I like the notion of a ringed engine. No particular reason; I just do. The ST 51 Ring I put on my first trainer 15-20 years ago broke in after a couple of tanks, never gave me any trouble, and ran like a top. Same for the ST 61 ringed engine I purchased next. Left the hobby only to return last year. Bought a Magnum 91 Four-stroke for my new Hobbistar trainer and so far its been great. However, I picked up a new ST 75 ringed engine shortly afterwards so I pulled the Mag 91 off my trainer and put the ST75 on it. It broke in well after a couple of tanks and seems to still be getting better. I've installed the Mag 91 in another plane and hope to be flying both of them once the weather turns better & warmer.
All I've run in either engine is Wildcat Premium fuel (16% oil content) with 6oz of castor added to the new gallon. The ST has been run on 10% nitro and the Magnum on 15% nitro. (These are the % on the fuel before I added the castor)
SuperTigres then and now seem to like to shake their exhausts loose. What I remembered from way back was to clean the screws and threads with alcohol, add a dab of locktite (blue nowadays) and tighten everything down real good on the engine. I have used the fibre gasket when doing this with a light coat of RTV on both sides of the gasket and really snug it all up. On the very first run of the engine while its still very hot I retighten every screw and that has always been it.
The only aggravating thing I've experienced on two of the three is I had to install the brass nipple on the muffler that pressures the fuel tank. It will twist in half if you just breath on it hard. Here's the trick - be sure you are comfortable and sitting at a well lit table. Use a wrench that fits the flats on the nipple fitting. Because my eyes aren't good anymore I wear a magnifying lens so I can see really well.
Put a dab of blue locktite on the nipple fitting and lightly turn in to the muffler with finger tips until its tight as you can turn by hand. Then while viewing closely and using the wrench gently turn it another 1/3rd turn. NO MORE. Do not turn it until you feel it tighten down because you never will...it will snap in half in a blink. Trust your fingertips first and then with the wrench; your eyes.
Then with plenty castor in your low nitro fuel break it in with atleast three 12oz tanks of fuel and don't fiddle with the low-end needle, just the high end. Oh, and when you mount the carb just pay attention to the seal and press down firmly and hold while tightening the carb retainer. Be sure the carb is all the way seated before tightening the retainer.
None of this is hard and its ashame SuperTigre doesn't already have this done when the engine comes out of the box but; they don't. So what!
I know 3 engines hardly proves anything but the doggone SuperTiger - "other Brand" argument was going on 20 yrs ago just like it is now. The folks that say use low nitro, add CASTOR to bring your fuel up to a 20% oil content by volume with your SuperTigre seem to know what they are talking about. And I've noted that a good bunch of the folks unhappy with their SuperTigres (and Magnum 4-strokes) are folks that detest CASTOR. Maybe its because they are ringed engines?...who knows? But I've read a gagillion posts from folks that I believe are telling the truth and my limited experience has been positve so far.
You might laugh but I still like the look of a SuperTigre engine head and still wished they used allenhead screws instead of slotted.
Regards,
Clay