Crankcase Vent Line??
 

I have installed a Saito FA 82a in my UCD .46. I have it broken-in and tuned, on the ground anyway. It will be time to maiden and install the cowl soon, if the rain lets up long enough. I have some questions for the experienced 4-stroke guys.

1) The engine is inverted and the vent line is coming out the 'top', (I have a long tube connected to it running it down behind the engine). How do I rout the vent line out of the cowl and keep it short, the mfg says 3" or less....

2) How large should the cowl vent be in order to allow proper cooling. I am running 10% to 15% glow fuel. I have heard that a smaller vent slows down the air and allows better cooling, but I don't want to cook the thing.

3) I have heard that a clogged or long vent line could lead to high pressure inside the crankcase which could blow out bearings or crack the case, has anyone else heard of this?

Thanks!!

Mark

RE: Crankcase Vent Line??
 

the vent line doen't do much for cool it's ment for discharging oil out of the carnk case. If it clogs it could pop the case but that is nearly unheard of

as far as the line glue a piece of brass tube to the firewall sticking about an 1/8 inch out the cowl

RE: Crankcase Vent Line??
 

agexpert, ive had lots of expierence with the 46 and the saito line of engines, the vent can be more than 3 inches, just make it long enough to run out the bottom of the cowl and it will be fine;)
also if the line should become plugged(not likley) what it would do is limit the flow of oil to the crankcase and you would ruin the bearings, the crankcase vent has a positive outflow because of blowby and this delivers the oil to the crankcase!!

as far as the cowl opening for cooling the bigger the better, as rule of thumb the out hole should be at least 3 times bigger than the inlet, i will post a pic of mine at bottom.

you have a great flying plane, good luck!!

RE: Crankcase Vent Line??
 

Agexpert,
With the case vent line just barely sticking out the cowl it may cause a lot of oil blowing on the fuselage.
This is ok if you don't mind more cleaning.
What I do is use medium fuel line from the case vent to just exit the cowl connected to inside of larger fuel line. I then run the larger line down the landing gear to exit just behind one of the wheels. The case vents just fine, no presure build up and the plane stays a little cleaner.

RE: Crankcase Vent Line??
 

Gary,

After much consternation I put a 14x4W prop on it. Any better ideas? (Remember, I am a beginner). Only 10 gallons thru my planes, including solo).

Thanks

RE: Crankcase Vent Line??
 

Just looking at how 4 strokes operate, I have always assumed the vent to simply be a crank- case breather. I think both positive and negative (vacuum) pressure is developed in the crank-case by the motion of the piston. Yes, It is also a place for lub oil to escape; but, I would consider this to be a secondary mission for the vent. I think the negative (vacuum) pressure is the reason the length of tubing would be restricted as per the manufacturer's recommendations. If the diameter of the vent-line is increased before the length restriction measurement takes place, this should be the same effect as keeping it's recommended length. This would allow the vent to funnel goop away from the plane.

RE: Crankcase Vent Line??
 

agexpert, the 14x4w is a great choice for you with the 82;)

and modeone, you are right about the vents primary mission being a crankcase breather, but were back to killing two birds with one stone, because it also allows oil into the case on the power stroke with blowby, this is where the positive flow out starts thereby oiling the innards.

the length of the tubing out needs to be 4 inches because if any shorter it will suck in outside air(with dirt) back into the case on upstroke because the vacum amount equals the hose capacity at about 3 inches.

hope this makes sense to you[&:]