Products - Frequently Asked Questions (FAQ)

I did not find the answer to my question here. How do I get further assistance?

My brand new 2-stroke ABN engine is very hard to turn over by hand. It seems to 'stick' at one point and I can't turn it past that point without using a lot of force. Is something wrong?

An ABN engine has an Aluminum piston and a Brass liner with Nickel alloy plating.

A ABN engine's liner is tapered towards the top. This causes the piston to "grab" as it moves towards Top Dead Center (TDC) when the engine is cold. (Some engines will actually seize if you turn them over when cold, requiring considerable force to turn them through TDC.) When an ABN engine is run, the heat of combustion causes the metal parts to expand. Because the piston and cylinder liner are made of different metals, they expand at different rates. The liner expands just enough to make a nice fit for the piston once the engine warms up. The liner is tapered because the cylinder is hotter near the top. The different temperatures cause different amounts of expansion, making a perfect fit when your engine is at optimum operating temperature.

You may interpret what you feel as play in the connecting rod. This is almost never the case with a brand new engine. What you are feeling is a slight springing of the connecting rod as you force the engine through TDC. The piston doesn't go all the way to the top, causing the rod to flex slightly, which gives an "over the center" feeling. Many people have interpreted this as play in one of the rod ends, but it is not and is perfectly normal.

How do I break in my new ABN engine (for example, 40FX)?

Your ABN engine must be broken-in at full throttle. You don't want to run it too rich. Too- rich running will not allow it to warm to proper temperatures, so the liner does not get properly seated. Lean it until it is running just out of what is known as "four-cycle" mode, then gradually work leaner with each run. You can lean it to peak RPM as soon as the engine will accept it.

You should prop your engine to allow higher RPMs. ABN engines work better at higher RPM. You should also use a fuel that contains castor oil in the lubrication mix. Castor oil helps the engine run well and is the better lubricant for our ABN engines. All-synthetic fuels have been known to cause difficulties in running at times.

Once properly broken-in, your ABN-type engine will serve you well and deliver lots of reliable performance.

I want to change the bearing in my out-of-warranty engine. How do I do this?

We recommend you send your engine in for service rather than attempting to change your bearings yourself. If you've got a blown bearing chances are good your engine has suffered other damage as well which you might have missed. However, if you're REALLY comfortable working on engines, these steps will assist you in changing your bearings. If you are unsure how to complete any one of these steps, we caution you against disassembling your engine and recommend instead that you send it to our warranty and service center for non-warranty repair.

If you need further help, you may want to consult modeler's engine books such as those printed by Model Airplane News orHarry B. Higley & Sons, Inc.. They have comprehensive pictures and explanations on model engines.

I recently purchased an OS CV engine. Wow is it cool! But it sure is different from my other engines. Can you provide me some tuning suggestions?

Absolutely! First, set your engine back to the factory settings, then we can help you tune it from there.

The initial settings for the carburetor of your O.S. CV engine are easy to set. First, close the high- speed needle valve and open it 2-1/4 turns out from closed. This is the initial setting, and is a rich setting. You will have to lean the engine from this point as you drive the car.

To set the idle mixture needle, which is the grey screw in the center of the throttle arm, inside the chrome barrel, you must be able to see into the carburetor. Remove the aircleaner from the carb so you can see what you are doing.

Open the throttle to the full-open position. Inside, you can see the idle needle and the fuel nozzle. Adjust the idle mixture screw until you have a gap of 2 mm to 3 mm between the needle and the nozzle when the carburetor is fully opened. You can also double-check this by looking at the head of the idle mixture screw. It should be sticking out of the chromed barrel by about 1/32". This is an initial setting, and is a bit rich.

When you start the car, you can leave the clip-on battery attached to the glow plug for some initial running. As you run the car, it will be a bit rough. Adjust the high-speed needle until it just stops running rough. You can then adjust the idle mixture needle and the carburetor throttle opening until you can have the car stopped, but with the engine running smoothly. If you release the brake or stop holding onto the car, it may tend to ease forwards, just like a full-size automobile with an automatic transmission. This tells you that you have the correct setting.

Now go out and enjoy running your R/C gas car with your O.S. Max CV engine!

This engine seems to smoke a lot. Does that mean I am running it too rich?

