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Author Topic: OS FP 25 EZ Questions  (Read 1014 times)

Offline Larry Fulwider

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OS FP 25 EZ Questions
« on: December 10, 2009, 03:02:23 PM »
What is the stock venturi ID of an FP 25 (I’m guessing ~.255)?

Is the engine in the picture the older cast iron FP? (That is true of 35s)

What do the letter codes stamped on the bottoms of all OS mounting lugs mean?

Anyone got a spare stock FP 25 muffler for sale?

   Larry Fulwider
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Offline Bill Adair

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Re: OS FP 25 EZ Questions
« Reply #1 on: December 10, 2009, 05:24:52 PM »
Larry,

All I have to measure are the Sears dial calipers I use for reloading, so inside diameter readings are not precise, and were taken down the throat of the venturi while on the engine.

I have two NIB FP 25 engines, one reworked by Tom Dixon, and the other stock.

The Dixon engine reads approximately .255" ID, and the stock engine reads .257".

That doesn't seem to correlate with the metric sizes OS sold, unless that error is in my measurement method.

I think a small magnet slid into the exhaust port, with the piston at (or near) TDC will be attracted by the steel liner, but fall out of the ABN engine. Haven't tried that, as both mine are ABN. Other ways to tell are by the ABN pinch at TDC, or the brass color of the ground edge of the liner in the exhaust port.

My crankcases do not look like yours, which has the pronounced bypass tunnel.

Bill

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Offline Steve Helmick

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Re: OS FP 25 EZ Questions
« Reply #2 on: December 10, 2009, 05:36:43 PM »
ABN cylinders are plated inside & out, so no brass will be showing. The magnet is a good test. I don't think any were made in ABC, but then again.... 

The muffler that sells with the current OS .25LA is the "good" one for the dreaded BBTU .21FP setup. The earlier PN's are not highly sought after, so should be cheap or free. Just tell 'em that Da Dirt said free would be a fair price...  LL~ Steve 
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Offline Brett Buck

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Re: OS FP 25 EZ Questions
« Reply #3 on: December 10, 2009, 11:03:13 PM »
Quote from: Larry Fulwider on December 10, 2009, 03:02:23 PM
What is the stock venturi ID of an FP 25 (I’m guessing ~.255)?

Is the engine in the picture the older cast iron FP? (That is true of 35s)

What do the letter codes stamped on the bottoms of all OS mounting lugs mean?

Anyone got a spare stock FP 25 muffler for sale?

   Larry Fulwider


    I am pretty sure that one is an iron-liner motor.

     Brett
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Offline Geoff Goodworth

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Re: OS FP 25 EZ Questions
« Reply #4 on: December 10, 2009, 11:19:27 PM »
I have been buying venturis from Tower to convert RC FP 20s and 25s and the diameter is .258" (6.55mm) which I agree, looks a little strange. However, that's the size as measured with a brand new digital vernier.

As the crankcase is the early model, the liner is in all probability, steel. However, I have one engine bought from eBay, supposedly NIB that has the ABN P&C.

I think the letter codes are to identify production batches. Certainly, I use them to identify all my engines.

The suggested magnet trick works. I even epoxied a small magnet to a piece of plastic kit sprue to make a test 'instrument' for evaluating my eBay purchases.

Cheers, Geoff
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Offline Larry Fulwider

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Re: OS FP 25 EZ Questions
« Reply #5 on: December 11, 2009, 11:18:56 AM »
I should have titled this EZ Questions for OS FP 25, but no smarty-pants asked, "Where are the other 21 questions". Ah, well, this is not a grammar or spelling forum with "shinny finishes" and "loose - lose" confusion.  ;)

Thanks Bill, Steve, Brett, and Geoff.  H^^  Every question answered with confidence and completeness -- what more could you ask for from a forum?  CLP**

I didn't have a magnet small enough to test the piston / liner, and don't want to pull the head. From what y'all said, I'll run it as a castor only engine.

I'll advertise for a free muffler and see what happens.  ::) Great info on the "good muffler", but those suckers (LA 25) are heavy (2.3 oz per Tower). For a non-competition plane, the old Plain Jane FP 25 "silencer" should do just fine! I'll keep that in mind for possible future use, as I know that is one of (Brett's, Dirt's?) performance keys. For now, it is strictly a "sport" engine.

I may keep the ST NV and calc a bigger than .258 venturi, or just swap back with an OS NVA, as I have a .256 and .259 in the drawer. In any case, I got the cross section now, so whatever is easier.

Thanks again!

     Larry Fulwider
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Offline Brett Buck

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Re: OS FP 25 EZ Questions
« Reply #6 on: December 11, 2009, 06:38:03 PM »
Quote from: Larry Fulwider on December 11, 2009, 11:18:56 AM
I'll advertise for a free muffler and see what happens.  ::) Great info on the "good muffler", but those suckers (LA 25) are heavy (2.3 oz per Tower). For a non-competition plane, the old Plain Jane FP 25 "silencer" should do just fine! I'll keep that in mind for possible future use, as I know that is one of (Brett's, Dirt's?) performance keys. For now, it is strictly a "sport" engine.

     I think that the "2030" muffler on the current LA *is* the "plain jane" 25FP muffler. I have no information on the previous "832" muffler but it may work as well or better. But its not likely to be any lighter. I just use them. 2.3 oz for a good-running and extremely quiet engine is a good investment. If the airplane comes out nose-heavy, add lead to the tail. Even a little bit better propulsion completely overwhelms any small weight disadvantage.

    Brett
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Offline Howard Rush

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Re: OS FP 25 EZ Questions
« Reply #7 on: December 11, 2009, 07:48:19 PM »
Will one of these engines pull a Ringmaster?
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Offline Brett Buck

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Re: OS FP 25 EZ Questions
« Reply #8 on: December 11, 2009, 09:15:32 PM »
Quote from: Howard Rush on December 11, 2009, 07:48:19 PM
Will one of these engines pull a Ringmaster?

   Could probably fly a biplane Ringmaster with this kind of power.

    Brett
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Offline Bill Heher

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Re: OS FP 25 EZ Questions
« Reply #9 on: December 13, 2009, 09:05:35 AM »
They fly a Ringmaster great, i've had a couple different FP 25s on 3 different Ringmaster and I rcommend this combo to anyone who wants a good flying, easy starting, reliable sport plane. 

It is also a great engine for a Flite Streak, I've never flown a FS with the much revered .20 set-up, but have had a couple with the .25 and they flew as well or better than the Ringmasters did.
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