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Engine basics => Engine set up tips => Topic started by: Curare on October 22, 2018, 04:49:18 PM
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Hi guys, looking for some advice here, I've just come back from the field, with a 35S that won't stay running and fistfuls of hair in my hands.
It's an unknown origin motor, but seems to have very little time on it, enough to tan up the internals, but that's about it, it's nice and smooth with pretty snappy compression. Venturi is stock, and is running a 703 muffler. Tank is a 4oz plastic type set to unfilow and suction.
Fuel is 20% castor, 5% synthetic, 7% nitro. Prop is a wood 10x5.
I can get it to happily 4 stroke all day long with the glow driver attached, but once I unclip, I have 3-4 seconds, and then shut down. Doesn't matter what plug I use, I've tried a thunderbolt long RC, OS 8 OS 7, OS LC3, Enya 3, and they all do the same thing, without fail.
I am at a loss.
What's going on here? What should I be looking for?
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Up the Nitro? I dont know. Im just guessing lol
Sent from my SAMSUNG-SM-G891A using Tapatalk
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Just 4 weeks ago, we were starting up an OS 30s on a Brodak P47 profile. It had a strap on 703 muffler. We couldn't get a flight out of it to save our lives. Finally I decided to remove the muffler altogether. It's been flying great ever since. A muffler may be a requirement where you are, but can you remove it just for testing?
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Thanks for the Muffler number. I was looking for something to replace my Jetstream. I have been running an OS35s since the 70's. My experience points to Nitro - mine acts just like yours under 15% in the summer, 10% in the winter. Something is keeping the temperature down. I also run shielded plugs. It could also be the muffler. The OS35s was designed before mufflers were required. I can only pass on my experience. When it comes to the actual technical stuff, I am a spectator.
Good luck - Ken
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Ken, be warned the 703 is extremely restrictive - the outlet from the outside looks decent enough, but tapers (to cast it presumably) to something around 3/16" internally.
I bored mine out a few sizes.
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Ambitious types have the odd drill or two around .
The Same Shape muffler ( casting same ) on OS 15 , 20 , & 25 , has a 5 mm , 6 mm , & 7 mm outlet bore .
Theyre pretty D*#n fragile , often split , if you dont keep your nose right , so a rat tail file might be better ,
The OS 40 703 was a mm bigger bore outlet than the 35 , would always drill to that Diameter .
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under ' silencer ' here :
(http://sceptreflight.net/Model%20Engine%20Tests/OS%20Max-H%2040%20RC%20page%202.jpg)
bigger scribble , http://sceptreflight.net/Model%20Engine%20Tests/OS%20Max-H%2040%20RC%20page%202.jpg
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Ken, be warned the 703 is extremely restrictive - the outlet from the outside looks decent enough, but tapers (to cast it presumably) to something around 3/16" internally.
I bored mine out a few sizes.
Thanks, I will. The Jetstream is really just a "legalizer" with a huge hole in the back that blows crud all over the fuselage so having a real "muffler" or "silencer" as they called them "in the day", will probably cut the power a tad. May have to open up the Venturi some. Does the 703 have a baffel?
Ken
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HI Greg. Just how fresh is your fuel? Methanol makes the filament glow, but if there is water in the fuel, it won't. The driver is keeping just hot enough while on of course, but "dry" methanol is need to keep it hot. Our fuels just suck up humidity like a sponge and it is bad as the fuel level in the container nears the bottom. Worth a try to change to new fuel.. D>K
I had same simptoms years ago with my Merco 61 and Stalker 46 the same day…...suspicious mind, as Elvis, told me to open a new methanol botle and.....YES!!!!!......The fuel was recently made, but suprisingly, the methanol had water, new and fresh fuel with fresh methanol solved al the problems…….
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Ty, there's a possibility of there being some contaminants in the methanol - I mix my own, and my club buys 55 gallons of it at a time, but I don't see the process of getting it out, I just see a 5 gallon drum appear at the club for me.
I could certainly mix a new batch and see what I get.
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I reamed my 703 muffler out to 8mm on the outlet for my 35S and haven't had that problem since.
I used a great planes metric prop reamer, but if you do not have a metric one, use a fox reamer and go to the nest to the last
reaming section of the reamer. it come out to just about the same size hole.
I also turned the rear section of the muffler to its' lowest position so that it would not dump too much goop on the back end of the plane.
and by all means, fresh fuel.
Carl
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Carl, I just worked my way up through my drils, just gently pecking away at it until I was clear - I'm probably close to 8mm now.
I *think* I may have found the cause - will report tomorrow as to whether I'm right, or I need more help!
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Thanks for the Muffler number. I was looking for something to replace my Jetstream. I have been running an OS35s since the 70's. My experience points to Nitro - mine acts just like yours under 15% in the summer, 10% in the winter. Something is keeping the temperature down. I also run shielded plugs. It could also be the muffler. The OS35s was designed before mufflers were required. I can only pass on my experience. When it comes to the actual technical stuff, I am a spectator.
Good luck - Ken
Ken, you want my 703 muffler to try?
