aa1a

My Feedback: (4)

Hi Everyone,
I am working on a small twin and I am considering what engines to use. I can buy 2 GMS 25s for the price of 1 OS 25AX. But I had a GMS 120 and had lots of problems. Anyone have any experience, good or bad with the GMS 25s?
Thanks for any help you can offer.
Jim

earlwb

the low cost Chinese engines are somthing of a crap shoot as to whether they work Ok or not. Most of the time the engine itself is Ok, but not the carbs. So far all the engines I dealt with had leaky main needle valve assemblies. They would suck air in past the needle valve. So you will likely need to seal up the main needle valve to get the engines to run OK.

I would look at the Thunder Tiger engines as they have better quality control than the Chinese are providing.
A couple of the TT Pro 36's would be pretty good.

Broken Wings

My Feedback: (20)

How much do you like the model? If you built it yourself I'd buy the best. If you have little emotional value invested you could buy a less exspensive brand and you might get a couple good ones. One good one and one bad one would probably be a problem on a twin. Just my opinion...

jimmyjames213

My Feedback: (2)

i would buy gms .32's they weigh less than the .25 yet make more power.
the one (.32) i have runs great (on a combat plane) and i wouldnt spend the cash on anything else.
i also have a gms .47 which runs great as well


i say go for it
they are well made and run great

still4given

I wonder if any of the folks who just gave you advise have owned a GMS .25. I have one and it runs like a top. I wouldn't hesitate to recommend it. As a matter of fact, I just did.

mike109

G'day Twins are all about consistency and reliability. I have owned a GMS 32. I sold it cheaply. It was not a great engine.

I have direct experience of about half a dozen other GMS engines. None of them have impressed me. All were difficult to tune. On all the GMS engines I have experience of, the carby was the weak point.

If I were building a twin, I'd use a Japanese engine. Or German/Austrian/British/Taiwanese but not Chinese. Yes, they are cheap and as individuals they may be OK but the consistency is just not there for me.

If what you are building is a cheap ARF then perhaps it is worth the risk. If it is something more worthwhile, I would not risk it.

JNorton

My Feedback: (2)

I second that.

earlwb

I have a few GMS engines here at home. They all had bad carbs. I have some Magnum, and ASP engines too, they all had bad carbs.
I would be extremely reluctant to use these low cost engines in a twin. Now I did get a couple to work good by swapping out the carbs for better carbs. But I had the carbs on hand to use. If you have to buy a good carb, the low cost engine just wound up costing almost as much as a better engine then.
The problem is the Chinese like to put on big bore carbs that are too large for the engine itself. Thus the engine has problems drawing fuel from the tank due to the large bore carb. Then the needle valves have threads that are cut so that the needle valve is loose and then the O-ring they may or may not have in the needle is a poor quality rubber and flattens out and lets the needle suck air. You can usually correct the problem by using a short piece of fuel tubing over the needle to serve as a gasket seal. But sometimes even that doesn't work.

MJD

My Feedback: (1)

I had recent experience helping someone else with their GMS .32. It seems they have a problem with either fuel draw at high throttle settings and/or air leakage. The engine makes gobs of power, but the top end needle setting is indeed a sore point. In this case, the owner wanted to fit a pipe, so that of course is not stock treatment, but the problems are related to the issues folks reported with their stock .32's. The issue came to be the fact that it would not flow enough fuel/stop sucking air on the pipe to allow it to be richened into a 4c from wailing flat out. Not that I wanted to run it there, but I sure as heck expected to be able to needle it there and back, but opening the main needle to the point where it was about to drop out would not result in enough fuel flow. Increasing fuel pressure slightly fixed it, so we will play with pressure nipple location, but the fact is I dropped in an older OS 4(A,B,C forget) carb from a 25 year old or so Max .40 with what looked to be nearly identical inlet area - and it instantly gained the ability to draw enough fuel. The owner also reported issues on the top end when flying before with the muffler - but as a somewhat new modeller naturally I would assume that ground settings and plumbing issues were the biggest suspects until I saw otherwisxe myself. We'll mess with it more this weekend. Once set up with the OS carb though, it ran like a top on the pipe and spun an 8-6 APC over 18k and an 8-7 in the low-mid 17's. The engine is all there, but the carb as usual seems to be the thing that makes or break the reputation.

I second the advice that with a twin, don't screw around - go for dead-nuts reliability and don't cheap out on the powerplants. Poor carburation is the LAST thing you ever want on a twin, and probably the FIRST thing you buy into when shopping for cheaper engines. Otherwise your twin adventures may be frustrating enough to make you say screw it why bother, and that should not be the outcome.

MJD

MJD

NM2K

My Feedback: (14)

If one has any brains at all, they would completely break-in both engines on the bench and they would know whether to bolt the engine to the model long before a bad experience occurred in the air.

Should one or both engines prove to be problematic, you give the importer/distributor/warrantor a chance to make the problem right.

Personally, were I looking for two engines in that size range for twin engine duty, I would consider buying Sanye (ASP/Magnum) or Thunder Tiger, if I could get the latter at a good price. I'd forget about the GMS engines, if I had to buy new at normal prices. GMS quality wanders all over the place.



Ed Cregger

aa1a

My Feedback: (4)

Thanks Everyone for your responses. Your input is appreciated. Sounds like there are a few people that have had good experiences and many that have not. My twinstar has been flying for 2 years with OS LA40s and I've only had 2 engine failures. They are nearly perfect. I am leaning toward a pair of LA25s for this project. In case you are wondering, It is a Flyboy Models C119 flying boxcar.
Thanks again for the help,
Jim