apwachholz

Hello All -

I'm working to tune up a Satio .72 purchased at auction and was/am having issues getting it to run properly. When I opened up the engine I noticed the 'classic tan' of what appears to be a castor blend run engine. My question is this:

Can you go from running an r/c airplane engine on a castor blend fuel to a completely synthetic fuel? And why or why not?

Some say you can, others say no.The reason I ask is at first I ran the engine with a castor blend (assuming it was run previously on castor)and it wouldn't keep a decent RPM and ran horrible. I then switched to a synthetic blend and it ran better but still has issues. Thanks to anyone with help.

Or, if you can point me to a location with helpful information that would be great as well. Cheers All!

jeffie8696

No reason in the world you cant switch back and forth. Synthetic and castor are fully compatible. I think you may be seeing a problem relating to the fuel or the fact your engine prefers a certain blend. Imostly run fuels with a blend but dont see any reason full synthetcs dont have a place in the world.
Ifound Morgans Cool Power to run well and was easy to set up . Iprefer SIGPyn Plus for the higher oil percentage.

blw

My Feedback: (3)

There isn't any reason you can't run it with any oil you wish. You could run a different type of oil every tankful if you wanted.

Your .72 should run about the same with same percentage nitro and castor, or synthetic, or a blend. You may be seeing a difference in jugs of fuel. Also, if the engine has been stored away for a while, it may run poorly for the first few minutes. Castor will protect your engine better than synthetics.

The .72 is a very good engine.

apwachholz

Thanks for the advice and insight on the castor fuel versus the synthetic fuel blend. I've posted elsewhere and am getting much the same answers. As for my Saito 72, I'm narrowing down the issues with the engine (I think). One of the heads/rods seemed to run hotter then the other. Way more then I was expecting - so upon cracking open the engine, as you can see, I noticed the piston next the exhaust (pardon me, I'm new to engine terminology) was way more corroded then the other. Plus, this is the one that was sticking somewhat as I was manually testing the rockers.

Either way, I'm going to re-seal, re-clean, re-assemble the engine and hope it starts to run smoother. Thanks for all the help everyone. CU in another thread.

_me

jeffie8696

Ithink what you are seeing is simple carbon buildup. When oil burns it deposits on the valves (and whatever) as a black residue. It is especially bad on the exhaust valve since the hot exhaust gasses are flowing over it during the exhaust cycle. If this valve was sticking it probably just needs a good cleaning, nothing abrasive just a good parts solvent. Iuse Dawn power dissolver from the dish detergents isle . Dont let it stay on too long, it will eat up the parts too.

TimBle

I was going to suggest to you that you should take teh engine apart and inspect the internals for the source of poor running. A blocked carb or sticky valve is not uncommon. Glad to see you took the initiative and did it yourself. Yip, its engine coking. thats from two things.

running the engine too rich.

running the engine on too much castor oil.

Castor oil is a fantastic oil, blah blah blah. Yes I hear it all the time.
It was especially fantastic in older engines that were not manufactured to the tolerances we have today. AND the repeatability in manufacturing.

Too much castor will gum up and also coke up the engine. If its a ringed engine, oh dear then too much castor can lead to residue build up between the ring and piston, causing excessive wear and eventually failure.

throw out the old ideas of Castor being the best lube, the hobbyhas moved on. A small percentage of castor is helpful, especially in ABC/ABL/ABN engines but for ringed engines, use a good synthetic oil in the fuel or buy a fuel with good synthetics in the blend.

for four stroke engines, an oil that keeps the valves clean is vitaly important to reliable long term running. I would advise to steer clear of castor oil based fuels for such engine and run only synthetics in them.

But hey what do I know

TimBle

Hi Jeffie,

the deposits are from unburned hydrocarbons. These hydrocarbons did not participate in combustion, they are simplyheavy residues left over after the combustible stuff oxidised.

think of an oil frying pan, throw in some oil and heat it up. It will start to smoke and after 30 min you will be left with a hot sticky mess in the frying pan, yet there was no fire.
In the hydrocarbon processing industry we call this "cracking" where longer chains are broken to make smaller chains but theres insufficient time to break the chains down to small enough parts to start burning.

it should be simple enough to clean the engine parts by leaving them overnight in some gasoline that the manufacturer claims cleans the engine. COncentrated forms of the detergent can be purchased in motor spares shops. I beleive companies like Wynn's, STP, and even a couple of l;arger compnaies like Chevron market these concentrated valve cleaning additives. Ihave used this type of concentrate for cleaning other metal parts and it works.

