Author Topic: FP .25 Help Please (Read 3375 times)

Paul Taylor · « **on:** January 01, 2011, 12:26:01 PM »

So I am going to take a FP 25 apart for the first time. I can not get a consistent engine run on this engine. So I am going to pull it apart and see if there is some issue with the engine. I have eliminated the tank and fuel lines.

I pulled the head off.

First question - Can you put this head on either way? I see nothing that really keeps me from mounting this back either way.

Thanks
Paul

RandySmith · « **Reply #1 on:** January 01, 2011, 12:54:06 PM »

Quote from: Paul Taylor on January 01, 2011, 12:26:01 PM

So I am going to take a FP 25 apart for the first time. I can not get a consistent engine run on this engine. So I am going to pull it apart and see if there is some issue with the engine. I have eliminated the tank and fuel lines.

I pulled the head off.

First question - Can you put this head on either way? I see nothing that really keeps me from mounting this back either way.

Thanks
Paul

Hi Paul

Yes there is no front or back either is fine, the motor is not hard to disassemble, so you should have no problem

Randy

Paul Taylor · « **Reply #2 on:** January 01, 2011, 01:14:26 PM »

Thanks Randy,
I have it disassembled. Took the heat gun and the P&L slid right out.

Now more questions.

No head shims.
Would it help to add one or two?

Ports? I see three in the case and 4 slots in the liner. Do I need to file or block something here?

What size should the venturi be?

Bill Little · « **Reply #3 on:** January 01, 2011, 05:21:44 PM »

Quote from: Paul Taylor on January 01, 2011, 01:14:26 PM

Thanks Randy,
I have it disassembled. Took the heat gun and the P&L slid right out.

Now more questions.

No head shims.
Would it help to add one or two?

Ports? I see three in the case and 4 slots in the liner. Do I need to file or block something here?

What size should the venturi be?

Hi Paul,

I'm going to ask a question or two, knowing Randy will over rule if necessary.

What was "wrong" with the way the engine WAS running?

How do you WANT it to run?

Not being a smart a$$, really.

BTW: the head shim can be hard to "see" and "hard" to remove, sometimes. There have been a shim present that I have missed in the past.

(take over Randy, this is your area of expertise, not mine! LOL!!)

Bill

Paul Taylor · « **Reply #4 on:** January 01, 2011, 05:59:30 PM »

Hey Bill,
I have never got a good engine run on this engine. One of my flying buddy's suggested that I change out the head screws with socket head screws. So I swapped out all screws on the engine with socket head screws.
Still not much better. Engine would still not run good. I check the tank and lines, swapped out the tank and lines. Nope. Swapped out the NVA and put in a ST. Nope still not happy with the engine run.
So I figured I would take it apart to see if maybe something was not put together right.

The piston top is very black. Would it help to try and put if flat on glass with a polishing compound?
The other thing is when I took the back plate off the gasket is broken. Not sure if I broke it taking the back off or it was already broke. But I have some gasket paper, or just put a little permatex on it.

I am not a engine expert so really looking to you guys to help me fix this thing.

Thanks

Bill Little · « **Reply #5 on:** January 01, 2011, 06:49:16 PM »

Hi Paul,

So, how did the engine "run" when you ran it?

No power, couldn't get the rpm to stay steady, wouldn't run in a 2 cycle, would run too lean or too rich upright or inverted, cut off with no warning at anytime??

When you say you couldn't get a "good engine RUN", that is just to broad and could mean a LOT of things.

caveat: I am not an "Engine Expert" either. LOL!! (but the guy who's name is at the top is, and I have learned more than he realizes from him at least as far as running an engine in model airplane)

Just explain what the engine is/was doing and some answers will come, I am sure.

Bill

Russell Shaffer · « **Reply #6 on:** January 01, 2011, 06:57:59 PM »

Paul, don't use Permatex. Alcohol is the recommended clean up method. The stuff melts in glo fuel.