Not necessarily. If the engine is now smoking more than it has in the past, and everything else is exactly the same (same fuel, plug, conditions, etc), then your engine is probably running a little more rich than it has previously. But the amount of smoke is not an absolute indicator that an engine is running overly rich. Different fuels will smoke differently when the engine's properly-adjusted. Get the engine adjusted properly, and then see what kind of smoke trail you get. If the fuel smokes a lot, even though the engine's running well, your fuel has an oil that encourages smoke. Don't worry about the amount of smoke output, and never sacrifice your engine's oil intake just to minimize the 'vapor trail' it leaves in operation.

Why did my prop come off my 2-stroke engine?

With almost all R/C model engines, the direction in which the propeller nut tightens keeps the propeller nut from loosening when the engine is running. The direction of the power pulses tends to tighten the nut. It's very possible that the nut became loose when the engine backfired during starting. Backfiring is a sign of flooding or other deficiency in starting technique or a problem with the engine.

The most common reason propeller nuts become loose is that they were not tightened enough. Instead of using a "4-way" wrench to tighten a propeller nut, you may use a six-inch box wrench or adjustable wrench for propeller tightening. We use both hands and arms to tighten the propeller nut onto an engine, with propeller held in one fist, with the wrench in the other. We apply enough force that it takes both hands to loosen the propeller later. When it's properly- tightened, we have rarely seen a propeller loosen itself on a small 2 stroke engine.

I heard about a new product which is not yet listed on your web site. How can I get more information?

If a product is not yet listed on our web site, chances are good that we do not yet have information on that newly released product. Please visit your favorite hobby shop and our web site regularly for new technical information as it becomes available.

How much faster will my model be if I change my engine X for an OS engine Y?

Unfortunately, we cannot estimate the running speed of your vehicle, even in attempting to compare one engine's performance to another. Speed is dependent on a large variety of factors, including gearing, engine break-in, running surface, fuel and plug, assembly accuracy and, of course, skill.

What temperature is ideal for my engine?

It's not possible for us to give you an actual temperature or temperature range for your engine. The specific temperature is determined by too many factors. There is only one way to determine at what temperature your engine should be run - get it running just how you like it, then find out what temperature the engine reaches.

Make sure your engine is operating properly and providing the performance you expect. Be sure you are not overly lean and shortening your engine's lifespan. Use the exact setup every time...fuel, exhaust system, plug, measurement location, and so forth. If you change anything, the temperature will change. Once you have the engine running the way you want it, take your measurement. You will have to take measurements over time to find out how the weather affects it. As the air temperature and humidity change from day-to-day, the operating temperature will change. Eventually, you'll find a temperature range that you can use.

Engine temperature is not an absolute number for setting your engine. It is only a guide, and can help alert you to potential problems. The only sure way to make sure your engine is running correctly is to see how it's running. An engine can be operating at "correct" temperatures, but not running well, or seem to be running "hot" or "cold" yet is performing flawlessly.

Finally, use any temperatures you read about, or people tell you, as rough information. The only useful numbers are the ones you actually measure when your engine is running correctly. If your engine is running correctly, then what you measure is correct, even if some else says it's too high or too low. Don't worry about the differences. Each engine is in a unique installation with a unique set of circumstances, so there can be wide variances in engine temperature.

How do I set the timing on my OS single cylinder engine?

We recommend you send your engine in for service rather than attempting to set the timing yourself.

However, if you're REALLY comfortable working on engines, these steps will allow you to set the timing. If you are unsure how to complete any one of these steps, we caution you against disassembling your engine and recommend instead that you send it to our warranty and service center for non-warranty repair.

The proper way to set the timing in all O.S. single-cylinder engines with the front camshaft is:

  1. Rotate engine so that the piston is at Top Dead Center.
  2. Locate the timing mark on the side of the cam gear.
  3. Insert the cam gear so that the timing mark is in a direct line with the center of the cam followers and the centerline of the pushrods. It is NOT at a 90 degree angle to the crankshaft. The angle will be slightly back.
  4. Replace the cam cover and you're ready to go!

This should get your engine running well, if the timing was off. If it is still running poorly, be sure to send it in for service to avoid accidentally doing more damage.

Someone told me to use the idle needle to set the midrange on my 2 stroke engine. Someone else told me that the high end needle sets mid range. What's right?

With most 2-stroke engines, you don't set midrange by using the idle mixture adjustment. The idle mixture adjustment is for idle only. (IN A HELI? As with most engines, it's not easy to break it in and find initial settings by flying the engine in the heli. It should have some test-stand time with an airplane propeller.)

