Topic: Honda CB550 Air Filter

[HondaMan]

The breather/vent tube from the valve cover was disconnected from the air box (photo shows still connected) and is now vented to the atmosphere.  I am certainly not a Honda mechanic but IMO Honda's decision to vent oil vapors through the air filter box was not a good step. The air filter needs to clean air and stay clean for as long as possible to do its job correctly.  There is no gain in function or performance by clogging it up and degrading its effectiveness and reducing its lifespan by adding additional contaminants.
 

You're right on all counts: at the time, this change (like many others the 550 suffered) were political in nature, not practical. The reasons for this are noted in my book. Like many political things, it doesn't make sense: it just is (was).

Honda at least put the fumes in at a physical point where it doesn't immediately clog the air filter: it takes a [long] while to do it. American cars suffered this same oddball sort of design in their similar PCV systems, clogging the air filters in half their normal lifetimes.

[jlh3rd]

The breather/vent tube from the valve cover was disconnected from the air box (photo shows still connected) and is now vented to the atmosphere.  I am certainly not a Honda mechanic but IMO Honda's decision to vent oil vapors through the air filter box was not a good step. The air filter needs to clean air and stay clean for as long as possible to do its job correctly.  There is no gain in function or performance by clogging it up and degrading its effectiveness and reducing its lifespan by adding additional contaminants.

the emission gods, at least the U.S., forced that. The PCV systems in my '70s' chevys worked the same way, a "valve" grommeted into a valve cover used a hose going to a "filter" in the air cleaner housing.
No performance engineer wants that.

[kyle750]

All sorted now with earlier CB500 air filter and simple CVS ventilation to atmosphere.  Nothing fancy here 

[kyle750]

I just found an older breather/vent thread that I found very interesting with a completely different viewpoint:

http://forums.sohc4.net/index.php/topic,77061.0.html

In fact, engine breather vapor recirculation improves engine power and efficiency.  Many racing vehicles benefit from this

There is no rational justification to dumping crankcase vapors into the atmosphere beyond ignorance or maliciousness.  Both reasons are injurious to mammals.

I am definitely ignorant about this subject but malicious? (ouch)   If ALL air filters are changed at the proper interval then "in theory"  I can see how this might be beneficial but  . . .

 . . .  "in the real world" . . .  prematurely clogged air filters from increased vented vapors will decrease air flow and engine efficiency and lower gas mileage (km/L) with corresponding increased emissions.  All of the above are not good for the engine or mammals.  Am I missing something?

Late Edit:  And the additional manufacturing involved in producing additional air filters required for a PCV system and the disposal of prematurely aged air filters with increased landfill needs are not good for the environment.

[Jan187]

*Some performance could be gained when the engine gets vacuum... more vacuum results in less push-pull air movement underneath the pistons and less drag on the crank
On single piston engines a check valve on the crank breather is real efficient, on multiple piston engines the air in the crankcase just moves between pistons, so some engines have a more elaborate vacuum system to extract as much as possible. (like a bimmer I owned)

If you have a good catch tank or well designed air filter like later vehicles, the vapors are cleaner when they hit the filter (contain less oil and soot) and affect the filter less.
On the early systems the learning curve was still steep, hence clogged filters etc...

I'm pro, this reduces harmful fume emission as well, and doesn't result in losses performance wise.

[jlh3rd]

just goes to show there's 2 sides to every story. In the 70's, books were published on how to disconnect and circumvent emission devices on cars. My '77 monte's cat used pellets, so you just unscrewed the fill plug, started the motor and blew out all the pellets. Stuff like that.
Years later articles were published showing how disconnecting emission devices decreased performance.

Current cars' PCV systems inject crankcase vapors after the filter, so there's that. But then that probably contributes to intake valve deposits, especially direct injection motors...🫤
Chevy had to redesign their left valve  cover on the V8's because of deposit build up from the PCV system.

[Deltarider]

Well, if Nixon has done anything good, it was the founding of the EPA. It was about time. In 1973 I've seen that yellowish/brownish smog hanging over LA area from a far distance and boy, it was bad. Something had to be done. Back to the subject. Honda was forced to improvise something on an already existing (and succesful) model: the CB500. Its successor, the 550, had the same frame, air plenum and so about the same space which was not much. I've seen filters in CB550s that had that typical soft and sometimes discoloured spot. I don't know what was worse: the oil vapour or the humidity caused by the condens. The latter would pass that special blowby gas filter very easily.

[kyle750]

Looking closer at the air filters of the CB750 and CB550 the actual interior filter elements look  like they might be different.  The CB750 appears to be paper and the CB550 looks much thicker almost like foam? To my eye the CB550 filter element is higher quality.  I'm not sure if this is a correct observation?   If indeed the CB550 is foam I would think it could be cleaned and reused and last a very long time??

[kyle750]

A quick note.  I showed the old CB750 air filter to Kannika.

When I suggested using an air compressor to clean the old filter she said "too much power" quickly followed by:

"You can clean with water no problem.  Cannot soak in tub for long time but OK to spray from hose and then let dry in the air (not full sun)."  Hard to argue with Thai Practicality. Honda NOS air filter already ordered so have at it 

[bryanj]

CB 500/550 filter is paper

[kyle750]

NOS Honda CB750 Air Filter arrived today from Japan All sorted now!

