Author Topic: OS Max .25 vs. .25 FP (Read 8732 times)

nathan Metzner · « **on:** June 28, 2012, 09:20:15 PM »

I am currently trolling E-Bay looking for an OS .25 in order to build a duplicate of my flight streak. I am basically learning and after reading posts here I have come to the conclusion that having a spare airplane is the way to go. I am currently running an OS Max .25 she is turning a 9X4 about 15,000 how does this compare with an OS .25 FP. The FP's are more available and I can get venturi's and NVA's for them. My old Max is running in R/C trim. I know the FP's are considered hotter engines but the Max isn't running too bad.

Brett Buck · « **Reply #1 on:** June 28, 2012, 09:47:32 PM »

Quote from: nathan Metzner on June 28, 2012, 09:20:15 PM

I am currently trolling E-Bay looking for an OS .25 in order to build a duplicate of my flight streak. I am basically learning and after reading posts here I have come to the conclusion that having a spare airplane is the way to go. I am currently running an OS Max .25 she is turning a 9X4 about 15,000 how does this compare with an OS .25 FP. The FP's are more available and I can get venturi's and NVA's for them. My old Max is running in R/C trim. I know the FP's are considered hotter engines but the Max isn't running too bad.

What OS Max 25 are you talking about? If it's a 25S (baffle piston) I am a little skeptical about the 15,000 and if it is really doing that, expect the crankshaft to come flying out the front in the very near future. That's what happened to mine, and it was running around that speed - but on a 7-6.

Brett

philip metzner · « **Reply #2 on:** June 28, 2012, 10:01:52 PM »

Brett I have both a .25 and a .15 of this model they are labeled as os max .15 or .25 no other designation. They are early to late 70's model motors. The .15 I have run the guts out of and she keeps on ticking running a 8x4 about 15500. I am using a 10% Nitro 23% oil fuel and using no 6 os plugs. Both of these motors run like champs and show no sign of giving up. I'd love to find out how hard an FP .25 would turn a similar size prop.

nathan Metzner · « **Reply #3 on:** June 28, 2012, 10:09:56 PM »

LOL sorry wrong computer. Yeah these models have no other designtion other than MAX. Mine run great, I just bought another .15 in fact. The problem is that I cn't get venturi's for the 25's without custom making one and the FP's are more plentiful on EBay.

Brett Buck · « **Reply #4 on:** June 28, 2012, 10:54:49 PM »

Quote from: nathan Metzner on June 28, 2012, 10:09:56 PM

LOL sorry wrong computer. Yeah these models have no other designtion other than MAX. Mine run great, I just bought another .15 in fact. The problem is that I cn't get venturi's for the 25's without custom making one and the FP's are more plentiful on EBay.

Like this one? This is a 25S (from about 1975 or so, since thats when I bought it):

nathan Metzner · « **Reply #5 on:** June 28, 2012, 11:17:30 PM »

The OS website lists the motor as a 1971 model listed only as a .25 R/C they also clim to have made C/L versions of this engine yet, I have not found any on Ebay.

nathan Metzner · « **Reply #6 on:** June 28, 2012, 11:19:45 PM »

http://www.osengines.com/history/ostimeline05.html Here's the historical page on OS. I also have the paper work that came with the engine. Anywho how hard does a .25 Fp turn round about and with what prop is it happiest a 9X4 would be nice lol.

Brett Buck · « **Reply #7 on:** June 28, 2012, 11:30:46 PM »

Quote from: nathan Metzner on June 28, 2012, 11:17:30 PM

The OS website lists the motor as a 1971 model listed only as a .25 R/C they also clim to have made C/L versions of this engine yet, I have not found any on Ebay.

   That is the same engine I showed - and it came as a C/L motor. It was the second engine I bought with my own money. If you are running it at 15,000 you are in very serious danger of breaking the crank. I ran mine on a 9-6 at much lower revs. Or a 7-6 at about 15,000 when it broke the crank after about 10 flights.

   It's a nice engine, not gutless, but nothing like as strong as a 25LA or 25FP.

