RE: Os 120 4 stroke overhaul help needed

RE: Os 120 4 stroke overhaul help needed
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RE: Os 120 4 stroke overhaul help needed - 4/23/2008 7:23:30 PM

Posts: 78
Joined: 7/16/2002
From: Hallowell, ME, USA
Status: offline

Successful Maiden flight.

After installing the new parts supplied by Neol Jensen and several months of refurbishing, I had a successful test run and first flight of my 20 plus year old BUSA Cub and OS 120. The engine started right up and ran very well. I only had to adjust the low idle setting on my transmitter and a slight highspeed needle adjustment to get a good transition and power. I taxied up and down the grass strip a couple of times and then pointed it into the wind. After a short roll at 3/4 throttle it lifted off and headed up! A few clicks of down trim and it was flying very nicely. Loops and stall turns are very nice and the landings are a non-event with a good idle. I look forward to many years of flying this big bird.

Thanks to all for the help with rebuild and parts.

The engine is a single cylinder but looks like a twin, thanks to the very well built wood dummy engine on the left side of the cowl!

I have a short video of the sart up I'll try post as well.

Jay

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< Message edited by Jaybird -- 4/23/2008 10:15:02 PM >

(in reply to Jaybird)

RE: Os 120 4 stroke overhaul help needed - 5/6/2008 2:42:44 PM

Posts: 78
Joined: 7/16/2002
From: Hallowell, ME, USA
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Here is a link to an engine start and flight video.

http://www.rcgroups.com/forums/showthread.php?t=854104

I'm finding that i'm having tuning and run issues as time goes on that are perplexing. I've listed the problems on the video thread. Does anyone know what o-rings there are in the carb and what size?

Jaybird

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(in reply to Jaybird)

RE: Os 120 4 stroke overhaul help needed - 5/7/2008 1:58:34 AM

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Joined: 6/20/2006
From: Hamilton, OH, USA
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I don't think that your left cylinder is firing at all! <GRIN> Knowing what engine was supposed to be in your plane, I did a double take (pun) when I saw the picture of a twin. That looks VERY nice!

Seriously, your engine sounded like it was running very well in your videos. What happened?

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(in reply to Jaybird)

RE: Os 120 4 stroke overhaul help needed - 5/7/2008 1:34:39 PM

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Joined: 1/16/2003
From: Paris, ON, CANADA
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I have found that a Perry oscillating pump improved the running characteristics greatly on my 2 OS 120 FS engines. No more leaniing out as the fuel level drops.

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(in reply to Ken6PPC)

RE: Os 120 4 stroke overhaul help needed - 5/7/2008 10:31:49 PM

Posts: 78
Joined: 7/16/2002
From: Hallowell, ME, USA
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It was suggested that i try switching from my cool Power 15/18 fuel to 20/20 fuel by a modeler who had the same engine and same problem. It did run great for that video and then started running poorly the next few flights afterward. I'll keep you posted.

Jaybird

(in reply to Waco Driver)

RE: Os 120 4 stroke overhaul help needed - 5/8/2008 8:39:39 PM

Posts: 78
Joined: 7/16/2002
From: Hallowell, ME, USA
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I did a quick test run with the new 20/20 fuel and it seemed to like it. it started right up and idled very nicely without any external glow driver. I'll have to continue tuning to make sure it continues to cool enough. It did seem to transition well from idle to full power without loading up as before. What I do still have to contend with is something metalic rubbing somewhere and causing bad intermittent elecrtrical glitching. Not sure where to start. I can duplicate it without the motor running by touching a screwdriver the cylinder head, but that seems typical. I'll keep looking.

Jaybird

(in reply to Jaybird)

RE: Os 120 4 stroke overhaul help needed - 5/10/2008 3:31:01 AM

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From: El Segundo, CA, USA
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Are you running muffler pressure on your 120? I run it with mine and it runs well like that on 15%; I've tried 20% in it but it didn't seem to run as well. I prefer 15% in mine.

Also, I'm using a Zinger 15x6 prop.

(in reply to Jaybird)

RE: Os 120 4 stroke overhaul help needed - 5/12/2008 8:11:42 PM

Posts: 78
Joined: 7/16/2002
From: Hallowell, ME, USA
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Hi Sub,

Yes I am running muffler pressure to the tank. The motor had a 15x6 Master Airscrew on it when I bought it. I replaced it with a 16x6 Master Airscrew for my first run. I was thinking of trying different props as well.