[Deltarider]

Personally I would abstain from washing a cellulose air filter element. I've read about it in the French forum, but I estimate the result cannot be good. The big advance of an OEM filter element is, it can be replaced within 15 seconds. Never understood why people wanted to replace it by foam filters which are are already inferior from the start.
In spite of a pic in the manual showing the use of compressed air, I will never use it. You may want to reread what I've posted before on the working of a paper filter element. Handle with care: if you must, must, you could tap it gently, but I never felt the need in 46 years.

[kyle750]

Based on the actual amount of riding on the CB750 and CB550 I have now logged in a staggering total of 0 Miles (Zero).  At this rate I estimate that my newly installed NOS air filters will last for eternity (or at least until the very end of time).

I am very slow in getting the bikes fixed up and running. I have made good progress on getting quality tools and am now comfortable using them. I am really enjoying learning about the bikes and I greatly appreciate all the helpful advice and assistance.   Perhaps I should spend less time on jackets and more time on trying to understand wiring diagrams and carburetors    

[bryanj]

Depends on how determined your local rodents are!

[kyle750]

Depends on how determined your local rodents are!

Laughing my ass off.  I actually found a wasp starting a nest on the CB750 engine. It looked like a small rock and I thought what is a rock doing in the engine??


In the background of this photo sitting on the chair is a Thai Rat Trap.   The Thai traps are pure genius with a spring loaded door and hair trigger bait hook. 

[kyle750]

Brakes and Shocks - I'm getting closer but now need to buy a C-Clip pliers for rebuilding the master cylinders.  The old CB550 front brake pads were totally rusted inside the calipers but I was able to get the pads and piston out New stainless steel piston, piston ring, and semi-sintered brake pads ordered and will be included in the next shipment of parts. Caliper was stripped, cleaned, and repainted in a high temp ceramic black spray paint and then heat treated. 

The KONI shocks (16mm Ø inner sleeve) would not fit on the CB750 (frame shock bolts 17mm Ø) - this might be a JDM frame anomaly (I really don't know).  I had a machine shop drill out 1mm from the inner metal shock sleeve and they now fit perfectly. KONI shocks for the CB550 fit perfectly and slipped right on. 

This photo was taken earlier today

[bryanj]

The circlip pliers are prettey special as long and bent plus wont get out stuborn clips.

If i said a plumbers torch using a disposable canister would you know what i mean?

Push the piston all the way in then play the flame down the hole to remove all the rust and corrosion BEFORE attempting to remove the circlip or you will break off the "ears" and then you are in a whole new heap of do do

[Deltarider]

As far as the master cylinder, not many undertake the work of a rebuild. For a few bucks more you will have a very good repro. I have chosen one some years ago and it is better than the original.

[Little_Phil]

Being a cheapskate, I've managed to do a couple of master cylinders with an old pair of long nosed pliers that I filed down to fit the circlip. Put the lever pivot bolt back in and used a screwdriver as a lever to hold the plunger right down out of the way.
But the rebuild kits are pricey.
I had a repro one but thought lacked feel and sold it.

[kyle750]

Being a cheapskate, I've managed to do a couple of master cylinders with an old pair of long nosed pliers that I filed down to fit the circlip. Put the lever pivot bolt back in and used a screwdriver as a lever to hold the plunger right down out of the way.
But the rebuild kits are pricey.
I had a repro one but thought lacked feel and sold it.

I like the idea of making your own tools. IMO not cheap at all . . .  but resourceful    Good idea with the modified needle nose pliers.  I hope to be going back to my favorite Japan Second Hand shop later this week where they have an entire room of used tools from Japan. I remember they have piles of needle nose pliers of all shapes and sizes.   I never know what I will find there and everything is priced at 300 baht or $10 per Kilo.    So Much Fun Hunting through the Junk!

[kyle750]

Here is the Master Cylinder Rebuild Kit I bought for the CB750.  The front brake on the CB550 was working when the bike arrived.  Shocked    Brake fluid was clean in the reservoir and excellent pressure - not spongy at all. I am hoping the Master Cylinder is OK with the CB550. We'll see!

[kyle750]

KONI 7610-1296 shocks for the CB750 did not fit my bike and I had a local machine shop drill out the inner sleeves from 16 to 17mm (photo).  Sleeves were then coated in heavyweight 90W gear oil to prevent rust.  The lower clevis on the KONI is thicker than the stock Honda shock so I also had to buy longer lower shock bolts.  KONI shocks slipped right on this morning with NOS chrome upper acorn nuts, all bolted up with longer lower bolts, and ready to go! They look AMAZING with the aluminum bodies but the big question is will they still be able to handle the weight and perform OK on the road??

Late Edit:  I bought the wrong lower shock bolts with the incorrect thread pitch so I had to order twice.  Shipping was fast but still a mistake that costs me about 6 weeks of time.  I just laugh at all the mistakes and delays and try my best to take them in stride.   

[kyle750]

One more KONI photo 

[Deltarider]

Kyle, why do you always begin with buying/modifying parts and then ask questions? Very frustrating. As far as your Konis (thank you for buying a Dutch quality product) I bet the ones you have are for another model bike (probably CB500/550) and not for a 750.

[kyle750]

Kyle, why do you always begin with buying/modifying parts and then ask questions? Very frustrating.

Right now you are parroting nonsense.  The KONI 7610-1296 (13.25 inch) is the correct KONI shocks for the CB750 K0-K6 so I definitely bought the right shocks

I bet the ones you have are for another model bike (probably CB500/550) and not for a 750.

The correct KONI shocks for the CB500/550 is the 7610-1302 (12.5 inch) which is exactly what is now installed on my CB550