The ST 51 is certainly not up to the legendary ST60, but some folks seem to get them to work without too many mods. The best one that I've witnessed was that of Henk de Jong from the Netherlands. If I'm not mistaken he just added head shims to lower the compression. From my own experience, this was a must otherwise the thing just runs away after a few good loops. My last model with this engine in it used to run away after the triangles.

One guy that is a whizz with modifiying ST's is Tom Lay, so I would suggest contacting him if you want to go this route. One more thing, please don't use the stock muffler..........it weighs too much and is HUGE! I was lucky to get one of those German Kuentz (not sure about the spelling) mufflers, but there must be a few others around the USA that you can get hold of. Big Art Adamisin used to make them a while back. Good plugs that worked for me were the Thunderbolt 4-stroke or the Enya no.3. The prop that worked the best was a 12 x 5 wide blade wood prop. I used mainly Zinger 13 x 5 that I cut down to 12" with rounded and thinned tips.

Venturi size is important as well but if I remember correctly, the stock C/L venturi worked fine. I gave up on the ST 51 when I went over to the MVVS stunt .49 which was a much better deal all around. Unfortunately the factory stopped making them a few years ago when electric motors started taking over. When I could not get a good 2/4 break, my final version of the 49 was a diesel head, and this worked very well for me for many years. I could not diesel the ST 51 because it is a ringed engine. I suppose that you can but cold starting is a problem. Good luck with the new stunter!

Keith R

   Do a search on the site here and you should find quite a bit on the ST.51. I have used this engine almost exclusively since 1994 and have two stock engines that have an untold number of flights on them and still on the original ring. The basis of my set up is the following: One or two head shims as needed, tube type muffler (like a Scott Dinger, Big Art, or Randy Smith muffler) Glow Devil R/C Long plug ( or similar hot plug) APC 12.25 by 3.75 prop, at least a 6 ounce tank with uniflow on muffler pressure and SIG Champion 10% fuel that has at least a couple more ounces of castor oil added. I usually mix regular SIG Champion 10% and SIG 10% ALL Castor 50/50 and this leaves enough Klotz synthetic in the fuel to help keep things clean. The .51 is a ringed engine and the use of castor oil is important for lubrication and to help carry heat out of the engine. It makes the plane all gooey and messy, but paper towels are cheap and engines are expensive. The APC 12.25 by 3.75 is the best prop I've found yet. Take off RPM will be between 9500 and 10,500 RPM depending on your model weight and such. The APC is the first prop that I was able to really experience the flat pitch/high RPM effect  on holding a model back from winding up in the wind and gets the engine up into the heart of it's power curve. If you use too much pitch you can get it to run away. I have used the Master Airscrew 12 by 6 three blade cut down to 11 inches ( it actually pitches out at 4 inches of pitch on my Prather Pitch Guage ) and it works well but it can run away if RPM is too high. I plan on experimenting with pitching one down to 3.5 inches as time permits. I have a SIG Magnum that I let the weight of it get away from me (72 ounces) and the ST.51 flew it as well as could be expected. Won a contest or two with this set up in this airplane. I think the .51 has about as much power as the old ST.60 but it is a different kind of power, not as much torque from the .51 as it won't turn a 13 inch prop like the .60 will. The .51 gets it power from RPM in the 9 to 10,000 range while the .60 likes it best down in the 7500 to 8500 RPM range. I've been flying both engines in comparison for the last several years to be able to make that conclusion. This set up I mention above has been very repeatable in several models and is always where I start out with. I can also HIGHLY recommend a Tom Lay reworked engine. I have a couple of those in models also and they are very good deal. Tom checks out the cylinder to make sure it's round, changes venturi and needle location, adds a hardened Bowman ring and I'm sure a few other odds and ends. All of this adds up to an engine that will live a LONG time if cared for properly. There was some concern when Super Tigre moved operations to China, but I have not heard of any problems with the production engines since the move. If you order rings from Frank Bowman, he'll ask you which version you have only if you ask him to gap the ring for you, as the China version has a bore that is only a fraction of a gnats hair larger than the Italian version. if I remember correctly. The only issue I have ever had with the ST.51 is the prop drive washer, which is cast aluminum and can crack if you over tighten the prop, but I have only done that once and they may have fixed that problem. All in all, either stock or rework, the ST.51 is a pretty good buy for a stunt engine and I think you'll like it.
   Good luck and have fun,
   Dan McEntee

I gave up on ST 51 in the full fuse model because it was difficult to start. I had to use an electric starter which was not the most practical option.
I have installed the same engine in a profile – no problem starting.

