This pic shows the carb rack with its mounting paraphernalia; at top is the rack of carbs and on the right is the manifold for carbs 1&2 with everything assembled and ready to install. At left, we have the installation components spread out for clarity: the # 3&4 intake manifold (with O-rings) and carb insulator boots, along with the attachment clamps. At bottom are the overflow drain tubes, and the vent tubes draped over the rack should be noted as well
The carburetors have been thoroughly cleaned and rebuilt, then bench-synced, leak tested and had their float heights checked via the clear hose method. The rubber insulators are new from BikeBandit, and all the other hardware came from "Box-'O-Bolts" auctions on ebay.
To begin installation, I mounted the intake manifolds to the carbs. These have the vacuum ports for carb sync testing built into them; they're plugged with a screw and copper crush washer. Later manifolds don't have this feature as the port is on the carb, IIRC, so it's best to make sure you have the correct manifold for the right carbs. They come as a right or left set; the little port screws and the "bridge" connecting each manifold pair should be oriented downward when mounting the manifold to the carbs.
I installed the manifold o-rings (these are the same o-rings used in the valve adjustment covers, BTW) and smeared a little grease on them to help them seal...
...then inserted the whole assembly onto the head. I had to spread the manifolds apart slightly to get them to fit down over the studs, but the whole thing slid on easily enough
I then attached the manifold/carb assembly to the head using eight flange nuts (no washers of any type used with these)
Once the carbs were in place, I connected the overflow hoses to the outlets on the carb bowls and routed them down the back of the engine, along with the carb vent hoses, which are attached to vent outlets between carbs 2&3 (upper left). All of these hoses are gathered together using a little hard plastic band (lower right)...
...then route down between the engine and swingarm. The vent hoses terminate at the swingarm, while the overflow hoses are gathered by this little bale on the frame
Now that the carbs are in place, it's time to install the air induction unit (or airbox, if you prefer). Here is the infamous stock airbox assembly spread out for your perusal (and, if I may, a note to those who are thinking of putting pods on their bikes: you might want to keep a copy of this picture around for... you know... later
)
Moving boustrophedonically (... now, there's a $5 word for you! You can pronounce it by repeating this rather grisly little phrase very fast: "
Boo Stro fed
on Nick Lee", with the accent on
Boo and
on. It means "as the ox plows [or turns]" - in other words, moving from one side to the other and back again in a zigzag pattern, like oxen plowing a field. It's a Greek concoction and is interesting in that its definition is actually shorter than the word itself. I like it, though; it has great rhythm).
Anyway, major digression here. As I was saying, moving boustrophedonically, starting at the upper right we have the plenum drain hose, the filter/element case drain and the element box/breather cover coupling hose; all with attachment clips. Next comes the element cover, the foam element, a rubber element cover seal, the separator plate (AKA seal plate, punching metal, etc) and the filter/element case.
Continuing "as the ox plows", we find three tiny little metal bits (and we'll get a closer look at them later): two small tubular spacers and an old friend, a case washer identical to the one we used on the chain case. Next comes an oval case "nut" that fits down into the filter case, followed by two airbox support brackets with mounting bolts, the air filter clamp and the front air filter cover.
In the bottom row are the tool tray, the air filter element, the airbox plenum and, finally at the very bottom, the plenum to carb clamps.
Now, if you'll pardon me, I'd like to do a minor rant here for just a second. That's a whole passel of parts, no matter how you look at it; it's also a prefect example of why you shouldn't rely on just the Clymer book. Take a look at their section on the air filter and compare it with this picture, for one example among many.
I'm not saying don't get the Clymer book, just don't try to rely on it alone. Get the Honda manual as well - in fact, I'd get it first. You can download a version of it from this site, but don't get cheap on me; go out and actually buy a copy you can hold in your hands. The hard copies are different than the digital versions here on the site and, at least in the section I compared together, more comprehensive. Besides, it's difficult to study a digital version when you're asses-to-elbows in grease trying to set some critical gap .
And they come in a nifty spiral setup so they lay flat and help you keep your place, too!
'Nuff said. I thank you for your indulgence (but
do get the Honda book, OK?)
I started out by installing the plenum to the carbs. Now, with nothing else on the bike, it's a little easier to do than it would be with all of those pesky electrical geegaws and cables and bothersome what-not that can
just get in the way, but there's still a bit of a trick to it.
