Topic: Question about CB550 airbox

[IndyFour]

I have a '74 CB550 with the stock airbox setup.  Needing a new filter, I ordered the Uni oiled foam type filter rather than the paper type.  I'm ready to put it in, but a question first....

In this schematic, can someone tell me what parts 27-30 are for?

http://www.bikebandit.com/assets/schematics/Honda/HJ0906W0130012.gif

Basically, it appears to be another filter in the bottom of the filter box with a tube that goes straight up into the main air filter.  Mine is basically just a rusted bunch of pieces with no filter media of any sort in it anymore.  There is a grate type material at the bottom of the air box that covers a section with a drain tube going out. 

My new Uni filter appears to have a small piece of red foam covering a hole where you could put this tubed "apparatus" through and use it....or leave the red foam in place and do without.

What does this part do?....and can I remove it and run the main filter without it?  It doesn't look like it does much of anything to me.  I'm sure it has/had some purpose or it wouldn't be there.

Thanks for the help.

[OldSchool_IsCool]

I believe that's where the crank breather tube connects.  It feeds blow-by gasses back to be burned more.

[IndyFour]

I believe that's where the crank breather tube connects.  It feeds blow-by gasses back to be burned more.

I thought that too at first, but the breather tube inlet is in the other box between the filter box and the carbs.  The filter box does have a nipple for a tube pointing straight down, but it appears to be a drain.  That's why I'm confused as to what this contraption does. 

[delay pedal]

you dont need anything in there it will still run fine

[IndyFour]

I figured it would probably run fine without it....but now I am doubting that my engine breather tube is hooked up to the right place.  I think that OldSchool may be right.  There are two holes in the bottom of the air filter housing going into the bottom of the contraption in question.  It looks like one might have been the inlet for the crankcase vent and the other a drain.  Both of these holes are just open with no hoses attached.

Pic of inside of air filter box...


Here's where my breather tube is currently hooked in.....to the nipple on the bottom of the box between the air filter box and the carbs....


If the hose is in the wrong place....what's supposed to go here?  Was it a drain in case the fuel overflowed the carbs?

[TwoTired]

Wow, this topic has been discussed a lot recently.
To better understand the engine breather, check out chapter 8 of the Honda Shop manual CB500/550.

For the uni NU-4055, it fits both the CB500 and 550 Filter boxes and the 500s don't have the engine breather set up.

The air plenum just behind the carbs has a drain fitting.  This hose is a reduced diameter hose that routes behind the engine and in front if the swing arm.  The end is open but rather small to allow any gas that might over flow into the chamber to drain.  If would be very bad for that chamber were to fill with gas.  And back fire could ignite it and ingesting raw liquid into the engine cylinder can bend/break a piston rod.

The fitting at the top of the engine goes to the side of the filter box (NEVER the air plenum chamber).  The filter box also has a drain tube at the bottom that is capped.  The cap has a slit in it, that is pinched at maintenance intervals to drain collected water condensate.
The bottom of the filter box has the parts you see in the picture you posted.  Those parts; gasket, foam element, and metal assembly are there to keep the engine vapors from fouling the air filter element.  It will ruin the stock paper element very quickly with oil and water vapors/droplets.    The foam UNI type will survive this much better, but the cleaning and re-oiling interval will shorten.

Cheers,

[IndyFour]

Wow, this topic has been discussed a lot recently.
To better understand the engine breather, check out chapter 8 of the Honda Shop manual CB500/550.

For the uni NU-4055, it fits both the CB500 and 550 Filter boxes and the 500s don't have the engine breather set up.

The air plenum just behind the carbs has a drain fitting.  This hose is a reduced diameter hose that routes behind the engine and in front if the swing arm.  The end is open but rather small to allow any gas that might over flow into the chamber to drain.  If would be very bad for that chamber were to fill with gas.  And back fire could ignite it and ingesting raw liquid into the engine cylinder can bend/break a piston rod.

The fitting at the top of the engine goes to the side of the filter box (NEVER the air plenum chamber).  The filter box also has a drain tube at the bottom that is capped.  The cap has a slit in it, that is pinched at maintenance intervals to drain collected water condensate.
The bottom of the filter box has the parts you see in the picture you posted.  Those parts; gasket, foam element, and metal assembly are there to keep the engine vapors from fouling the air filter element.  It will ruin the stock paper element very quickly with oil and water vapors/droplets.    The foam UNI type will survive this much better, but the cleaning and re-oiling interval will shorten.

Cheers,

Thanks so much TwoTired.  That makes total sense.  I did a search and saw something mentioned on another thread, as you mentioned, but I thought it was in reference to a 750.

The previous owner had the breather hose routed to the plenum chamber...now I know to change it to be correct.  I suppose now I will have to decide if I want to put this contraption back into service or just open vent the breather hose to the ground underneath.  I guess I could make a new filter element for this breather with some sort of foam.  I suppose the purpose of that lower filter is to collect as much of the oil out of the vapor as possible before allowing it to join the airbox inside the main filter.

BTW - I have looked high and low for the real honda shop manual for this bike.  The faq has lots of different links, but all of the ones I need appear to be old and dead.  I did find one link that got me an .exe file of the manual and parts list, but being a Mac user, I can't open it.  Tried to open it at work on my PC and still no go.  Any idea where to get one for the 550?  I have a Clymer and it is just about worthless except for very basic stuff....and pretty vague for even that stuff sometimes.

Thanks again.

[mark]

..........  I guess I could make a new filter element for this breather with some sort of foam.  ......

I used the prefilter from a Briggs 12hp - folded in half and trimmed the end a bit.

[daredevilsadvocate]

I have a '74 CB550 with the stock airbox setup.  Needing a new filter, I ordered the Uni oiled foam type filter rather than the paper type.  I'm ready to put it in, but a question first....