Tim Wescott · « **Reply #7 on:** January 01, 2011, 07:17:34 PM »

While you're answering Bill's questions -- did you buy the engine new or used? If used, what was the condition?

A bad backplate gasket can cause all sorts of mysterious problems, but they rip easily on disassembly and I wouldn't expect an engine to have a bad one from the factory. If the engine is used it may have been take apart and reassemble incorrectly (including a torn gasket). OTOH, if you bought the engine new and haven't opened it up then chances are that you just ripped the gasket when you took the backplate off. So knowing what it was like when you bought it and what you've done to it would make a big difference.

Socket head screws look cool and are easier to wrench on, but the part of the screw that matters to the motor is the part that touches the motor. Changing to socket head screws will make the screws themselves last longer if you're constantly tearing the motor down, and they'll make it look better to a gearhead (like me), but a properly installed Phillips head (or straight head) screw is going to perform just like a properly installed socket head screw.

Paul Taylor · « **Reply #8 on:** January 01, 2011, 07:48:18 PM »

Quote from: Bill Little on January 01, 2011, 06:49:16 PM

Hi Paul,

So, how did the engine "run" when you ran it?

No power, couldn't get the rpm to stay steady, wouldn't run in a 2 cycle, would run too lean or too rich upright or inverted, cut off with no warning at anytime??

Hey Bill,
Yes and Yes.

Well let me see if I can explain it a little better.
I would maybe get a good run. Wait my turn again to fly, and I would start the engine and might have to tweak the needle. It would take off then half way into the flight it would go lean, or maybe sag. I could not get two runs back to back to be the same. Some said I had a air leak. I ran with and without muffler pressure. I ran a clunk tank, and last was with run a uni-flow tank. I had a fuel filter in the fuel line. I took the filter out of the line and put one piece of fuel line in it's place. It never has just cut out. This engine was on my SkyRay. I got this engine second hand so I'm not sure what happen with it before I got it. I just know I have not been real happy with the performance. And my flying buddy that suggest that I put the cap screws in it made a statement that has stuck with me. He said "I have never seen that engine run right".

It might run OK on a test stand, but that is upright and not on a profile plane under load.
I hope this helps.
Thanks Big Bear!

Paul Taylor · « **Reply #9 on:** January 01, 2011, 07:51:15 PM »

One more pic.

It show a little wear on the back plate, but that might be from using a electric starter early in it's life. I had start it.
Also the piston top is black. Not sure if that tells you anything.

Bill Little · « **Reply #10 on:** January 01, 2011, 08:11:38 PM »

Hi Paul,

Yeah, I would say "something" needs fixing. You have the engine apart, so might as well do as best you can to make sure the "guts" are good.

I am sure you checked the NVA or replaced it. Funny, but I have seen that, and nothing else done, "fix" an engine, but who knows!

One of the guys at Huntersville a couple years ago couldn't get the engine to run consistently. we took it over to a table, pulled it off the plane and I tightened the back plate screws first off. That was ll it took. Of course it was an LA with a plastic back plate so that is the first thing to look at with one of those. Sometimes it is a head scratcher, for anyone. Aaron had a "special" OS .40VF on pipe at his first NATS. It ran perfect here the day before we left. Second practice flight at Muncie it flamed out in level flight RIGHT BEFORE the reverse wing over. That continued ALL DAY! You would not believe all the guys who tried to help fix it. Bob Gieseke, Bill Rich, Mikey Pratt, Dave Hemstraugth, Randy, Billy, Ted, Windy........ new plugs, new tank, and the list went on. If it could be changed, it was. Bob G. even gave Aaron his turn on a circle to test fly (and he did it in a very funny way! LOL!!) 10 hours, multiple efforts, never "got" to the R.O. 4 or 5 laps after launch and land! We DID have a spare engine at the hotel, so the next day things were perfect (with the spare engine that is!). The first night, Billy took the engine held it up to his ear and said something to the effects that something sounded funny. I handed the engine to Randy to take home and see what he could find. WE got it back in the mail a couple weeks later and it never had a another problem! (and still don't know what he had to do to fix it.........but I think a bearing had starting going bad for whatever reason) Geee.............. engines sure can be FUN!

