Topic: Smoke coming out the breather tube from the rocker cover.

[Vincent P]

Just rebuilt the top end of the motor on my 73 CB750.

Cylinder head machined new valves, and valve seals. Have great compression 145 plus on all cylinders. When I had the head off I looked at the cylinders and they is no scoring or bad wear.

Now when I run the motor I get an awful lot of smoke out the breather hose that is at the top of the rocker cover. No smoke out the exhaust though.

Anyone have any ideas what could be happening.

Note: oil level seems fine.

[scottly]

Is it smoke, or water vapor? Smoke tends to linger, while vapor dissipates. Any running issues?

[Vincent P]

It does not appear to be water vapour.

[Lostboy Steve]

I have the same thing on my 77 cb550k after a complete rebuild. It seems to be getting better after the first 500. We'll see what happens. I routed the breather back into the air filter box and now I don't see it at least.

[Vincent P]

I took the breather box off and installed the single cones on the unit, so routing it into the box is out. 
I will run it and see what happens.

Thanks,
VP

[Lostboy Steve]

Yeah I had pods. I made a catch can and put a little uni filter on it and that calmed it down as well.

[lucky]

Make sure the top end is getting oil.
Many on this forum have made mistakes putting engines together not getting the oil seals right.

Does it seem normal otherwise? no noise?

Is it jetted for pods???

[Vincent P]

Running normal a far as noise; but not jetted for pods, jetted for the stock air filter box.

[CycleRanger]

Just rebuilt the top end of the motor on my 73 CB750.

Cylinder head machined new valves, and valve seals. 

What about valve guides?

[Vincent P]

Completely redone by a very reputable shop here in town.

[CycleRanger]

Completely redone by a very reputable shop here in town.

The valve guides were replaced with new ones or were the old ones just reamed?

[TwoTired]

Is it smoke, or water vapor? Smoke tends to linger, while vapor dissipates. Any running issues?

I'd bet on water vapor too, particularly if it is white.  Dissipation time depends on outside humidity level.  (You got any humidity there is AZ, Scottly?  Is it monsoon season?)
Anyway, get the entire engine and trans unit up to operating temperature and keep it there for 15-20 minutes.  That's a rough guideline to ensure all the water has been vaporized and evaporated.

You may never get the far ends of the trans hot enough to convert all the water, while idling in the shop, or driving it leisurely around the block.  And every time you cool it down, it will pull more humidity from the air and collect it inside the engine/trans.

Cheers,

[Vincent P]

It is a pure white smoke come to think of it not a bluish like when you burn oil.

Hmmm, something to try.

[CycleRanger]

It is a pure white smoke come to think of it not a bluish like when you burn oil.

Hmmm, something to try.

Check your oil tank and see if there's some chocolate-milk looking residue on the cap or inside the top of the tank. That's moisture.

[Vincent P]

Will give that a look.

[scottly]

Valve guides/seals cannot cause blow-by out the breather; they might cause oil smoke out the exhaust. Blow-by is caused by bad ring seal, and it doesn't sound like that is the issue in this case.
Yes Lloyd, the monsoon hit here with a vengeance about 2 weeks ago. I made my weekly grocery run today, and on my last stop parked on a slight incline; when I came out 10 minutes later, there was a small stream of water running from under the car, condensed from the AC. It's not a "dry heat" right now..