In this schematic, can someone tell me what parts 27-30 are for?

http://www.bikebandit.com/assets/schematics/Honda/HJ0906W0130012.gif

Basically, it appears to be another filter in the bottom of the filter box with a tube that goes straight up into the main air filter.  Mine is basically just a rusted bunch of pieces with no filter media of any sort in it anymore.  There is a grate type material at the bottom of the air box that covers a section with a drain tube going out.  

My new Uni filter appears to have a small piece of red foam covering a hole where you could put this tubed "apparatus" through and use it....or leave the red foam in place and do without.

What does this part do?....and can I remove it and run the main filter without it?  It doesn't look like it does much of anything to me.  I'm sure it has/had some purpose or it wouldn't be there.

Thanks for the help.

Interesting this question came up ...I was about to post something about my 78 550 and part number 31 in that drawing..long story short...I don't have it..it was cracked and barley hanging on when i got the bike..didn't notice it til i took the airbox off for the carbs...do I need to replace this downtube?..or will it be ok without it? or can i jus put a replacement downtube on there?  Thanks!!

cheers,

~dd

p.s...i have a cracked boot between the airbox and carbs..can this be fixed? or am i going to have to switch to pods? and live through that headache...these boots as twotired have said are nearly impossible to find....

[IndyFour]

..........  I guess I could make a new filter element for this breather with some sort of foam.  ......

I used the prefilter from a Briggs 12hp - folded in half and trimmed the end a bit.

Good idea.  Thanks.  I'm assuming that the foam piece goes between the part that fits into the bottom of the box and the metal piece with the tube going up?  Looks like a piece only about 1/2 inch thick would fit.  Is that about right?

[TwoTired]

BTW - I have looked high and low for the real honda shop manual for this bike.  The faq has lots of different links, but all of the ones I need appear to be old and dead.  I did find one link that got me an .exe file of the manual and parts list, but being a Mac user, I can't open it.  Tried to open it at work on my PC and still no go.  Any idea where to get one for the 550?  I have a Clymer and it is just about worthless except for very basic stuff....and pretty vague for even that stuff sometimes.

You could try Helm inc. for a hard copy manual.
http://www.helminc.com/helm/product2.asp?class_2=AHC&mk=Honda+Motorcycle&yr=1978&md=On-Road&dt=Shop%2FService+Information&module=&from=result&Style=&Sku=6137407&itemtype=N&mscsid=R8B93XGJQ7HH9K69FD56LQ02QJUQ4FFD

[Bill/BentON Racing]

PM me and I'll fax you the pages you need,Bill

[Laminar]

Here's the manual.

http://depositfiles.com/files/uffzbj1fu

[SohRon]

Here are some views of the airbox and breather hose. Breather connects at the breather cover:

...and goes to the connection at the bottom of the airbox here:


Here's the airbox with all of the "environmental" controls intact. These "innards" can be found on e-bay for pretty cheap, and the filters are available from Honda or parts suppliers like Bike Bandit


This shows the box with its special drain "snout", or rather, the "snout" that goes with the plenum. I've learned that there were two of these specifically made for each componant (airbox, plenum), but now only the longer plenum drain tube can be had. So I picked up two and used the plenum drain tube here, on the airbox. It has a small screen at the end of the tube, and I figure it's got to be better than nothing there. They're cheap.


Drains from the airbox (left, with the carb overflow tubes), and from the plenum (right, through the bale in the frame)

Hope this helps you to get a better grasp on how this should go...
Ron

[TwoTired]

The tube at the bottom of the air filter box should be capped, not screened.  It is only opened when draining the water collected by the breather element system.

[SohRon]

The tube at the bottom of the air filter box should be capped, not screened

What would you recommend we use as a cap for this application? I understand that we don't want to be sucking road dirt up into the airbox... would just a plain old rubber stopper work?

[OldSchool_IsCool]

Excellent camera work Ron!  Very clean bike too.

[TwoTired]

The tube at the bottom of the air filter box should be capped, not screened

What would you recommend we use as a cap for this application? I understand that we don't want to be sucking road dirt up into the airbox... would just a plain old rubber stopper work?

Just about anything that blocks it would work, a solid rivet, perhaps?  The stock one had a cap with a slit in it.  It blocks incoming air, and then when you pinched it, it would release the trapped water, oil, sludge, etc.

Cheers,

[SohRon]

Excellent camera work Ron!  Very clean bike too.

Thanks! The bike is a project I've been working on for a while. Here's the URL:

http://forums.sohc4.net/index.php?topic=49551.0
 
Two Tired, thanks for pointing this out. I found a little plastic plug that fits perfectly; tight enough so it won't fall out, but I'll still be able to remove it for draining.

It's these little details that can get you, in the end.

IndyFour, hope this has helped.
Ron

[fastbroshi]

So that's what that little bale is for.  I was using it to hold my battery vent hose.  Just zip tied the vent hose to the carb vent hoses.

[mono]

Resurrecting the dead here, fellas -- with SPRING around the corner I'm trying to get prepped for the summer and get all the loose ends on the 550 tied up.

Has anyone found a source for these replacement tubes?  both the one from the crankcase to the airbox, and the airbox drain tube?

If yes, links would be SWELL 

[SohRon]

BikeBandit, for one. They carry both types of hoses.

[mono]

BikeBandit, for one. They carry both types of hoses.

thank you, sir.

[RAFster122s]

I found one of the hoses, breather #26, but not the drain hose #35?  Not fun...

[SohRon]

Here's the Bike Bandit pn for the drain hose: 596326. Do a search on their site. This hose is originally for the plenum drain but will work for the airbox; cut it to fit, remove the foam filter in the mouth of the tube and make sure it's properly plugged at the bottom end.