   Brett

Tim Wescott · « **Reply #8 on:** June 28, 2012, 11:32:43 PM »

If you can swing it, just get a new 25LA. It'll be stronger than the 25S, it'll be happy as a clam on a 9-4 (or a 10-4), and it'll pull your Flight Streak with ease.

nathan Metzner · « **Reply #9 on:** June 28, 2012, 11:51:45 PM »

Tim, Thats the idear. I am hoping to make the two planes as similar as I can. As for the durability issue that Brett is saying I have not found this to be the case with these models of motors. Mine seem to be very happy and smooth and I have about 30-50 runs on the .15 size of this model and it turns harder. The tach we use has been very consistant so far but maybe it lies for these motors lol. I suppose I can just get the FP and if it is too powerful I can just put it on EBay or something. As fr as n LA to be honest I have an LA .15 and I don't like it all that much. It won't keep up with my old .15 and I've had some stability issues with it.

Dennis Moritz · « **Reply #10 on:** June 29, 2012, 06:47:26 AM »

La 15s are run in Clown racing. They can howl. Also they get put on bladder with the venturi removed. Run in CL combat. I believe they are the required power for at least one class of RC Combat. Replace the remote needle with a threw the venturi needle. Add nitro. LA25s can be run sweet. I have seen many ARF Flite Streaks doing no fuss no muss patterns powered by an LA25. I think the prop is a 9x4, usually. Through the venturi needle, best way to go. If you are inclined, up the nitro some, and let it howl. Fp 15s and 25s seem to have even a bit more guts. We see FP15s topping out at over 20,000. Fp 25s. Near that. Both run fine on bladder with the venturi popped out. Screamers. Very entertaining. Cheap considering what they will do. So far no broken cranks. Even tho folks are working at it. In many ways these engines are superior in speed limit combat to the high priced, hard to get, dedicated combat engines. The crank bushing will take a beating, going into the ground, without needing a bearing redo.

Andrew Tinsley · « **Reply #11 on:** June 29, 2012, 08:24:49 AM »

Hi Nathan,
If you want a really good running engine, use an FP20 with the Brett Buck tune up (BBTU). I have accumulated lots of them, because I never want to run out!
The 20FP with BBTU is an absolute gem in a Flitestreak and I couldn't recommend the combination more highly. Look up past posts on the BBTU Brett and Dan Rutherford have covered the topic extremely well.

Regards,

Andrew.

Brett Buck · « **Reply #12 on:** June 29, 2012, 09:51:12 AM »

Quote from: nathan Metzner on June 28, 2012, 11:51:45 PM

Tim, Thats the idear. I am hoping to make the two planes as similar as I can. As for the durability issue that Brett is saying I have not found this to be the case with these models of motors. Mine seem to be very happy and smooth and I have about 30-50 runs on the .15 size of this model and it turns harder. The tach we use has been very consistant so far but maybe it lies for these motors lol. I suppose I can just get the FP and if it is too powerful I can just put it on EBay or something. As fr as n LA to be honest I have an LA .15 and I don't like it all that much. It won't keep up with my old .15 and I've had some stability issues with it.

   The 15 may be a different story than the 25. They, of necessity, are going to spin faster than the big ones.

The 25 is a different story. I question how fast the airplane is going, assuming 15000 with a 9-4 - gotta be WAY faster than the airplanes we fly, and, for example Ringmaster + 9-4 + 12000 ground rpm = 3.5 second laps. 15000 sounds like it would be around 3 flat.

   I am pretty sure at that kind of power/rpm level, something is going to give up the ghost in pretty short order. Do as you will, of course, it's just a friendly suggestion from someone who has been down this road.

   Brett

Brett Buck · « **Reply #13 on:** June 29, 2012, 10:00:56 AM »

Quote from: Dennis Moritz on June 29, 2012, 06:47:26 AM

Screamers. Very entertaining. Cheap considering what they will do. So far no broken cranks. Even tho folks are working at it. In many ways these engines are superior in speed limit combat to the high priced, hard to get, dedicated combat engines. The crank bushing will take a beating, going into the ground, without needing a bearing redo.