Just remeber, no smoking and no sparks anywhere near the liquids because the vapours are highly flammable. No stomach for that, try one of those diesel fuels also with some detergent additive in it. Diesel is less flammable at room temperature and has a higher flash point so safer to use.

Judt leave overnight in the fuel and remove in the morning with a wire brush

apwachholz

Lot's of thanks everyone. This has been a great amount of help.

Jeffie / TimBle -

I was thinking along the same lines as to why that specific piston was all "worked over" as it's the exhaust piston, however, TimBle, you really clarified some things. You really seem to know ur stuff.

Got a question or perhaps a conversation comment:

When I was chatting with myfiancéeabout my engine issues she mentioned it seemed odd that I would run aCastoroil fuel in an airplane engine after it's broken in. She's a pilot and mentioned that all piston aircraft engines that need to be broken in are done so with natural oil. But after the engine has been set (per a certain amount of running time determined by the manufacturer) she says they switch and stay to synthetics as they run cleaner and prolong your engine life.

Needless to say I was very ponderous after that and wondered, why aren't we doing the same thing? Granted, I'm not sure the reason for usingstrictlya Castor blend in the past but, with todayssynthetics, why would you risk "clogging" your engine when alternative fuels perform so much better? Again, I'm not knocking Castor, just looking for more insight to it's past use and current use.

let the conversation go on....

TimBle

WE could in fact switch to pure synthetic oil fuel after breakin, if you have a ringed engine or ABC engine.

The ryder to that is  ABC/ALL/ABN engines are a little different though because of the taper bore. Once it cools there is a lot of clearance between piston and liner and any oil drains to the bottom and out. Castor has the wonderful characteristic of polymerising at high temp so it leaves a light varnish on the piston crown. This protects the piston on start up. Hence its a good idea to always have a little castor oil in the fuel for a ABC type engine. I won't do the whole XXX/XXX thing again.
That should not stop you wanting to use a synthetic though because fuel with a synthetic oil will have additives in the oil that will coat the metal parts to prevent that metal to metal rub when we start up the engine after a week or so. I still use a fuel with castor in it but heck I don;t need 20% castor, 2-4% is sufficient by volume to provide that coating action. You will find that the Castor oil creates what we call viscous drag which slows the piston down. The hotter the engines the more the drag. think about pulling knife through butter vs peanut butter.  
You'll get higher performance with a synthetic lube in the fuel, cooling will not be affected and wear will remain minimal. Model Technics have a fuel thats 10% synthetic oil, and thats the total volume of lubricant in the fuel. So its not sacriligious to run low oil volumes and have no Castor Oil in the fuel. You just need to know how to tune an engine so it does not lean out too much. HIgh oil volumes just make it simpler to get teh engine in the air while still have a big safety margin.

For ringed engines its an entirely different story. Some castor is good for break in but really not necessary. Pistons with rings can compensate for expansion since the ring is split and has a spring action. So across a wider temperature range the fit is almost constant. Viscous drag here is bad news because the ring can break or with castor, you get the residue build up on the ring and behind it which prevents it from springing back into its seat which means as the engine cools it pushes harder against the cylinder liner.Now you start up and the ring breaks. Some think this is good news because the piston is saved but they forget that the metal parts have been thrown up into the engine and can have liely scored teh piston and liner. One engine on the re build bench...


So to answer your question, yes you can use a lower quality oil in the fuel for run in but that means a special batch and if you don't know how the oil will behave you could end up with a seized engine. Running in Oils are highly technical products, not just simple mineral oils. They have a balanced additive package that is designed to work for break in (spiked high with dispersant additives and low on anti wear, have relatively normal viscosity modifier and are high in total base number (ability to neutralise acids))  [this is used in the automotive industry]

We don't have those specialised oils for our hobby engines so its probably a good idea to run a gallon of fuel with a bit of castor through any engine and then switch.For ringed and four strokes, the lower the castor the better because of the fouling nature of castor.
I think for four strokes there are fuels with 2% castor, use those for running in and then switch to synthetic. SOme engines have their own special requirements, follow those since "special = expensive"

blw

My Feedback: (3)

One thing to remember is that no synthetic oil will protect at the higher temps castor will. You get better protection against those lean runs. There is the rust protection that you don't get with synthetics. Also, there is enough evidence that castor protects better than most synthetics in hard metal to metal contact. I always use Omega with several ounces of castor added.

