efish

My Feedback: (5)

Hi, would really appreciate it if someone could help me out on this one.

I've been running an OS FS-30S four stroke engine for the last couple of months or so. Broke in 2 tanks extra rich on the ground then a lot of really rich and gentle cruising around after that for a while. Things have been generally pretty good performance wise after the break in period - hand starts ok, enough power to hover at 1/2 throttle etc. Had a couple of good flights on Friday, but on the first flight Saturday morning, I noticed a distinct lack of power. Popped it in a hover and even at full throttle, the plane would start to tail slide. There's enough power left for easy sport flying, but I have stopped flying the plane for fear of (further?) damaging something.

Prior to this, the only time I had problems was towards the end of the breakin period - the engine ran erratically for a couple of flights and deadsticked. Readjusted the tappets then and the engine performed great. Checked the tappets this time and they are as I set them - 0.05mm about in the middle of the recommended range.

Any thoughts on what I should check/try?

It's a ringed engine, so I thought of changing the ring since they are not too expensive. However, compression does seem reasonably decent. Would have to break the engine in again too. I've got about 150 flights on the engine - could be a little more but probably less than 200. It's my first OS 4 stroke, but surely they'd last longer than that?!

Thanks.

efish

My Feedback: (5)

Oh should probably add that the bearings seem ok (no rust, grating or noise) and the engine appears to run fine - except its only putting out about half as much power as before....

Always ran it rich and never had to hit full throttle for more than a few seconds so I'm kinda puzzled as to what might be wrong.

NM2K

My Feedback: (14)

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Just a hunch, but check to see that you haven't broken a valve spring.

Does the lift (view rocker arm) look like it was as great before? I'm wondering about cam wear.

You are using fuel with a tad of castor oil, right?

Have you tried changing to a fresh glow plug?


Ed Cregger

efish

My Feedback: (5)

Hi Ed, thanks for helping me out (again)!

Will have a closer look at the valve springs again, but they seemed ok when I checked the tappet clearances over the weekend.

I'm using Omega (it's got castor as part of its lube package).

Tried changing out the plug, but I didn't fly with the new plug since there didn't seem to be a noticeable improvement. Guess I should just try 1 flight to eliminate this as the cause. Will do so just in case but I thought I read somewhere that glow plugs were an all or nothing thing - either they work outright or they don't?

Thanks again.

Patxipt

Make one simple test:
Remove the rockers, silencer and carb. Now turn the engine by hand slowly and see if you hear any hiss during the upwards stroke. With the engine at BDC, push on a valve to let air in and repeat.
I you do ehar a small hiss coming from either admission or exhaust holes, remove the head and the valve springs. Open the valves with a finger and see if the seats have some dirt. With small plyers turn the valves one way and the other rapidly while pushing them up, this will create a kind of valve seat lapping. Reassemble everything back and make the hiss test again.
Put some more castor on your fuel, it may happen that the ring is starting to become worn out and a bit more casdtor will seal it properly.
Good luck!

NM2K

My Feedback: (14)

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I have had glow plugs that glowed very well with power applied, but which did not work worth a hoot. There are a few things that can go wrong with glow plugs, but which will still let them glow beautifully.

One is being coated with silicon/silicone (not the same compounds-by the way). Silicon rich compounds are alleged to have left a thin glass coating over the element, so that no catalytic reaction is possible. Ditto silicone compounds. My memory is a bit fuzzy on the topic these days, but I am positive that glow plugs can fool you with a bright orange glow, but still not be usable.

Any metal moving through the engine can contaminate the glow plug element and cause it not to work well. Again, interference with the catalytic reaction is at hand.

Let's hope it is just a defective glow plug.


Ed Cregger

efish

My Feedback: (5)

Hi Ed, that's really interesting, wished I had paid more attention in High School when they were explaining the difference between Silicon and Silicone.

Anyhow, changed out to a fresh OS F plug and gave it a go this morning. At the typically rich settings I run, there's still not enough power to hover. Out of frustration, I leaned it out to just below peak, and there's just enough power to hover. Didn't hold it for more than a few seconds to avoid the bog. Quickly landed the plane and put it away after that.

Bottom line is that the power loss is still there, so the glow plug is not the culprit.

