Run away engine

I see debate about setups that have run away performance. My OS 40fp-s with tongue muffler and 11x4 prop won't turn up, just sort of growls along, pretty slow, not good line tension. Put a 10x5 or 10x6 on it and it has a purring 2 cycle sound, runs steady every time,more rpm, good line tension, yee-haw flies everywhere well. Is this what you call run away? I see in here where some setups are using 11 inch and even 12 inch props, I don't think my motor could pull that. By the way I'm using Sig 15% with a custom blend oil, 24%- half syn half castor.

LAST EDITED ON Mar-18-04 AT 09:55 AM (CDT)
 
The FP's first became available about 1985, I think, but not in a CL version right away. In the meanwhile, OS had stopped producing any CL oriented engines larger than 15's from about 1984 or 1985 (they were still selling some Max-S and Max-H engines for RC after dropping the CL versions of those). After a 3-5 year period of not offering any CL engines (maybe none in any size), they decided to sell FP's in CL guise.

Some folks had already been tinkering around with converting the earlier OS engines with Schneurle porting, such as the FSR's, but OS pushed the FP-S's with discounts and advertising. I got one of each larger one, a 35 and a 40. Like a great many other folks at the time, I tried to run them the same way I would with a Max-H or Max-S (a breaking 4-2-4 type run). For that type run, we were using 10-5's and 10-6's on 35's, and 11-5's or 11-6's with 40's.

Both of my original FP's in stock condition would "break too hard" if you set them to run slowly in a 4-cycle. They accellerated pretty strongly compared to older engines, creating timing problems in maneuvers. Also, they often would refuse to break back out of a two cycle after they did break. So they were going pretty fast in level flight. Consecutive maneuvers got the biggest criticism, each succeeding one being faster and faster, much the way you get from high winds.

When they were too fast with 5" and 6" pitch props, I tried some 4" pitch props, with a wet two cycle needle setting, and still thought that the 40 in particular wanted to go too fast even then (11-4 wood prop, probably a Rev-Up, but I can't recall clearly. It's been 15 years now). I tried the idea of detuning with extra head haskets, but didn't like that, either. I didn't try a 10-4, and didn't try more than my "usual" fuel in the FP's. These days, I feed my FP an oilier fuel, and run a cut-down 11-4 (to 10 1/2).

.

Kiwi

My OS .35 FP has been a dream right out of the box. Nice mild, predictable breaks. Not a single mod. The OS .40 on the other hand behaved as you describe. I added 2 or 3 head caskets and that seemed to help.

But, listen to the other folks here. They have a lot more expierience than I do.

>My OS .35 FP has been a dream right out of the box. Nice
>mild, predictable breaks. Not a single mod. The OS .40
>on the other hand behaved as you describe. I added 2 or 3
>head caskets and that seemed to help.
>
>But, listen to the other folks here. They have a lot more
>expierience than I do.

You are right, the 35 out of the box works much nicer than the 40. Although the timing is identical, the 40 uses wider porting which makes a problem. Some of the earlier ones used larger venturis which can also make a difference. By all means, check the venturi size.

Wow. I haven't seen those since the French Revolution.

>Wow. I haven't seen those since the French Revolution.

I suppose you have a special access to a Boeing version of Dexter's Way Back Machine? Head Caskets, indeed!

.

Kiwi

>I see debate about setups that have run away performance. My
>OS 40fp-s with tongue muffler and 11x4 prop won't turn up,
>just sort of growls along, pretty slow, not good line
>tension. Put a 10x5 or 10x6 on it and it has a purring 2
>cycle sound, runs steady every time,more rpm, good line
>tension, yee-haw flies everywhere well. Is this what you
>call run away? I see in here where some setups are using 11
>inch and even 12 inch props, I don't think my motor could
>pull that. By the way I'm using Sig 15% with a custom blend
>oil, 24%- half syn half castor.
>
>Terry Clark

Maybe the tongue muffler is too restrictive? That's my #1 guess. How big is the venturi? Did you buy the engine new, so you know it hasn't been retimed? Another thought, maybe the cylinder is turned in the case? Something's not right. Steve

I bought it new from LHS,it came with 2 venturies, tried the large one, then the small one, even one for 20-25 motor. This with a stock muffler and lots of tail weight. Got a tongue muffler from Leonard, got rid of lots of weight, switched from coolpower fuel to Sig champion, put larger stock venturi back in (believe it's about .280). The tongue muffler seemed to help it breath better and added muffler pressure to GRW narrow wedge tank which gave consistant runs to the end of the tank.Tried various 11" props, 3-5" pitch, just didn't come alive until the 10x5 prop. I'm getting use to flying with this setup, way better than before thanks to all the things I've tried that I've learned on this forum.

