That is not quite true...

The design of the ST differ greatly from the GMS/T.H.

I've got a bunch of all three.

The GMS & Tower Hobbies engines differ primarily in slight changes to the displacement, but otherwise they are identical.

The S.T. engines are a different beast altogether. The S.T. uses an entirely DIFFERENT type of design for everything, down to the materials used.

I've never have had to do anything to the GMS/T.H. engines to get a good transition other than break the engine in properly and tune them up well.

On the S.T. these forums are repleat with the problems these engines have at times with transitions. People find that due to the way the LS needle is designed, you have to richen the LS needle to the point that idling is a problem.

The S.T. solution of angling the spray bar ( something you CANNOT do with the GMS/TH engines ) does not work.

However I have fixed the S.T. idle problem by slightly filing out the throttle barral opening as suggested by a recent magazine article.

This fixed all of the idle and transition issues I've had with the .60 and .75 ST engines.

The S.T. have an air leak problem, the GMS/T.H. really do not... the latter is mostly due to either lack of pressure when installing the carb ( it does not come PRE-installed ) or that the sealing rings have been pushed off center... once you are aware of this, it is easily taken care of.


The SuperTigre design is of Italian origin I believe while the GMS/TH are Chinese design. The former designs were adopted by the same plant that also manufactures the GMS/TH engines, but the tooling and castings are very different.

One thing to keep in mind with this plane, is that it is a very light plane, and many people report that it flies better with engines at the lower end of the recommended size.

I won one in a club raffle, and decided to try out with this electric motor in it:

http://www.hobbycity.com/hobbycity/s...idProduct=3887

I fly it with a 45A ESC, an 11x5 e prop and a 2200mAh 3S Lipo. The all up weight is only around 3 1/4 pounds.

You will definitely want to beef up the firewall before hanging that 46 on it. You may also want to add some beefier landing gear.

Good luck. It is a really fun plane.

Whatever . . . The three brands are still made by the same company.

Even the current ST carb spray bar is cut just like the GMS and tower except you can twist the ST spray bar easier than on a GMS or Tower.

Do you have any S.T. and GMS/Tower engines?
Ever take them apart?

I have...

Unless the S.T. carb has been modified within the last 3-6 months ( most of mine are older than that ) this is NOT true... I see no changes to new engines on the S.T. web site as well.

The S.T. uses a monolithic brass spray bar with a venturi vent cut into the bottom of a rectangular piece of brass stock.

If you look at the bottom of a S.T. carb you see what appears to be a slit cut into a square brass piece.

The HS needle screws into a hole from the opposite side, that closes the aperture WIDTH. The spray is pointed downward into the engine.

The GMS/Tower on the other hand use a steel round shaft nozzle, with an opposing "stopper" type L.S. needle. This is completely different and far more similiar in design to the way the O.S. carbs are built.

You cannot "twist" the spray bar on the GMS or Tower AT ALL, as they are ROUND to begin with with no preferential direcition on the opening...

SuperTigre says you can adjust the midrange by angling the square exhaust aperture, though I have found this of little to no help.

I've owned three Tower 46's from when the first came out as well as worked on and adjust many other's Tower engines.

I also owned a GMS 61 for a few years. Though I never had any trouble with the 61, some of the Tower/GMS engines that belonged to others were a hand ful to finally get to run correctly

I've worked on a Tower 75 for the last three years whenever it had a problem including the carb. Every time I go flying, it is the only engine the other guy has.

I've put bearings in two Chinese ST 40's and one Chinese 61

I've owned 12 different Italian ST engines and some of them I worked on extensively in the past 40 years and worked on many other people's ST engines in the last 45 years.

The design of the genuine Chinese ST carb spray bar inside the venture is no different from the GMS/Tower design when you closely look at it.

The GMS spray bar is pressed into the carb body whereas the super tiger spray bar has a flange whereby it is held into the carb body with two clamp screws from outside the high speed side of the carb body. The ST HS needle is threaded directly into the spray bar assembly instead of the carb body or being a separate assembly mounted on the rear of the engine..

When the Chinese started making the carb parts they changed the design of the fuel metering part of the spray bar from the way the Italian ones were made. This was some 5 years ago. I cannot say the redesign was bad for the All Chinese ST engines I've experienced run very well even in midrange.

I have had no trouble getting either the GMS, Tower, or any of the ST engines running well. The design of the ST carb (Italian or Chinese) works as well as most any two stroke glow carb.

You can go ahead and condemn whatever brand you like. I'm well experienced and have no trouble with them.

My point is that if you remove a current production Tower 75 carb and a current Super Tiger 75 carb and look in them from the engine side, the spray bars look identical up in the venturi. What you will see is that the LS screw goes inside the spray bar and there is a notch milled across the spray bar where you will see the end of the LS screw half way across the notch when the throttle is wide open. Yet the carbs are made rather different elsewhere.

