Topic: Where do I route the valve cover breather?

[drumstyx]

I've decided against using the mess of hoses the EPA loves up top, but now I'm not sure where the breather should go, and what to do with the open hole at the top of the airbox. Can I just cap the airbox and route the breather to atmosphere? Does it need a filter?

[TwoTired]

I've decided against using the mess of hoses the EPA loves up top, but now I'm not sure where the breather should go, and what to do with the open hole at the top of the airbox. Can I just cap the airbox and route the breather to atmosphere? Does it need a filter?

Yes, the older bikes did this very thing. Vent to atmosphere.  Won't hurt the engine.  Just everyone who is still breathing.  Add a filter if you don't want bugs and dust inside your engine.

The re-breather is not just for the EPA though.
Besides oil vapor, the re-breather system also sucks piston blowby gases/particles out of the engine crankcase and back to the cylinder to be burned off.  I'd rather not have the blowby particles in the oil supply (or my lungs).

Some engines use this negative pressure to help seal the piston rings. Don't know for sure this is effective in the SOHC4.

Anyway, routing the vent pipe back to a vacuum source, is likely going to restore basic function of the re-breather, wherever you connect it.  However, the stock one has a water separator incorporated, so condensate doesn't get fed back to the intake system.  Water vapor still flows through the motor.  But, I'd rather have that vapor condense outside the engine proper.  Don't particularly care to invite corrosion.

Cheers,

[drumstyx]

It's just *so bulky*! It's hard enough fitting everything else in place without that giant separator.

I hardly see how it's connected to a vacuum source though. The airbox is a negligible vacuum, being on the airbox side of the throttle valves.

I may change my mind, I still have all the parts. But I've been at this for 2 years now, and I'm thisclose to getting it on the road. All I need now are decals on the tank and another couple coats of clear, and I can RIDE this thing!

Good to know I can just throw a little filter on there though.

[Scott S]

 The XS650 guys have been using PCV or Reed valves for years. I ran a few from the local auto parts store. This is the one MikeXS sells now. I currently have my CB500 style breather vented to the atmosphere. I wonder how the SOHC4 would like a PCV valve on the breather line?

[TwoTired]

I hardly see how it's connected to a vacuum source though. The airbox is a negligible vacuum, being on the airbox side of the throttle valves.

It doesn't take much pressure differential to move air.   And, cruising down the road, the throttle valves are open.  Hold your hand over the airbox inlet and rev the motor.

There be vacuum there mate. #-

[Lostboy Steve]

On my 77 550 i routed mine right back into the air box plenum, it's been that way for miles and works great.


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[drumstyx]

On my 77 550 i routed mine right back into the air box plenum, it's been that way for miles and works great.


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I was thinking of exactly this, just an incredibly simple hose straight to the airbox. My only concern was oil blowby, which I imagine is what the separator was supposed to deal with. The airbox doesn't have a drain like modern airboxes (that expect oil to make its way to the airbox). Of course, the intake is at the bottom, and I'm sure the oil would make its way through the filter (possibly not good?) and out that intake, rather making a mess...

[Deltarider]

If I owned a CB550, first thing I'd do is to disconnect it and have it routed like on the CB500. I've seen enough airfilters elements with that typical soft (humid) and light brown spot indicating moist and oil vapour passed the breather element. Back then Honda dealers would often disconnect it as they knew it could be a problem. Maybe you can prevent it by checking things more often. My impression is that US generally favours cheap aftermarket products more than Europe that tends to stick to genuine Honda parts, so I suspect many riders have turned to a foam filter (inferior in all aspects) to address it but my first choice would be to continue to run the stock paper filter element. If you continue to have the breather connected, maybe check the breather element as well as the paper filter element more often than sceduled.

[TwoTired]

To reiterate:
I maintain the re-breather is an effective and useful device on the SOHC4 as well as millions of other internal combustion vehicles, and was put on vehicles well before any EPA mandate, for very good reasons.

[Jimray23]

With that hose unhooked, like mine, at high rpm's it can cause blow bye around the rings but i haven't had any issues so far

--------------------------------------------------
Jim
1979 kz1000b ltd
    stage 3 cams
    pod air filters
    4-1 open exhaust(no muffler)
    full rewire
    dyna-s ignition
    dyna 3 ohm coils

[Deltarider]

None of us in the states has a filter restrictor on their air filter as Delta has on his 500.

Why oh why do you always reply with a remark about the cover over the airfiltercase on my model? It seems like an obsession. As in many other threads: it has NOTHING to do with the subject. I have a CB500 NOT a 550, so I don't have a breather connected to the airfilter case, never had and never will, nor did any owner of a CB500 ever had one. I only try to help people by informing them on what every mec at a Honda dealer at the time knew.

I gauge it as a factor in his filter fouling (added chamber turbulence and increased vacuum).  He does not.  So, you decide for yourself, reader.
We've been over this many times in the forum.

I'm lost .. sorry, I don't get it. Why do you think my airfilter foules? It doesn't, it never did and it probably never will as there's no breather connected to the airfiltercase. But I have seen this fouling on several CB550s. I spell it for you: five hundred fifty, not a 500, which is spelled fivehundred.

I just don't understand why a realization that a bike with the snorkels/restrictor doesn't behave differently than those in the rest in of the world, when it is such an obvious difference.

Do you even remember what the subject was? Anyway, for who is interested p. 170 of the Honda Shop Manual CB500-CB550 shows how the breather tube on models that don't have a breather element is supposed to run. I just pass on the info I have, all info (from documents, from pro's and from own experience. it's not an opinion and everyone can decide what to do with it.

[TwoTired]

You're right delta.  I mis-spoke.  The CB500 lacks the improvements found on the 550.  I'll edit my prior post.  My apologies.

[Deltarider]

No problem, TT.
Another practice I heard of was that CB550 owners that kept the breather tube connected, did not top up oil to the upper mark on the dipstick but halfway the two marks and claimed the airfilter element was no longer fouled anymore. But this is from hearsay, I have no experience with it myself.

[TwoTired]

That's plausible.
I had a 360 Lycoming engine that, toward the last half of its life, would throw out the 8th quart of oil, right out the engine breather tube and coat the bottom of the fuselage.
The previous owner had marked with felt tip pen on the access door "Fill to 7 Qts only".  If you did that, there was no oil loss between change intervals.
After I had the engine overhauled, it was happy to keep 8 Qts inside.   Had to be something to do with blowby pressures.

But, I have 40K miles on my 74 CB550.  The filter only gets marked in one spot during the winter when there is a lot of condensate in the breather sponge due to short 20 minute trips.  Of course the UNI foam in there now doesn't care, and washes clean at tune up intervals.

I've also noticed that some of the stand pipes that come up from the breather are shorter than others, placing the exit nearly in the center or just below center of filter.  Of course, the shorter ones mark the filter far less (if at all) than the taller ones, even in winter.  Perhaps Honda addressed filter contamination with that part change?