Please give me a list of probables to try.

Try the gaskets. Cheap and easy to give it a shot.

LAST EDITED ON Mar-18-04 AT 09:29 AM (CDT)
 
Something is not right--that engine should spin an 11-4 EASY. And it should be WAY too fast with a 10-6.

Do you have a tach? what is the rpm on the ground pre-launch?

Also, what brand props are you comparing?

Maybe the engine already has too many head shims.

Also, prior to launch, if you pick the plane up and point it 45-60 degrees up, does it pick-up speed?

Are the back-plate and head screws tight? Glow plug?

The sleeve rotated would be likely as well as already indicated, but there is a pin in the case and a notch in the sleeve to align the two.

Where are you located?

FWIW

Just re-read the original post. This ain't run away, it's not run enough

Forget the head shims for now. We are getting proper power some how. The 11x4 should be very easy for the OS to spin.

>I see debate about setups that have run away performance. My
>OS 40fp-s with tongue muffler and 11x4 prop won't turn up,
>just sort of growls along, pretty slow, not good line
>tension. Put a 10x5 or 10x6 on it and it has a purring 2
>cycle sound, runs steady every time,more rpm, good line
>tension, yee-haw flies everywhere well. Is this what you
>call run away? I see in here where some setups are using 11
>inch and even 12 inch props, I don't think my motor could
>pull that. By the way I'm using Sig 15% with a custom blend
>oil, 24%- half syn half castor.
>
>Terry Clark

One thing, Terry, not all props are created equal. There is a vast difference between one 11-5 and another 11-5. What brand of props are you running? Also, what venturi is on your engine? Does it still have the OS needle? Which tongue muffler are you using? Some of these are too restrictive and could use a few more holes.

That said, if the plane is doing fine with the 11-5 or 11-6, but not with the 11-4, I suspect you have the engine running too lean (still could be caused by venturi or muffler not allowing ample power).

But what you are talking about is not the runaway. That happens when the engine slams into full lean and doesn't come back. There is also wind-up, which happens when the engine picks up too much rpm in the maneuvers and they get too fast on you. This, too, can be a matter of prop, deck height, head clearance, and venturi. But, your 15% nitro can also cause it. With more nitro you are going to get more boost and require more head clearance. We seldom run more than 10% and mostly 5% nitro. Did it on the 35/40 FP engines. Doing it now on the pipe set-up. In fact, getting ready to order another ten cases or so of fuel and it will all be 5%.

Thanks for the ideas from everyone! Pulled the muffler and checked the sleeve and it was in place. Piston sides are black. Always adjust needle from 2 stroke to rich when it starts to 4 stroke then in 2 or 3 clicks. Figuire its on the rich side of 2 stroke. I don't have a tach. The motor does get a boost on downside of manuevers, really picks up speed like a tailwind would give, but always goes back to its normal speed. How long to break in, about one and a half gallons thru it now. What glow plug should I use, have stock # 3 in it now? Props so far are Master Airscrew, Zinger, APC, Topflite. Zinger worked great, just broke them all landing in my semi-rough back yard. All screws on backcover are tight. Stock nva. Motor is varnished enough to give it a soaking in crock pot. I'll look deeper into it then, a little timid about disassembling it.

"Pulled the muffler and checked the sleeve and it was in place. Piston sides are black."
"How long to break in, about one and a half gallons thru it now."

Terry,

I estimate that your 1 1/2 gallons of fuel used equates to about 5 hours of engine run time ( 1.5 gallons= 192 ounces, 192 ounces/4 ounces per flight= 48 flights, 48 flights x 6 minutes per flight= 288 minutes=4.8 hours). After 5 hours of run time your engine's piston should NOT be black. It should be aluminum colored or have a light tan coloring.

I keep a log of every flight and the OS .40FP in my Banshee has over 32 hours of run time (295 flights over a 3 year period) and the piston is still a nice light aluminum color. I do have an OS FP engine that I bought used off EBAY and it arrived with a "black piston". It had so little compression that it was very difficult to start by hand. Hot restarts were impossible. And it had very little power. It would not turn an 11-5 Zinger (my normal prop for my OS FP's). With the 11-5 prop, if I tried to lean it out from a rich setting into a fast 2 cycle it would just quit. However, if I put a smaller 10-6 on it, I could lean it out into a 2 cycle.

Does your engine feel like it has decent compression? Has it's compression faded from when it was new? My "NON-EXPERT" opinion, given your engine's "black piston" and inability to turn an 11 inch prop, would be that your engine's piston/cylinder may be prematurely worn out.

