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New (to me!) '77 CB400F - US model
mattsz:
If I run into specific issues, I'll ask separately, but I'll add general thoughts here...
I've been digging through the archives, and I found a 2017 thread started by Nurse Julie about idle issues - this was before her epic engine rebuild!
http://www.sohc.co.uk/index.php/topic,12977.0.html
In that thread, she said:
--- Quote ---as Trig said before, the engine does need some internal work done as she has oil vapour in the airbox.
--- End quote ---
So I'm wondering - does oil vapo(u)r in the airbox always suggest the need for engine work? And, what does it look like? In my bike the little breather foam filter beneath the air filter is disintegrating, and is quite oil-soaked. The air box around it is damp with oil, as is the bottom of the primary air filter. It this an indicator that internal engine work is definitely in my future?
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taysidedragon:
It's hard to be sure because you don't know how long it has been since the oil trap was last cleaned out. It could have built up over a long period of time.
If it built up quickly it could indicate engine wear, probably piston rings/rebore or valve wear.
zebedee85:
this can happen if the oil is ever overfilled as well.
if your air box doesn't fill with oil quickly, you don't encounter blue smoke, your cam chain can be adjusted via an non-seized adjuster mechanism and any head oil weeps remain insignificant I'd leave it alone until it was worth pulling apart.
Nurse Julie:
No point thinking about engine rebuilds until you know how long the trap and air filter box hasn't been cleaned for. Mine filled with oil vapour quite quickly due to internal damage the engine had sustained previously causing raised crank pressure. Give it all a good clean out, fit new foam (make your own out of a kitchen foam scratchy thingy) and air filter,ride it and observe. Even if there is nothing particularly wrong with your engine, its an old engine so internal wear is to be expected but oil vapour doesn't give conclusive evidence that there is a problem that needs immediate attention. As has already been pointed out a combination of oil vapour and blue smoke would give more of an indication that there may be a problem.
mattsz:
Thanks all! I wish I'd paid more attention when I rode it 3 years ago - it has only a few hundred miles more since then. But I wouldn't have known what to pay attention to anyway, as far as noises and such on these engines go. Blue smoke is universal, however! I don't recall any at the time...
I won't worry about it now, just a fact-finding mission, if you will...
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