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I can get it to happily 4 stroke all day long with the glow driver attached, but once I unclip, I have 3-4 seconds, and then shut down. Doesn't matter what plug I use, I've tried a thunderbolt long RC, OS 8 OS 7, OS LC3, Enya 3, and they all do the same thing, without fail.
I am at a loss.
What's going on here? What should I be looking for?
I don't really know, and you have gotten some good ideas (but please try it without the muffler before *drilling holes in something that hasn't been made in 50 years*). But for absolutely certain, try it with a good-quality commercial fuel - 10% SIG, 10% Powermaster "Air", Byron 10 or 15% "Classic" or equivalent. If it was me, I would try Byron first, because it has solved "flame out" problems for me in the past, when nothing else would work.
Brett
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Hi all.
I am with Brett.
I try everything possible before to (crying) sodomize some unobtanium decades ago materials....even a previously damaged and repaired one as the ST46 cranckcase who I am using in my Smoothie. They are jewels.....
Kind regards.
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I don't really know, and you have gotten some good ideas (but please try it without the muffler before *drilling holes in something that hasn't been made in 50 years*). But for absolutely certain, try it with a good-quality commercial fuel - 10% SIG, 10% Powermaster "Air", Byron 10 or 15% "Classic" or equivalent. If it was me, I would try Byron first, because it has solved "flame out" problems for me in the past, when nothing else would work.
Brett
Brett, don't run screaming for the hills just yet - the 703 I've drilled in not the "good" one but one that I got given in a pile of junk many years ago - it's met terra firma at least once in it's life. At any rate if I want to fly this thing, I am somewhat commited to the muffler, we're too close to houses to get away with barking 35's unmuffled.
As regards fuel, Australians for some reason don't buy premix (well, this australian doesn't anyway), so we tend to buy the bits and 'roll our own'. I've thrown out the last mix which I suspect had contamination, and mixed a new batch - 25% oil (50/50 coolpower and castor) and 10% nitro.
Will report back on whether it's fixed or not.
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Soooo.... I snuck down the the field this morning for a bit of a test.
New fuel (25% oil, 50/50 castor synth and 10% nitro) and an OS F this time, meant that it was running, but a little ratty. We decided to launch, and I'd get 5 laps out if it before it'd fart out again. My flying buddy offered me a thunderbolt Idlebar plug, and I had nothing to lose so we jammed it in.
The engine just happily burbled along for the entire tank, if maybe a little lean.
Next flight was confidence inspiring to try a weak rendition of the sequence. It beeps along in overheads and verticals but seems to richen up after a manuevre. The wind was up so may have been playing havoc with the uniflow.
Still, I guess thats' the trick. If in doubt, wedge an idle bar plug into it.
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Route a secondary length of fuel hose from the uniflow inlet into the backplate cavity to get air to the tank without 'fluence from the wind. I made a small sheet aluminum fitting to hold the fuel hose location steady in the backplate cavity. I don't hook it up until on the circle and ready to start. Try it, and you'll like it! D>K Steve
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Well the plot thickens on this turd...
Having done nothing more than check the fuel tank for leaks, and wipe down the plane, I set out this morning to do some flying, and what a suprise, the engine is back to it's old tricks again!
I tried and tried, and things seemed to get more and more desparate, till I finally gave up in disgust and flew my electric instead.
On the way home I had a bit of a think about things - when I first installed the engine I ran it in the backyard with freshly mixed fuel and it was fat but happy, 7 days later at the field and it won't stay lit.
Mix a new batch and head to the field and modicum of success with an idle bay plug. Fast forward a week and she's back to her old tricks.
I am now wondering if perhaps my fuel bottle is somehow 'tainting' the fuel? It's a food grade squeezy bottle with a crap trap on the end, and thats it! Surely it couldn't be the culprit?
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"Fast forward a week and she's back to her old tricks."
By this, do you mean that it's running the way you want it to run, or is it running crappy? ??? Steve
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Given the general tone of the rest of it, I suspect he's unhappy with it.
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Yeah, but I wasn't certain. I was wondering if he'd turned the turd's spraybar to a clocking where it won't draw fuel properly. And then, there are those OS NV's that get bent and go from rich to lean in a half click. I avoid them.
I also shuddered when he "jammed in" a new idle bar glowplug, remembering Mike Haverly's recent experience at Centralia/Chehelis Muni trying to screw in a new idle bar glowplug. The idle bar wasn't welded on perfectly centered, and "jamming" it in would have stripped out his cylinder head. There's a first time for everything, I guess. #^ Steve
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Yes, when I say it's up to its old tricks, I mean the engine won't stay running, although the period of running is longer - about 60 seconds or so, long enough to fool you into thinking you're going to have a decent flight, then shutting off, whether airborne or on the ground.
'Jamming' something in is a bit of a colloquialism, I didn't realise my Australian turn of phrase would cause such a response, but I assure you all care was taken in placing the plug into the engine. No threads were harmed in the making on this thread
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Didn't read the whole thread but, I had the same problem with the same model engine. It was a crapped out connecting rod. Come to find out those engines are famous for eating rods.
Motorman 8)
Yes, they are, but it's not the rod.
If you hadn't read the thread how did you figure you have the same problem? Ouija board or tarot cards?