You mentioned using Cool Power fuel. This is a fuel with a relatively low oil content and it is 100% synthetic oil (i.e. no "engine-friendly" castor oil). Using this fuel could lead to premature wear especially if used during the engine's critical breakin period and if the engine is run with an overly lean needle setting. The 32 hours I put on my OS .40FP without any noticeable wear or power loss was done using several brands of fuel with adequate lubrication (i.e. PowerMaster 10% nitro 22% oil 50 castor/50 synthetic, Wildcat Plus 10% nitro 18% oil with 5 ounces added castor per gallon, and Omega 10% nitro 17% oil plus 6 ounces added castor per gallon).

I hope I am wrong and your engine's piston/cylinder is not worn out and there is another explanation for it's performance. Please keep us informed on your progress.
DennisV

Dennis, sadly you may be right on the engine. It only takes one bad run to cook it, especially if there is insufficient oil. If Cruel Power fuel was used at one time (they should never sell the stuff) that could do it in.

Also, one should never need to peak the engine. Having a tach is a good idea, but only if it is used as a reference. The engine needs to be set at the rich side of lean at all times, even when aimed up or in tight maneuvers. I would suspect, like you, that there may be some issues here with a cooked piston.

As for the use of Cool Power fuel, I like to quote a local hobby shop owner. He told me once "I stock Cool Power because the RC guys want it. I don't care. I'll sell them a new engine." In RC use you can shut it down if you know enough to do so.

In cl you sre stuck until the engine runs out of fuel. So, what do you do with "Cool Power"? John Lowrey, while he still worked for Fox, offered a suggestion one day. Mix it one to one with the Fox fuel designed for the Fox 35 (29% all castor.) The 14% all synthetic in Cool Power combined with the 29% castor makes a blend of about 21 1/2% total oil that is two thirds castor, one third synthetic. Not a bad idea.

Just an aside comment regarding breaking all of your props when landing. When you put a new prop on and before you tighten it up, rotate the propellor CCW against the engine compression until it is at about the 1 to 2 o'clock position when viewed from the front with the plane in the normal upright position (on it's landing gear).

After tightening the prop check to see that when you flip it that it bounces against the compression and comes to rest some where around the 3 o'clock position. This will give you max ground clearance and makes it difficult to snag a prop and break it.

Hi

I think a run away is like when my thin profile fuselage broke off the wing in flight (oopsy). Taipan 2bb schnuerle ported rear exhaust racing engine and fuse really ran away that day. Fly be free and unfetted!

Oh well, you learn by these things!

How about a 11x3 or 12x3?

Can't help but wonder if the liner is not installed incorrectly. Can't remember if the FPs have a locating pin or not. Regardless, I've purchased "sick" used engines only to find the liner in the wrong orientation.

"Can't remember if the FPs have a locating pin or not." >Randy Ryan

Yep. The .35 and .40 FPs have a pin in the top of the case that lines up with a notch in the top lip of the cylinder liner. I do have one Ebay special FP where the pin had been forced down flush with the top of the case (probably by someone who just reinstalled the liner out of position and then put the head on and proceeded to crank down on the head bolts). On that engine I just eye-ball the cylinder notch to align with the pin "counter sunk" in the case.
DennisV

Then a question for Terry,

Is the liner in correct position or has it been moved like Dennis mentioned? I doubt the FP will run with the liner 180n degrees out, but if it were rotated enough to allow cross communication between the rear transfer port and exhaust port it would run on the sickly side. This condition would also restrict the port areas both transfer and exhaust. Pop the head off and see if the pin is in the notch or not.

I agree with Capt. Curt - the first thing to check is how tight the head screws are and the glow plug as well. I've seen this too many times when someone is too afraid to strip the threads and the engine is running at 5% capacity because it's leaking all over the place.

Here's my proven OS-40 FP-S setup:
stock engine;
stock muffler;
stock venturi (the smaller of the two that came in the box);
K&B hot short plug (most hot plugs will work);
APC 11.5-4 prop;
PowerMaster 5% to 10% nitro, 22% lube (half syn, half castor);
uniflow wedge tank with muffler pressure;
release at 10300-10500 RPM on the ground. Runs steady like a pipe.

Piston skirt should never look black - could be a sign that the engine was fried. Start from a new FP, and this recipe works 100%.

And this is an FP ie nickel plate. THat combined with green fuel could have led to a meltdown. THe Tower 40 piston and sleeve was quite reasonable if still available.

My comments were made prior to the black skirt info and fuel type being listed. But it does sound sick.

