How To Clean A 2 Stroke Crankcase

I am worried that when i did a top end rebuild some dirt may have fell into the crankcase. so, i am wondering what is the best way to clean it out. I am not apposed to taking it apart, however, if i can just send some fluid through it that would be a lot easier. thanks.
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110octane New Member

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Do not run any type of fluid through it. the only way to make sure there isnt anything in there is to take it appart again. Get a small attachment to place on a shop-vac vaccume cleaner, or make one if you have too. Suck out what you think is in there. Then get a clean rag and place it on top of the flat side of the crank ballancers and rotate your crank around so it takes the rag with it, Be care full not to ge it stuck (if you do rotate it in the opposite dirrection) Do this a couple of times.
Maybe its the bottom end im thinking of. When i took off the topend its the things right below it. It looks like its filled with oil or something...couldnt i just drain the fluid and fill it up and drain it a couple if times?
110octane New Member

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Its not the bottom end your talking about. When you said Crank Case you were on the right track.
Trust me its not the bottom end your refeering too. In order to see inside the bottom end you have to split the cases (not an easy task)

In this case you cant just drain it, because draining the tranny oil is in the bottom end and the top and lower halves are not connected.
110octane New Member

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take a look at www.bikebandit.com and their schematic of the blaster cases and let me know where you are seeing this fluid/dirt.
this diagram will also give you a clear understanding of how the two parts of the cases are divided into thier 2 compartments.
Hi, I thought I'd clean up a few things here (no pun intended). The "bottom end" includes the piston, connecting rod, crankshaft, and associated bearings. As opposed to the top end which includes the cylinder head in a two-stroke (and in a four-stroke engine, the camshaft, rockers, valves, and guides) The oil you are seeing in the bottom of the crankcase is actually two stroke oil from the fuel mixture that has fallen out of suspension. All two strokes will develop this condition, pretty much regardless of their mixing ratios- even a lean 100:1 ratio. This oil accumulates at low engine speeds-at idle and low rpms. But when the engine starts turning faster, there is more chance for it to be picked up again and burned. So when the engine is revved up and a healthy puff of smoke comes out the exhaust-the oil is getting burned up. But it is hard to get all of the oil out. I've seen some 50cc moped engines-which are subject to long stretches of higher rpm running-with quite a bit of oil in the cases.
Unfortunately, there is no practical way to get that oil out of there without splitting the cases or turning the engine upside-down to drain it. I think sending a rag around the flywheel is tricky because there are only a few millimeters clearance between the cases and the weights, and there is a chance it would get stuck.
If you think that some dirt fell into the case while you were working on it, there is a good chance it can get into the main bearings and also the big-end rod bearing where it will accelerate wear. It could also be slung up to the cylinder by the flywheel's motion where any tiny particles can score the cylinder wall.
If you have already run the machine and you use it for racing and heavy riding, and you think a sizeable chunk of foreign matter dropped down there, it would probably be best to play it safe and take everything apart and clean the parts. This would necessitate splitting the engine cases to get to the bottom of the crankcase, and this procedure can get kind of involved, but it's not impossible.

If you think a lot of dirt got in there, but you haven't ridden the machine yet, you could try to flush it out. You would have to take off the head and barrel. Then you can either take the lower end of the engine off the frame and gently rinse it out and turn it upside down to drain the oil/dirt (don't forget to drain the transmission case oil first) or flip the entire quad to get everything out. I would rinse it several times with a very light cleaner or even water. Don't use any kind of carburetor or strong cleaner, because that eats the sealant between the case halves and is hard on the oil seals. Be sure to quickly oil everything right away with a light coat of two-stroke oil or assembly lube after you are done; rust develops quicker than you think.
Its wherever the crankshaft goes into. When i took off the top end and the piston, the rod that the pictonn head was attached to was not taken off. when i push that up and down it tunes the engine and i can see and hear some sort of oil spashing sort of..i cant see the oil just some on the crankshaft when it turns through it. But i am afraid that minor pieces of dirt got into it from me taking off the top end. So i was wondering what that fluid is so i can poor it from the top so it brings the dirt through it and then maybe drain it through the bottom (if thats possible) sorry if this is confusing this is the first atv i have taken part. basically all i did was take the top end off and the piston head...now im lookning down into whatever is below it and moving the piston rod up and down and can hear some sort of sploshing around and wanted to clean it out.
But it looks like the crankshaft is getting lubed up quite nicely from this oil. and no i dont think i got dirt in it, i said that becuase i dont know if there is dirt in it. I just bought the 4 wheeler and im trying to clean and fix everything wrong with it. I
And after looking at those schematics its most def. oil in the crankcase
110octane New Member