My Tower 46's had a spray bar more like an OS engine that was completely different from a Super Tiger

Not to nit-pick but why then call the carbs similiar/identical when they are so vastly different?

If I didn't know that the engines were manufactured in the same plant, it would be almost impossible to tell.

I remember when I was a a kid not to long ago,
I think everyone I knew owned a small 02 and a Jet-X engine.
I still find it amazing that as fast as they turn they hold up very well
Vegas/

What makes an engine better?
A ringed piston with BB crank or a non ringed piston with a BB or non BB crank?
I guess this topic can go on for ever but for the prices you can't go wrong.
I assume some cheap engines just wear out sooner but still stick together at those high RPM's
Vegas/

The choice is yours. People argue the merits of ringed or ABC/ABN engines all day

The Tower engines are ABC as is the smaller GMS engines. The GMS 61 and bigger are ringed.

ST 40 is ringed, 45 is ABC, The 51 is ringed. The 61 can be either ringed or ABC. The ST 75 and larger are ringed

Yeah,
Your right.
I'm not an engineer and all I know is what I read about them.
However I seem to get another engine before the previous one wears out.
As log as it keep by plane up i'm happy[8D][8D]
Vegas/

There you go that's what is most important.

IMHO and everybody has one, is that ABC engines were originally developed for high performance racing engines. But they also evolved into sport engine use because of the simplicity of break in. OS and Thunder Tiger came out with the ABN engines and they are even more simplistic and trouble free. They are new engine to the field and fly for most people.

The ringed engines have been around a long time and for some reason I prefer them. But they require more of a break in episode when new.

Be opportunistic and seek the best deal.

I got both ringed and ABN engines this year from OS - their larger engines come ringed and smaller come ABN. There really is not a heck of a lot of difference to the newer pilot, just follow the proper break-in procedure (which for OS is actually the same, but after reading these forums I am not as quick to lean it out). I feel like I notice more a power curve with more power at the low end on the ringed engine, but it's probably my imagination. Definitely not enough to say "I want this one" or "I want that one". Tower Hobbies sells Super Tigre engines in both ringed and ABC in the same size; I would buy whatever is available or least expensive. I guess one advantage to ringed is that you can replace the ring, or the ring and cylinder, and not have to replace the piston, but if you treat your engines right hopefully you'll never get to that point.

I think the general consensus is the engines with ball bearings are definitely preferred to engines with bushings. The least expensive engines come with bushings (OS LA series, and others), and the high end engines are not offered with bushings.

RCfield you have good thoughts

Generally a ABC/ABN engine cylinder/piston set will last longer than the ring in a ringed engine. I think Frank Bowman gets around $14 for a ring to your door.

The only ruined ringed type cylinders I've seen were destroyed by some one improperly disassembling/assembling the engine

I am running a .47 GMS, .61 GMS, .76 GMS and a Tower Hobbies .75. The TH .75 and the GMS .47 are ABC and the .61 GMS and .76 GMS have a Dykes ring. What I have found differance between the .76 GMS and TH .75 is that the TH has a slight bit more power than the GMS on the same fuel (5%) and prop sizing 13x6 (about 300 rpm diff). All are great running engines. I also run a ST G90 on 5% and it is also a fantastic motor. It took a while to get her dialed in but she is purring sweet now also.

Curt

Sorry to drag up an old thread, but was wondering if the GMS .61 and GMS .76 are the same size externally?

I have a Flycat46 Pusher Jet on the way and it calls for a 46-61 2 stroke.
If the .76 is the same physical dimensions and a similar weight I might grab one of them instead of the .61.

Thanks

Yes the GMS .61 and .76 are the exact size dimension wise except the.76 has a little shorter cylinder head height and weighs a little less also. The .61 is a great engine, but being the .76 has more power, weighs less and has the same dimensions as the .61 then I would go for it and enjoy. I have both and they are fantastic.

Cheers
Curt

I've used the GMS .76 on a Bobcat 50 pusher, and it turned that plane into a fairly fast beast when used with an 11x8 Graupner prop.

Thanks opjose.

Exactly the info I was after.

Only concern I have now is weight.
Apparently the Flycat needs nose weight with aa 46AX so just looking up some info on the weights of the engines I am looking at.

What I did, is I removed the former in the nose ( I worked it loose with a bit of heat and acetone ) then stuck a decent sized 3000mAh 4.8v battery pack in the nose ( $17.00 from BPHobbies ).

I had no problems with the balance after doing this.

BTW: on my first flight my nose gear collapsed because it did not lock down properly.

I placed a steel rectangular guard where the plane scraped the tarmac, so should this ever happen again, the fuselage will not be abused.

Cool thanks opjose.
I have a large 3600MaH 6v pack here I might use.

Not sure if the Flycat 46 comes with retracts or if its fixed. I have some litho plate here I can make a skidplate out of if it has the retracts tho.

Cheers