So I bought a FP 40 used and threw it on a airplane, thought it vibrated more than it should.  Flew it and it just ran away wild.  I've seen on here about adding a head gasket. So I pull the head gasket of the motor and  put on a different FP 40 that was R/C. Took the needle and venturi off, the venturi was .290. I've read to use a FP 20-25 venturi. I've got a new one laying around, it measures .260. So I put that on.  It has a 843 muffler, maybe I should of used a 892. I have no idea what the right muffler is.  Both FP 40s are the steel ones. Anyway I set the needle right when the engine starts to break and about 1 or 2 laps and it runs away wild too. Engine runs out of spunk in the stunts running lean.  Basically the head shim and smaller venturi didn't do anything different. What can I do now to tame it?

I've got 2 FP 40 abn engines as well,  I assume they run wild as well?

I could chuck up the head and remove materal but I have no idea how much...

Chris

DO NOT cut up your engines.

What prop (brand, model, diameter, and pitch)?  What fuel?  What launch RPM?

I was just flying with a Tower 40 today, which as far as I know is an FP clone.  It flew great on an APC 11-4 and some Omega 10% Nitro that's been doctored up with some extra castor oil to bring the oil content up to 22%.

If you try to run an un-modified FP like a Fox 35, with a 6-pitch prop and a 2-4-2 break, then it'll run away every time.

APC 11-4, 10% 11.5 11.5 Brodak fuel. I didn't tach it, I just cranked it up till I heard it break.

So I bought a FP 40 used and threw it on a airplane, thought it vibrated more than it should.  Flew it and it just ran away wild. ....

<snip>

 Anyway I set the needle right when the engine starts to break and about 1 or 2 laps and it runs away wild too. Engine runs out of spunk in the stunts running lean.

<snip>

    That's just what they do, time after time. I despise 40FPs for many reasons, but mostly because the "engine rework industry" was kept alive by people trying to get 40FPs to run properly (and usually failing in one way or the other).

   My advice - sell them to an RC guy and use the money to buy an Aero-Tiger.

     Brett

So I bought a FP 40 used and threw it on a airplane, thought it vibrated more than it should.  Flew it and it just ran away wild.  I've seen on here about adding a head gasket. So I pull the head gasket of the motor and  put on a different FP 40 that was R/C. Took the needle and venturi off, the venturi was .290. I've read to use a FP 20-25 venturi. I've got a new one laying around, it measures .260. So I put that on.  It has a 843 muffler, maybe I should of used a 892. I have no idea what the right muffler is.  Both FP 40s are the steel ones. Anyway I set the needle right when the engine starts to break and about 1 or 2 laps and it runs away wild too. Engine runs out of spunk in the stunts running lean.  Basically the head shim and smaller venturi didn't do anything different. What can I do now to tame it?

I've got 2 FP 40 abn engines as well,  I assume they run wild as well?

I could chuck up the head and remove materal but I have no idea how much...

Chris

What needle  are  you using?   Do you have a tongue muffler that will fit it?   Fuel  ?  are you sure the crankshaft is straight?

Randy

Well that's no help,  I wanna tear up the skies tomorrow with the old girl. Maybe I can put a pair of pantyhose or two on and not run for 20 minutes on 4.5oz's. Someday I'm gonna bring back the LA 25 post too cause I can't get a stock one to not be a disappointing dog either.

On my Tower 40, and my 46LAs, I launch at somewhere between 9600 and 9800 depending on the plane.  If they run away, I put on pantyhose and launch at a speed that'll get them through the pattern.  If they thin out at 45 degrees and in the overheads, I remove pantyhose and try again.  Eventually this stopped working on the Tower 40, but a night in the crock pot with some antifreeze cured that very nicely.

If Brett's right, though, you're out of luck -- I can't say, because the only 40FP I have is on a carrier plane.

What needle  are  you using?   Do you have a tongue muffler that will fit it?   Fuel  ?  are you sure the crankshaft is straight?

Randy

A stock OS needle, 20-40 FP .135 thick spray bar. I do have a couple tongue mufflers around.  Brodak 10% 11.5 castor 11.5 synthetic. Both used 40FP I have tried vibrate a bit.  Cranks appear to be straight.

Chris

If This Dosnt Cure My FSR , I'll tear its head off . 

Said to MAINTAIN SQUISH BAND CLEARANCE Whilst Lowering C.R.

the clearance is required for the shock wave for the turbulance for the mixing / C R ' Shock ' , at t d c .

-------------------------------------------------------------------------------------------------------------------

Tho OS FP injun tests on sceptre flight , the Combustion Chamber Volumes are differant , C/L to R.C.
So Presumeably the R C head & the C L head are NOT the same ?? on the FP 40 .

any comparisons there ?

My buddy reworked my fp40, and it starts on the first flip, never runs away,  and 4-2-4's perfectly.
I believe he changed the timing a little,  added a shim,  and puts on a (I think) .240 venturi. It's got an ST nva. Edit- this engine has a .256" venturi.
Whatever he's done,  it works. Launch is in a mode between 2 cycle and 4 cycle, and we are running a  uni-flow tank.
Hope you get yours sorted.
R,
Chris

Chris,
Bob Z also posted a similar picture of his mods to the FP.40 head, so you can compare the two if you can find it. He posted it within the past year either in the open, or more likely the engine forum. It changed mine in my full fuse Oriental from running away after the first few stunts, and it ran a nice dependable 4-2 after that. You don't have to run it with a 4-2 break, I don't believe it was intended to anyway. FPs are notorious for running great on every flight except officials.

Mine had a stock FP.25 venturi and NVA. I ran an APC 10-1/2 x 4-1/2 prop with 10/22 Powermaster fuel. Tongue muffler an extra row of holes and pressure to the uni vent. Adding head gaskets did nothing to improve mine before I gave up and turned it over to Bob.
Rusty

EDIT: I found the picture he gave me, and that is it above in Matt's post.

Good to know Rusty thanks! Do you know with your head mod still has the extra head gasket or just one now?

Chris

A stock OS needle, 20-40 FP .135 thick spray bar. I do have a couple tongue mufflers around.  Brodak 10% 11.5 castor 11.5 synthetic. Both used 40FP I have tried vibrate a bit.  Cranks appear to be straight.

Chris

The 290 venturi with a FP 20  needle  is  WHOPPING  TOO  big.. This is the equivalent of about a 325 Venturi . The normal OS NVA  diameter was .157  before they started to  use the  FO 20 Needle, you should  try a  255 to 260 venturi  maximum .
The ones I set up, and I have setup over 300 of them use that size, if you use a PA, ST , Enya, OLD OS  Needle assembly  use a  280 venturi .
 The STOCK head does NOT need to be cut, This is normally just a way to reduce power by cutting the compression out of it   , it works very well as is  with 1 or 2 head shims, it needs no more.
I use a  11x4.5 ,  11x4, 12 x 4  11.5 x 4.5  prop, 5 or 10 % nitro  and 20% oil fuel with at least 1/2 synthetic oil.
In many ships this setup will launch about 10,7 to 11,100 RPMs, launch in just barely a 2 stroke or cackling back in forth in  4-2
The engine will unload and richen as the first lap goes... if it does not check your tank,  Do NOT run pressure, or the  742   muffler, Use a tongue or  open tube type that has an exhaust of at least 310 ID
Also  it is not normal  to  have that much vibration, the most common cause of this is a slightly bent crank, and  no  you cannot see it with your  eye. You need to check the run out with a dial indicator

Randy

Good to know Rusty thanks! Do you know with your head mod still has the extra head gasket or just one now?

Chris

Just one.

Brett- just for the sake of accuracy,  my buddy that set up the FP .40 says my engine has a .256 venturi (with the .156" ST needle valve running through it.
Boost port not blocked.

R,
Chris

Anybody know how you check for a bent shaft? I could put a dial indicator on the end of the prop shaft and turn the motor through but it's not going to be much of a reading bouncing up and down on the threads.

Anybody know how you check for a bent shaft? I could put a dial indicator on the end of the prop shaft and turn the motor through but it's not going to be much of a reading bouncing up and down on the threads.

Yes  I spin  mine, by hand on the lathe, or setup in bearings,  and then use the 1/4 x 28 sleeve I turned over the threads , or I use one of my Spinner couplers (that are cnc and true)  over the threads, then just slowly turn it with the dial indicator on it.
Other way is to chuck up the entire front threaded part and indicate off the of the main journal
If I get time I will try to take a photo

Randy

Maybe Randy can tell us what an acceptable tolerance is. Do you get any change when you apply side pressure back and forth?

One of the 2 has a bit of a sloppy shaft bushing, I think it was about .010-.015, probably some jerk that didn't balance his props.

Hi
001 run out will not make it vibrate and is OK, that said  , with that much bushing slop you cannot  test it that way, you would need it out of the  case. I assume you are keeping the  motor still and turning the crankshaft?
If you test that way you would need to remove the head, and try to spin the crank consistently without moving it up down or side ways in the bore, also if you have any drag in the piston sleeve then remove it too before testing

Randy

Hi
001 run out will not make it vibrate and is OK, that said  , with that much bushing slop you cannot  test it that way, you would need it out of the  case.

      I am far from an aerospace machinist but I would be tempted to remove the crank, put the thread in a 1/4" collet, then put the dial indicator on the smooth part of the shaft. That will tell you if the crank is bent WRT the threads.

    What it won't tell you is if the plane of the drive washer it perpendicular to the crank, which might be just as important.

     Brett

      I am far from an aerospace machinist but I would be tempted to remove the crank, put the thread in a 1/4" collet, then put the dial indicator on the smooth part of the shaft. That will tell you if the crank is bent WRT the threads.

    What it won't tell you is if the plane of the drive washer it perpendicular to the crank, which might be just as important.

     Brett

Why not indicate the front of the drive washer wile in the collet then?  Good idea though, I always forget about collets.

Chris

Because I do have a good dial indicator but no good way to fixture these cranks to check run out.... I have never tried

BUT if I did, I would probably gut the engine down to only the crank and bearing(S) ...super clean and dry, then very slight coat or ARO and indicate off front drive washer that the OD should be concentric with a prop tightened down

last year, I had one engine that vibrated a lot more than I thought was right >>>compared to several other of same lineage

I set to get one good prop properly balanced and each tip in plane....convinced myself the hub was flat and square to the blades
This was on an Enya 5224 .35 with collet compression drive washer.... tried several different prop clocking and still vibrated
When I checked for the prop tips in plane, now on the engine, I discovered the drive washer was not perpendicular WRT the crank shaft...swapped drive washers and vibration went away.....


FWIIW I now have a robust collection of OS LA/FP/FX engines from .20 to .46 and so far all of them seem to run the smoothest of any of my other similarly sized engine brands

BUT a year ago I did a bench run with brand new APC prop one time with a NIB OS FP .25, and learned a lot about a badly out of balance prop.... OR was it that horribly off center placed drill hole....hummmm

Yes Virginia I did remove the sticker and glue

and yes, NOW I do check the balance and correct for all my to be in use props


Funny how for years I got away with never balancing a Top Flite/Torpedo/Grish 1/2a prop or any Rev Up .35 / .36 combat engine propellers

Hi Chris
The bushing should have no more than .005 thou slop on a OS FP, they have less when new and run very well, as far as how much runout, I would not use the crank if it has more than .003 to 4 thou

Still, as I said the best way to test is to remove the crank, and test it that way, you can also load the drive washer with spacer rop washer nut  and test the  runout on it  too, I would put the spinner back plate on just to  have another point to run the dial indicator on

Randy

Thank you for the information Randy!

I assume the same tolerances apply for the LA series engines?

Chris

looks Marvelous . theres half a dozen heads in the mail on the way . 

I know I am going to regret this, but can anyone explain why you think lowering the compression will keep the engine from running away?

Are you asking me? I just read a bunch of people had problems with the engine and everyone's cure was a extra head gasket or if that didn't work getting the head machined. I have 4 of them and I'm willing to give anything a try when I run out of ideas. I really have no idea what more or less compression does. I'm just trying what has worked for others, if it don't work for me I just waisted my time and move on to something else. I think most of my problem is a weak fuselage causing vibration.
After running the engine with a machined head it seemed to be breaking from 4-cycle to 2-cycle at 8300rpm so that seems to be following what your saying.

The  tweek from there .
Other things that help  are a solid motor mount, stiff frontend, well made tank mounted to help minimize vibration, keep the tank close to the  engine,
Randy

Randy could you show me a good example of a padded tank mount that will minimize vibration for a profile?

Thanks
Chris

I think the only place where I really differ from Randy is purely a matter of personal preference -- he likes to use a 0.157 needle; I just hate having a motor that's had holes drilled out, so my tendency is to make a venturi of a size that's proper for the OS needle assembly, and run with that.

But he's telling you pretty much the same thing I was.

Dang.  Now I need to go get a 40FP and give it a whirl in a plane...

I'm reluctant to drill mine out as well. However lately when I see 1 click almost change 300rpm I think it might be nice to have a more fine adjustment. Looking on "list your LA46 setup" almost everyone is using a PA needle valve.

It's only @ .010" off each side of the hole. Practically nothing. So much easier than what you did (a beautiful job of) putting the head on the lathe, for sure.
It's worth it alone for having a needle valve without "clicks" at all. We like the Brodak NVA's as well.
Any needle valve with an adjustable tension collet on a smooth needle is awesome, they seal wonderfully and have infinite adjustment. Just what you want in a needle valve.

DO IT! :-)

Hope you come back with a happy result!

Try my sized (.256") venturi and the .156" NVA, and see what happens. I believe we are running 8% nitro, and 11/11 oil, so aim for 5% or 10% nitro with that same venturi and needle and your results should be close.

Thank you! I'll hack up a 40FP without much heartache, buuuut I have a hard time cutting up my beloved LA46's. They seem to have increased in price a lot on eBay lately. Plus then I have to turn around and buy all new needle valve assemblys. This hobby will make you broke fast.  Maybe just maybe I'll take the giant leap in the near future and try one but I may need someone to pull the trigger on the drill for me

Chris