Clean all the carbon out, make sure everything is put back correctly, and make sure the BP, NVA, and head seal. Might throw another NVA in it if you have one. If it has good compression, good seals, good NVA, good glo plug, good fuel (and all else that goes with the "plane setup"), it should "run good". If anything is bent (crankshaft, rod, etc) or the NVA is bad (bent, not sealing or not sealing to the case), or there is a leak somewhere, all bets are off.

Steve Helmick · « **Reply #11 on:** January 01, 2011, 08:20:46 PM »

You might want to clean the carbon off the top of the piston, but it probably won't help. It could be the backplate gasket. An extra head gasket might fix it right up, or just a change in glowplugs. A short glowplug won't run worth a spit, and some long ones won't be much better! I avoid Fox glowplugs like the plague, for instance.

There's a lot we don't know about your "setup"! Muffler, prop, fuel, glowplug. I've seen guys run 9-4 APC's, 10-4 APC's and 11-4 APC's on their .25FP's, and they run fine on all of them...just different.

I tried a couple of Sullivan clunk tanks, one worked, the other leaked like a PIG! The #1 simple and reliable clunk tank is the Hayes standard type. You can't hardly make it leak, and it cannot leak, or engine will be unhappy.

Steve

Tim Wescott · « **Reply #12 on:** January 01, 2011, 08:21:23 PM »

I have had troubles with bad crankcase gaskets, and it sure has the symptoms that you describe. It's certainly an air leak, just not in the fuel system.

You may want to get or make up a good case gasket (I've heard that playing cards work well, but haven't tried that trick). Put it all together, and try it again.

When you're done, check the head, glow plug and piston for leaks. The head and glow plug shouldn't show bubbles if you drip fuel on them and slowly bring the prop through a compression stroke. Make sure to check the top of the plug (although I expect that you've swapped plugs by now). You should be able to bring it to top dead center and hold it there for a second (or several) and feel as much compression coming down as you did going up.

I don't know about the FP specifically, but my OS max engines have an O-ring to seal the carb/venturi. Pull your venturi, and check the condition of the O-ring. If it's hard and compressed (if the outside is flattened and doesn't spring back when you disassemble it) then air can leak around the carb. AFAIK this wouldn't cause massive problems, but it's still something to check.

Good luck, and if someone who actually knows what they're saying contradicts me -- believe them.

Bill Little · « **Reply #13 on:** January 01, 2011, 09:17:25 PM »

Hi Tim, and Steve!

I'm glad y'all are pretty much in agreement with the things I wrote! Makes me feel better.

Sometimes I get accused of "not knowing nothing"! LOL!!

I would mildly disagree with one statement. To strong, is all! LOL!!

Quote

It's certainly an air leak, just not in the fuel system.

It doesn't "certainly" have to be an air leak......

(but a real good probability!)

Saw an engine with a bent crank once. Not noticeable with the naked eye, took a run out dial to find it. That engine would do everything BUT run good. But, if you held your mouth just right it would run decent,,,,, maybe once a day.

Got a "brand new in the box" OS .46VF once, and it actually was! Hadn't been out of the box since the day the dude on the assembly like packaged it. Ran it on the bench and luckily didn't ruin it. It ran, sorta, but you sure couldn't put it in a plane! The sleeve had been installed almost 180* rotated from where it should have been on the assembly line....... and there is a tiny pin in the case and a tiny notch in the top lip of the sleeve to prevent that from happening!

Bill

Tim Wescott · « **Reply #14 on:** January 01, 2011, 09:26:12 PM »

Quote from: Bill Little on January 01, 2011, 09:17:25 PM

Quote from: Tim Wescott
It doesn't "certainly" have to be an air leak...... (but a real good probability!)

