yakfish

My Feedback: (27)

Ijust got home from the hobby shop. Ipaid 169.99 for the motor. Icould have saved a few bucks ordering it online but Ilike to support the local shops and Ihate waiting for shipping!
Ihad a question about break-in. should I follow the manuals instruction or is there some other method I should use instead. Ihave broken in a few motors in the past but Iwant to this one right. thanks

Doctp1885

Heya and gratz. I just bought a lrp 28 and broke it in.

from my experience with mine, HSN and LSN was set rich so I had to lean it. I also followed the manual. The LRP is a simple break in process. My only concern was that these LRP stayed cool. the idle process, I had to wrap aluminum foil and give it 1/4 throttle every couple min just to get the temp up to 190-200 range.

HerrSavage

What he said..

Alu foil around the head, maybe even an old sock around that, get the temps to 200-220, shut it down, let the piston cool completely at the bottom-most position, then repeat - like 10-15 times..  Should take 4 or 5 tanks..  Don't give full gas til after like ten tanks.

That's what I do..

Important is to get the temps up and let it cool completely with the piston at the bottom.  And repeat... 

Midget

Also, I wouldn't even Bother trying to start it, unless you preheat the head with a hairdryer, or some head source...

yakfish

My Feedback: (27)

Well I finished the 1st tank it started on the 3rd pull each time. for the first half of the tank I let it just idle with the wheels off the ground for the second half of the tank I drove on the road and though my front yard . it never got more than 1/2 throttle and for only a couple little blips. I kept it around 1/4 throttle most of the time. it nver got above 210-220 degrees when it did Ishut it off and put the piston at BDC. I have to leave for work tonight so I'll have to finish the break in tomarrow. I have never had a motor with so much pinch even with the plug out it is extremely difficult to pull. I might have to find a roto start for it.

BudBud

It will free up shortly, about the time you start running it wide open. I would encourage you to get the heat a little higher as you go along and listen for the engine to start working. My last LRP, a 30, had very close piston to sleeve tolerances and I did and extended break in on it. What we are actually doing is wearing the piston to match the sleeve. That aluminum piston is not nearly as tough as that chrome lined sleeve. As your engine gets progressively warmer, it will be a tighter fit in the sleeve. I would rather make a couple of short trip up in the temperature range than just drop the hammer on it. Glen

ShoestringRacer

I hate to be the bearer of bad news but that is incorrect and totally backwards. As the engine heats up to operating temperatures the piston/sleeve fit or "pinch" decreases. The pinch does not increase with temperature/heat. This is because the brass sleeve expands more than the piston so that when it is at operating temperature the pinch is less than at ambient temperatures. The upper portion of the sleeve expands to fit the piston; the piston does not expand to fit the sleeve.

If you think the piston sleeve fit gets tighter as the engine warms up, then the pinch would be even more than is felt at room temperature when turning the engine over by hand. And anyone that has turned over an ABC type ringless engine cold knows you can practically feel the piston grinding into the top of the sleeve, especially on an unbroken-in engine. I can assure you beyond the faintest shadow of a doubt the pinch decreases as the engine heats up. If the pinch were to increase with heat there is no way the piston could last any practical amount of time and turn over the rpm that it does with that amount of friction/drag.

The high silicon content of the ringless aluminum piston allows the piston to expand at a slightly slower rate and to a lesser extent than the plated brass sleeve surrounding it. In other words, the sleeve expands ever so slightly more than the piston. (of course non-ABC/ABN/AAC engines are different as are ringed 2 stroke or 4 stroke nitro engines)

The whole design and operating principle of the ringless ABC type nitro engine is such that the upper portion of the sleeve expands at operating temperatures to form the tight yet free running, blow-by free combustion chamber. The pinch is almost, but not totally, gone at operating temperatures. The pinch at operating temperature is much less than felt when turning the engine over cold. This is why there is a much tighter pinch felt when turning the engine over cold. (doing this should be avoided especially with an engine that hasn’t been broken-in). When an engine is cold the piston experiences the most wear - that is because the upper portion of the sleeve hasn’t expanded to its optimal design operating size. And these are very, very, small tolerances which is why preserving the piston/sleeve fit is so important and critical during break-in and general operation.

