as a slam. flame, or insult, but have you read the directions that came with your engine?? It talks about the pinch at top dead center. I try to remember that when all else fails, I should have read the directions.

Dru.

RVator

My Feedback: (1)

I broke in 2 Tower Hobbies 46's last summer that were the same way. You could barely turn them over. I used the heat gun trick and then started them up.

flyguy60

The Tower engines are the same as GMS from what I hear.. All of mine were the same way. It's the ABC construction and it's fine. You can expect it since it's new. After you break it in real good it'll be smooth.

I didn't even use a heat gun. Just prime the hell out of it and fire it up. Shouldn't even need a starter...

My 2 cents....

JimRoss

Damn, you guys make it difficult to be hard headed. ALRIGHT! I'll do it your way just to prove how I can actually be incorrect in my assumptions. Never had to break in a NIB ABC engine before so I did not know that.
I do, however, retain the right to read the instructions only as an absolute last resort. You can't make me. Actually, I'm going out to the garage right now to get them. So there!

Thanks Guys, I really do appreciate your input.

JimRoss

P.S. what is GMS' phone number anyhow?

blvdbuzzard

I like your last resort. It is better to read them then order a new piston and liner.

Dru.

Mainspar

My Feedback: (27)

I don't care what they say, Mr. Jim Ross. That there is a mighty fine avatar. Is that what they call a "Big Ol' Texas Grin" whar yer from?

My compliments, Sir.

JimRoss

YUP!

That there is the picture of a guy who is so happy he could spit straight up.

JimRoss

hoveralot

I have two of those same engines and they are really tight when new but I just prime it and fire it by hands, set it to a two stroke rich mixture and after 30 minutes running I open the engine to found that everything was just rigth. This engine takes about 60 or 70 minutes of brake in to get its full power.

Since then this is a strong running engine with no problems at all, not a single dead stick.