running in oil for 4stroke

Glow/Nitro and gas engines, propellers, fuel and other stuff associated with making lots of noise and thrust.

running in oil for 4stroke

Postby AE25 » Sat Oct 16, 2010 7:20 am

would like to get a few opinions on this. from my research it's obvious there's no clear answer :?
Engine in question = asp61fs.
The one page instruction that comes with it says 'any good commercial glow fuels (preferable with 10% nitro) should be suitable'. well thats easy. ;) but no particular mention of using this for running in.
The downloadable instructions for the Magnum XL61RFS (same engine but much more detailed instructions) says, use power master 10% 2stroke blend. then later says -"use a fuel that contains no more than 10% nitromethane and no less than 20% castor oil lubricant. synthetic lubricant fuels should not be used during the break in prodeure."

A wee visit to a couple local hobby stores for opinions on break in, and both said 'we use and recommend fully synthetic oil/fuel'. hmmm. they didn't sell castor by itself and came across as saying that using castor is 'old hat'. contrasting!

I know you don't use full synthetic oil to run in a real car engine. but then, the honed surface finish is much more coarse with different loads involved where a low grade mineral oil allows the rings to bed in whereas automobile synthetics are so good that bores can be glazed and never actually wear in. But are we adapting the same theory on a model engine??
Castor is an excellent naturally occuring lubricant that contains esters. It is the esters that has been synthetized in synthetics. the main advantage of caster is it's ability to lubricate at higher temperatures due to it's thermally unstable properties where the oils polymerize to create heavier oils and continue to lubricate if an engine is leaned out and overheated. compared to synthetics which has a lower flash point and will burn off in a hot engine. The downside of caster is it has more impurities, it can create carbon build up and over time gets gummed up with varnish. (polymerised castor oil).

but in terms of 'lubricity', is there really any noticeable difference between them that it would affect the run-in of an engine?
Is there any noticeable disadvantage (not theoretical) to running in a model engine on synthetic oil? Or is it the impurities or other properties in castor that help an engine break in?
I ask this because i can't just go to my local hobby shop and buy 80/20 meth castor fuel. :evil:
-Mark
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Re: running in oil for 4stroke

Postby RCModelReviews » Sat Oct 16, 2010 7:58 pm

General rule of thumb... run your engine in on the same fuel you intend to fly it with.

If an engine is so poorly made that it needs masses of castor oil during the break-in process then you might be better off looking for a better engine in the first place.

The reality is that during the break-in process you actually *want* wear to occur.

The whole reason for running-in an engine is to allow the various moving parts to "wear to fit" by burnishing the still slightly rough surfaces created by machining and allowing the fit between parts to establish an equilibrium.

If you have 100% perfect lubrication then no metal to metal contact will occur within the engine and no wear will take place -- hence, your engine will never be run-in.

For a 4-stroke, just use a good quality fuel and follow the Saito method of running-in.

1. Run for 5-10 minutes with the engine filthy-rich. So rich in fact that you have to keep the glow heat-on or it will stop, the RPMs should be around 5,000 -- set the throttle to suit but you should need to have it quite a way-open because the really rich mixture will also limit RPMs. Raw fuel and oil should be spraying out the exhaust and the engine should feel almost cold to the touch.

This stage simply ensures that any microscopic particles left from the machining processes are flushed out of the motor and that any really "high spots" are cleared -- with the resulting particles of metal flushed out of the motor before they can do any harm.

2. run the engine for another 5-10 minutes with the needle a little leaner -- so that it "just keeps running" with the glow-heat removed. Raise the RPMs to about 7,000-8,000rpms for these runs. It's better to give the engine several short runs of 2-3 minutes each rather than a single long run. This time the engine should feel warm but not hot.

3. lean the engine out a little further and this time run the engine for a total of about 10 minutes, varying the throttle between a fast idle and full throttle. It should make no more than 8,500 RPMs and still be blowing copious amounts of smoke because it's still "rich".

4. Now lean the engine out so that it reaches peak RPMs and then richen it up until it's about 400rpms slower. Run it like this with 20 seconds idling, 20 seconds full-throttle for a total of about 5-10 minutes.

5. Bolt it to your plane -- go fly. Just make sure that for the first hour or two of flying, you avoid long periods of full-throttle. Best to give it full throttle for 20-30 seconds so as to climb to a reasonable height, then putter around on low throttle for 30-45 seconds -- or until you get low again.

To summarize...

In the very early stages of the break-in process you want the engine very rich so as to flush out the particles that may be knocked loose as the moving parts "wear to fit".

Later on you want to keep the engine rich (so there's plenty of lube and some "flushing" action) while varying the throttle/RPMs so as to "heat-cycle" the engine. Because the parts expand as they heat and contract as they cool, you need to force the engine to go through a heat/cool cycle a number of times -- so that the clearances are adequate for idle and full-power settings.

Then, once the engine is freeing up, you want to focus mainly on the heat-cycling aspect but avoid prolonged hard-running at full throttle.

Of course this is the "ideal" way to break in a 4-stroke (or 2-stroke *RINGED*) engine -- but most of us really don't bother.

You can go through quite a bit of expensive fuel this way (more than the cost of a "cheap" Chinese engine) so what I tend to do is just give the engine one slobbering-rich run then tune it up so that it's rich but running reliable -- and then go fly -- just making sure I don't go hard-out for extended periods during the first few tanks of fuel.

I've never wrecked one yet :-)

BTW: this is *NOT* the way to run in an ABC/ABN engine though. Running those "slobberingly rich" will do them no good at all.
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Re: running in oil for 4stroke

Postby AE25 » Sun Oct 17, 2010 3:48 am

thanks heaps for such a detailed reply!!! im sure this will help others too.

good thing i didn't follow the ASP instruction supplied with the engine. it said use a setting of 1.5 turns of high speed needle to initially start the engine. it quotes this more than once.
The engine came set at 2.5 turns which after a minute running at 1/4 throttle would reach 8500 on a brief full throttle blip. ran it 5mins at half throttle and richened up by another 1/4 turn as it was smokey but not sputtering or running excessively rich. let it cool down 10mins, then ran it another 3mins (tank ran dry) at full throttle dropping back to idle occasionally.
-Mark
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