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I beg to differ. The top end includes the piston, rings and wrist pin.
but every thing else sounds great, your very knowledgable "ben" thanks for the clarification here.
So basically, there is no way to clean this out besides flipping the engine over and dumping it out. what if it gets too full? it sounds like there is a lot in there.
110octane New Member

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Weird, that you say there is a lot in there "Ben" you want to chime in here?
my suggestion would be drain the tranny oil then, and see if there is still oil in the portion your speaking about. my assumption is that there would be. If there isnt and you drained the tranny oil, that would tell me there is a hole between these two chambers. (in this instance new casess are in order)

And yes the tolerances are really close to get a rag through there, but I have done it on mine and it worked like a charm. No easy task thats for sure, and its a last resort b/c I did not want to split the cases.
Hi, I stand corrected, 110octane. I always try to give good information, but the fingers were going slower than the mind in that case. Sorry again, and I'll start double checking everything from now on. jtomasi1, to answer your question, there won't ever be too much oil here. If the level does rise up to the crankshaft, the motion of the flywheels and connecting rod will help generate turbulence to get the oil back into suspension in the fuel/air mixture (the situation is very different on four-strokes, but they're not a concern here). If you can get at the right angle, it probably looks like there's a lot of oil down there, but I can confidently say you don't have to worry about it; it means things are normal.
Just to be clear here, the crankcase is separate from the transmission/primary drive on all two-stroke engines, the Blaster being one. The transmission needs oil to lubricate the clutch, gears, and bearings inside. The crankcase, however, MUST be separated by a seal (located on the crankshaft between the crankcase and primary drive) from the rest of the engine because fuel/air flows into that area before shooting up into the transfer ports and then into the cylinder above the piston as the transfer ports are uncovered by the piston. In fact, there is such a thing as crankcase compression because pressure in the crankcase created by the piston moving downward on its stroke and the tuned exhaust creating its own pull makes pressure for the fuel/air to be forced into the cylinder for good cylinder-filling.

If there was a hole in the crankcase, the quad would not run very well, if at all. There would also have to be a cause for such a hole such as a chunk of piston skirt getting slammed into it or a rod bearing going out and making the connecting rod dance inside the case (I have witnessed both). In either situation, your engine would be blown and you DEFINITELY would know about it.

From your other post, you don't seem very sure there is even a problem at all. You seem more concerned about the oil itself rather than dirt in the oil. So right now I can say that you shouldn't worry about the oil in the crankcase; it is a sign of a healthy two stroke. So you should not waste your time trying to drain it out or whatnot. Go riding instead, that makes anyone happier.
dirtyblaster New Member

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holy sh*t ben you are one of the most experienced that i know on this forum you can type a sh*tload but most of us are lazy lol! i've wasted too much of my time drianing the old crap out, like ben said just go riding.
I was too quick to apologize there, 110octane. After doing some research, the "top end" does, in fact, include the piston, top rod bearing, and wrist pin. I have confirmed this with several sources including A. Graham Bell in both Two Stroke Performance Tuning and Four Stroke Performance Tuning. It has just become common for people to refer to a "top end rebuild" as including a new set of rings or oversized pistons. I think that's where the confusion comes from. Thanks for the thought provoking posts though.
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humm, interesting. Ok great thanks for your dilligence here. Its great we can teach these young motor heads here a thing or too, along with schooling eachother. I only did a short research and ony found 1 instance where it called the parts in question top end, and I have no proof of what they said is accurate.
thanks again Ben.