Argh. I hate it when I say something that seems perfectly clear, but turns out to be mangled in hindsight. I meant that a rear cover leak is certainly an air leak -- not that Paul's problem is certainly an air leak.

I certainly (and I do mean certainly) didn't manage to communicate that effectively, however!

Tim Wescott · « **Reply #15 on:** January 01, 2011, 09:30:45 PM »

Quote from: Bill Little on January 01, 2011, 09:17:25 PM

The sleeve had been installed almost 180* rotated from where it should have been on the assembly line....... and there is a tiny pin in the case and a tiny notch in the top lip of the sleeve to prevent that from happening!

Ahh, you can try making things idiot proof, but then they just go and invent better idiots.

Bill Little · « **Reply #16 on:** January 01, 2011, 09:33:50 PM »

Quote from: Tim Wescott on January 01, 2011, 09:30:45 PM

Ahh, you can try making things idiot proof, but then they just go and invent better idiots.

Geoff Goodworth · « **Reply #17 on:** January 01, 2011, 10:41:48 PM »

Guys, I'ver had more experience with FP 20s but it sounds like a back plate leak to me as well.

However, if the engine has not been dismantled before, I would be very wary of there being no haed gasket. I have seen them lock into the groove so that they are impossible to see unless you work an edge. I would expect one head gasket—whether it is readily visible or not.

Happy New Year, Geoff

kenneth cook · « **Reply #18 on:** January 02, 2011, 07:37:58 AM »

Paul, I highly recommend the use of Permatex. Bob Z turned us onto the Anaerobic Permatex. It comes in small tubes and is highly fuel resistant and can be easily dismantled and assembled in minutes. In fact he never uses any gasket in his engines.I've used this countless times on Fox .35's as the backplate on those can be finicky if distorted. This comes in handy to have in your box at the field. I would suggest taking a peak into the o-ring under the venturi. If you combine a bad or leaking o-ring with the weight of the springy needle valve flopping around, your going to get a poor and inconsistent run. I generally remove the spring and solder a small washer on the top with a few serrations filed on it. This not only stops the vibration, but it puts the needle out of harms way. The symptoms your describing sounds like this may be the culprit. The Permatex that I've described dries when the two parts mate not like RTV which dries in the atmosphere. In the event the o-ring is bad then a tad bit of rtv would suffice around the base of the venturi assuming you cleaned all traces of oil off. Keep in mind that there is most likely a small notch in that liner for a tiny roll pin sticking out of the case which lines the liner up correctly. I was just making mention of it if you weren't aware of it. Ken

kenneth cook · « **Reply #19 on:** January 02, 2011, 07:41:33 AM »

Okay, inserting foot in mouth as Tim already made mention of the venturi o-ring. Ken

Tim Wescott · « **Reply #20 on:** January 02, 2011, 11:38:06 AM »

Quote from: kenneth cook on January 02, 2011, 07:41:33 AM

Okay, inserting foot in mouth as Tim already made mention of the venturi o-ring. Ken

Nah -- for really good expository writing you try to make each point twice, in different places and with different wording.

RandySmith · « **Reply #21 on:** January 02, 2011, 11:51:52 AM »

Paul

Your getting good advice from the guys, You need a new cover gasket and a new head shim, Also look at the very tip of the ST needle to make sure it is not dinged or bent, then look thru the spray bar to maake sure the orifice hole is not bent outward or damaged, many times this happens to ST valves from running the needle too deep.
Next look at the sleeve to make sure the plating is not coming off, and that you can see no brass spots on the inside of the sleeve, This happens many many times on these motors.
Mount the engine solid when you get it back into a plane and let us know how it goes

Regards
Randy

Paul Taylor · « **Reply #22 on:** January 02, 2011, 11:56:18 AM »

K. Thanks guys!!!
Going out today to try and find some Permatex Anaerobic Gasket Maker. Will check the sleeve and needle.

Guess I will not worry about the dark color on the top of the piston?

I will keep ya'll posted.
Paul

Paul Taylor · « **Reply #23 on:** January 02, 2011, 01:18:12 PM »

K, have not went out to NAPA yet to get the Permatex but did check the sleeve and needle. I looked at the needle under a magnifying glass and saw a few little "cuts" for lack of a better word. I could not feel anything but a #11 blade seem to snag on it a little. I kept going over it with the blade lightly until it did not snag any more. The only thing that I see on the sleeve is about 1/8 in silver ring around the top end of the sleeve. It is a different color then the rest of the inside of the sleeve. Oh and I did find the head gasket.
Would it help to add one made from a coke can so that I have two?
Headed out to NAPA... wish me luck in finding the Permatex.

Paul Taylor · « **Reply #24 on:** January 02, 2011, 05:02:27 PM »

I found the Permatex. Wow $18 buck. But hey if it will fix my problem.....
I also put Permatex around the NVA. I also took the #11 blade and lightly scrapped off the black soot on the top of the piston. Now it looks better.
Test flights to happen this spring.
Stay tuned....

Brett Buck · « **Reply #25 on:** January 02, 2011, 05:24:24 PM »

Quote from: Paul Taylor on January 02, 2011, 05:02:27 PM

I found the Permatex. Wow $18 buck. But hey if it will fix my problem.....

I don't think I have ever heard of that sort of gasket material. I use the Permatix "Ultra Copper" header gasket material but truth be told regular old clear silicone II bathtub caulk is good enough for for tuned-pipe header connections. I don't see a lot of reason for anything a lot better.

Brett

kenneth cook · « **Reply #26 on:** January 03, 2011, 03:42:58 AM »

Paul, the tube I purchase is about 2 inches in length. I generally pay about $7.00. The tube is red in color and that little bit has lasted me two years now. I've used it more for my motorcycles than planes. Maybe its available in larger sizes but I wouldn't purchase a $18.00 tube myself. I've had good success with Ultra Copper as I've found it to hold up better than Ultra Blue or Ultra Black. I've seen many guys use the Ultra Blue but I've personally had it soften under harsh fuel exposure. Then again I was using 40% nitro. Ken

Paul Taylor · « **Reply #27 on:** January 03, 2011, 08:10:36 AM »

Yea, I will use this for other things as well. I got the large tube.

Bill Little · « **Reply #28 on:** January 03, 2011, 08:22:23 AM »

Too late now, and what you got will work fine, but any of the automotive silicone sealants work fine for our sealing issues.. I use some high heat "red" Permatex stuff most times.

Big Bear

Dennis Moritz · « **Reply #29 on:** January 03, 2011, 09:25:01 PM »

A worn crankcase bushing will also cause erratic running. If that's the problem, time to toss it. A shortcoming of bushed vs ball bearing engines. Tho I've seen Dan Banjok redo worn out cases, machining out the old bushing and fitting a new one. Done it to Foxes. Why did Dan bother. Because he's Daniel Banjok. I've had at least one FP35 suddenly go sour after much running. Dan diagnosed it as too much play in the bushing, causing an air leak in the crankcase. Your problem could also be the dreaded profile bad vibe. I had an ARF Flite Streak powered by an LA25 that ran with no muss or fuss for a season and a half. A remarkably consistent runner. Then the nose fell off. After following the widely published methods for reinforcing the nose including embedding cut pieces of carbon fiber arrow shaft, the LA 25 run was awful, no matter what. Tried two or three different engines (and different tanks), nothing worked. Club gurus' verdict, the dreaded profile bad vibe. At which point I went on to other birds. Also check the o ring on the venturi, should have a tight fit to the case when the needle is jammed through. If not, double the ring.

Dennis Vander Kuur · « **Reply #30 on:** January 24, 2011, 02:37:00 PM »

Quote from: Paul Taylor on January 01, 2011, 07:48:18 PM

Well let me see if I can explain it a little better.
I would maybe get a good run. Wait my turn again to fly, and I would start the engine and might have to tweak the needle. It would take off then half way into the flight it would go lean, or maybe sag. I could not get two runs back to back to be the same. Some said I had a air leak. I ran with and without muffler pressure. I ran a clunk tank, and last was with run a uni-flow tank. I had a fuel filter in the fuel line. I took the filter out of the line and put one piece of fuel line in it's place. It never has just cut out. This engine was on my SkyRay. I got this engine second hand so I'm not sure what happen with it before I got it. I just know I have not been real happy with the performance. And my flying buddy that suggest that I put the cap screws in it made a statement that has stuck with me. He said "I have never seen that engine run right".

It might run OK on a test stand, but that is upright and not on a profile plane under load.

Paul,
You have gotten a lot of excellent advice from knowledgeable people. I don't claim to be an expert but will put in my 2 cents worth anyway. In the previous reply Dennis mentioned the problem encountered when you have a weak nose on a profile airplane. I've seen this first hand. Last year at our field we had a couple profile airplanes (an ARF Pathfinder and an ARC Tutor II) that exhibited EXACTLY what you are seeing with your OS .25 on your Skyray. The owners tried changing EVERYTHING, like you did, and nothing cured the problem. That was because the problem wasn't with the engine, prop, tank, filter, fuel, etc. It was a problem with the plane. These planes had been crashed and repaired. However, ARFs and ARCs are notorious for having weak front ends to begin with and repairs don't always provide enough strength. The problem is that the profile's weakened front end lets the nose vibrate excessively. This excessive vibration will tend to aerate the fuel flow and this leads to erratic engine runs like you are experiencing. The erratic fuel flow means the engine will not get the right fuel flow throughout the entire flight from start to finish.
In trying to solve the problem with the repaired ARC Tutor II, I swapped in the entire power system (engine, prop, tank, fuel line, fuel filter, etc) from one of my known good airplanes (a Pathfinder I). The known good running engine system, installed in the ARC Tutor II and flown, now exhibited EXACTLY the same erratic engine run as the original engine system. I then installed the engine system removed from the Tutor II into my Pathfinder I without doing any other changes, flew it, and it ran perfectly. The problem was the plane, not anything related to the engine system.
You mentioned that your .25 ran OK on the test stand but not in the Skyray. This leads me to believe that your plane may be the problem. I could be wrong but has this Skyray had any "unplanned" landings. If so, it is possible that the weakened nose is letting the fuel aerate in the tank and causing your erratic engine runs. Have you tried this engine on any other planes besides this Skyray?
Hope you have good luck solving the problem.
Best regards,
DennisV
(Past participant in the world famous "Cheese-head Fly-ins")

Paul Taylor · « **Reply #31 on:** January 24, 2011, 02:58:17 PM »

Hey Dennis,
Yes, I did a few figure 9's in the past with the SkyRay. But I have now put a FSR .25 on the Ray and it runs like a scalded dog!

Can wait to fly it again.
Hope to see you this year at the CFF. (Cheezehead Fun Fly)

Go Packers!

Dennis Vander Kuur · « **Reply #32 on:** January 25, 2011, 07:28:49 AM »

Quote from: Paul Taylor on January 24, 2011, 02:58:17 PM

Go Packers!

Ouch!!!

Ward Van Duzer · « **Reply #33 on:** January 25, 2011, 11:45:33 AM »

This was a lot of reading Paul, and I believe you got a bunch of good advice, (sounds like a backplate leak to me also)
but, I don't remember reading anywhere where you changed the plug! (If you did I missed it!) I believe many of us are using the Thunderbolt R/C long plugs. While not perfect, they seem to be the most reliable.

W.