Here's the correct way to set the carburetor:

  1. Make sure idle mixture is set excessively rich.
  2. Start engine and get it to full throttle.
  3. Adjust engine so that it's running properly at full throttle...this means that it will be leaned to just below peak RPM. This setting keeps your engine just rich enough so that you won't go lean of peak when the tank gets low.
  4. Retard the throttle and adjust the engine until you have a proper idle setting. The idle setting should also allow a reasonable acceleration.
  5. You then must accept what you get for the midrange. If the high and low end needles are properly adjusted, and you are utilizing an appropriate plug, propellor and fuel, and your engine is operating properly, you should have an acceptable mid range at this point. You may need to adjust high or low slightly to a compromise for a mid-range you are pleased with.

You will not get the needle valve set correctly unless the engine is run at full throttle. You cannot use the idle mixture adjustment to help with the midrange. We've found that once the high-speed needle's been properly-leaned, and the idle mixture set, most 2 strokes now have a good midrange.

My airplane does not have as much vertical performance as I would like. What can I do?

Prop selection is absolutely critical in determining if your model will have a lot of top end speed or a lot of vertical performance (ability to climb straight up). The same airplane with the same engine, fuel, etc, can change DRAMATICALLY just by changing props. It is very much like shifting gears in a manual transmission automobile—high diameter low pitch props are like low gear - they have tons of pulling power and the plane will have good vertical performance relative to a low diameter high pitch prop which provides lots of speed and momentum but very little pull.

One important note: a high diameter low pitch prop at very low RPMs acts like an air brake - just like putting your car in low gear and dumping the clutch to use the gearing to slow the car down. So if you are just starting to experiment with low pitch props, be sure to practice landing approaches with some altitude so you can get a feel for how quickly pulling your throttle back to idle will slow the airplane.

Your engine specifications give a BIG range of props. How do I know what is the best prop for my airplane?

Prop selection is absolutely critical in determining if your model will have a lot of top end speed or a lot of vertical performance (ability to climb straight up). The same airplane with the same engine, fuel, etc, can change DRAMATICALLY just by changing props. It is very much like shifting gears in a manual transmission automobile—high diameter low pitch props are like low gear - they have tons of pulling power and the plane will have good vertical performance relative to a low diameter high pitch prop which provides lots of speed and momentum but very little pull.

One important note: a high diameter low pitch prop at very low RPMs acts like an air brake - just like putting your car in low gear and dumping the clutch to use the gearing to slow the car down. So if you are just starting to experiment with low pitch props, be sure to practice landing approaches with some altitude so you can get a feel for how quickly pulling your throttle back to idle will slow the airplane.

Can I use a helicopter (-H) engine in an airplane? Why or why not? What muffler should I use?

The large cooling head on heli engines often provides too much cooling for the high-airflow application of an aircraft. Occasionally in a tightly cowled scale design a heli engine may be preferable to resolve cooling concerns. If the engine is produced in both forms (heli and aircraft), then the aircraft exhaust can be used on the heli engine and vice versa. Under no circumstances should an aircraft engine be installed in a heli application without a heli head or other extensive cooling precautions taken.

I used to own product X. I can't find it on your web site now. Do you still make it? If not, will you produce it again?

If the product you are seeking is anything other than an accessory or repair parts for another item, then unless a product is brand new, if it is not listed on our web site then the product is no longer produced. Unfortunately, we cannot answer whether or not a product will be reproduced in the future.

I am building a twin and want my engines to spin their props in opposite directions. Does OS make an engine with a counterrotating crankshaft or a means to convert an engine to counterrotating?

No, OS does not produce an engine with a counter rotating crankshaft. Until 2 years ago we stocked a reverse camshaft for the smaller OS four strokes to allow you to do this, but these are no longer available either. A standard engine cannot simply be 'reversed' in any means. However, you could go to a gear reduction system for both your engines with the reverse direction engine having one more or one less gear in the gear train. However, we are not aware of anyone who makes a product specifically for this task.

How do I know when my engine needs to be rebuilt or replaced? How do I know what to replace?

This is a hard question to answer, as it is quite subjective. An engine rebuild is always based upon performance. If the engine has been used so much that it's performance is no longer acceptable, it should be rebuilt.

