I'm having trouble finding initial settings for a new sc 40

[Bob Moore]

Hi all

 

Like the title says. I have a new SC40 rear needle and I'm having some trouble getting it right.  (I've only ever had one new engine, all the rest have been used.)

 

It's starts easily enough, but whereas it's obvious on my front needle sc25 when you lean the mixture, where you've gone too far, I can't find a good spot with this.

 

Run it a little bit rich I've read. Too rich will damage the engine, I read. Too lean will damage the engine I'm sure. Blooming e bay. Maybe I bought a duffer 'unused engine' ? It didn't appear to have been run anyway?

 

How easy is it to damage a new engine by getting it wrong, too lean too rich?  I'm only running it for a few minutes at a  time , then letting it cool so as not to stress it.

 

It seems to tick over ok for a while and will pick up and run full throttle for short bursts?

 

Plus, is it better to run in in the model, ie fly. Or on a bench as I'm doing? I suppose it gets slightly better airflow on a model when flying?

Edited By Bob Moore on 21/10/2010 11:54:11

Edited By Bob Moore on 21/10/2010 11:55:22

[Stephen Grigg]

Ive always run my engines in the model,but a lot of guys run at the field on a bench.Im not your true engine guru and usually put a couple of tankfulls through as rich as itll run and I keep every minute or so leaning out to max revs to clear it out.It doesnt take that long because your putting the fuel so rich.I finish off the running in  flying the model around a little rich,like to see a bit of smoke.Running lean is probably worst as it will make the engine run hotter.I also do the finger test where if its to hot itll burn  the tip of your finger.Never had a problem with an engine Ive run in.

[Lee Smalley]

Hi Bob assuming the slow running needle has not been touched do the following, close the main needle don't lean on it that will damage the needle seat then open 3 full revolutions prime and it should run with throttle opened 1/3 max let this run for about 10 mins and lean out until engine is breaking between a four stroke and proper two stroke run (this is still a rich setting ) after a further 5 mins or so stop engine and allow to cool , restart and repeat slowly leaning mixture out over a few tankfuls ABC engine will not be damaged by a rich mixture unless you try to start them whilst hydraulic locked ABC engine do not liked to be ran in too rich it does not promote the bedding in process but a lean run is by far the worst case, do not do this during the break in 

[Stephen Grigg]

And if it was me Id be more inclined to do what LEE suggests,he knows loads more than I do

[Martin Harris - Moderator]

The accepted wisdom is that an ABC must be run in close to normal temperature in order to avoid damaging the rinning fit at the top of the tapered bore.  If it is not hot enough the fit is made too loose at running temperature meaning that compression will suffer.

 

How much is too cool (rich) is the million dollar (well £50) question and one which needs a metallurgist to answer.  Best bet is to use the extensive resources of the manufacturer which should be encapsulated by their running in instructions!

 

Failing that I'd go along with Lee -adding that the important thing is to avoid ticking over or running excessively rich - or lean - and overloading the engine. As soon as an ngine will hold constant revs at a slightly rich setting I like to get it in the air (in an adequately cooled installation). Fly at varying throttle settings and no prolonged prop hanging!

[Bob Moore]

Thanks for the input guys.

 

Haven't touched the slow running as I'm hoping it's factory set.   (I will once it's had a couple of tanks through if necessary, but very cautiously.)  I've had it running at a fast tickover for  a few minutes at a time with the odd burst of full throttle and it seems to be improving. Doesn't feel blisteringly hot to the touch. I don't thnk it will cope with three revolutions out on the main needle, seems happy at 1 1/4, plenty of oil coming out the back and smoke.

 

When I got it it was at 3/4, that may mean nothing though.

 

Have put three quarters of a tank through now.

 

Biggest problem is the blooming noise. My neighbours will no doubt be pleased when I've finished!

 

edit:  just richened it a quarter turn , seems very happy. Have put a tank through now and it's smoother all the time. From what I have read of these, it can be hard to get a reliable slow speed tickover till it's had a few tank fulls through.

 

thanks again.

[Lee Smalley]

Hi Bob it sound like you are nearly there the thing is we can't say to you open 1 and 1/2 turns then run it as each engine is different and if you did that and it ran lean and ruined your engine you would blame us thats why i allways say 3 turns out and then start going in from there, my ASP 108 runs normally at 2/13 turns open weired eh !! the majority of engines should be around 1 to 2 turns open when ran in but it is allways wiser to be slightly rich than the other way round , but the lads are right get it in the air as soon as you are happy its reliable thats where i run all of mine in  

[flytilbroke]

I am surprised still, although I should not be.

 

A new 2st engine normally arrives with the manufacturers "running in" instructions. Other than the old, now needless advice to use Castor oil the instructions given with all the general engines is correct.,

 

Start them rich, lean out and then back off a few clicks slightly richer , run at full revs for one minute then back off the main needle and run very rich for twenty seconds. Repeat till tank empty. Let engine cool. Repeat that routine for three or four tanks (tank size depends on engine size)

 

ABC 2st engines need to run at slightly less than maximum revs,during this period. After too, if you want them to last.

 

You should not need to adjust the low running setting until a Gallon/5Litres of fuel has been though it. Then only by very small amounts.

 

Have fun

[Lee Smalley]

i think he said he got it off ebay as unused, i dont think its new from the shop

[Bob Moore]

Yes it was new and unused from E Bay but without box or instructions. I have the instructions from another new SC at home that I bought from my dealer, but to be honest, they're not very helpful.  There's more useful advice online!

