Topic: Valve cover leak: 750K1

[Gordon]

Allright, so I'v got a weeping valve cover gasket.  I just replaced all the gaskets about a year ago, so I'm trying to avoid having to pull the engine just to replace a still new one (besides, it's riding season). 

I thought it might be caused by excess pressure building up due to a blockage in the tube that runs from the breather to the oil tank.  I replaced the old tube with a new stronger one that won't kink, but it didn't help. 

So I pulled the tube off and rode around the block, and there was no leaking around the gasket, but a small amount of oil had come out of the breather housing.

I blew a lungfull of air through the tube while it was still connected to the oil tank.  There was a decent amount of resistance at first, and then it went through and I was blowing bubbles in the tank.

So I guess what I'm wondering is do I have a faulty valve cover gasket, or is the bike just building up too much pressure in the breather tube and not allowing the air/oil to flow the way it should?

Gordon 

[Mark M]

I think we are all wondering the same thing,
I have seen posts in the past where leeks have finaly been tracked down to blocked breathers but thtas been
from the crankcase breather.
Sorry not much help      

[Gordon]

OK, I'm bumping this up because I have another variable to this problem:

I'm beginning to think that maybe the breather hoses aren't routed/connected properly.  They're set the way they were when I got the bike, but that doesn't really mean anything.  Nothing in my manuals about where the hoses are supposed to connect, and a search of the archives only confuses me more.

The current setup is this:
Valve cover breather hose connects to the outlet near the bottom of the backside of the oil tank.
Crankcase breather hose connects to the outlet near the top of the oil tank.

After some consideration, this doesn't seem right.  I would like to know what the setup is on some other folks' bikes.

Thanks!

[Bob Wessner]

Gordon,

 I believe you are correct about something being amiss re: the current routing of those hoses. First, I have to make an assumption that may not be correct, that being the K1 is similar to the orig 750, or K0 with respect to the hose rounting. On my K0, both the oil tank breather and the valve cover breather hoses are open and route down behind the swing arm a head of the rear tire. The valve cover hose routes over the airbox, then down. Hope this helps.

[Gordon]

Thanks Bob,

Does the crankcase breather vent to open air as well?  And what connects to the outlet near the bottom on the back of the oil tank?  I'm guessing the top outlet on the back of the oil tank is the one that vents to open air?

Gordon

[Bob Wessner]

All the tubes vent to the outside air on my bike, including the valve cover hose. I couldn't quite figure out what you meant by upper and lower on the back of oil tank. Here is what I found. I popped the tool tray out and near the top rear of the oil tank is a small canister-like thing. Coming out of the top of this cannister is a right angled metal connection and attached to that is a large diameter vent hose which runs down and vents in front of the swing arm. on the bottom of the cannister is another connection and attached to it is a vent hose of smaller diameter. Both drop down to the same area and vent to the atmosphere also. This was back when no body cared about emissions. 

[Gordon]

I think the main confusing factor in this is that each version of the 750 has a different breather system, so it's hard to figure out where everything is supposed to go.  Not to mention the fact that after 30-ish years, nothing us usually where it's meant to be anymore. 

My oil tank has two separate tubes for hose connections on the back.  One at the top, and one near the bottom.  The bottom one oozes oil if the hose is disconnected, so it has to be connected to something. 
The way I have it set now is like this:

Valve cover breather hose routed over the airbox and down in front of the swingarm.
Crankcase breather hose attached to the bottom outlet of the oil tank.
Outlet hose on top of oil tank routed down in fron of the swingarm.

I'm hoping this works, as I'm getting tired of messing with it when I'd rather be riding.
I am a little concerned about the amount of oil that was previously coming out of the valve cover breather.  It may be time to do a top end rebuild anyway.

Thanks,
Gordon

[kghost]

Both my K2's are hooked up the was you described the first time. Valve cover to top oil tank inlet crankcase to bottom.

One seems to carry a little pressure in the oil tank thouight. Would like to see a definative answer.

[Bob Wessner]

It took some digging in the shop manual, but it seems what Honda calls "breather tube A" should be returning any oil separated out back to the engine. Breather tube A is the smaller hose at the bottom of what they call the "breather chamber." This is the canister-like attachment at the upper-rear of the oil tank. Looks like this was always open to the atmosphere on mine, will have to look at that tomorrow.

[kghost]

Would that be the small hose that goes from the bottom tank fitting to the crankcase?

[Bob Wessner]

By tank fitting do you mean the breather chamber in the above diagram?

[kghost]

No, mine doesnt have that pipe in that location. Instead of being on the bottom of the canister on the upper back of the oil tank its below that.

[Bob Wessner]

Hmm, much below that would seem to put it near, or below the oil level in the tank??

[kghost]

Yeah. pretty close. Not to say theres not a chamber or pipestand in the oil tank itself. I hooked it up just like my other bike but the recent overhaul seems to pressurize the tank slightly. Just sort of chauked it up to ring blowby prior to full break in but if some one has a different idea?