I have a brand new Pro Series Thunder Tiger .61 two stroke engine which binds fairly badly on the top half of the compression stroke. I have never started it and It came in a sealed plastic bag with no glow plug. I am afraid to turn it over as it seems to be too tight. I have added a very light oil but this does not help. I can't see any scratches on the piston. I don't know what to do. Any suggestions would be greatly appreciated.I bought it at a swap meet about two months ago,paid cash with no receipt so I doubt the Manufacture would take it back.
Web Herman

Sounds like an ABC sleved/piston set. They feel VERY tight at top because of the tapered sleve. Sometimes so tight... a starter has a hard time turning them over on less than 14.4 v.

Drip 4 drops fuel n the glow plug hole, put the plug in. Hook up the fuel tank... crank it. Run it BARELY rich from max rpm for a full 10 oz tank (you will have to adjust the needle at least once) It will free up.

This is normal for this style piston and sleeve.

Mr. Herman, If I am not mistaken, the Thunder Tiger .61 pro is an ABC engine (AluminumBrassChrome) and what you are experiencing is absolutely normal. As a matter of fact, when your engine no longer has this squeaky tight fit it is worn out. Heres why, an ABC engine has an aluminum piston that runs in a chrome plated brass liner. This type of engine has no ring as in a conventional engine, instead it relies on a very precise fit between the piston and the upper cylinder wall to effect a gas tight seal. The expansion rates of the piston and liner are engineered to give a very slight clearance when the engine is at normal operating temperature. When cold however the brass tends to shrink more than the aluminum giving the tight feel. My recommendation is to install a fresh glow plug, start the engine and run it. After the run while the engine is still hot the tight feel at top center will be gone.
One word of caution, do not run an ABC engine excessively rich or you risk connecting rod damage. This happens because the rich mixture lowers the cylinder head temperature enough to interfere with the normal hot clearance.
This will cause a slight binding at top center which will very quickly wear out the connecting rod bushings. Run the engine just slightly rich of maximum rpm and you should be fine. One last thing, what is the advantage of the ABC design over a ringed engine? Without the drag of a piston ring, the engine has much improved performance, especially at high rpm. Hope this helped.

Well running them in barely rich may be OK...but both Jett and Rossi (and I'm sure many others) specifically state to run them in rich. Rich in this case means the point where they occasionally break into a 4 stroke for an instant. It's also best to use at least the smallest recommended flying prop, or even smaller, and have some castor in the fuel.

I have to disagree with the comment about ringed versus ABC too because the majority of helicopter engines are ringed and they fly at very high revs although some of that may be because they are in a hover close to the ground kicking up dust and ringed engines are far more tolerant of dirt. There's no difference in power between a ringed or ABC variant of the same engine.

G'day Downunder, are you the original "Thunder from Downunder" I've been hearing so much about lately? Anyway, I think our only disagreement here is on quantifying what constitutes "rich". All information that I have on ABC engine breakin specifically warns against operating in a four cycle mode. Dubb Jett in his excellent technical library says to break the ABC or AAC engine in "rich" but does not define the term. Super Tigre recommends just breaking in to a "two stroke" when breaking in their ABC engines. My understanding is that operation in a "four stroke mode" with an ABC engine will quickly destroy the engine hence my advice to Mr. Herman not to run too rich. By the way, ABC engines are more tolerant to a lean run than their ringed counterparts. As far as the superiority of ABC, AAC and ABN designs to ringed engines with respect to performance, I believe is a well established fact. Super Tigre states that the ABC design (which they pioneered) gives a more effective compression seal and hence superior performance over ringed engines.
Dubb Jett is well known in racing circles, if ringed engines were superior for high performance, he'd be building them. I don't fly helis and don't know why they use ringed engines, it could be, as you stated that they are more tolerant of dirt ingestion than ABC designs. Anyway I believe that we all agree that Mr. Herman has an ABC engine, it sounds healthy and maybe he should pick up an owners manual for the engine and follow the specific breakin procedures for that engine.

Boy Thanks for all the responses! I feel a lot better knowing that this tightness is normal. Thought I had wasted $93.00.
I have been looking for a home for my questions regarding my gas planes and I believe I have found it. I have this engine installed in a RCM Senior Telemaster and can,t wait to fly it. I will break the engine in on a test stand.
It,s 11 degrees F here ..too cold for this old man to fly..even electric.
Web Herman

Glad we could help. For more info on ABC engines try this site http://www.hobbypeople.net/rcsource/faqs.htm
There is a good explanation of the tightness you are experiencing in your new engine as well as proper breakin procedures. Good Luck

johnybravo...yes, I'll grant you that even the best of the manufacturers (like Jett) are a bit vague as to what they mean by "rich". The Rossi instructions take a lot of working out in their fractured "Inklich" [img]i/expressions/face-icon-small-smile.gif[/img] because they suggest the exhaust should be greasy [img]i/expressions/face-icon-small-smile.gif[/img]

The Jett instructions to open the needle 2 turns more than factory set and that you may need to leave the plug connected for the first minute leads me to think it's maybe a full 4 stroke.

But like you said, the problem comes with quantifying what's rich. Because there are only 2 distinct sounds an engine makes then if you shoot for the point where it's either swapping between both sounds or maybe just barely into a clean 2 stroke then it's something that everyone can do. This at least lets plenty of fuel (meaning oil) go through the engine in its first critical moments. After the first one or two tanks even an ABC can be run in a full 4 stroke without any harm. This is done all the time in CL stunt.

