Differences between plain and bb engines!
 

I want to know more about what you gain from a ringed engine in comparison with a plain one.
When we say "plain" we mean that our engine has "bushings"?
And what exactly means the word "bushing"?
So,post the differences between RINGEDand PLAIN engines.

RE: Differences between plain and bb engines!
 

You are slightly confused by the terms. "Plain" refers to the crankshaft bearing -- a "plain" bearing is also called a journal bearing, or a bushing --- instead of a set of ball-race bearings.

A ringed engine has a piston ring to seal the gap between the loose-fitting piston & the wall of the cylinder. This is the same type of arrangement that is used in automobiles & just about every other reciprocating internal combustion engine, although the larger engines use more that one ring. When the ring wears out, the engine can usually be overhauled just by fitting a new ring & some minor prep-work to the cyl walls.

Many model engines used lapped pistons instead of piston rings. In this configuration there is a very close fit between the un-ringed piston & the cylinder -- close enough to seal against compression & combustion pressures without using a ring. Years ago, the pistons were hand lapped into the cylinder with a very fine abrasive, to make the tight fit. This fit is specific to each engine & when the fit wears too much the engine needs a new piston & cyl sleeve.

Now with CNC machining, I'm not sure if they are lapped anymore.

"Lapped" piston types include ABC, ABN, steel-mehanite, aluminum-ceramic -- & I'm sure that I'm forgetting some other combinations here.

RE: Differences between plain and bb engines!
 

Kostas1,

You are confusing pistons which have rings and bearings which support the crankshaft. Pistons come in ringed or non-ringed engines. Non-ringed engines have a tapered bore that gets smaller toward the top (refered to as the pinch). Ringed engines are not tapered and rely on the ring for compression.

Now plain versus bearing engines. Actually both are forms of bearings. A plain engine has a sleeve made of some softer material like brass. The crankshaft fits inside the sleeve and relies on the oil in the fuel to provide a lubrication layer between the crankshaft and the sleeve. A very effective and inexpensive method of providing bearing support. The sleeve is referred to as a bushing.

The other bearings are ball bearings used to support the crankshaft. There is a small bearing up front and a large bearing inside the front face of the crankcase. If you remove the coverplate in the back of the engine you can see the large ball bearing. The balls ride in a race, there is an outer race and an inner race. The same is true of the smaller bearing up front. The inner race supports the crankshaft and the outer race mates the crankcase.

Ball bearing engines are a little bit heavier than their cousins with bushings. Both are reliable and prefrom well. Ball bearings can be replaced and often suffer from rust, the bushed engines are not rebushed (it can be done but is very expensive compared to replacing ball bearings).

Many think that ball bearing engines have less friction due to the use of the ball bearings and thus rev up to higher RPMs. There may be some advantage there but the real advantage is being able to replace the ball bearings pretty easy. I have never heard of anyone replacing a bushing though I guess it is possible.

Ball bearing engines cost more, usually referred to as the "Pro" series in Thunder Tiger and Magnum 2 cycle engines. Almost all four cycle engines have ball bearings due to higher impact forces of the compression and firing implues.

Thus all OS LA engines are sleeve or bushing engines, all the OS FX series are ball bearing engines. Note the cost difference.

Cheers,

Chip

RE: Differences between plain and bb engines!
 

The OS LA series are ABN engines.
So they are plain engines?
Without rings,correct?
Also the fact that you have a ringed engine,will increase power or sth else in comparison with a plain engine of similar displacement?

RE: Differences between plain and bb engines!
 

OS LA enignes are plain engines without rings. Fewer parts thus cost less.

Ringed engines do develop more power. But they are getting rarer to find, for example the OS .50 is ringed but the OS FX .46 is not ringed. Most of the engines in the 40 to 50 range are not repeat not ringed. Super Tigre .51 is ringed. Thunder Tiger Pro 46 is not ringed.

Ringed engines are harder to break in, take longer to develop their power.

Cheers,

Chip

RE: Differences between plain and bb engines!
 

Thank you.
You "made" my mind!

RE: Differences between plain and bb engines!
 

I have to disagree -- I'm sure that there are exceptions, but generally speaking, ABC/ABN/Lapped piston types make more power than ringed engines.

RE: Differences between plain and bb engines!
 

What has not been mentioned here is that ball-bearing engines typically have more expensive machining of their internal ports which accounts for the power increase.

RE: Differences between plain and bb engines!
 

I was reading a post on here a few days ago about the OS65LA being as powerful as the FX or ball bearing engines. I wonder if that is true. I kind of doubt it. If you have actual rpm test data lets hear it. The bushing engine it ran once was the Thunder Tiger 42 it didn't have that good of power but ran very well. It wouldn't pull a profile plane verticle very far and you could forget hovering.

RE: Differences between plain and bb engines!
 

You have to remember that when all things are equal, port timing, carb size compression ratio, etc. the bushing and BB engines will have equal power. The same goes for whether it is ringed or AB?

RE: Differences between plain and bb engines!
 

Just a minor point. Journal bearings and bushed bearings are not the same thing. Bushed bearings are made of a medium hard metal, but softer than the shaft. They are lubricated with free flowing oil, or grease. Journals are made with a very soft metal of usually an alloy of tin, lead, copper, and antimony. This alloy is called babbit. Journals are lubricated with pressurized oil and, execpt for startup, the hard metal shaft never touch's the soft metal journal.

RE: Differences between plain and bb engines!
 

http://www.modelairplanenews.com/cli...60engines1.asp

Here is a link to Dave Gierke's .60 sized engine shoot out. There are some surprises here.

RE: Differences between plain and bb engines!
 

As for the 65LA having more power, that is not true. The 65LA is rated @ 1.7bhp @16000 RPM. while the 61FX is rated @ 1.9 @ 16000 RPM.
Sometimes we get hung up on power ratings. Do you know of anyone that runs their sport plane @ 16000 rpm when flying? That speed is not attainable with props that are used on most planes. I would rather have an engine that idles reliably, and starts good rather than one that will pull the firewall off. Don't get me wrong, I like power, but if a bushing engine will do for me what a PRO or BB engine does, I'll use it and save some bucks in the process....Just my opinion.

RE: Differences between plain and bb engines!
 

You are missing sth.
The OS 65 LA is more powerful than the OS 61 FX.
Unless you'll use a prop with 12'' dia and 7'' pitch.
Otherwise is MORE powerful.

RE: Differences between plain and bb engines!
 

The difference between a plain bearing engine and a ball bearing engine:

About 300RPM.:eek:

Plain bearing:
bronze ferrite BUSHING to support the crankshaft in the crank case

Ball bearing
steel balls inside a race--pressed into the case--supports the crankshaft

ABC/ABN/ABL:
piston without a ring--chrome sleeve--tapered at the top

Ringed:
piston with a ring--chrome sleeve--straight bore

RE: Differences between plain and bb engines!
 

You are making the mistake of believing OS's advertising [:'(]

Go back to torque wrench's post (#12) & read Dave Geirke's dyno-test data. The OS 65 LA does, in fact, out power the 61 FX. It also makes more torque -- at the real-world RPMs that we use.

RE: Differences between plain and bb engines!
 

Thanks Brit, that's the exact reason I chose the LA .65 for a Diesel conversion.

RE: Differences between plain and bb engines!
 

Good concise stuff

Additionally, ringed engines may have a steel sleeve rather than chromed & some lapped-piston types (Enya, in some examples) have steel cyl liners without significant (or any) taper.