If it was an FP, I wouldn't be too concerned. 25S is another story. Mine and my Uncle Donnie's broke in the same place - the crack will start at the corner of the crank port and be a spiral around to the opposite corner. We think it started at the trailing rear corner and then moved around to the front leading corner.

Brett

nathan Metzner · « **Reply #14 on:** June 29, 2012, 12:31:01 PM »

I'm not doubting your experience at all. In fact, I am questioning why they would build an engine that when propped as they suggest with the fuel they suggest will self destruct. I was plenty surprised when I began testing the motor and it ran that well. She is stable as can be and when I fatten it up it becomes unstable. That is just strange to pieces. It is highley possible that the reason this engine runs as it does is the R/C carb tune. I know R/C's are not necessarily designed to run all out all the time so it may be that the venturi area is too large for my needs. If this is the case I should have some fuel pickup issues once she gets in the air. I have yet to fly this plane so I can not comment on the speed of the laps I have been doing engine testing up until now. I may be best suited to find out which venturi and NVA best mimicks the stock ones that you have Brett.

phil c · « **Reply #15 on:** July 02, 2012, 08:06:57 PM »

Nathan, the 25S was designed for RC. RC guys rarely fly wide open for more than 10-15 seconds. The plane goes out of sight. So they are constantly using the throttle and the load on the engine is much less.

If you have a spare crank, fine, but I'd take Brett's friendly advice and throttle it back to 12-13,000 rpm. A little piece of bent wire run from the upper right backplate bolt to the throttle can be used as a speed adjustment. If you like the speed run an 8/5 prop at the lower rpm.

nathan Metzner · « **Reply #16 on:** July 02, 2012, 08:17:20 PM »

Yeah phil I have a rod made up that goes to the front corner engine mount. I'm gonna take his advice and throttle it back some. Once I thought through the R/C ramifications I figured this was the situation. If I could figure out a venturi and NVA for it that would work that would be cool as well. Anyway I still would like to know if the published OS performance numbers are acurte or not. I have seen the light on the os 20 fp and am on the look out for one but they are not as plentiful on Ebay. I hve recently got .35 FP that I am thinking of building built up oriental for.

Chris Wilson · « **Reply #17 on:** July 02, 2012, 08:37:41 PM »

Quote from: Brett Buck on June 29, 2012, 10:00:56 AM

If it was an FP, I wouldn't be too concerned. 25S is another story. Mine and my Uncle Donnie's broke in the same place - the crack will start at the corner of the crank port and be a spiral around to the opposite corner. We think it started at the trailing rear corner and then moved around to the front leading corner.

Brett

Hmm, sounds like the inlet port in the shaft should have been radiused instead of square cut, the sharp 90º inside corners will promote a spiral crack emanating from the inlet port (source of drag at the prop end) and propagating towards the crank pin (source of power).

Brett Buck · « **Reply #18 on:** July 02, 2012, 09:42:30 PM »

Quote from: Chris Wilson on July 02, 2012, 08:37:41 PM

Hmm, sounds like the inlet port in the shaft should have been radiused instead of square cut, the sharp 90º inside corners will promote a spiral crack emanating from the inlet port (source of drag at the prop end) and propagating towards the crank pin (source of power).

Well, probably, or the walls could have been thicker. In any case, I didn't design it. I did manage to break it.

Brett

nathan Metzner · « **Reply #19 on:** July 02, 2012, 10:48:00 PM »

Hopefully I'll keep mine in one piece lol. I love the consistancy of that motor and I think it will pull that FS around like a champ. Thanks for your advice Brett, it took a while for my beedy little brain to wrap itself around it.

nathan Metzner · « **Reply #20 on:** July 05, 2012, 08:18:06 AM »

I have a .20 FP on the way. It is in R/C trim so I am going to have to swap it over. I'm unsure if the muffler that is on it is the right one per BBTU so I'll check that. I also do not know how to check if it is n ABN or not without disessembeling the engine (which I would rather not do.) I have a .35 FP that is waiting on me to build a plane for it and I'm unsure of how old it is as well. It's never been run and the box was an older type that slipped together rather than a flap. So how do I tell the difference between the older models nd the newer ones? DOes it even matter?