If the bearings have become rough through use or corrosion, you should replace them. If the crankshaft has visible movement inside the connecting rod, and not just oil squeeze, when it is turned, you need some new parts.

Outside of obvious physical damage, a rebuild is always a judgement call by the modeler. Sometimes, it costs less to buy a new engine than to buy the parts to rebuild it.

If you feel your engine has lost performance but don't know what needs service, send the engine to an engine specialist. If you're not familiar with proper disassembly and service, you might do irreparable damage to your engine which originally required only a small amount of parts.

Why does my recoil sometimes slip and not start my engine?

There are 2 reasons why the one-way bearing is not catching when the recoil is being pulled:

1. The one-way bearing is worn out and needs to be replaced.
2. The one-way bearing has dirt and fuel in it and needs to be cleaned out. To do this, use some Engine Clearner or WD-40 (purchased from an Automotive Store or Hardware store of your choice). Clean bearing and let dry then lubricate (may use 4 in 1 oil or any weight shock oil).

How do I know how to set the air bleed screw on my engine?

Always follow the printed instructions for your engine. As a general guideline: As the air bleed screw won't affect the way the engine runs with the throttle barrel more than a couple of mm open my suggestion, turn the screw all the way in until it stops (DON'T over-tighten it). This will give you your maximum rich idle mixture. Now set your high-speed needle as instructed in your manual.

You can then back out the screw a little at a time. In order to see if you have too rich or too lean an idle mixture, pinch the fuel line closed with the engine idling. If it speeds up noticeably immediately, then the mixture is too rich and you need to back the screw out some more. If the engine dies immediately, the mixture is too lean. If it idles steadily for a few seconds, then speeds up, then dies, it is just right. Between each adjustment run the engine at a high throttle setting for 15-20 seconds or so to clear out any excess fuel which will make it harder to determine the correct needle setting.

(Remember that the high and low needles affect one another so you will need to work back and forth between them to get a perfect running engine.)

I have an older engine with a good bit of time on it. I am using fresh fuel and plugs, both of which I know to be good from running in a different engine. When I start it up I have to run it very rich or it will run hot and seize. After two tanks of fuel have been run through rich I lean it up and it runs great the rest of the night. What could be wrong?

Your engine may have varnish buildup to the point that it is worn out. The varnish buildup will cause the clearances to be too close so that immediate leaning will cause the parts to start to seize, but rich running will lubricate it enough until it warms up. When the engine warms up, it expands enough so that the parts plus varnish have OK clearances. If the engine is devarnished, it may not run well at all due to the wear from the varnishing.

I am thinking of installing an engine inverted. What do I need to know?

There are a few things to know about the nature of setting up and running any engine inverted. RC engines are small, lightweight and fairly simplistic engines. They do not have all the complex equipment available to competition aerobatic full size aircraft engines or similar machines; therefore, when asked to run in inverted mounting, sometimes they can be a bit more challenging to set up than an upright installation.

First, realize that your engine may be full of fuel PRIOR to starting, risking hydrolock which can do severe damage to your engine, especially if the aircraft has been stood on its nose or even just nose low during transportation. Always flip the prop over to check the compression prior to using a starter. If it seems harder than normal, remove the glowplug and flip through several times or spin the engine with an electric starter to clear it and avoid the possibility of hydrolock.

Next, ALWAYS follow your manufacturer's instructions on engine break-in. In almost every case, the engine should be broken in on a test stand where it can be properly watched, cared for, fueled, drained, and adjusted easily and safely. If your manufacturer recommends in flight break-in, just be aware that it will be soft on power until the break-in period is completed and always be prepared for a dead stick landing during those break-in flights.

Then, once it is broken in, it can be installed. Please note that it is best to try to locate your engine so that the needle valve is in line with the centerline of the fuel tank if possible.

In some cases tuning in the inverted installation is a little more challenging due to the tank/carb relationship combined with the inverted mounting. If this is the case, tuning with the aircraft inverted/engine upright will help get the engine running flawlessly, then it can be run inverted.

Finally, some engines, especially inexpensive bushinged budget engines like the LA, will not like to start in an inverted position, again due to carb/tank positioning and fuel flow. In those case, you may need to start the aircraft inverted and turn upright to fly when running.

Can I use your aircraft/heli engine in a ground vehicle? If so, where can I purchase parts to allow me to do so?

