This is one that will prevent coughing extra oils/fuel out the exhaust.
I claim no credit for this. This is taken from Duckworks Magazine.
I'm simply re-posting because this one looks important, relatively easy, and this way you don't have to do any clicking.
Crankcase Bleeders
This modification is relatively easy. In a two-stroke engine, the fuel/oil/air mist is drawn through the crankcase. Some of the oil condenses on the relatively cool crankcase walls and runs down to the bottom. If you leave it in there, it will be blown out whenever it builds up too much, or when you open the throttle further (increasing air flow). This small reservoir of uncontrolled fuel will cause uneven operation and fouled plugs.
So the engineers put in drains to get that oil out of the crankcases. These bleed the oil through check valves so the crankcase doesn’t lose any vacuum. On each compression stroke it blows a little oil through a small reed valve, then the reed valve closes to avoid “diluting” the vacuum or sucking the oil back in.
This is what it looks like:
The small reed valves on the lower left side of the gasket mating surface are the bleeders. Here’s the side view:
The top two arrows point to the channels that drain oil from the bottom of each crankcase. These go though the upper and lower sides of the check valve assembly. The lower arrow points to the outlet channel, which runs to the base of the powerhead. There, the wasted oil is discharged into the spent cooling water. That’s right, it just spits the oil into the water. These motors were designed in a very different time. Clearly it would be good if we could clean this up!
Fortunately, it’s easy to do. First, we need a way to add a hose barb to the manifold. Unfortunately there isn’t enough metal to tap into.
JB Weld to the rescue! A Dremel or similar tool is by far the quickest way to take the paint off this area. You were looking for an excuse to buy one anyway, and it will help you with those fantasies of being a dentist.
Once the paint is off, wash with a degreaser – I use Spic-n-Span. Rinse and dry, obviously. A final cleaning with acetone is not a bad idea when using epoxy. Then add a little “dam” of masking tape. This holds the JB Weld in place while it cures.
We will need an 11/32” hole for a 1/8” pipe thread. But just in case, drill a pilot hole first. Do this from the inside, and center punch before drilling. You don’t want any unpleasant surprises, like your hole overlaps the gasket mating surface.
My hole didn’t leave quite as much metal as I would have liked, so I added more JB Weld. Now it looks like this.
While you are mixing the JB Weld, you may as well plug the bleeder drain. (Max would say to use hard-setting gasket sealant in case you ever want to reverse the process. But I don’t think it’s much harder to drill JB Weld. And I can’t think why I would want to go back to spitting oil into the lake.) Degrease the metal and put a small dab in the hole. Flatten it under a piece of masking tape and let it cure. When cured, very carefully file it flush with the rest of the surface. You may need to lap the entire surface with a piece of plate glass and Crocus cloth or #00 Emery. Just make sure that your modification doesn’t prevent the gasket from sealing, and even more important, that you don’t cut away too much of the gasket mating surface! (In case you were wondering, the other piece of tape is for Max's "ditching the pressure tank" mod, as seen in the book mentioned above.)
View attachment 6
When all looks well, we enlarge our hole to 11/32” and paint. I used Rustoleum spray primer and enamel. When it dries we can cut threads. Watch carefully so your threading doesn’t cut into the gasket mating surface. Pipe thread is tapered, so you have to start from the outside, and the hole gets wider as you cut deeper. Remember to keep firm pressure on the tap as you’re starting it, or your first couple threads will get stripped.
If your engine really doesn’t have space for 1/8” pipe threading, you could always center bore a 10-32 or even ¼” screw and use it as a hose barb. It is very tedious to end-bore a screw, since you have to stop and add oil often to prevent the tiny drill overheating. It might also be possible to JB Weld on a hose barb, but I think a hole tapped at least partly in metal will resist vibration better. This may be superstition. If you do make a threaded hole, use the yellow Teflon tape – the white stuff isn’t meant to resist petroleum.
After putting the engine back together I clamped a couple feet of hose to my excuse for a hose barb. This line leads to a catch jar made from an empty pill bottle. I used a green veterinary pill bottle so it would match the engine. Such vanity.
First I bored the lid to tightly fit two hose barbs. One is double-ended. Once these were fitted, I clamped them in a vice and added JB Weld to lock them in place. (I don’t own stock in JB Weld or anything, by the way. I just find it very convenient.)
Then I added hoses. This is how they should look. The inlet is the double barb. We add a short section of hose to make sure the waste fuel ends up in the bottom of the bottle. The other barb is the vent. It’s hose is zip-tied into an inverted “U” shape to keep water from easily splashing into the bottle.
We still need to mount the bottle somewhere. It would be slick to mount it to the leg of the motor, but I went with a simpler solution. It hangs by its hose. Winter is a good time to come up with a better bracket. I’m thinking it will screw to the back of the exhaust “telltale” housing. But if it tilts with the motor, be sure the vent faces aft so you don’t dump the oil when you tilt the motor up!
No matter how it is mounted, any oil collected in this jar correlates exactly with pollution you prevented. Over a one-hour run I burned less than a half-gallon of fuel, but collected about 20 mL out the bleeders. This may not seem like a lot, but remember this is only one hour. It amounts to maybe a half cup over 6 hours of running. How much would this amount to over an entire season? With a bigger motor? In any case, it makes me feel a lot better about using a two-stroke and it cost hardly anything to implement.
Some people will be thinking of piping this fuel back to the tank. I wouldn’t. seems to take on a little water in the crankcase, and this makes the oil precipitate far too readily. Dispose of it with your waste oil.
opcorn:
