4 stroke crankcase breather and after run oil

[J.N.]

I would have expected this topic to have been covered in the past but after carrying out a search cannot find the answer.

I will be fitting my first 4 stroke, an OS52 surpass, into a partially enclosed engine bay.  The glowplug may prove to be very difficult to remove in situ, the venturi to the inlet valve, and the carburettor,  can only be accessed by removing the engine from its mountings.  I have yet to bench test the engine and have no idea how much oil will be expelled from the crankcase breather nipple.  I recall reading somewhere that a piece of flexible tubing can be fitted to the breather to direct the expelled oil into the slipstream and that a "T" piece union should be used.  The "T" part is open to atmosphere and allows air to flow into the crankcase on the piston up stroke when the lower part of the "T"  is full of expelled oil.  

Can someone please tell me if I have got the above right. 

 

Normally I apply after run oil through the carburettor however it will not be possible in this case, in addition I may not be able to easily access the glow plug.  I recall reading that after run oil can be applied through the crankcase breather.  Can someone please put me right.

Thanks.

[Bruce Richards]

Jeff, yes you can/should put after run oil into the crank case breather. I think the use of a t piece is only where the breather pipe is long (over 2 -3 inches). I also put oil down the exhaust on 4 strokes.

[Steve Hargreaves - Moderator]

Works for me.....I usually extend the breather tube so it exits the cowl & then squirt a bit of after run into the breather tube.......two points however.....1) make sure there is no debris in the breather tube before you squirt some oil in there...otherwise the debris will get sucked into the crankcase along with the oil 2) make sure the piston is on the upstroke before squirting some oil in....turn the motor over & said oil will get sucked into the crankcase. If the piston is on the downstroke then, when you turn the motor over, it will blow all the oil out again....

 

Another thing to consider is to route some 3mm brass tube along the firewall but formed so that it ends just over the carb opening......extend this tube to outside of the cowl & use it to squirt after run oil into the carb at the end of the day......above note about dirt in the tube applies......useful on the new OS motors which have an internal breather system.....