We cannot recommend or support this, as engines for car use and boat use are designed very differently and have very different cooling supplies than an aircraft or heli engine.

I am interested in using a 3-or 4-bladed prop for a more scale appearance. How do I decide what size prop to purchase?

Please be aware that 3-bladed props are less efficient than a 2-bladed prop, so you are going to lose some performance. Additionally, 4-bladed are less efficient than 3. If your model is already marginal on power on a 2-blade, we strongly recommend against a 3-blade prop.

If, however, you have plenty of power and are willing to give up some performance for scale look and sound, then a 3-bladed prop is for you. You will want to start with a prop with either 1" less diameter or 1" less pitch than your 2-blade prop as a rule of thumb. For example, if your engine happily turns a 13x6, try a 12x6 or 13x5 to start with. Then adjust from there as needed.

To go to a 4-bladed prop, decrease an additional inch in either dimension. If your normal prop choice is, for example, a 11x6, you would begin with a 10x5 and work from there to find a 4-bladed prop that best fits your circumstances.

How do I install my FS-70 or other 4-stroke engine, which has a choke on the back, into a short nosed, cowled aircraft?

The choke on the FS-70 is not needed in many installations, particularly in cowl mountings where access to the choke would be restricted anyway. Feel free to remove the choke from the engine to ease these installations where you could not easily access the choke anyway.

When should I use a 2-stroke engine vs a 4-stroke?

A 4-stroke gives you more torque, more power off the line, better vertical performance, and slower more scale flight speed because it turns larger diameter, lower pitch props. A 2-stroke is generally lighter and more powerful for the same displacement (not always) and goes faster, turning higher pitch lower diameter props.

Can you give me radio/car/driving/set up tips to run my X car under XX conditions?

Unfortunately, no. We do not have this type of information available as it will vary drastically based upon the model and condition of your car, your track conditions, driving style, fuels used, etc.

I have an older vehicle with an O.S. 12CZ installed. Can I replace this with a 12CV or 15CV?

Yes. The 12 and 15 CV have the same mounting dimensions as the 12CZ and are a direct replacement.

Can you explain to me how a glow engine works? Is it just like a diesel truck engine?

Glow engines are a hybrid between diesel and gasoline engines in regards to their mode of operation. In a glow engine, the catalytic action of the platinum glow plug coil is what ignites the fuel-air charge rather than a spark or the heat due to compression of the mixture in the chamber. As a consequence, the compression ratio used tends to be higher than in a gasoline engine but lower than a diesel engine.

What is a 'pusher' prop or 'pusher' engine? What advantages are there to a pusher engine?

In a pusher installation the engine/prop are mounted on the back of the fuselage or the wing. This keeps the wake of the propeller unobstructed by the fuselage or other parts of the aeroplane - and is the primary advantage of the pusher configuration. A pusher propeller is twisted in the proper direction for airflow in a pusher installation.

I cannot get my engine far enough forward on the mount to reach the measurement called for in my plan's instructions. (For example, 5-3/4" from the firewall to the back of the spinner.) What can I do?

Some engines have very short case lengths and so cannot meet the measurements given. Simply use washers or plywood spacers to shim the motor mount away from the firewall until you can mount the engine properly to the mount and match the desired measurement.

What is this extra nipple on the bottom of my 4-stroke for?

All four-stroke single cylinder R/C engines have a crankcase breather to allow the lower end of the engine to 'breathe'. You may put a fuel line on this to vent the excess fuel/oil out the bottom of your aircraft, but DO NOT block this line.

How do I use after run oil?

We recommend application through the glow plug hole or through the air inlet. When O.S. states to not put after-run oil into the carb, they are referring to the fuel inlet. If you introduce the oil into the air inlet, you will have no problems.

When you use after-run oil, 2-5 drops are next to useless. You'll need to literally flood the engine with oil, so much so that the next time you start the engine, it will be difficult. We use at least a 1/2 teaspoon of oil, and sometimes more. A 3 oz. bottle of oil lasts about a dozen flying sessions.

If you are going to store your model and are worried about it dripping out, you might try a shower cap over the engine and also cotton plugs in the exhaust to avoid dripping. We also recommend a cotton cloth in the carb to minimize fuel leakage.

I want to use a 60-sized pipe on my 140 RX (it fits in my pattern ship better). How can I do this?