Marek

They like to rev , and will switch with load .Not a ot of nitro needed , if any .
Id giv it a litre on the bench , another in the air , then give it grief shamelessly .

They sound as if the top will blow off on a 10 x 4 three blade , so fit extra gaskets.
nough grunt to haul anything through any wind .70 Oz givs them some work to do
and gets all the pressures / switch thing happening .

12 x 6 is a good run in prop for a profile , steady speed .
needs less prop for good yachting weather .

I've been flying the Chinese ST's in R/C and C/L planes for about 7 years now.  I fly two of the G-51 C/L motors box stock -- one inverted in a Legacy, and one on its side on a profile.  Both are 1 or 2 flip starters that purr along nicely with a light 4x2 break in stunts spinning an APC 12.25x3.75 burning Wildcat Premium Extra 10% nitro amended to 22% lube.  I'm using Randy Smith tongue mufflers on both with the holes drilled out the next size larger to reduce back pressure a bit.  I also fly a couple of the ST G-34 C/L motors, with a few minor mods to reduce head bulk and setup a remote needle valve, in combat planes.  It's a great S/L combat engine for the price and delivers a nice steady run on 10% nitro fuel with 20% oil, APC 9x4, and bladder.  Green, I've found the ST ringed engines to be no fun whatsoever with low compression and erratic performance so make sure yours is thoroughly broken in before making changes.  I was given two new G-51's (one R/C, one C/L) by frustrated modelers who couldn't get them to run right.  In both cases, break in solved the problems.  Unless you plan to have the ports re-timed to mimic the behavior of a Fox 35, use a low pitch prop to keep you and your motor happy.

Agree, the R/C version is different.  I fly mine on an R/C Hangar 9 Twist.  The ones on my C/L planes are C/L motors.

I have a Randy Smith ST .51 that runs very well, currently it is in a Nakke, I highly reccommend getting one from Randy, he balances and blueprints the engine, and sets it up properly, and he is easily accessible to answer questions. All for around $159.00, ready to go, cheaper than other modified ST's. Hard to go wrong, there, I believe!  

Well, looks as if I am in a minority. I too had an Italian ST51 and it just wouldn't run consistently. I tried all the ususal tricks, that are to be found in the archives and absolutely no joy. It really was a bit of a disaster, several of the top stunt pilots in the UK have not got a good word to say about standard ST 51s, they claim that a rework is mandatory and even then there are much better engines than the ST51. I agree with Keith about the MVVS 49 in both standard and diesel trim.
I replaced the ST51 with an ST 60 and what a difference, a real pussy cat. Mind you, it does vibrate more than a bit.

Regards,

Andrew.

Andrew,

     I have to agree with you:  my experience has been that all Tigre G-51's do not run when box-
stock, right out of the box.  Some do, but most do not.

     Perhaps, this is why we hear from those who, either found one of the few that do run well right
out of the box, or who fly engines which have been modified. 

     I love my two G-51's now that they have been reworked and run decently, and I'm just glad that
I had other engines to fly until I got the Tigres back from the rework guys.  Were I too do it over I
think that I would just buy the reworked engine from Randy and be done with it. 

     Best regards,

Uh...Timing, Balance, Cleaning (interior), heat sinks, fitting, PROPER assembly and torqueing, Venturi shape & size, NVA, and position and...

W.

All the things Ward speaks of above do really figure into how a engine runs, of course.  I have never asked Tom, nor Randy, what they actually do to a ST G.51. 

I am sure that balancing and "blueprinting" are in the mix.  I suspect that Tom does some mild retiming which keeps the engine in check while not dropping a ton of power.  So far his examples have shown to be able to pull a large stunter with plenty of authority.  Randy's are the same way!  Again, I feel that horsepower wise, the ST G.51 rates pretty even with a ST .60, but not in the torque range.  It will just not swing as big of a prop as the ST .60.  But the higher rpm run, coupled with less pitch gives the HP to fly a pretty good size stunter.  Let's be realistic, there are those who know how a stunt engine should run and what to do to make them do that.  There are also others who "rework" an engine but the "guts" are gone when finished.  Not a whole lot of people can make the engine run and still have acceptable power.