First, I made sure all of the intake boots (available new from David Silver Spares @ $36 a set) were secure and correctly oriented in the plenum. This doesn't matter as much with the center boots, as they are symmetrical, but the outer two boots for 1 & 4 carbs are angled and must be oriented correctly. Fortunately, Honda helps with this by molding small dimples into the plenum face with corresponding extrusions on the boot. Just line them up and you're good to go (note that Honda originally glued these to the plenum, but it was merely to accommodate assembly at the factory and glue is not necessary here. You can use it if it helps keep the intake boots in position)
Next, I removed the upper rear engine hanger bracket to make some room, then inserted the plenum from the left side of the frame kind of catawampus in through the electrical panel "bay", extending the "shoulder" of the plenum down and out through the space vacated by the engine bracket. A couple of things to note are that I've pre-installed the boot clamps onto the plenum, and though the intake boot kissing the carb bowl may look a bit distressed, it can handle it; after all, if done correctly this entire process takes approximately (as Spock would say) 7.33517 seconds to accomplish...
...bringing the rest of the plenum down 'til all boots are level with the carb bowls...
...then gently pushing the left "shoulder" past the down tube 'til the whole thing just "snaps" in to place (Note: The plastic on the plenum shoulder is pretty soft, but you might consider putting a sheet of paper [or whatever] in between the shoulder and downtube if you're concerned about your paint. I didn't use anything, and it didn't even smudge the powder coat)
With the plenum in position, it's a simple matter to slip the intake boots over the carb throats and tighten down the clamps
This interesting and vaguely pornographic shot reveals the installed plenum from the rear, with the two filter case connection points top and bottom, and a
vagin oval shaped air corridor surrounded by a rubber grommet
There's a matching opening in the filter case, with a protruding lip surrounding its perimeter that slides into this grommet (this is a NOS plenum and, while the rubber itself is still nice and pliable, the 30+ year old glue on the grommet has dried a bit, as you can see)
Now, there is an air tight fit between the grommet and case lip, and you have to wiggle the filter case around and use a fair amount of force to get it to slide into that oval-shaped opening in the plenum. My NOS grommet, being a virgin, was just too tight, and no matter how I pushed or wiggled it, I just couldn't get the case lip to penetrate the opening. I finally used a little P-80 lubrication, after which it gently and easily slid right in... all the way... and it was sooo... and... I...
OK, that's enough of that...
Now that I've, er, mated the filter case to the plenum it's time to consummate the deed. This is the airbox (and I'm using "airbox" to designate the combination of both the plenum and filter/element case) mounting hardware
At left are two little tubular spacers that fit into corresponding holes in both the plenum and filter case, while the oval-shaped "nut" secures the lower case mounting bolt. Next is the rear mounting bracket with bolts and washers, while at the bottom is a case washer similar to the one we installed in the chain guard. Last (but not least) is the front mount aith its associated bolts and washers.
I began by installing the spacers. These fit between the plenum and filter case, connecting them together; one on top (below left), the other on the bottom (right)
They're necessary because, without them, tightening the connecting bolts and nuts would compress the ABS plastic, causing it to flex and eventually tear.
Spacers in place, I installed the plenum/filter box connecting bolts and washers. The lower sections of the plenum and filter box are secured together by a 10mm 6x25 bolt, an 18 mm washer, split washer and this special oval "nutplate", which fits down inside the filter box (right)
The top 6x25 bolt not only completes pairing of the plenum and filter case together, it affixes the front airbox mounting bracket to the assembly. The bolt, with a split washer and 18mm washer, is inserted from the inside of the case through the case body and into a nut that's welded to the back of the mount
Next, the rear mounting bracket is attached to the rear "nose" of the filter/element case utilizing the case washer, another 10mm 6x25 bolt and split washer...
..the bolt screws into a nut on the back of the bracket, just like the front bracket had. Note the orientation of the bracket, with the longer "leg" extending away from the airbox
Here's an overall view of the airbox as it sits in the bike. The front bracket mounts to a plate welded across the frame with a 10mm 6x12 bolt (and the plate is slightly angled, so the bracket is "bent" to match it), while a 10mm 6x40 bolt attaches the rear bracket to the bike at one of the frame cross members. The inset gives a more detailed look at the orientation of the brackets...
The two final parts that finish up the installation are the drain hoses for the filter/element case and the plenum. They come in two sizes, and while they may look similar, they're actually quite different
The longer hose is the plenum drain hose. It is has an internal foam filter
Foam filter. Remove this when using hose for drain on the filter/element caseIts primary purpose is to drain any gas that might somehow escape the carbs and splash into the plenum. The foam acts as a kind of barrier that lets gas out but doesn't let in a lot of air or debris, so that the correct pressures are maintained inside the plenum during engine operation. It connects to the plenum via this outlet formed into the plenum body where it's secured by an omega clip
It then routes down and through this bale on the frame, which it will eventually share with the battery vent
The shorter hose attaches at the base of the filter case and is actually no longer available; however, the plenum hose can still be had and, with a couple of mods, will work fine. Just cut it to length and remove the internal foam filter mentioned previously. The hose differs from the plenum drain in that it uses no internal filter; it's (obviously) shorter (@11"), and it terminates in a special tip that looks and operates like this :
This hose and tip are necessary because one of the functions of the air filter element stack is to condense liquid vapors from the blow-by gasses as they're being cycled through the PCV system (more on this in Part 2). The condensate (mainly water) dribbles down here and collects at the little tip; just squeezing the bulb opens a slit in the side that lets it all drip out. Nifty, eh? Now, because this is part of the air intake system it needs to be air-tight, and that's another thing the little tip does; it closes off the drain tube and helps maintain a negative atmosphere within the filter/element box, a condition that is necessary for proper functioning of the air filtration and crankcase ventilation systems.
