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OS 52 c/case vent

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Cpt Biggles17/11/2008 23:26:00
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95 forum posts
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Hi All

just a very quick (2) questions about the crank case breather on the underside of the engine which I think is for inserting after run oil into the crank case.

should it be plugged when running the engine??? if not would it not be an air leak !!

the reason for this Q is that it is not running as sweet as I think it should.

what size prop would be best.

I do not have the instructions for this engine as I bought it second hand fitted in a airframe

Cpt Biggles17/11/2008 23:27:00
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95 forum posts
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I left out that it is a 4 stroke

kind regards to all

00118/11/2008 01:13:00
2212 forum posts
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Cpt Biggles. Never block off the breather, or fit an extension tube to ut of more than about 30mm long. The reason is that the only lubrication of the lower end of the engine, (crankcase) where the big end, small end bearings etc. is due to oil and fuel being blown past the piston. You can use it for after run oil but that is not its primary purpose.

If it is not running too well, the most common problem would be fuel supply, or the wrong or 'worn out' glow plug, try to get an experienced flyer to look at it for you.

Props, try between the range of 10 x 9 - 12 x 6, smaller ones for light sports aircraft, larger ones for heavier scale types. Generally 11 x 7 should be a good starting point.

Simon Chaddock19/11/2008 00:32:00
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5708 forum posts
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Hi Cpt Biggles

As Richard points out on a 4 stroke the crankcase breather is just that. The piston going up an down alternatively tries to compresses and evacuate the air in the crankcase. Given that piston "blow by" is the only source of lubrication for all the bearings on these engines (frightening isn't it!) the less pressure in the crankcase the better.

Matt Brewster17/12/2008 23:44:00
24 forum posts
1 photos
Just thought it might be worth a mention. If you don't no the history of the engine it may need the valve clearance's adjusting witch could give poor performance if out of the tolerance range.
frank killan18/01/2009 00:12:07
55 forum posts
1 photos
To Richard Bond
                                 Hi Richard
In some cases crank case pressure is used to pressurise the fuel tank via a nrv also incorporating a pressure regulator to the carb.  Would it therefore matter to have an extention tube longer than 30mm , say 120mm asI have been using on my OS FS. I would be grateful to clear this point up.
                                                                                        Thanks in anticipation Frank killan.
00118/01/2009 16:45:13
2212 forum posts
1 photos
Frank, I have not heard of a 4 stroke with a set-up like that. 2 strokes occasionally.  The danger of having a long extension would be overheating and dirty oil being sucked back into the engine. If you want to pressurise the fuel feed it is normal to use exhaust pressure or a separate fuel pump. If you just want to keep the model clean, you could insert a Y shaped brass tube thingy into the extension close to the nipple, this will stop pressure build - up.. 
Peter 'Ivanna Crashalot' Savage18/01/2009 16:51:04
1557 forum posts
58 photos
i thought it was to remove oil, as the oil in a four stroke does not go out the exhaust:s
frank killan19/01/2009 18:50:47
55 forum posts
1 photos
Thanks for your reply Richard. The non return valve is provided to prevent anything going back into the crankcase. I like the idea of the 'Y' piece, only trouble is getting after run oil in. I have seen a number of systems as I described, the only one I can recall at the moment is on the 'Iron Bay Model Company' website. I look forward to your reply.
                                                                                                                           Regards
                                                                                                                              Frank Killan.
Peter Miller19/01/2009 19:19:53
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11068 forum posts
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Another possible cause of poor running is an air leak in the carb induction tube. Not common on OS engines but Saito were very prone to this.
 
Try dribbling a little fuel on any joints while the engine is running. If it runns rich for a moment, you have an airleak.

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