Brett Buck · « **Reply #21 on:** July 05, 2012, 09:18:20 AM »

Quote from: nathan Metzner on July 05, 2012, 08:18:06 AM

I have a .20 FP on the way. It is in R/C trim so I am going to have to swap it over. I'm unsure if the muffler that is on it is the right one per BBTU so I'll check that. I also do not know how to check if it is n ABN or not without disessembeling the engine (which I would rather not do.) I have a .35 FP that is waiting on me to build a plane for it and I'm unsure of how old it is as well. It's never been run and the box was an older type that slipped together rather than a flap. So how do I tell the difference between the older models nd the newer ones? DOes it even matter?

I don't know if it matters, but all of my experiments have been with the ABC version and the E2030 muffler. Post a picture from the side opposite the exhaust outlet and we can tell, but there are numerous example photos posted here and on SSW, like in this thread:

http://stunthanger.com/smf/index.php?topic=25650.0

Brett

nathan Metzner · « **Reply #22 on:** July 05, 2012, 09:25:06 AM »

Thanks Brett, It's an older iron steel style. I looked for a thread like that for quite a while before I posted lol. My search techniques must be dwindling. I have no idea yet which muffler it will have. I just won it so it'll be a week or so before I get it in hand. At that time I'll order the C/L stuff and a muffler if it's the wrong one. Thanks Again

nathan Metzner · « **Reply #23 on:** July 09, 2012, 02:12:52 PM »

I got the .20 fp today she's a little castor crudded up and a back plate screw is missing. I ordered a screw kit for it but am having a time trying to find a gasket set. I can make my own but I was hoping for the right stuff. The muffler is an 842 so I am going to have to order a 2030. All in all it is in fair condition I hope when I get her cleaned up and put back together it runs good.

Bill Little · « **Reply #24 on:** July 14, 2012, 01:42:54 PM »

Quote from: nathan Metzner on July 09, 2012, 02:12:52 PM

I got the .20 fp today she's a little castor crudded up and a back plate screw is missing. I ordered a screw kit for it but am having a time trying to find a gasket set. I can make my own but I was hoping for the right stuff. The muffler is an 842 so I am going to have to order a 2030. All in all it is in fair condition I hope when I get her cleaned up and put back together it runs good.

Hi Nathan,

I am going to ask the obvious question so forgive me if you have done it..... You did try Tower for the gasket set, right? I know I got a couple of sets from them.

BIG Bear
RNMM/AMM

nathan Metzner · « **Reply #25 on:** July 15, 2012, 12:24:27 PM »

LOL, yeah Bill I tried them. I do not know what crosses with these engines so I was left trying to get the part number that OS lists. Basically tower could have it under another designation and I would never know; howver, I did look s best I could through every vender I know of nd they are all out, this includes E-bay.

Trostle · « **Reply #26 on:** July 15, 2012, 04:46:40 PM »

I have a bit of experience with both the OS 25 Max and the OS 25 FP. The OS 25 Max is like a little brother to the OS 35 S. The OS 25 Max came with an RC throttle or you could get a straight venturi for CL. (I know because I have or at least had several venturis that fit the 25 Max.) It is a nice running engine and is happy with props around 9" diameter and maybe 5" pitch. I had a really nice combination with the British Pagan design for OTS by John Coasby swinging a narrow blade APC 9.5/4.5 (that went out of production years ago - there is a heavier APC 9.5/4.5 for the FF guys but does not work nearly a good on this engine). I had a lot of luck with that combination. Without a muffler, it made a lot of noise.

One reason I wanted to use it was that the 25 Max is about an ounce lighter than the 25 FP. That was important on that Pagan.

On the other hand, the 25 FP, as mentioned, is an ounce heavier, but it runs smoother and will swing whatever size prop being used for comparison faster. I have used both in several moderate sized OTS designs and have been happy with both. I would still go to the 25 Max if weight was critical for the given design.

Keith

nathan Metzner · « **Reply #27 on:** July 15, 2012, 06:44:27 PM »

Thanks Keith for the review. I didn't know tht the old max was lighter. I have had some serious issues trying to get a venturi for mine so I am running it in R/C trim. I can't wait to get her in the air.

Bill Little · « **Reply #28 on:** July 15, 2012, 07:02:39 PM »

Quote from: nathan Metzner on July 15, 2012, 06:44:27 PM

Thanks Keith for the review. I didn't know tht the old max was lighter. I have had some serious issues trying to get a venturi for mine so I am running it in R/C trim. I can't wait to get her in the air.

Hi Nathan,

I feel very confident that Jim Lee (Lee's Machine Shop in the Vendor's Corner) has a venturi for you. Don't know if he is at the NATS.

Bill

Trostle · « **Reply #29 on:** July 15, 2012, 08:12:31 PM »

Quote from: nathan Metzner on July 15, 2012, 06:44:27 PM

Thanks Keith for the review. I didn't know tht the old max was lighter. I have had some serious issues trying to get a venturi for mine so I am running it in R/C trim. I can't wait to get her in the air.

Nathan,

You are welcome. I did some checking on my inventory. I have several NIB OS 25 Max engines with the CL venturi. I did not know until I just checked the parts list, but OS has two venturis for this engine beside the RC carburettor. They are listed as

Venturi S Part no. 22012007
Venturi L Part no. 22012100

There are some people who have OS parts, but I do not know who they are.

I used my own venturis on for my application and I do not know the difference in these. However, if you cannot find something, like from Jim Lee, I will remove one from one of these new engines and send it to you. I will also send the NV that goes with it as it it different than their carb or the OS 35 S. Let me know and give me an address.

Keith

nathan Metzner · « **Reply #30 on:** July 15, 2012, 11:05:11 PM »

WOW, Keith I have been looking for these for years.

Brett Buck · « **Reply #31 on:** July 16, 2012, 12:22:54 AM »

Quote from: Trostle on July 15, 2012, 08:12:31 PM

Nathan,

You are welcome. I did some checking on my inventory. I have several NIB OS 25 Max engines with the CL venturi. I did not know until I just checked the parts list, but OS has two venturis for this engine beside the RC carburettor. They are listed as

Venturi S Part no. 22012007
Venturi L Part no. 22012100

There are some people who have OS parts, but I do not know who they are.

I used my own venturis on for my application and I do not know the difference in these. However, if you cannot find something, like from Jim Lee, I will remove one from one of these new engines and send it to you. I will also send the NV that goes with it as it it different than their carb or the OS 35 S. Let me know and give me an address.

Mine would definitely not run properly on suction with the larger of the two. It worked well on the smaller venturi. I had a 20 and a 25, and I think both small venturis wound up on someone else's 35S's. I filled in the large one with Epoxolite and then reamed it out until it seemed to work, but I never measured it.

Brett

Trostle · « **Reply #32 on:** July 16, 2012, 10:34:40 PM »

Quote from: nathan Metzner on July 15, 2012, 11:05:11 PM

WOW, Keith I have been looking for these for years.

Package is on its way with the OS venturi and a Jim Lee version and the OS NV. Have fun.

Keith

nathan Metzner · « **Reply #33 on:** July 18, 2012, 06:14:10 PM »

I got my care package today. They fit terrrificley. I haven't had a chance to run it yet but that'll be tomorrow I think. I cn't wait to get er run and tached.

nathan Metzner · « **Reply #34 on:** July 19, 2012, 05:59:28 PM »

Thanks for all your help guys, I flew the engine today with the new parts that Keith so generously donated and she flew great. The engine turned about 13,300 on the ground but it was a little inconsistant on the ground. Once in the air it flew great. Ran consistant with a wet two and a strong overhead pull wehn it was needled correct. Thanks again you guys are awesome!
Nathan