I will site Lou Crane and Larry Foster who "rework" Fox .35s.  They work to make the fits correct and reduce vibration.  With these mods the engine picks up power with out losing it's run characteristics.  I know there are others who do a wonderful job, but I site these two because of the engine (Fox. 35! the "Ancient of Ancients"!) and the simplicity of what they do to make the engine so much better.

So, are reworked engines worth it?  I would give a resounding "YES", as long as the person doing it has a well established record and his engines are known to work better than stock.  Before the advent of PAs and RoJetts, almost every top level flier had a reworked engine to some degree.  If nothing more than to make the engine more reliable. 

Do "ALL" engines need to be reworked to perform as we like?  NO.

Big Bear

If a G-51 is giveing you GRIEF reciprocate in kind .
Its a detuned 16.000 rpm R/C motor of 1.6 H.P..

Throw a 10 x 6 prop on it on the bench , stand back,
and wind'er up for a few tanks. This should blow the
cobwebs out of it, or put the rod through the side.

Bit like a V-12 Jag , biggest problem is theyre mostly under used.

What do you do if you meet a Tigre on a Dark Night ? ?

Tickle its tummy till it opens its mouth ,
Then reach down its throat and grab it by the tail .
Then give it a good tug and turn it inside out .

Pussy footing around will most likely let it get the better of you .
Fuel correct and everything tight and ship shape , she'll take a
real work-out , and come back for more .

Box stock it should loaf around the scedule on a 12 x 6 ( nylon and a 3 in spinner gives it a bit of flywheel ) in a 2 kilo plane .
Two 11 x 5s lap jointed will get it in the ball park for dragging monsters . It may have less accesable Tourque below 10.000
than a V-60 , but let it of its leash and itll tear up anything in site. So well have none of this pussyfooting , itll get you nowhere .

 

It depends on youre definition of civilised ; Defn ? see Maseratti Ghibli ! 

I have done the low pitch high rev scenario and still the runs are inconsistent. It just doesn't work like an FP 20. To be perfectly honest I don't care how it runs as long as its repeatable. It is almost as if there is some crap floating around in the NVA. I hasten to add that there isn't, but that is how it runs, just no consistency. Faced with a problem like that, I have just given up.
I really have spent a lot of time on this engine and literally have tried every suggestion in the archives (and that is a lot of options!). I am too old to waste any more time on it. I just want an engine that I can run straight out of the box. The big Mercos and ST 60s are just trouble free until the ring goes. An FP 20 and LA 46 seem to be bullet proof and user friendly and so is the OS 40 VF and Thunder Tiger GP42. With engines around like this, why bother with anything else?

Regards,

Andrew.

Thanks for the tip Don, it wasn't my problem as I have had 3 different types of NVAs in my ST 51 and they all behaved the same.

Regards,

Andrew.

 If it's a stock engine, plan on at least a 5 ounce tank. There are metal units available out there in that size if you can't build one. Six ounce if you have the room. Plastic tanks are fine, and use both with uniflow on muffler pressure. As temperature ranges change, you will find changes in fuel consumption. In the heat of the arly summer at the SIG contest I have had to short tank it down to 3 3/4 ounces to shut down in time. When the temps get below 60 degrees, it gets back closer to 5 ounces. At SIG this year, on the Tom Lay rework I have in my Charmer, I ran out of fuel in the clover with 4 1/4 ounces on board, in the cool air of the morning. I think I was one of the first three. In the warmer air of the afternoon, approximately 15 to 20 degrees warmer, I over ran by 10 seconds on the same amount! It pays to keep some sort of notes or records and I should do that, but I'm a little lazy. Your nitro content will affect fuel consumption also, but if you can put a 5 or 6 ounce tank in it, you should be fine.
    Good luck with the project and have fun,
    Dan McEntee

Hi fellas from a drizzly Charente.

I had all the mentioned problems with my ST51 , the c/l version.
It was properly run-in and had decent fuel but still ran away.I tried everything.

Solution : I sent it to Tom Dixon and it came back in double quick time . It's now my BEST performing stunt engine.

I'm sure Randy or any of the other engineers could wave their magic wand and solve any running issues.

Just my few cents worth ,

Robin.