Air box drain question

4104GA · May 04, 2009, 07:44:40 PM

Jack your drain system is very close to the system I have on my 6 71 in my 4104. Works great and really helps
to stop most of the crap on the back of the bus.
Sam
4104GA

bottomacher · May 05, 2009, 06:02:48 AM

How often do you have to drain the tank? It looks like it would hold over a gallon.

JackConrad · May 05, 2009, 06:25:26 AM

Quote from: bottomacher on May 05, 2009, 06:02:48 AM
How often do you have to drain the tank? It looks like it would hold over a gallon.

We drain our about once a year, never get over a cup or 2 our of it. Jack

RickB · May 06, 2009, 07:03:12 PM

It should be noted that jack's picture does not show the air box drain tube check valve. His is just a 90 degree brass connector going into a tube. My 8v71 has an actual check valve with a spring and ball on both sides of the motor. The check valves are supposed to close around 800 rpm. The rationale being you want it to slobber at idle but not when you are putting your foot into it. Jack, I made an identical set of PVC slobber tubes. I was surprised how little my bus was slobbering to make that big of mess all over my toad and the back of my bus. It must vaporize at speed.

Rick

akbusguy2000 · May 06, 2009, 11:02:02 PM

I'm not sure DD ever actually made one, but they commonly installed a system made by Walker Engineering. Here's what it looks like, with enough information for you to make yur own:

http://www.walkerairsep.com/pdf/installation/Airbox%20Drain%20Kit%20AJ4120KT.pdf

tg

Dreamscape · May 07, 2009, 03:20:20 AM

Jack, Do you happen to have detailed instructions with photos on how to build one? That is something I would like to do, just don't know the correct way to go about it!

~Paul~

JackConrad · May 07, 2009, 05:02:30 AM

Paul,
A section of 3" PVC pipe (length to be determined by mounting location, approx. 12-16"), 2 end caps, 1 hydraulic tank vent, one 1/4" drain valve, and two 1/4" barb hose fitting (only one shown in photo).
Drill and tap 2 1/4" holes in top for the barb fittings, and a 3/4" hole for the breather. Drill & tap a 1/4" hole in the lower area of one of the end caps for the drain. Install all fittings and glue end caps in place, making sure the drain is near the bottom. We attached the tank to the bus frame with a hose clamp.

JohnEd · May 07, 2009, 09:53:45 AM

I have no exposure on this subject other than actually seeing those coffee cans hanging off of the bottom of the engine that collect the drain tube outflow. It looked discouraging, honestly.

Now reading this thread some things are making sense. That comment about the check valve being open a idle and closed at operating rpm caught my eye. Are those check valves, the ones that need replacing every 500 operating hours, EVER being serviced by most? If the air box is loading up with "oil", is that the reason why these engines sometimes SMOKE AT STARTUP? I guess my question is "DD went to a lot of trouble to incorp this design feature so it must have a purpose. What is the symptom of this check valve being plugged or even stuck open, for that matter? Inquiring minds and all that.

Thanks,

John

Dreamscape · May 07, 2009, 11:05:49 AM

Jack, Thanks, I'm going to copy it add that to my list, save it for the future when I have nothing to do!

OK with you?

~Paul~

JackConrad · May 07, 2009, 11:07:33 AM

Quote from: Dreamscape on May 07, 2009, 11:05:49 AM
save it for the future when I have nothing to do! ~Paul~

Paul,
You own a bus, that will never happen!!! LOL Jack

RickB · May 07, 2009, 11:54:45 AM

Your question was:

What is the symptom of this check valve being plugged or even stuck open, for that matter?

The symptom that it is stuck open is alot of oil all over your tow vehicle and the back of your bus with no other leaks to attribute it to.

If it is clogged I would imagine if your bus is dumping a fair amount of oil into the tubes due to blower seals, or cracked or worn oil rings that you would find your motor a bit reluctant to come back to idle after letting off the throttle, due to it burning the built up oil in the airbox. Our two strokes will run on motor oil. The check valves are there to help prevent runaway motors.

One of the possible reasons for a DD smoking at startup is due to excessive oil being in the airbox and draining into the cylinder, My bus doesn't smoke at startup it smokes blue for a short time after it has been idling, the general consensus on that symptom is a cracked oil ring or blower seals. Neither of which neccesarily has to be due to high mileage since your las overhaul. It is my understanding that it is not difficult to damage rings on these motors during overhauls and the blower seals don't like long periods of inactivity and are subject to brittleness due to age.

That's my two cents worth... which won't buy you a wodden nickle.

Rick