I've got my first engine here and when I flip the prop to start it I can hear a FFFFFP sound during the compression. I have gotten it started several times for testing, but only about 1/2 the times I've tried with a chicken stick.
Is it normal for a ringed engine to let the compression leak if you are flipping the prop slow to get it right up to the compression point? I have checked the head and crankcase bolts to make sure they are tight.

If the compression didn't release you wouldn't be able to turn it over.

Jester, you need to get with someone in your area to help you get this thing going. There are probally 100s of people aroung Fourt Worth that would love to help you.

Well not so many that jump up and offer like they would in small towns, but I am going to join a club once I get my plane ready for the final inspection. I just don't want to show up to the field and have to leave without flying because of some small problem that I have to go home in order to fix so I ask the basic questions here.
buzzingb- Are there many flyers in Calhoun county? I'm from Derma originally.

Jester, the next time you start it let it run a bout 4,000 rom for several minutes then speed it up to about 5,500 for a half hour or so, it will have lots of compression after that. Does your fuel have plenty of oil in it?

Paul, I am the only one that I know of in the whole county now. I originally started flying at Oxford and they disbanded because for lack of field to fly at. Now when I want to fly with other ever week or so I go over to Wren MS to fly with a group out of Wren, Nettleton, Tupelo area. I like them better than any people I have flown with so far because they are friendly and like to fly. Flying alone doesn't bother me at all. I have just gotten Super Tiger 51, 61, 90, and 2300 running and love the engines. I post here about them often but it won't tollerate not being setup correctly. Do as Hobbsy suggests revit up midrange transitioning occasionally to work the parts together to get that wear fit. The ST engines need extra fuel most of the time to get broken in. The run the breakin prop to start. Make sure you use fuel with some castor in it at 18% oil and then add 2oz. of extra castor for breaking in. This will give you extra protection in case of lean run. After breakin just run 18% with some castor. After bench breakin (maybe 2 ten oz tanks) set the high needle first by using a tachometer running wideopen and leaning the high needle to top rpm (watch tach closely and noter rpms) and when you get a slight drop in in rpm (too lean now) , very quickly richen up by about a round and readjust to about 600 rpms under peak rpms. Set the low end by leaning needle about 1/8 of a turn and check transition, you are looking for just a sligh hesitation for the initial breakin flight, this keeps the still new engine will oiled and cool till everything wear fits together. All this sounds simple but it is harder that it sounds. Many people have been flying for years and still get it wrong. The Super Tiger instructions are ok too but the pinch method is dependant on how long you pinch and a good ear. FInal word once you mount the engine on the airplane you must recheck needle settings because it can all change there. Also, need to check the vertical setting by getting someone to hold the airplane vertical and make sure it doesn't lean out in vertical position, this has crashed many airplanes and this is why it is good to get help. Crashing isn't fun especially for a beginner.

Jester The secret of chicken stick starting is the amount of prime to get a cold engine started ,just like the choke on an old car. You can prime with a squeeze bottle or plug carb throat with finger and turn prop several times or plug exhaust tip and turn prop several times to get enough prime. I like the exhaust method because you don't have to jack with a small bottle of fuel and because of cowls and such you can't always get to the carb throat. By the way -do not put igniter on glow plug till after you prime good. We don't want it to start chewing up your fingers right off the bat..............as your turning the prop.

Well I have already run 3 8 oz tanks through it. The first was super rich at WOT like the manual says, the second was up and down on the throttle, and the third was to get the high speed needle set to slightly lean. I didn't build a test stand, so I've been running it on the plane (SPAD Debonair).
I think the cause of my starting troubles has been that the engine was mounted too high. The carb fuel fitting was about 3/4 inch higher than the output from the tank, so after I primed the fuel was falling back into the tank. I lowered it yesterday to only about 1/4 inch higher (the best I could do) so when I get the time I'll see if it's any better.
Speedster- I don't have a cowl, so I will try pouring some fuel into the carb to prime. How much should I put?

Well good ? Just put a squirt in carb throat. Probably about an eye dropper full. If you use the exhaust method -you watch the fuel tube at carb and when the fuel reaches carb a couple extra turns of the prop is usaully enough.

It is not totally out of the realm of possibility that it is leaking too much compression. I purchased a GS .40 a year ago and it had weak compression and would just pop a little. It had just enough compression that I questioned whether it was operator error, or if there was something wrong. I ended up sending it back, and it was replaced with a new engine with MUCH better compression right out of the box. Ringed engines do need more break-in that ABC, but they should have enough compression to start up, so you CAN break them in the rest of the way. After a couple tanks of fuel, most of the leak should be gone and it should have "decent" compression.
Ross

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Just don't be fooled into thinking that a ringed engine needs tons of static compression (non running) in order to run very well. Also, rings are prone to sticking some times and will display poor static compression when in other wise perfect condition. It takes a while to get used to ringed engines and all of their quirks.


Ed Cregger

Ed is right too! Also, engines with dykes rings will not have as much static compression either.

Ringed engines don't run with as much compression as ABC engines and it is normal to have compression leak or blow-by. As the engine gets broken in the piston and ring will seal better but with alcahol engines it isn't as critical. One way to judge about what is going on in the engine is to get the tachometer out and see how many rpms it will turn say an 11X7 prop.

I am recalling what a motorcycle mechanic in Bruce tought me back in the 70s about motorcycle and some automotive engines, and that is that some pistons aren't round. Not round at all, they are oval. The man ask why they put oval pistons in round cylinders, and I said I thought they were round. Then he held one up that he had on the bench and sure enough much space on two sides. This allows for thermal expansion in the aluminum pistons. I must admit I have never checked a glow piston to see if they are round or not. It isn't as critical in small engines and some spall engines have rounder pistons. The bigger the piston the more expansion that occurs. I have a Honda engine (with many hours of use) that smokes profusely on start up but give it about one minute of warmup time and it all stops. This is because of the thermal expansion that seals the piston/ring/cylinder gap.

Well once I get mine started it spins my 11 x 5 pretty fast, especially when I give it a pinch to check the mix. I don't have a tach, but it sounds like no slouch to me.
I probably just need to get some experience with it and let it get broken in well. It had more static compression new than it does now, so that was my biggest worry. But it sounds like static compression isn't going to be very high on this ringed engine anyway because of the gap. At operating temp and high rpm that's not going to be a factor, so I'll just fly it.

I had the same engine and it really started coming on after about a gallon of fuel.....

Hi Jester,
That 11-5 prop may be a little on the small side for break in, manual suggests 10-8 or 11-6.
My old and well worn G51 would turn a 13-4 at over 13K static, on a H9 Twist 40
Good luck,
Pete

Mostly of all model engines are piston not oval. They are made tapered, top of piston are smaller than wrist pin zone to allow expanding to near same diameter as bore.

I has model engines who has home made piston with ring, works well. The diameter of top of the piston are calculated by temperature range when the piston are full expanded. See what i maked the parts in my OS 61 : http://www.rcuniverse.com/forum/m_4929500/tm.htm

If compression are not good enough, it will take a time to run in the engine before the ring are adapted to cylinder wall. It is normal there are a little leakage cause the ring gap let it compression pressure leak out of cylinder. When the engine are running , there are leakage not big enough to make engine trouble..

Jens Eirik