Unknown breather nipple on OS Gemini - RCCanada - Canada Radio Controlled Hobby Forum
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Old 04-22-2019, 10:47 AM   #1
Rudie
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Unknown breather nipple on OS Gemini


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Hi Guys, this is an odd one, I acquired an OS160 Gemini a few weeks back. Spent time cleaning and loosening things up from it sitting for a few years! I noticed it had a breather nipple installed into the base of the carb housing! My only thought that this was installed, to let let excess oil run out of the engine after flying! And when your flying, you'd plug up the hole with some fuel line to stop the vacuum leak .....any other thoughts out there?
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Old 04-22-2019, 11:25 AM   #2
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Re: Unknown breather nipple on OS Gemini

I built up a 160T from two wrecks, both with the air bleed carbs and neither has that extra nipple, (no other pics I have seen, nor the manual, either).

Most of the oil will be in the case and drain via the stock one on the rear housing. Not much should remain in the intake or combustion chambers.

I have two suspicions, first being that fitting was used to inject something while the engine was running such as after run oil, but that would be a bit iffy since too much ran the risk of hydrolock. Another would be a home made smoke system where they tried to create it through combustion rather than exhaust heat.

Another possibly, to supply low level vacuum to an onboard device? To be honest, never saw anything like that, but people will tinker.

Are you able to post a pic a bit wider field? Wanted to see your muffler arrangement since I am aboot to test a similar setup myself. Engine is not loud, but just want to see how that works out. Need to add extensions to clear the cowl on the Waco and figured this would lengthen the exhaust in a useful manner.
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Old 04-22-2019, 12:54 PM   #3
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Re: Unknown breather nipple on OS Gemini

Hey Gary, thanks for reading, ya I thought of smoke injection but that would mess up the engine running dumping smoke oil! The vacuum line is a thought...I have attached a wider view shot, you can see he's added two mufflers, they are compress fitted with silicon tubes! Going to mount it on a stand to fire it up this week.....
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Old 04-22-2019, 01:14 PM   #4
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Re: Unknown breather nipple on OS Gemini

Interesting, although I'm a bit confused as to how those mufflers attach. I have a pair of bent tube adapters that the original pipes bolt to so they clear the prop and aim aft more, (yours seem to be aimed further aft than my stock pipes as it is). Even though a boxer style and incredibly smooth, worried about the extra mass on the jug threads so may not work long term. So far have not found any silicon tubing to extend below the cowl.

Don't leave that plug on the case drain when running, (obviously!).

One other point to make is this engine had 3 different connecting rods, the first two prone to failure. Hoping the fact you have the later version 2-needle carb also means the latter version rods. Even with those best to keep the max RPM down in the low 9K range.

Here is a pic of the 3 versions, newest at the bottom. Also included a pic of what happens when one breaks. This was the first engine I grabbed. The second was relatively unscathed with a bent crank so donated most of the bits needed. It also had the latest version rods so bonus.
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Old 04-22-2019, 02:11 PM   #5
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Re: Unknown breather nipple on OS Gemini

Wow, what a mess .............mine is the older I am guessing, it has the air bleed screw on the carb! Yes, agree on the RPM's, I normally don't run the crap out of my 4 strokes ....different with gasers and two stroke glow versions LOL!! Since you needed to pull the engine apart! Any issue setting up the timing gear with the crank shaft? Is there timing marks? when i looked at the engine explode view, looks like the cam gear will fall out when the back plate is removed! Like I said this engine I acquired has not been run for several years and am kinda interested pulling the plate and looking at the bearings! Right now they have been lub'd in Marvel Mystery oil and it seems nicely freed up and excellent compression! My mufflers as I said are press fitted on with silicon tubes over the exhaust stacks ....the mufflers were fixed to the air frame ...I guess to hold them on!
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Old 04-22-2019, 02:41 PM   #6
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Re: Unknown breather nipple on OS Gemini

They likely used it to prime the engine . I had a old saito twin that had a similar setup for priming
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Old 04-22-2019, 04:43 PM   #7
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Re: Unknown breather nipple on OS Gemini

If you keep the nose down when removing the rear cover the cam should stay in place. If not and you need to have a boo it may be worth pulling the heads and valvetrain so no tension on the cam followers. That way nothing breaks when and if the cam does come out with the cover.

Timing is no issue since both the crank and cam are marked. You can align the two with the cam in the case before the rear cover goes back on.

Doubt you have the airbleed carb since no screw in the bulge in the outside of the carb body and yours has the throttle arm that locks with a set screw similar to most modern style units. That allows you to access the LS needle that screws into the barrel itself.

Easy to check. If there is a straight screw head in the center of the throttle arm that is your LS and it is a 2-needle carb.

That screw with the lock nut in your pic facing forward and down is the barrel retainer that also sets closed limit. You want to set that so the barrel opening just goes past full closed.

ps. See from your location you are north of TO. If I still lived in North Bay travelled up and down the 11/400 corridor every few weeks and could have set it up for you on the way by. As it stands work has me pretty busy and only travelling is to the Goderich event in August. There the full weekend. This season hope to bring the Waco yanked behind that engine.
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Old 04-23-2019, 07:19 AM   #8
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Re: Unknown breather nipple on OS Gemini

Quote:
Originally Posted by Rudie View Post
Hi Guys, this is an odd one, I acquired an OS160 Gemini a few weeks back. Spent time cleaning and loosening things up from it sitting for a few years! I noticed it had a breather nipple installed into the base of the carb housing! My only thought that this was installed, to let let excess oil run out of the engine after flying! And when your flying, you'd plug up the hole with some fuel line to stop the vacuum leak .....any other thoughts out there?
That is definitely a breather hole. Check out the manual:

http://www.os-engines.co.jp/english/...ual/ft-160.pdf



Because the cranskshaft has the pistons moving in sync with each other (both compress on the same stroke) there is going to be large pressure changes in the crankcase each revolution.
The rear one is there to allow the crankase pressure to be relieved on the intake/power strokes.
Its the middle nipple on the intake manifold that has me mystified. Given the fuel nipple in up front with the carb, what is the purpose of the middle nipple? that to me looks like it would need to be plugged, otherwise you are sucking air from the nipple and not the venturi!

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Old 04-23-2019, 07:29 AM   #9
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Re: Unknown breather nipple on OS Gemini

I agree with max. What it looks like is somebody installed a priming tube of sorts. A way to inject some raw fuel into the carb.
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Old 04-23-2019, 07:44 AM   #10
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Re: Unknown breather nipple on OS Gemini

I remove the choke assemblies from all my 4-strokes, (as OS and Saito are doing now, as well) since found not required. Opening the throttle to slightly under 1/4 lights them off.

Oddly enough this one has no provision for pressure fitting so asked OS to confirm open tank vent. Seems that too is not required and my own running shows no issues at any power setting on the test stand. Difficult to get perspective from the pic, but best positioning I could get was tank bung even with the carb inlet fitting.

Of course, that does not mimic the real world so only flight line testing will show starting and/or performance effects.

This is the entirety of their instructions regarding tank positioning:

Quote:
The ideal fuel tank location is with the top of the tank 5-10mm (1/4-3/8") above the needle valve. However, model design will usually require the tank to be located higher than this and there should be no trouble with such a tank location provided that you do not pursue spectacular aerobatic flight.If the tank is located high, fuel will flow into the carburetor when the tank is full. Therefore, pinch the fuel line with a clip, when the engine is not running, to prevent flooding and loss of fuel.
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