There are two ways to go to a smaller tuned pipe without damaging the 1.40 RX. The first is to purchase the FI engine, which will tune itself to all ranges at all times and provide you truly the finest performance in the industry.

The second is to use an in-flight needle setup with the 1.40 RX. A smaller tuned pipe, such as the Hanno 60's pipe OSMG2943, leans the engine out on the high end dramatically, causing you to have to set the high-speed needle very rich. As a result, the mid range is blubbering rich to the point of being essentially unusable, especially for pattern flight. However, setting up a throttle-to-needle curve and using OSMG6460 in-flight needle for the 1.40, results in excellent engine performance at all RPMs. (The Futaba 8U Super and 9Z World family radios both offer in-flight needle programming (called Throttle-to-Needle) to aid in this type of setup.)

How should I set the airbleed and throttle stop screws on my glow engine?

Barrel stop screws are typically factory set between 1/16 to 1/8" open, which is about 1 mm. The air bleed screw is set so that the screw covers up half of the hole located on the side of the carb body.

My engine is overheating or running hotter than I would like. How can I get it better cooling?

Most people make the mistake of thinking more is better when it comes to the air INLET at the front of the cowl. This is a common error and while it seems logical the reverse is actually true.

To properly cool your engine you need more OUTLET not more inlet. You want at least 2:1, preferably 3:1 air out to air in otherwise it makes a 'dam' and the air can't come into the cowl because it has no where to go OUT of the cowl. If your engine is not cooling properly, try blocking off the other air inlet or opening the belly of the cowl further to better cool your engine. See the instruction manual for the Top Flite Corsair (pages 35, 40) for an example of making a baffle to properly cool your engine.

What's the difference between a marine engine and an aircraft engine?

There are several differences between marine engines and airplane engines. First, marine engines are usually water-cooled (special head). Second, marine engines require a special "flywheel" and "coupler" to connect and start the engine. Third, due to the high performance nature, most boat motors are designed for this application and usually have ball-bearings.

I have an old airplane engine that is in good shape and runs. Can I put the engine into a boat?

Like most modifications, this CAN be done, but is difficult, complex, and not recommended. There are a LOT of things to take into consideration before you attempt this. Listed below are only a few problems you might encounter:

  1. Is there an engine mount for the engine?
  2. How to start the engine?
  3. Will the engine be cool enough while running?
  4. Is there a water-cooled head available for the engine?
  5. How to connect the engine to the driveshaft?
  6. Will there be a weight difference between the marine engine and the airplane engine? Will it affect the boat's CG?
  7. Do I have the tools to do any modifications if needed?
  8. How will I run the exhaust if the airplane engine is side exhaust (most are) and the boat requires rear exhaust (most do)?

The questions above are just a guide to give you something to think about before attempting to place an airplane engine into a boat. You might also want to consider going to the following web site ( and posting a note on the bulletin board and ask other modelers what he/she had encountered in making this change. Please note that this information in no way condones or supports the idea of this type of conversion, but rather is intended to give you some basic ideas of the problems involved. We cannot assist you in making such a conversion in any manner, and doing so will void your engine's warranty, and probably your boat's warranty, too.

How are gas boat engines started?

There are two ways to start marine engines—one is a starting belt; the other is a pull start system located on the engine.

What the difference between an outboard engine and an inboard engine?

The main difference is the placement of the engine. The outboard is mounted directly on the transom; the inboard is mounted inside the hull.

Important Engine Safety Precautions

No list is all inclusive, but here are some basics to watch for:

NOTE: Failure to follow these safety precautions may result in severe injury to yourself and others.

How long can I store unopened fuel? how about opened fuel?

  1. Unopened fuel which is stored out of direct sunlight is literally good for years. We have opened 10-year old containers and had the fuel be fully potent and usable. However, in general it is a good idea to use the fuel off your shelves annually, especially if exposed to sunlight.
  2. Once fuel has been opened, it has been exposed to air which includes moisture. Both water and sunlight are your fuel's enemy, so the more frequently or the longer it is exposed the more rapidly it will deteriorate. In general we recommend customers use all open containers of fuel in a single modeling season then properly discard any remaining fuel.

How Do I Break In My R/C Car Engine?

The break-in process of model engines, especially R/C car engines has been affected by a wide variety of myths and misconceptions. The main one is that the engine must be run at idle for several tanks' worth of fuel before the model is run. There is nothing farther from the truth! In fact, running the engine at idle for several tanks' worth of fuel will not only insure that your engine won't break in properly, but it could also reduce its overall life!