Kurt,

The Tower .40 Sleeve and Piston is available and in stock per the link below.

http://www2.towerhobbies.com/cgi-bin/wti0001p?&W=000430869&I=LXJB06&P=K

Thanks again everyone for all the things to look for. I think you may have the answer. Pulled the head, felt like screws were tight, but in my opinion the head gasket was leaking. I will crockpot the engine tonite. Piston is black, if it is fried, how can I measure or more important what do I measure to see if the piston/cylinder are usuable? I have a 40 that some R/C guy crashed on first flight, cracked the motor mount into case, but the rest of the engine is like new. I got it on ebay for the price of the backcover and spinner. Should I just use those parts instead of chancing the black piston? By the way what exactly is the damage done when the piston gets black? Does it distort the piston, change metallurgy or what?

LAST EDITED ON Mar-21-04 AT 01:18 AM (CDT)
 
Terry,
This is just my "non-expert" opinion again.

"Piston is black, if it is fried, how can I measure or more important what do I measure to see if the piston/cylinder are usuable?”

You could try to use a micrometer, dial calipers, etc. if available but the tolerances are so small you may not be able to measure them adequately. Probably the best measurement is just if the engine has strong compression when you turn it over by hand. I asked before if you where able to tell if the engine felt like it had less compression than when it was new. Does it feel noticeably weaker now? How does it compare, compression wise, to other engines (i.e. the crashed 40 you bought off Ebay)?

“By the way what exactly is the damage done when the piston gets black? Does it distort the piston, change metallurgy or what? “

If there is excessive wear of the piston/liner then the piston cannot properly seal against the combustion gases. Therefore, some of the combustion gases will ”blow by” the piston. This means you lose some compression and lose power. I believe the gases blowing by the sides of the piston are one of the reasons the piston sidewall turns black (a healthy engine with a good seal can have black carbon build up and black coloring but mainly on the piston top – but not the sidewall). It is also possible that the worn piston experiencing “blow by” runs hotter and thus is more susceptible to carbon varnish build up on the sidewalls. The black does not distort the piston or change its metallurgy (but is an indication that you are getting “blow by” because of excessive clearance between the piston /liner).

“I have a 40 that some R/C guy crashed on first flight, cracked the motor mount into case, but the rest of the engine is like new. I got it on ebay for the price of the backcover and spinner. Should I just use those parts instead of chancing the black piston?”

Sounds like you have a cheap source for repair parts. If this is another OS .40FP, I wouldn’t have any qualms about pulling the piston/liner assembly out of it and exchanging them for your existing “black piston” piston/liner unit. Just make sure you get the notch in the top of the liner positioned over the pin in the top of the case.

There were two types of construction used for the OS .40 FP. The earlier ones were iron pistons with steel liners. The later ones were ABN (aluminum pistons with nickel-plated brass liners). The ABN engines can run with less oil (i.e. 20%, preferably with some part being castor). However, the iron/steel engines need more oil (i.e. 25% , preferably with a good part of it being castor). The attached picture (see next post)shows the different outward appearance of each type to allow you to identify which type you have.
DennisV

LAST EDITED ON Mar-21-04 AT 02:00 AM (CDT)
 
Finally got the picture to upload.
DennisV

Thanks Dennis, that cleared it up for me. The compression doesn't feel that bad, but not as good as a new one. I pulled the head and it appears the head gasket may have been leaking. The engine did have a lean run while on the coolpower when I was experimenting with tank setups.
When I get it cleaned up the new piston and liner will go in(it is the same, thanks for the picture).
If you would email me with details and knowledge you care to share, I have a Banshee also. Sounds as if you have a lot of to learn from. There are no other fliers nearby that I know of yet, and this forum helps a lot but first hand with a Banshee is valuable.

"I have a Banshee also. Sounds as if you have a lot of to learn from. There are no other fliers nearby that I know of yet, and this forum helps a lot but first hand with a Banshee is valuable"

Terry,
I'm a retread who came back to CL about 3 years ago. I bought a Banshee and read all the info here on the SSW forum about suggested changes. By using this info the plane turned out great. You can do a search for Banshee on this forum and you should get lots of helpful info. Below are just a few posting sites that popped up when I did a search for banshee. Just click on them and they will take you to the postings.
DennisV

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=4937&forum=DCForumID1

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=334&forum=DCForumID1

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=2032&forum=DCForumID1

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=2262&forum=DCForumID1

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=2693&forum=DCForumID1

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=3012&forum=DCForumID1

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=3206&forum=DCForumID1

>Finally got the picture to upload.
>DennisV

Thanks for the picture and the information on telling the difference between the two.