So, the obvious idea is that the hose needs to be kept plugged until it needs to be drained. The biggest problem with this is that the fancy schmancy little hose tip demonstrated above is made of unobtainium, and is dang nigh impossible to find. I managed to snag one through the kind auspices of a fellow forum member (Thanks, G-man!!), but what I originally had to resort to was a small plastic plug that fit tightly into the end of the drain tube and could be removed for draining when necessary...
It's actually a weatherstrip grommet from an early Corvair and is still available - here's a link:
http://www.corvair.com/user-cgi/search.cgi?part=C8500. They're around three bucks for a pack of 10 (so you've got a couple left over. Who knows what use you might find for them).
Whatever works to keep the hose plugged. Meanwhile, the hose routes down through the same wire bail as the carb overflow tubes, as shown in the above pic.
Now that the airbox is mounted in the bike, the next step is to install all of the anti-pollution goodies, and this is such an important subject that I'm going to take a closer look at it.
To clear the crankcase of noxious gasses and acid vapors, the CB550 (and all of Honda's SOHC bikes) utilizes a system known as crankcase "evacuation" as opposed to crankcase "ventilation". The crankcase isn't ventilated like a normal engine; there's no inlet for air to get into the case and as such it's known as a "closed" system. It's pretty simple: intake air drafts over the opening in the element cover, creating a negative atmosphere in the case and drawing blow-by gasses from the crankcase. The biggest problem with this type of set-up is that intake volume and blow-by production don't always match - something the PC valve compensates for, and we don't use - which effects efficiency and tends to make the fuel/air mixture run rich; a condition that Honda's engineers took into account and designed for. There's no PCV valve or flame arrestor because that big 'ol plenum sitting out there with all of that airspace acts to homogenize the vapors more evenly with the incoming air stream, and to dissipate back-fires or fuel vomiting from the carbs.
Now, in the past, these gasses were merely vented out into the atmosphere via a "Road Draft" tube.
The official Honda designation for this collection of parts is the "Blow-by Gas Scavenging Device", and this is a drawing of it purloined directly from the Honda shop manual (find this in your Chilton's).
The first thing we'll look at is actually no. 2 on the list; the Breather tube. In the CB500 and other bikes this was used as the road draft tube, and simply extended from the breather cover, down past the overflow tubes, terminating just below the bottom of the engine. Honda took it and attached it to an air filter case modified to contain a crude catch can (5), where a series of filters refines the blow-by gasses to a more combustible form
The hose connects at the breather, then extends down between carbs 3&4 to this little plastic "elbow" at the base of the air cleaner/element case
But all of the action actually starts with something they call the "Element Cover" (10). It comes in the form of an inverted funnel: a cone with a boxed lip surmounted by a short tube that extends into the center of the air filter element. A metal "cage" surrounding the funnel acts as a support for the air cleaner element. Underneath, there's a plate that fits over the cone that is perforated with a series of holes that let the gasses pass through from the rest of the system
Element Cover
The element cover is important because it supplies the motive power for blow-by scavenging, and it's been carefully calibrated for the purpose. Like the road draft tube of old, it's the venturi effect of the onrushing intake air over the top of the tube that pulls the bad stuff from the crankcase via the Breather tube (2 - which I've just installed). Those vapors, starting out hot and moist deep inside the crankcase, travel up through the cam chain "chimney" and are gathered in the breather cover, where a combination of baffles help remove any heavy oil contaminants from the gasses and return them to the engine. The vapors then move up through the breather cover and are compressed into this long, narrow tube until they reach the separation chamber at the base of the air cleaner/element case. Once there, rapid re-expansion of the gasses, the sudden slowing of the rate of vapor travel and the relative coolness of the chamber cause water and vaporized oil to condense out of the emissions. The gasses are then pulled upwards into the Seal Plate (7), which consists of a small rectangular metal cup covered by a plate that has a series of holes punched into it similar to the element cover, but smaller and more numerous; and it's called the "Punching Metal" (8 - gotta love the Japanese) - AKA separator plate, condensation plate, etc.. The gasses move up through two small openings in the bottom of the seal plate and more oil and water vapor condenses on the punching metal, where it drips down into the separation chamber and then on to the drain (6).