These ABC type engines are also called "tapered bore" engines because the cylinder sleeve has a slightly smaller diameter or bore at the top of the cylinder sleeve than at the bottom. The reason for this is because the upper part of the sleeve, which is above the transfer and exhaust ports, operates at a much higher temperature than at the lower part of the cylinder/sleeve. (the piston/sleeve experiences unequal expansion and distortion due to cool air/fuel entering the cylinder in a different place than the hot exhaust gasses exiting it) The very top of the cylinder/sleeve experiences much higher temperatures from combustion. The top of the sleeve/cylinder therefore has a slightly smaller bore than at the bottom to compensate for this expansion when the engine reaches operating temperatures. This is necessary because the piston does not have a compression ring to seal the combustionchamber, as most other 2 or 4 stroke gasoline/automotive type engines have. (4 stroke nitro engines like my Saito's have a compression ring as well as some 2 stroke nitros such as the O.S. .91FX)

The only thing a tapered bore type ringless ABC type nitro engine has going for it to make a tight combustion chamber seal is the precise piston/sleeve taper. When that goes bad, as happens in a worn out piston/sleeve, the piston/sleeve fit becomes excessive which allows combustion gas blowby into the case. Combustion blowby results in decreased power, poor throttle transition and difficulty idling and starting..if you can even keep it running at all. An engine with a worn out piston sleeve may be able to start up but as soon as it warms up it will have trouble to keep running well - that is because the already worn out sleeve has expanded allowing blowby - when it was cold the seal was tighter. See how that makes sense?? Also, if an engine runs extremely hot you can notice a decrease in power - that is because the sleeve is too hot which has caused it to expand too much which causes blowby.

Anytime a piston seizes in the bore of an ABC type ringless engine it is because the upper portion of the sleeve has not expanded enough, not because the piston has expanded into the bore.

I mentioned this though to a lesser extent in this thread:

http://www.rcuniverse.com/forum/m_87...tm.htm#8764466

EDIT: link and text got all buggered up..too many browsers open

BudBud

I guess I stand corrected, so you are saying the aluminum piston beats the chrome lined brass sleeve, wearing it out? That seems backwards to me.

ShoestringRacer

EDIT: response in following posts

supertib

Pistons wear out, sleeves do not

Pistons also expand much more during operation then the sleeve does..Ihave seen it dowzens of times on the break in bench... the engine will be at its tightest right after operation, and as it cools it will loosen up.......reason being is the piston gets much much hotter during operation then the sleeve does....

yakfish

My Feedback: (27)

I just came in from the 2nd break in tank. the truck seems to be running great. I can't seem to get it mucj above 200 degrees going only half throttle or less. I was running with the body off so when I saw the temps weren't getting above 170 I put the body on to help restrict the flow of air over the engine and then they went up to about 200. I may try to lean it out just a tad on the next tank to try and get the temps up a bit more.

I bought this savage used and I haven't been able to run it before I got the new LRP so I am able to do some tuning to the truck itself like break linkage and steering. I noticed on the last tank that my slipper is a bit on the loose side. How tight are you supposed to set it? I would assume that you would go all the way tight and then back it off a 1/4 turn or something like that. I didn't get a manual with the truck or I would have checked there. For now I have just tighend it down as much as I can since I will be going easy on the truck through the break in procces and I'm not conserned about chewing up any gears.

One thing I'm really liking aboput this motor is that as long as it it properly primed I can start it with one pull! Ihave never been able to do that with a new engine before. but the pinch is going to kill me! Idon't like how low the pullstart handle goes down between the fuel tank and the rear shock tower. Imight try to put an extra peice in the string to let it sit up higher so it is easier to get ahold of.

yakfish

My Feedback: (27)

I'm still waiting for it to cool and I know how much every body likes pictures!

BudBud

Eventually you will get it running warm, when you do, if it is hard to start hot, it is because the carburetor is not unsulated and boils the fuel back out of the line. Just bring a short section of fuel line with you to prime the carburetor again on hot starts. They are a very nice engine. Glen

yakfish

My Feedback: (27)

I'm now on my 4th tank. I was just abot to start it when the knot on the pullstart handle let go an d went inside the pullstarter![:@] so I in the middle of the tedious process of rewinding the recoil spring and trying to put the pull starter back together. this may take while[:@]

yakfish

My Feedback: (27)

Got it put back together!

BudBud

You are a better man than I am.... I found that the frustration of trying to rewind a Picco starter is not worth the price of admission. I have not broken any LRP starters yet.

stussman

Buy yorself extra pullstarts. You will need them. It will really help if you heat the engine before pulling. A hairdryer works ok.

yakfish

My Feedback: (27)

Yeah my wife freaked out when she found me using her hair dryer on my RC's!!I have a rotostart on its way. bought it on ebay last night.

