[8D] I just got a ST90 and im not comfortable with the break in instructions. It says to run then pinch fuel line and if RPM increases lean high end and do this till it will run without RPM increase. I have never heard of this especially with a ringed engine. I have always broken in ringed engines messy rich so what gives with ST. By the way its going into a Cermark F20

Run the engine on the rich side, not slobbering rich though, maybe 400 to 600 rpm drop off of peak. Do this for 5 or so tanks and then fly. Just keep it on the rich side for a dozen or so flights then adjust it normally, 200 to 300 off of peak. Ringed engines take a while to break in.

The process begins at the point of fuel mixture that causes the engine to just break out of four cycling to two cycling. It then says to slowly lean the mixture as long as the engine can hold the new setting while giving the line a little pinch to assure that the engine gains rpm. The pinch test assures that you are never running the engine peaked or leaned out. They say this should take approx. 1/2 hour of running time until the engine can hold a mixture setting at the point where when the needle is leaned to peak and the rpm remains constant even during the pinch test. If at any time you pinch the line and the engine looses rpm immediately richen the mixture 1/4 turn and begin leaning again. You may find that the process takes even longer. I would say thirty minuutes should be the minimum running time before you find the actual peak rpm point. Remember you are dealing with cast iron and hardened steel surfaces with the ring and cylinder not aluminum and nickel. The object is obvious. Don't ever run the engine more lean than it will hold it indefinitly. Never run the engine more lean than peak rpm. These engines are capable of running lean until they burn up rather that just leaning out and quitting.

Personally I do not run any of my engines any more to the lean side than the point where I can pinch the fuel line and get a 2 or 3 hundred rpm gain no matter how used they are and more like 5 or 6 hundred rpm to the rich side for the first few flights. The pinch test is a very good technique for tuning all glow engines once you get the "feel" for it. You will also find that your Tigre will produce nearly the same power at a fairly rich setting and smoking fairly heavily rather than pushing it to the lean limits. If you make sure that you stay to the rich side your engine will last hundreds of hours.

Take care, Cliff

My ST .90 ran so well the first 3 minutes I had it running, that I decided to fly the plane I had it mounted on.

I used an APC 13x6 prop (as recommended). Fired her up, ran it up just shy of peak, and pinched it every 10-15 seconds or so. I brought it down to a very nice idle, jammed the throttle forward a couple times, and this thing just ran great. I've never had an engine run so well right out of the box. I still only have about 20 runs on it, and its my favorite engine.

With any ringed engine, you'd normally run it extrememly-rich at full throttle for the first 15 minutes or so...about 12-16 ounces for the SuperTigre .90. You would gradually lean it a bit at a time over the next 32-48 ounces of running. After about 48 ounces of fuel have run through the engine, it should be able to be leaned near peak RPM. The "pinch test" is one way to help you determine if the engine's needle can be leaned. If the RPM increases when you pinch the ine, then the engine has "room" to be leaned.

The method mentioned in the SuperTigre instructions has been proven over decades of use. It works very, very well.

Thanks guys I have been in this hobby 25 years now and I never heard of this method for break in ringed or not. I will do as the instructions say and hope I have better luck with this than my OS91 that I have been fooling with for the last 10 months. The problems that have been posted here with that engine I think I have had them ALL at one time or another. As soon as I would fix one problem another would pop up. Having said that I still think OS is a good engine its just the 91 turned out to be a lemon at least for me.

Be careful on the pinch thing. Thats for those who like to squeeze every last rpm out of it. I've had the same one running strong 3 years now with a 13/8 apc on a Shoestring. Dial it in to its peak rpm , then richen it up a tad, point it up and if it doesnt quit-- fly it.

The first thing to know about running in a ringed engine is that it's absolutely impossible to run them too rich. The richer they run the cooler all the parts are. This is a good thing for the first maybe 10 or 15 minutes. A ringed engine is similar to the old cast iron lapped pistons (or the new smaller Enyas) in that you have a cast iron seal against the liner. New cast iron is softer than the steel liner so it's used as a lap to polish the harder steel liner. If the cast iron (ring) stays cool it stays soft so when the liner has finished being lapped round and smooth you need to harden the ring. This is done by slowly leaning out the mixture from slobbering rich. The engine revs go up giving extra heat plus there's then extra friction on the surface of the ring. Short runs with a cool down heat cycles the ring and it gradually hardens until it's harder than the liner. This takes some time to do completely (several hours) but they're usually ready to fly after about an hour. You have to remember that you're working with totally different metallurgy to the usual ABC stuff.