Seal Plate and Punching Metal
Now, here is as good a time as any to focus on why that drain needs to be kept plugged. The element cover is essentially a vacuum collector, and it doesn't care where it gets its input. In order to positively clear the crankcase, all of the suction created in the element cover needs to be directed at the incoming gasses from the breather tube. With the drain open, some (or all) of that vacuum can be diverted to pull fresh air into the system through the drain hose, rather than working to clear the crankcase; and at the very least, the efficiency of the entire scavenging system is compromised. Two Tired put it (very well) this way: "The breather system needs to evacuate the engine crankcase. An open bottom hose will bypass/equalize any suction sourced in the air filter box that was intended for the crankcase. Think of a "Y" shaped drinking straw, with only one end in the fountain drink. Unless you suck REALLY hard, you'll stay thirsty."
Bottom line: if you don't plug the hose, you really suck (air, that is). It should be cleared at every oil change.
The seal plate just fits down into the air cleaner case with the two holes oriented downward and the "Punching Metal" facing up
The next step in the process is the wet filter (9). A 3" X 4" X 1/4" sheet of medium-density open-cell Polyurethane foam called "Element B". It sits in the little box formed on the bottom of the element cover and is sandwiched between the punching metal and the element cover plate described above. The foam element further refines the blow-by by removing any remaining water or oil vapor that might have made it past the seal plate and punching metal; the wet process also helps neutralize any acidic vapors before they enter the carb intake. The Honda Shop Manual says this should be cleaned with solvent, then dipped in ATF and wrung out for use just like the foam filter on your lawn mower.
All of this is kept separate from the rest of the filter case by a rubber U-channel seal (present but not indicated on the drawing; even Honda leaves stuff out) that fits around the element cover "box" where the foam element lives. It slides onto the stamped metal lip of the funnel, encircling it and sealing off the air filter chamber. Just like the plug for the drain, it helps insure that all of the vacuum being generated by the element cover is directed towards evacuating the crankcase, not being used to pull in extraneous air from the filter box. In addition, the seal acts as a buffer between the punching metal and the base of the element cover "box" so that they don't slide against each other.
Here's the element cover with the filter and seal in place.
It's installed down over the seal plate
Now, the element cover seal is nearly as elusive as the aforementioned drain bulb. I managed to snag two from "Box-O-Parts" auctions on ebay, but I was considering using a dense foam weather-strip wrapped around the base of the element cover before I found them. The important thing is to keep the condensation chamber (catch can) in the bottom of the filter case isolated, so if you can't come up with the proper rubber part, you might give the foam a try...
EDIT: Due to the efforts of various members of this forum, this important little seal is now being reproduced and may be had at this link:
http://www.claussstudios.com/id45.html . Clauss also has the elusive front air filter box cover (see below) as well as quite a few other hard to find rubber parts. Check him out.
At last, we come to the final step in the process. The blow-by gasses, now properly conditioned for use by the engine (like drinking water on the International space station; it comes from recycling... well.. never mind) flow up into the element cover, gathering speed as they move into the ever-narrowing space at the top of the cone. Now, because of where it sits in the intake airflow, the element cover is considerably cooler than the rest of the scavenging system, so as the vapors enter the top of the cone they begin to swirl and make contact with the body of the element cover, creating yet another filtering step as any stray oil or water vapor is filtered from the gasses via centrifugal force and condensation. The gasses then move up through the calibrated funnel tube to erupt like Vesuvius into the airstream being pulled in through the air filter (Element A). Honda says that the gasses are further filtered at this point, but the truth is that once they get here they don't hang out to chat; they're drawn directly into the gaping maw of the plenum with the rest of the intake air.
Incidentally, part of this will become blow-by once more, thus completing the great karmic cycle of sunrise and sunset, birth and death, summer and winter, fuel and blow-by...
Ommm...
Here, the air filter is installed. There's a hole in the bottom of the filter frame that slides down over the element cover tube (don't get me started, now...), and the filter rests on a large foam washer that sits atop of the element cover, through which the tube protrudes. Once the filter is in position, it's locked there by this little metal spring clamp (11) that simply slides into a slot formed into the rear case "nose"
At the front of the filter case, this rubber cover keeps water from entering the system during wet conditions. It has a channel molded into it that fits down over the case "nose" and holds it in place. This elusive part is now being reproduced; see above for a link
With the air cleaner mounted, we finish the BGSD installation with the tool tray/air cleaner cover. It's important to have this installed because we want the incoming air to be concentrated around the a/c opening; like everything else, it has been calibrated to work with the rest of the system in specific ways, so leaving it out disrupts the over-all flow and lets too much air in from too many directions for the element cover siphon tube to work correctly; not to mention the fact that it will cause the engine to run on the lean side...
So, here's a shot of the completed carb installation