Patxipt - thanks. Had a good long look at the rockers and valves and everything looks as good as it should; afterall, the engine's only been running for about a couple of months.

With the glow plug on, the compression seal seems good and tight. With the glow plug off, the fit does seem a little loose, but then again, this is a ringed engine.

Guess I'll have to try changing the ring and see if things improve. Would really like to figure out what is the problem though.... Thing is the engine starts (first hand flick today!) and runs fine apart from the very apparent loss of power. Don't have that much experience, and I've only worn out 1 other engine (an ABC 0.061) - that one became a beast to start and idle towards the end; a new piston/cylinder had it running good again. Wouldn't a ringed engine (albeit 4 stroke) with a worn ring display some other symptoms apart from a loss of power?

Thanks for helping.

w8ye

My Feedback: (16)

I doubt if your ring is bad. There must be some other problem like your fuel tank or an air leak or something?

efish

My Feedback: (5)

Thanks w8ye, can't really convince myself that the ring is bad either, but I'm kinda at a loss as to what to try. The engine literally went from good to bad overnight. Will try a different fuel tank and dismantle the carb tonight to have a look.

Would be mighty grateful for any suggestions anyone else can give. Will just keep trying everything, but right now, I've only got a pretty short list.

Motorboy

Never use the needle plier!!!
Patxipt are amateur to abuse the tool at the model engine.. [sm=50_50.gif]

It will set tool mark at valve stem and scratch out the valve guide who can make air leakage between valve stem and valve guide.

Jens Eirik

NM2K

My Feedback: (14)

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Have you changed anything in your model that would have added weight?

Do you hear a noticable drop in rpm compared to when it ran as you expected?

Have you changed nitro percentage in the fuel recently? Changed the prop type, diameter and pitch?

Without some additional data from observations, we're just shooting in the dark.


Ed Cregger

efish

My Feedback: (5)

Hi Ed, that's the strange thing - between the Friday when all was fine and the Saturday morning when the power dropped, I didn't change a thing! Actually, between the last flight on Friday and the first flight on Saturday, I didn't even touch the HSN. Just hooked up the receiver battery to my charger during the night as I always do.

Flying weight, fuel, prop etc have all remained constant!

Guess that's why its so frustrating - the plane was flown almost daily and was quickly becoming one of my favorites and now its been grounded with no logical explanation.....

Any thoughts/ideas/suggestions?

efish

My Feedback: (5)

Oh, I was having too much fun with the plane and never got round to taching it. But I guess if the power is down, it must mean the rpms are too (with the same fuel/prop)?

NM2K

My Feedback: (14)

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Did the weather change significantly?

Warmer weather will cause a reduction in power. And very noticeably too, in some instances.


Ed Cregger

efish

My Feedback: (5)

Hi Ed, thanks for trying.

here in sunny Singapore, the weather stays pretty much constant all year round. Except during the monsoon when it pours too much to fly!

gkamysz

My Feedback: (19)

You've checked all your linkages and verified the throttle is actually opening to full?

efish

My Feedback: (5)

Hi greg, yup, that was my first thought since I'm using a micro servo for throttle. Double checked the physical setup, plus the ATV settings and visually checked that full throttle meant fully open carb barrel.

Looking like this is gonna be a sticky enigma....

Thanks anyhow.

TimC

efish, it might be a good idea to pull the engine out of the plane and run it on a test stand. This will tell you if the problem is with the engine or the fuel system/set-up in the plane.

efish

My Feedback: (5)

Thanks Tim. Will do just that this weekend along with a detailed examination of the engine. It's really strange and seems to defy any explanation.

Went back to the local OS agent/LHS and they think that the piston ring is worn. But seeing as how they once told me OS ABN engines were really ABC engines (gasp!) and that the "A" REALLY stood for "Abestos" (double gasp!), I'm greatly disinclined to believe anything they say that doesn't make immediate and obvious sense..... thank goodness for this forum.

Guess its also a good thing they don't stock the replacement piston ring.

efish

My Feedback: (5)

Oh, they did also suggest that I set the tappet clearance at 0 to see if that changes anything. Would that be worth trying? Or just accelerate wear?

I know that too large a gap reduces power because the valves don't open fully, but my gap is now within spec at 0.05 mm.

