caesar148

I got myself an ABC engine (aluminium piston, brass cylinder, chrome lining) for the first time and I noticed that the engine is almost impossible to turn to top dead center by hand. I was told that this is normal. They loosen up when the engine heats up. Why are ABC engines designed this way and what is the benefit of ABC engines vs ring engines?

w8ye

My Feedback: (16)

The expansion rates, when hot, open this tolerance and the engine is free when warm. They run great and are trouble free.

Enjoy,

Jim

buzzingb

My Feedback: (2)

If you will use a hair dryer or heat gun to gently warm up the engine before fireing it up for break in it will expand the cylinder ever so slightly. This gives the piston a better chance at wearing to the cylinder without damage and making it easier to spin the engine with the electric starter. After the first tank of fuel, ran at a slightly rick two stroke, it will loosen up.

Rcpilot

My Feedback: (78)

Stop turning it over by hand when it's cold. You'll just cause unnecessary wear on it before you even fire it up for the first time.

You can do a search here and read about the design and theory behind the ABC engine. It's a fine engineering acheivement, and works fine. All you have to do is break it in right and treat it to good fuel. Never run it lean. It should last years--or in my case-------several models.

Motorboy

Read here about break-in ABC/ABN engine: http://www.rcuniverse.com/forum/m_1850473/tm.htm

Jens Eirik

B.L.E.

When running, the cylinder head and the top of the cylinder gets much hotter than the bottom of the cylinder does. The tapered cylinder bore compensates for this. At operating temperature, the cylinder walls are nearly parallel and the engine turns freely.
Try this to see for yourself, with the engine just cut off and still hot, remove the glowplug and slowly turn the engine over, no tight spot! As the engine cools off, the tight spot returns.

Ed_Moorman

My Feedback: (1)

Let me see if I can give you a little history and the why of ABC engines. Back in the 1960s when modern RC was in its infancy, one of the big international competition events was control line speed. Speeds on 70-foot lines were approaching 200 mph in some classes. Several engine manufacturers were into CL speed very heavily. Exotic fuels were used (many of which are banned today) and competition was fierce. It was not uncommon to see a lean run and a fried engine or a hole melted in a piston.

One of the main engine brands was Super Tigre of Italy. Mr. Garafoli, and I am not sure of the spelling, and his engineering staff at Saturno Micromechanica which made ST engines, devised the original concept to help preclude the damage from over lean runs. Most engines at that time used a steel cylinder with a porous iron piston. When correctly broken in, the iron piston gets a coating or seasoning much like your wife's cast iron flying pan that you are instructed to never put in a dishwasher. The seasoned piston is very slippery and low friction.

Super Tigre's new metallurgy used a lighter aluminum piston running in a tapered brass sleeve that had been hard chrome plated. The brass sleeve it tapered so the piston is tight at the top and looser at the bottom, reducing friction on the down stroke, but having good compression near top dead center. When heated up, the brass sleeve expands such that is is nearly a straight bore. Having it bored straight to start with would mean it would be too large under operating temperature when the engine is running. The chrome plating is to make the brass surface wear resistant.

Everyone knows that aluminum wears easily and expands greatly under higher temperatures. Ringed engines have a slightly loose fit piston with a cast iron ring for compression seal. If you ran a straight aluminum piston, it would wear out quickly. ST found a method of doping (mixing in another metal) for aluminum using silicon that both reduced the wear and the thermal expansion. The silicon makes aluminum harder to wear and also reduced the thermal coefficient of expansion to be less than that of the brass sleeve.

Now you have an engine that is tight when cold, but opens up to running clearances when running and leaned out. In addition, and this was one of Super Tigre's goals from the first, when you go over lean, which means a higher temperature that would normally melt a piston, the sleeve expands and the engine loses compression, slowing down. It isn't totally fool proof, but it did cut down on the number of burned pistons.

And it was all to make a CL speed plane go faster.

BarracudaHockey

My Feedback: (11)

Thanks for the great explanation Ed!

The_Pipefather

Great information there, Ed. But I would like to add here that high-silicon content aluminum pistons have been around for much longer than that. Actually I think they took birth in the early aero engines, somewhere around WWI.

Ed_Moorman

My Feedback: (1)

Right. I assume what Super Tigre did was to find 2 alloys, doped aluminum and brass, that would give the correct expansion under the operating temperatures of glow engines. I'll bet it took some testing to get it really tuned in.

Super Tigre had some interesting engine configurations in those days. Nearly all engines has straight cut ports and a deflector on top of the piston.

One of Super Tigre's ABC engines used the same size, single transfer port, but with an upward angle cut in the sleeve like the boost ports in todat's engines. Later when PDP ports were added, it became, for all practical purposes, a Schnuerle ported engine with very small Schnuerle ports (the PDP ports) and a huge transfer port (the regular transfer port).

They also had an ABCD configuration. That was ABC with a Dykes ring. I really don't know what they did this one for. I often wondered if they weren't able to get enough of the correctly doped aluminum and used regular aluminum with a ring instead.

Of course, they had their normal, ringed piston/steel cylinder Blue Head .61 which was later gived a PDP mod.

caesar148

Hi Ed, Thanks for the great post. Never knew Super Tigre had put so much research into their engine. And all along I thought O.S. had all the technology. Hmm....now which engine should we clone.....?

downunder

The only real advance OS made was to introduce CNC machining and that was because it was the only way to machine the Wankel engine. Their first normal engine to be made with the new CNC was the 40SR which later became the FSR. But the engine that put them on the road to success was the Max-I .15 back in the mid 50's that was used to set a world record in FAI free flight. That gave them notoriety and everyone scrambled to buy those cheap Japanese engines