 

Start them rich, lean out and then back off a few clicks slightly richer , run at full revs for one minute then back off the main needle and run very rich for twenty seconds. Repeat till tank empty. Let engine cool. Repeat that routine for three or four tanks (tank size depends on engine size)

 

That's pretty much my method!

 

I think I was more or less doing it right, just had the mixture a bit too rich to start and it wasn't very happy. Seems ok now. I'll put another tank through tomorrow.

 

 

[Stephen Grigg]

Glad it appears to be comig together and settling down.

[Bob Moore]

The ebayer has offered a refund on this engine, but two days back I thought I 'd really got it going well.  The idle needle was way way to rich, so much so that the high speed wasn't doing anything much and was very difficult to set.  Anyhow, two days back it seemed to be absolutely perfect, nice pick up, nice tickover, opening up well, not faltering afterwards and dying, so I figured I'd keep it.

 

Yesterday piddling with rain so couldn't try it again.  BUT today, ran it again and it's very irregular again.  Adjust adjust adjust, there must be something wrong here methinks.  I have spent hours and hours trying to tune this. Blow it, I just took it off the model and it's going back!

[Stephen Grigg]

Strangely Bob,I couldnt get an OS56 Alpha to run right in a Pup,took it out made a test bed ran perfectly put it back in the model and it was perfect.Ive got some old OS 40 max and there great no problems,and yet sometimes you get one like yours.funy old hobby.

[Bob Moore]

They're weird things for sure.  The annoying thing is I bought this 'new' sc because I had so much trouble trying to get an MDS 38 to run properly. (I guess that's more understandable though.)  My other  2 strokes , even the  old and oily battered ones, are good as gold, but I've spent hours and hours on this. So annoying that Thursday it was running beautifully and then today,  it's giving me trouble again.  I think it's just a very fussy engine and I have read of similar probs with the rear needle SC40.  (It is my first rear needle engine?)

 

Too many dead sticks are no fun!  It has to go!.

[Stephen Grigg]

Thats the problem Bob you just cannot take the risk.

[i12fly]

Maybe its too late now, but I would swap from the rear needle to the front, you seem to get better control that way. Check you've not got anything come loose and giving an air leak, and put a couple of drops of oil on the carb barrel to ensure no leak around that......

[Bob Moore]

Thanks for the suggestion,  but unfortunately it's not designed to be just swapped over. The carb barrel at the intake doesn't take a needle. They're two seperate components.  A main needle at the rear and a carb with a butterfly barrel and slow running needle at the front.

 

I actually removed the back plate and carb and sealed them with a smear of red hermetite so I'm 99.9% sure air leaks aren't the problem.

 

I Googled this engine problem and came up with a thread elsewhere where someone actually bought and fitted a carb at the front end, and his engine still wouldn't run well?

 

 

I really have tried everything I can think of and have had enough! A new engine it is going to be.

[Bp]

If I can add my 5 eggs, from what I have learnt from trying to get an SC46 to behave, I think the big problem could possibly be air leakage past the throttle rotor in it's housing. The tolerances on mine were awful and it leaked air like a sieve.

I arrived at this conclusion after listening to suggestions from various forum members and trying some pretty nerdy experiments in the shed!

In the end, I reassembled the rotor in it's housing with a graphite based anti sieze compound and made an external seal using 13mm heatshrink tubing stuck to the carb casting with a spot of silicone and shrunk onto the throttle arm shaft. It's a bit fiddly but it seems to have done the trick - on the bench any way - I hav'nt been able to get up to the flying field lately to prove it.

For good measure I also encased the whole external main needle assembly in some smaller heat shrink tubing.

Every thing still moves for adjustment and I ran the tank dry on the bench with no issues at all.

Best of luck!

 

 

 

[i12fly]

.....funny but an SC46 I had started with a rear needle but I was able to change it to the front with the parts in the box, can't remember exactly how though...

Oh well at least you'll be refunded, which many ebay sellors wont do. Good luck with your new engine

[Bob Moore]

I've run a couple or more tankfuls on the bench with this one,  it ran continuosly, no probs. Then I put it in a model and the problem I had was it dying when I lifted the nose. So I richened the mixture a bit.  No good.  Played with the idle screw. (Little by little.) Then you'd hold the nose up, open the throttle and drop the revs, and open (the kind of stuff that happens for real in flight) and it randomly died?  The annoying thing is, as said two days ago it  worked fantastically well and I thought I 'd cracked the problem.

 

With my MDS 38 (which at one time was a good runner and then started playing up) I tried all kinds of things, changing carbs etc., and it still wouldn't be reliable.

 

The other thing with the sc 40 is, it was sold as 'fitted in an airframe but never run'. It looked clean, but there were marks on the body where you can see it had been gripped in a vice. What numpty would ever do that with an engine?  I should have returned it immediately.

 

I'm a real tryer and have too much tenacity for my own good, but there has to be a time when you say 'quit'.

 

I guess I may lose the postage costs, but worth it after so much frustration.

[Stephen Grigg]

Interestingly Bob whilst answering a question from your gooself on another thread,I remember having a problem with a new OS 40 I fitted in a Magnatilla.Every time I went to take off the engine would die and be trublesome to start again.I was fairly new to I/C at the time.I lost the Mag due to lost signal.When I came to fit the OS 40 in a vintage model,I found the throttle arm was very loose.Im sure this was its original problem all along,it is still in the same vintage model,and has never given further problems,Im sure the throttle arm had been loose from New.

[Bob Moore]

It could well be something like that Stephen, but I have given up on it. It's bagged up and once the e bay seller confirms his return address it will be in the post!

[Stephen Grigg]

Hope I dont finish up buying  it Bob.