Don M.

My Feedback: (5)

You have probably check this but is there any chance something is partly blocking the exhaust / muffler. I had the insides of a muffler fall apart one time and the engine lost about 1/2 power until I found the problem.

NM2K

My Feedback: (14)

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When I answer, even to one person's specific request for info or just to chat, I behave as though I am addressing a large audience. There are always new folks, or those unfamiliar with certain aspects of the hobby. I have noticed that most folks use the terms silicon and silicone incorrectly. They are not interchangeable. Silicon is silica/glass based, while silicone is some hi-tech/hi-temp rubbery stuff. I'm not an expert either, but we should clarify in order to prevent the misuse of the compounds. No offense intended.

Things that would reduce power are a loose throttle control arm (hooked to servo via cable), loose intake manifold (leaking air), loose carburetor, cam timing off a tooth one way or the other, worn cam lobes (decreased lift), broken or malformed rocker arms/pushrod, stuck or partially stuck piston ring, loose cylinder head, bad glow plug, kink in fuel line, plugged or partially plugged carb spray bar, rotating needle valve, etc.

I hope you find the culprit soon.


Ed Cregger

gkamysz

My Feedback: (19)

Just a thought. A worn or stuck ring should be detectable by the amount of blow-by coming from the crank case breather. I have noticed that this varies engine to engine, however. You would have to know what it was like when it was running well to know if there is a difference. Kind of vague. But a poor compression seal should be pretty obvious when turning over by hand. This would probably be something you have experience with on a regular basis from priming and such. I've seen a few engines with nasty scored pistons and liners that still had good compression.

One other thing that has come to mind is a sticky tappet (or lifter, or cam follower if you prefer) . The vavle might open and close smoothly but if the lifter is sticky it will keep a valve open longer than needed and result in poor running. You could check it by removing the rockers. Ideally the lifters will fall under their own weight. Castor oil in the fuel could make this hard to determine unless the engine is freshly run and warm.

Just be sure to post when you do find the problem.

Ed, the silicon/silicone thing is a pet peeve of mine too. I worked for a hobby company that sold "silicon" fuel tubing.

efish

My Feedback: (5)

Hi Everyone, thanks for trying to help - really appreciate this. The FS-30S problems started just about when I was finishing up another plane - been working on that plane so I haven't really spent enough time on the FS-30, hence the delay in my responses. Hopefully I'll be able to put in some "quality" time this weekend. Just maidened that other plane this morning and what good fun that was!

Don - thanks. No, I didn't check that (sorry, newbie here...). And you may just have hit the nail on the head! I use plumbers tape on the exhaust threads and I did notice a little flap of tape sticking out the last time I worked on the engine. Could be that more tape has worked lose and is now partially occluding the exhaust manifold. Will have a look as soon as I can!

Ed - I have always been very grateful for your advice and help; you've been a font of wisdom and experience. I have never been offended by anything you've said and I'm sorry if it appeared that I was. Truth is, I really wished I had paid more attention during my high school science classes. Was making some calculations for a friend's electric plane recently and couldn't help but wish I had my old physics textbooks to look up some formulas. For whatever reason, it appears the older I get, the less I seem to know. Thanks for the concise checklist too - if it's not the exhaust, I'll just work my way slowly through your list.

Greg, thanks but the engine is still pretty new and feels pretty new. i.e. compression is pretty much the same as has been when the engine was working ok. I think hand starting the engine did give a me some familiarity. Had a good long look at the tappets and they all look really new and in working condition too. Although I use castor in my fuel, the weather here is pretty warm, so even at room temp, castor oil takes a long time to congeal into a gooey mess that would stick the tappets! Anyhow, they seem to be moving pretty freely.

Thanks so much again everyone. Will do what I can .... got my fingers crossed and hoping the problem is a partly blocked exhaust manifold caused by my inexperience. Will let you know!

wcmorrison

My Feedback: (2)

Hummm. An exhaust restriction could indeed be the cluprit. While checking your teflon tape check the flow through the muffler (since you are in Singapore, it might be a "silencer"). That can remove power real quick. I too use Omega in my Four Stroke engines, no problem there.

Good luck,

Cheers,

Chip