Upeer Crankcase- Drain Hole?

[houseowax]

Before I'm admonished to do a search, I did a search. But I still can't find an answer that satisfies my curiosity regarding this hole.
When I disassembled my crankcase i gave it it's first thorough cleaning. I found this hole that was blocked with dirt, It appears to be a drain, but wouldn't it just allow dirt and rainwater etc to enter the crankcase under the side cover?

Am I overlooking something?

[conbs]

House,

As you noticed when you took the side cover off, there is no gasket on the right side. The crankcase is sealed on that side by seals on every shaft so nothing that comes through that hole will get into the crankshaft. But it can get to everything under that side case.

I just looked at a couple of my cases and that hole is much bigger. The tube from the vent on the top of the head cover comes down the back of the jugs and goes out through that hole. I think I remember reading that Honda's idea was that any oil that condensed in that tube would drip onto the chain to lubricate it. If it misses the chain, it will either escape where the chain cover meets the side cover/case or through the vent hole in the bottom of the chain case.

In reality, I think that works until you get a little blowby and then as it drips more oil, the chain flips it all over the dynamo and soaks the windings with oil (which attracts a lot of dirt). A leaking seal behind the rotor or behind the front sprocket will add to the fun, but will probably be noticed as an oil leak.

Looks like you have a fun project going there.

[houseowax]

Thanks, Conbs. It is a fun project, albeit a protracted one thanks to an impossibly busy schedule. I'm hoping to get the rubber on the road before the cold sets in.

So...should I seal it up? It seems unnecessary and maybe even detrimental. Right?

[conbs]

I don't plan to seal mine. If you seal the hole and your carb leaks gas it will pool on top of your case. If it were to catch fire it would have a lot of fuel to burn for a long time. If you have oil coming from the vent tube it has to go somewhere.

I would rather have gas and oil drain through the hole and out of the bottom of the side case. To me the better idea is to keep the hole from getting plugged with dirt. You might consider making the hole bigger (as Honda did) to keep it from plugging with dirt.

One man's opinion.

[LOUD MOUSE]

That hole has been cast in every top case since the engine was made a Wet Sump.
It is to allow anything liquid/dirt to exit that area of the engine.
About 1964 HONDA changed the top vent hose from following the arch of the main frame to in front of the rear wheel to a sort of clamp which is mounted with a bolt at the left side of the cam chain tensioner then thru a cut out on the left front of the sheet metal valley cover then across the case to that hole.
May be wise to cut the hose a bit short of the hole so things can work as HONDA designed!
The vapor from the engine will now vent into the drive chain area and my experience is that you shouldn't notice a large amount of anything.
I'd say if you do you need a rebuild.
Plug it if you like but HONDA had a reason for it and issued MANY ENGINES WITH IT!!!!!!!!!!!!. ..........lm

Thanks, Conbs. It is a fun project, albeit a protracted one thanks to an impossibly busy schedule. I'm hoping to get the rubber on the road before the cold sets in.

So...should I seal it up? It seems unnecessary and maybe even detrimental. Right?

[houseowax]

Thanks for the replies. My mechanical ignorance is really showing through. I assumed that it would only invite water and dirt into the assembly - I hadn't thought about gas, oil or vapor or anything of the sort.

Almost done with my engine reassembly....