It's been too windy to do any test running or flying around here this past weekend so I don't have any new information.

Jaybird

(in reply to submikester)

RE: Os 120 4 stroke overhaul help needed - 5/12/2008 11:44:25 PM

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From: El Segundo, CA, USA
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I have only ever flown mine with the 15x6 zinger - I got it with that prop and it ran so well with it that I never considered changing it. Originally it was flying on a 13+ lb 4*120 and typically I would use 15% power master fuel. I tried a tank of 20% in it one time and was uncomfortable with the way it sounded, it's been a while so I don't recall exactly what made me uncomfortable but here we are.

Now I'm finishing up the assembly of a SIG P-51B and putting this 120 in it with the same prop (15x6 Zinger) and hoping for some majestic flight...

(in reply to Jaybird)

RE: Os 120 4 stroke overhaul help needed - 5/13/2008 3:10:40 PM

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Joined: 7/16/2002
From: Hallowell, ME, USA
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I've pulled out the homemade onboard glow driver system as it wasn't working well and I think may have been a sourse of radio interference. I'll also go back to the 15x6 prop (I'll buy a new one since I have no idea how old the old prop is) and see if that helps.
It's still really windy around here and rain is expected later in the week so it will be a while before I can do any more testing.

Jaybird

(in reply to submikester)

RE: Os 120 4 stroke overhaul help needed - 5/14/2008 9:26:35 PM

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From: El Segundo, CA, USA
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For your cub a 15x6 should be very good but in my Mustang I have just recently been testing it with a 14x8 APC and the results were very nice - I was quite pleased.

(in reply to Jaybird)

RE: Os 120 4 stroke overhaul help needed - 5/21/2008 12:20:20 PM

Posts: 25
Joined: 4/21/2003
From: York, UNITED KINGDOM
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Hi,

I've just acquired one of these old OS 1.20 singles...with the twin rocker covers.

It does run, but I can't get it to idle below 3,700, so I guess that something isn't right!

Anyway, I'd like to confirm that the valve timing is correct, but I lack any info regarding timing marks. This engine has been dismantled by a previous owner, so you never can be sure.

Hope that there is someone out there who can help with this information.

TIA
David

(in reply to submikester)

RE: Os 120 4 stroke overhaul help needed - 5/22/2008 2:14:47 AM

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From: Hamilton, OH, USA
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I check valve timing this way:

http://www.rcuniverse.com/forum/fb.asp?m=7442072

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RE: Os 120 4 stroke overhaul help needed - 5/26/2008 9:41:37 PM

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From: El Segundo, CA, USA
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Well, been flying mine a lot more recently and I have to say my original comments are now modified.

I am concerned that I may be running it too hard but I guess we'll just have to wait and see. I put this engine in my Sig P-51B, previously I had putted around with it in a 4*120. at 13lbs the 4* was in no way fast but I never tried to make it fast either. The Mustang however is only 8.5 lbs so I was hoping for some speed. I also had it installed inverted which I have been successful with in the past - it's just a matter of getting the tank in the right place and the mixture set correctly. I had previously said that I was uncomfortable running anything more than 15% in it but with the 15% I simply couldn't get a good reliable idle inverted like I did with 20%. So, 20% it is and it is running really well. 20% with a 14x8 APC and it's darned quick, not as fast as my buddies H9 mustang with a YS110FZ but quick none the less.

I may replace it in this airplane with a 110FZ myself but for now the 120 is running well (until I blow the bottom out of it...).

I looked into the heads recently to check the valve clearance - it's tight in there and difficult to work. Good thing it is within tolerance. Also, I noticed on the intake side there isn't much lube getting up there where as the exhaust side was quite wet.

(in reply to Ken6PPC)

RE: Os 120 4 stroke overhaul help needed - 5/28/2008 3:19:48 AM

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Joined: 1/1/2003
From: LEXINGTON, KY, USA
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Well I finally took mine out for a test run and flight. A club member helped me to tune the engine in. All is great but the idle is high. I’m running it with only a pipe, it came with no muffler. The question is how can I add back pressure to the tank to help with idle.

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(in reply to submikester)

RE: Os 120 4 stroke overhaul help needed - 5/28/2008 6:10:48 AM

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From: El Segundo, CA, USA
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Buy a muffler - I use a muffler off a Magnum 91 RFS (cheaper than buying the OS).

(in reply to Cub Man)

RE: Os 120 4 stroke overhaul help needed - 5/29/2008 9:07:26 PM