When Super Tigre developed the ABC set-up it was to overcome a problem with their cast iron piston .15 speed engines (in those days all small speed engines were like that) in that if they went slightly lean the end result was a seized engine. ABC allowed them to keep running without damage for enough time to allow the pilot to shut the engine down. The lighter piston also allowed better balancing. But the idea was so good it eventually became almost universal. They also pioneered Schneurle porting but in a slightly different form to what we have now.

Perhaps if Dub Jett references "from the factory setting" the most critical part of breaking in (conrod bearings, etc.) has already been done. George Aldrich used to have break-in instructions on his web site. Similar to above: small prop, rich side of peak for the first two minutes, then it didn't matter as much. The idea was to heat up the cylinder for proper clearance as soon as possible to lessen the stress on the moving parts. After the first two minutes the conrod, crankpin, wristpin, etc. have pretty much seated.
Part of how you break it in depends on how you are going to run it in your plane. Some racers are VERY careful to not let it run very long in a four cycle. In CL stunt you run it much slower so you need to break it in richer.
Some ABC engines seem to keep getting better as the run-in during the first hour.
This is just opinion, individual results may vary [img]i/expressions/face-icon-small-smile.gif[/img]

George

Generally... My definition of "rich" for break-in is about 4 clicks open from max RPM on the main needle. (just over 1/8 turn if you can't feel the clicks)

If you get it right... appx 3 min into the engine run the rpm will change SUDDENLY. Its practically always a reduced rpm due to the piston seating and... it goes richer. (needs the needle closed as much as 3/4 turn)

Before doing the break-in... check internally for filings and mold flashing. Remove backplate, pull the carb. Flush a little fuel through. Hold the carb down firmly with your thumb as you tighten the retaining nut when you reassemble.

I have two Jett engines and the instructions specifically state not to run the things rich. Run for short spurts close to max. Also, use the prop you are going to use when running the thing.

Max

Most of the info I have seen on break in for this type of engine recommends wide open for at least one tank of fuel. Does this mean the instant you set the starter down you nail it and dont let off? Im always a little hesitant to run any engine wide open until there is a little heat in the motor. Aluminum expands faster than brass so I would think the piston would grow faster than the cylinder and cause problems. Most of my experience comes from motorcycle engines so maybe it doesnt apply to glow.

Not WFO, but not slobber rich for the first runs. About 1500 to 2000 r's below max is right.
Max

Wow!!! Looks like we have opened a real can of worms here! I have noticed that no two engine manufacturers will agree completely on engine vbreak in procedures for the same type engine. A good example, I own Magmum, OS Max and Saito fourstrokes and each recommends a different break in procedure. The Saito engines are AAC designs while the OS and Magnums use conventional steel sleeves and rings so that may account for some of the differences. I think that the bottom line is that there may be more than one way to satisfactorily break in a given engine and get equal results. I think we can all agree that there are certain conditions that must be avoided like maximum rpm and lean operation during breakin but this excessive rich running thing on ABC designs is apparently a gray area. I've always run my ABC engines in rich but not so rich they fourstroke and have had excellent results. Once broken in I use this method to set the high end needle on all my engines(non-pumped):
Fill the tank 1/3 full, start the engine and point the nose straiaght up. Adjust for maximum rpm and richen slightly (APPROX. 200 RPM DROP) then go fly. This method seems to work great for me.

[img]i/expressions/face-icon-small-happy.gif[/img] Running in is always a big can of worms but maxtenet's 1500 to 2000 down from peak gets into the ball park. But to me the only problem with that is first you have to peak out a brand new engine. It's fine for guys who've had a couple of engines and are familiar with how they sound but the poor beginner has a problem. Even so, I think our engines are a bit more tolerant than we give them credit for especially considering the number of people that take an ABC out of the box, give it half a tank close to peak then go fly. I'm sure they don't last as long though.

Of course, when it comes to running in something like johnybravo's ringed engines, that's a whole different ball game [img]i/expressions/face-icon-small-smile.gif[/img]

I agree Downunder, these engines are very tolerant of abuse. I don't know how many times I've gone off lean with my fourstrokes and thougt I'd smoked 'em. Years later they seem to be no worse for wear. One thing that I am a believer in is castor in my fuel especially during break in. I've had no problems with botton end rust or engine damage from lean runs. I've heard that the castor will polymerize at high temperatures and create a protective varnish to prevent cylinder scuffing. I'm not a chemist, but the guys who run straight synthetics seem to suffer from higher engine wear and rusted bearings here in the humid Texas climate. My favorites are Castor/Synthetic blends from Byrons and Morgan fuels. Only down side is carbon buildup in the combustion chamber and muffler that must be delt with periodically. [img]i/expressions/face-icon-small-cool.gif[/img]

"If you get it right... appx 3 min into the engine run the rpm will change SUDDENLY. Its practically always a reduced rpm due to the piston seating and... it goes richer. (needs the needle closed as much as 3/4 turn)"


Mr. Herman is my Dad. Today we ran the engine in on a test stand. I set the mixture to the point of four stroke and leaned it out until it started to two stroke. I went a few clicks lean from there. Just as FHHuber stated a few minutes into the run it slowed down. This made me a little nervous because I thought maybe it was starting to sieze. This was not the case. I had to lean it out slightly to get it back to previous rpm. After a tank of fuel we shut it down and sure enough it had loosened up.