ShoestringRacer

Wellthat would be backwards.......if I had said that. But nowhere did I say the comparatively soft silicon rich (hyper-eutectic) aluminum piston is harder than the chrome (or nickel) plated brass sleeve thus causing wear to the sleeve exclusively. But that shouldn’t be interpreted to mean the piston is the only thing that wears either. The sleeve can lose its pinch even when you can not see visible wear (like something obvious such as a sleeve’s peeled plating as happened to many O.S. AX airplane engines a few years ago, or scoring from dirt ingestion..although the softer piston will show signs of scoring more than the harder sleeve). A worn sleeve along with a worn piston will cause combustion blowby as explained in my earlier post which necessitates replacement of both the piston and sleeve. I’ve seen many worn sleeves and even morepictures of them online in the airplane forums. The pinch zone or "interference fit", which is the area where the piston touches the cylinder/sleeve at top-dead-center, is very, very small zone and once that is compromised...well, I've made my point. Maybe I gave the impression the sleeve is the only thing that wears out because in one of my last sentences from my previous post I wrote, "that is because the already worn out sleeve has expanded allowing blowby " where I forgot to put "piston" in front of "sleeve", because when I amreferring to them I usually mean it as two items that each wear.

If the chrome sleeve does not change and lose its pinch and "wear" out then why do manufacturers sell piston/sleeve rebuild kits with both items? Shouldn’t they sell just the piston? When you rebuild a worn out engine, do you only replace the piston because the sleeve taper is as good as when it was new?

As for the hyper-eutectic aluminum piston, that is one of the first things that gets "broken-in" in during break-in. It doesn’t take nearly as long the time as as people waste time and fuel imagining they are accomplishing it. The soft piston is smoothed and matched to the fit of the sleeve sooner than the rest of the engine is broken-in, meaning heat cycled (which stress relieves the parts) and operating as a single and efficient machine from an assembly of parts. And that is true even if it only has barely afewmoving parts, depending on if one counts the two bearings or not.

ShoestringRacer

If the piston expands "much more" during operation than the sleeve, that would mean the pinch/compression that is felt when cold is even more at running temps. That is not the case. The pinch is almost but not totally gone at operating temps, as I previously mentioned. The tapered bore is specificallysized to allow for the differing expansion at the top of the cylinder sleeve, where it runs hottest above the ports,so that there is a tightyet free running, blow-by free, combustion chamber. And "free running" doesn't mean more pinch/resistance than is felt when cold.

How could an engine, and particularly the piston, run the high RPM that it does with even more resistance than is felt when the engine is cold? With that much friction is wouldn't last barely a couple tanks, likely much, much less.

O.S. Engines has some info online in their FAQ confirming that the sleeve expands to fit the piston, not the other way around.

If the piston expands to fit the sleeve,then O.S. Engines' engineers, designers,and manufacturing personnel don't have a clue what they are doing.

Taken from their FAQ page linked below:

"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 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."

They also have good info on "air leaks":

http://www.osengines.com/faq/faq-q687.html

http://www.osengines.com/faq/product-faq.html#q1

http://www.osengines.com/faq/product-faq.html#q590

supertib

I sell and break in dozens of engines, Iuse a break in bench with excleent results.... no matter what you say to me you will never convince me of anything but what I have experienced first hand...these engines are their tightest right after operation, as they cool down the pinch relaxes.... This is a fact based off first hand operation of dozens of engines on the break in stand.......I don't know why or how, its just what it is ...... maybe you can explain , but without question they are tighter imediately after shutdown then they are after they cool.....

BANKRUPTER

funny mine are loosest after shut down and tight cold .. tib are you just thinking backwards ? Really read what you just wrote.

ShangXin of savage central gets credit for this :
http://i83.photobucket.com/albums/j3...flowcharts.jpgwarning has swares

supertib

Iknow exactly what I am saying..... Next time I break in an engine on the bench I will try to get it on video..... Ireally can't explain why either.... my theory is that during operation the piston runs much hotter then the sleeve does, therefore undergoes a greater amount of expansion.. The sleeve is only exposed to a small amount of the combustion heat as well it is cooled on the outside by the fuel charge in the crankcase, whereas the piston face is exposed to the full heat of the combustion with no cooling jaket of fresh intake charge...... Buy yourself a break in stand and see for yourself ..IDK what else to say

edit...anyone who has installed fordged or hypereutectic pistons in a 1:1 car will have noticed that when cold the pistons will knock around till they get heat in them, in the winter if your not careful you will knock the skirt off the piston because it is so loose in the sleeve........ Just because the block temp is 200 degrees doesn't mean the piston is operating at 200 degrees..... The piston face is the hottest spot in the entire engine, therefore it is going to expand the most..... interesting thing tho is the material the piston is made from disipitates heat extremely fast, so if your going to test pinch after shutdown it has to be imediately after shutdown, it doesn't take long for the piston to cool off and relax in the bore..........

no hesitation

Anyone here know were to get LRPparts for LRP vehicles? I really want a Shark18 but can't find a good source for parts.

BANKRUPTER

that is when I feel my pinch I kill my mill and turn over the fly wheel to BDCwith in a second of shut down every time. My mills never sit at TDC. 3 times looser then cold every time. IDK what you are talking about and a ringed piston in cast iron block / sleeve is not even close to the same Neail dont know were your going with that.