You are using a Saito .72. These engines run great when tuned right. Tuning is everything with a Saito.

apwachholz

TimBle - May I ask what your profession is? You seem to be very knowledgeable about this topic. Plus, it's great to get some technical / engineering logic behind your reasoning. Which is really helping to clear up the "Castor or Synthetic" discussions I've had.

TimBle

my profession, mechanical engineering.My career, petrochemicals, lubricant and fuels product development.

TimBle

to answer part II about the polarised views on castor vs synthetic. Synthetic oils have a bad rep and unjustly so. A lot of the disadvantages on synthetics have been eroded by process engineering and additive technology. Does synthetics cause corrosion? Well do motor vehicle engines seize due to rust? No, and they produce some nasty chemicals that are only converted downstream of the engine. So why the bad rep? Early synthetics were not good. They were prone to creating sludge due to excessive polymerisation, they promoted corrosion. But this was 30yrs ago. Technolgy has moved on. Todays esterified synthetics are much better lubricants than the glycol alpha olefin lubes were

apwachholz

LOL! Awesome... you are the perfect person to be talking to about this subject.

jeffie8696

In automotive circles it is common to break in an engine with a non synthetic oil. The current thinking is that a synthetic oil will not allow the parts to break in properly since it is such a superior lubricant.
Ibelieve the piston rings are the biggest problem, they need to set themselves to the shape of the cylinder walls and snythetic oils are just too good at getting in the way.
As Imentioned before Ithink synthetic fuels are useful, so is castor.
Ihave had a lean run despite my correct needle settings. I had a bad fuel tubing on my muffler tap and the engine would go lean after a long vertical , the engine seems to have suffered no damage and Iwas using a blended fuel at the time. Would it have fared as well on a full synthetic? there is no way to know but Iwould guess not.

jeffie8696

Tim thank you for the clarification. Yes, unburned hydrocarbons from the incomplete combustion. This is common in the diesel engine field, ever see the black smoke coming from a diesel exhaust? Bad stuff, means the driver is throwing away money, the black smoke is fuel that didnt burn and provide power, normally means a very poor tune up or hack job of someone trying to hot rod the engine.
The original turbochargers of old were marketed to diesel trucks as "anti smoke kits". They provide the extra oxygen to the fuel to burn completely thus providing more power and less pollutants.

Augie11

I still like to have 2-3% castor in my fuel as we do a lot of float flying and have never seen a corrosion problem. And I keep the total oil content at about 19%. Had some bad luck with synthetics many years ago. I'm sure they have improved but why change a winning system? Perhaps if fuel manufacturers would list the quantity and type of synthetic on their labels I'd have more confidence.

jeffie8696

SIG, their Champion is 20% lube, 50/50 castor/Klotz mixed by volume not percentage of weight, says so right on the bottle. . Most around here swear by it.

downunder

The difference is that our model engines don't store their oil in a sump so they're not using the same oil over and over again. Sumped engines need all the additive packages to help keep the oil in as good condition as possible. What applies to full size engines has no relevance to our engines, all we need is an oil that remains a lubricant at the temperatures involved and has the ability to handle the loads placed on it in areas like the rod bushings and between the piston and liner. Both synthetics and castor have their good and bad points but a blend of both can bring out both of their good points in what's called a synergy. [link=http://www.go-cl.se/castor.html]Here's[/link] a link to what's probably the very best article on oils ever written for model engines.

The castor/synthetic debate will probably go on forever but suffice to say that I've used castor for over 50 years in all types of engines with never a problem. Admittedly the castor I use (Castrol M) is very good and not available in most countries, like the USA or South Africa, in which case a blend is desireable. My only foray into synthetics was the 5 litres of fuel blended with a gas turbine oil that worked very well but the cost was too high to continue with it.