The purpose of the break-in process is to run the engine so that its moving parts will polish each other to a perfect fit. This requires that the engine be run at a variety of throttle settings so that the different parts will be affected by changing pressures and temperatures.

Typically, we start out with a moderately rich needle setting and start driving the car right away. We accelerate to a medium speed and then coast. Turn around and come back the same way. If the high-speed needle is so rich that the engine tends to hesitate a lot when throttle is applied, we'll lean it a bit to eliminate most of the hesitation.

After a few minutes of this, we start accelerating to a high speed and then coast. Turn around and come back the same way. We do this for the remainder of the first tank.

During the next two to three tanks' worth of running, we gradually lean the high-speed needle valve until the engine will run at full throttle at a setting just rich of peak RPM. One way to tell that the engine is on the rich side of peak RPM is to accelerate to full throttle and carefully listen to the engine. It should accelerate up and hold RPM, and not sag back down.

With the CV-series of engines, we'll set the high-speed needle about 2-1/4 turns open and lean from there. When fully leaned, the needle will be between 1-3/4 to 2 turns out from closed. The engine may still run with a leaner setting on the needle, but that setting may be lean enough to allow the engine to gradually overheat and quit. An overheat is a bad thing, and it will cause the piston/cylinder fit to go bad very quickly. "Thermal overload" is just another term for overheating.

If the engine is set too lean, the engine's internal parts can be damaged because they'll be starved of lubrication. Remember, the engine's lubrication is contained in the fuel, and a too-lean setting means too little fuel, which translates into too little lubrication.

Finally, O.S. states in their engine instructions that you should use a fuel that has an oil content of no less than 18% by volume. Many so-called "R/C Car" fuels contain oil in the 12%-14% range. While these may work quite well when the engine's set correctly, low-oil fuels do not leave much margin of error if the engine gets a lean run. Nitro content can be as high as 20% by volume without worry about special engine tuning or setup.

My large two-stroke engine makes a "knocking" sound at medium to low throttle settings.

Large-bore engines, usually larger than .91 or so, tend to have a "knocking" or "clattering" sound when they are operated at less than full throttle. Many times, it sounds as if there is some kind of metal-to-metal contact going on inside the engine. Some modelers have suggested that one end of the connecting rod may have had too much clearance, which would cause the noise.

This has been extensively-investigated, and we've not been able to find any evidence of metal-to-metal contact that could cause such a noise. In fact, we've heard this sound from a wide variety of large engine sizes, and across several different brands. Engines that make the noise have been test run for considerable amounts of time and then disassembled so that all of the parts could be carefully examined.

No evidence of mechanical problems have ever been found. The noise comes from the exhaust system of the engine. Because model engines tend to run less smoothly at moderate throttle settings, the combustion process causes a resonance in the exhaust system that causes the clattering sound. It's not mechanical, just a result of the rapid expulsion of the exhaust gases when the engine's at less than full throttle.

It's nothing to be concerned about if the engine's running well.

My LA Series O.S. Max engine makes a rattling noise when it's running at less than full throttle.

Basically, the rattling noise is normal. It can't be eliminated, and your engine will not become damaged by it. Just make sure you're using a fuel with sufficient oil content. O.S. states that a fuel with no less than 18% oil content by volume should be used in the LA series engines.

The LA series of O.S. Max engines have their crankshafts supported by bushings and not ball bearings. As a result, the crankshaft must be able to move fore and aft slightly when a propeller is installed. With no propeller, you can push the crankshaft back far enough that it will contact the rear cover of the engine. It won't hit when a prop is installed.

Because the crankshaft "floats" in the bushing, it will move back and forth when the engine's running. At full throttle, though, the thrust of the propeller will keep the crankshaft pulled fully forward, and it won't move. When the power is reduced, the crankshaft will start to move fore and aft. This causes the drive washer and the crankshaft counterweight (inside the engine) to tap the ends of the bushing at the front and inside the crankcase. The rattling noise is the result.

All bushing engines will make this noise to one extent or another. The noise can be reduced by using a fuel that contains high levels of castor oil. A high oil content will act as a cushion and reduce the noise. Castor oil is desired because it is thicker than synthetic oils and makes a better cushion.

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