Augie11

Now that's my kind of labeling Jeff. You know exactly what's in it and get to make an informed choice. If you choose incorrectly, it's your problem. Yes, this is like the Coke/Pepsi debate and will go on forever.

Maybe I should switch to electric. NAH!

apwachholz

I appreciate and respect your insight downunder, however,based on the evidence supplied by TimBle and theevidencesupplied by your linked article,I'm inclined to disagree that there will remain a Castor / Synthetic debate. Actually, I'm not seeing a debate at all. To me it's a matter of ensuring that whatever fuel(s) you choose that they match the needs of your engine. Which also includes propermaintenanceand tuning of that engine.It's my belief that a majority of all issues surrounding rc engines is failure of the operator to properly run, tune, and use proper fuel selections. And I think this is where the "debate" stems from: Not properly understanding why or how the fuel effects yourengine.

And from my experience, it's those who haven't taken the time to learn about fuels who begin to take sides and blame one or the other when things go awry.

Additionally, I do believe that our hobby directly relates to full size be it in aerodynamics or engines 'n fuel. We come from the real world of aviation. Radio control was a product of the great air race so in my mind there is a directcorrelationbetween our two worlds. But that's just my feelings on the subject.

TimBle

You nailed it APWacholtz, operator error. Many cases of engine failure I've examined (this is on large diesel, passenger car engines and more recently little glow engines) the causal for the failure has been operator error.
Either, running the engine with too low a oil volume, or the wrong oil or "Snake Oils"  or with rc engines, too long running time in lean condition.
There are other cases where wear patterns seem to suggest too high a load on the engine (colkd be too big a prop or too small an engine for the airframe).
I'm not saying there are bum engines out there, but I would tend to lean toward operator error in most cases.

As downunder has stated, castor is fne there nothing wrong with it at all. Its just not as suitable in some engines in the same quantity as in other engines.
Castor Oil is also a feedstock for esterified synthetic lubricants so its not bad stuff at all.

As I have mentioned, there are synthetics that behave as well as castor and some that are better and some that are worse.

The chalenge ebven with castor is that there are so many grades. Castor can be made by cold extraction through crushing the beans and capturing the oil or through a solvent extraction process. Both Castor but with slightly different properties. So how do you know whats in your fuel. You don't. You buy any fuel on blind faith and reputation.

The polarisation will remain.

Jeffie, yeah you explained soot formation just perfectly. The analogy I like to use is that the diesel fuel droplet is like an onion. It burns away layer for layer but as the layers burn off the pressure is increasing. At the point where the pressure can no longer compress the fuel droplet, it cracks the hydrocarbons and forms a soot particle. Boof black exhaust. Hence all modern diesels are extreme lean burn engines. This is a major area where our little glow engines differs.

DownUnder, yes our engines don't have a sump and therefore they don;t need the highly complex additives. All they need is viscosity retention to provide hydrodynamic  lubrication to the conrod and gudgeon pin and for the piston in the liner, a fairly decent dose of anti-wear molecules to coat metal parts and some thermal and oxidation stability to live in an oxygen rich fuel like methanol. Castor does well at this but there are synthetics that do as good a job and some that are better.

This is why I firmly believe that fuels like Morgans Cool Power and Omega are not too different. I'd opt for Omega in an ABC and Coolpower in a ringed engine because I don;t want the castor gumming up the ring. But running a ringed engine on Omega once in a while is no big problem either.

Modern oils and fuels all tick the box for fit for purpose.

w8ye

My Feedback: (16)

I hope that engine still runs after you took it all apart?

apwachholz

w8ye -
Ihave every confidence that it will run after Ireassemble it. As a matter of fact, after learning much on this discussion Ithink it'll run better

apwachholz

Ohkay, I have some images that I'd like those who have posted or are looking at this post to take a peek at.

These are images of the top of my piston during cleaning of my Saito 72 4-stroke. I've never taken apart a Saito before and am not familiar with how the top of the piston should look. My concern is that the head appears to show metal fatigue in the center; as it's not completely flat. I know the grooves to the right and left are to be there, however, take a peek and let me know if this is 'normal'. Just need some insight.

Thanks All.