Topic: CB550 Performance Mods, A La HondaMan...

[Jonesy]

I tore into my wife's '78 CB550K over the holidays as the cylinder head oil feed O-rings had begun to leak over the summer. I had originally planned to just replace the offending parts and the head/base gaskets, but like any project, one thing leads to another... I'm sharing my experience trying this in case anyone else was thinking about doing these mods, and hopefully it will help them out.

I had PM'd HondaMan to ask about some stuff for my CB750. I mentioned that I had the 550 apart and was there anything in addition I should do with it. He suggested that I polish the intake valves, clean up the intake ports and match/smooth the intake runners. (All these are outlined in the "Thoughts of HondaMan" thread.) At first, I thought "Nah.. I've never done that kinda stuff before and we've been happy with the bike the way it is." After thinking over the reasons why I should leave it alone, I grabbed the Dremel and proceeded with Mark's (HondaMan) advice.

After a thorough cleaning of the head I assessed the situation. Sure enough, there was a bad mismatch between the intake openings in the head and inner walls of the intake runners. The insides of the runners are very coarse due to the sand casting cores. There were lots of casting marks inside both the intake and exhaust ports. There were also "ledges" in the aluminum around the valve seats from the machining operations that form the seat pockets. The valves were coked up badly with carbon. These were all things that could be improved upon, so I set to work.

Intake Ports
Here are a couple views of the intake ports before the work was performed, with notes:




I found the best bits for doing the work were high-speed steel hemispherical cutting bits for doing the primary metal removal (you can also go with the carbide ones, but the HS steel ones have larger flutes in the cutter, which works better for shaping aluminum), then small 3/8" flap wheels (both medium and fine) for smoothing out the grinding marks and polishing, and finally a small Scotch-Brite wheel for the final polish:



I started with the basic stuff, like removing the casting marks and blending in the port better with the ID of the valve seat. This made it easier to plan the next steps. The main thing is to narrow the valve guide boss about 25%, making for rounded "valleys" on either side of it. The top of the boss can be feathered into the tapered portion of the guide as well. Here are pics partway through:




After a bit more work. Still needs more clean-up work before the final polish (sorry for the poor picture quality as my penlight was dying- it doesn't really show the "valleys" too well.):




I'm really wishing I'd gotten some pictures of the finished ports, but I didn't have access to the camera and I had to get the bike back together. The next time the carbs are off I'll have to get a pic.

Some key things to keep in mind: Wear safety glasses and a dust mask as the cutting bits will throw little aluminum slivers all over the place and the sanding flap wheels generate a lot of metal dust. Also, I put a strip of heavy duct tape around the valve seat so as not to accidentally nick it with the Dremel. Be sure to wash the head thoroughly in hot water and detergent to make sure you've cleaned all the grit out of it.

Exhaust Ports
All I did here was remove the casting marks. I didn't remove anything else as the surrounding metal is important for conducting heat away from the valve guide and I am running a stock exhaust, which is pretty restrictive.

Valves
I cleaned the carbon off the valves and re-lapped them. For the intake valves, I polished the backsides. This can be done easily by chucking them in a drill or lathe and working on the backsides with emery cloth, making sure not to touch the sealing face, or neck down the valve stem. All the valves were reassembled with new seals. (Unfortunately, I didn't get before and after pics.)

Intake Runners
The inside surface of the intake runners had to be smoothed out. I used a large coarse flapwheel to accomplish this, followed by a fine wheel and then Scotch-Brite. Here are the results, before the final polishing:



When I went to match up the intake runners to the ports, I noticed there was a bit of slop in the fit of the mounting holes in the runners and the corresponding studs in the head. This could mess up the concentricity of the mating bores. To tighten up the fit, I bought a piece of small thin-walled aluminum tubing from the local hobby shop and made small sleeves to take up the gap. The 9/32" diameter fits snugly in the holes. On one side it only took one sleeve on one set of runners to hold them snug, and the other took only two. With the runners now securely positioned, I could match the bores. I wasn't able to obtain any spotting dye, so I had to do most of the work by feel. With the runner mounted to the head, I felt along the joint with my finger and noted the areas where I could feel mismatch. I'd then grind away some material and refit the runner, checking the joint. Once the joint felt smooth all the way around, I polished up the tweaked areas. I know, it wasn't the most scientific method, but it worked fairly well and the fit between the parts is much, much better.

Carburetors
Lastly, I checked the throats of the carbs to see if the screw plugs that seal the vacuum tap ports for balancing the carbs protruded into the bores. This can sometimes happen and disrupt airflow. This was not the case with my carbs, so nothing needed to be done here:



If they did stick out, I would have to grind them down flush with the wall of the carb throat.

I got the engine back together and test-ran it. It started easily and ran well once warmed up. The carbs will need balancing as the intake characteristics have changed, but I'll wait until it warms up some and I can test ride it (we're in the middle of an ice storm now, so no riding any time soon  ). I'll post the test-ride results as soon as I can. Then I might try the other tweaks, like adding 4 teeth to the rear sprocket, altering the spark advance curve and changing the jetting. As you can see, I'm no Mike Rieck when it comes to head work, but I'm happy with the way it turned out, being a noob. I probably could have gone farther, but I did what I was comfortable with.

I want to thank Mark for all his help, advice and encouragement during this project. I can't wait to test-ride it!

[medic09]

Hey Jonesy, excellent post.  Mark has gotten himself an able protege.  Thanks for showing all this to us.

[OldSchool_IsCool]

Well done Jonesy!!

After you have gotten some long over-due face time with the Mrs, I'll have a few questions for you!

[bill440cars]

        Hey Jonesy,

                       Looks like a job well done to me   Like to hear how the test run turns out, when weather permits it. I plan on going with the HondaMan procedures myself, when time permits. Nice pictures there too.

                                                      Later on, Bill

[doug_id]

Excellent post and pics.....thx!     

[kghost]

Very nice work and a great post.

[mwohlenhaus]

that's lookin sweet, but you need a little roughness in the intake to help swirl around the fuel and air mix and keep it from separating.  The exhaust is where you want polished ports so carbon has less to stick to.

[Big Jay]

That should show very noticable performance improvement.

Jay

[Jonesy]

that's lookin sweet, but you need a little roughness in the intake to help swirl around the fuel and air mix and keep it from separating. The exhaust is where you want polished ports so carbon has less to stick to.

The ports aren't perfect, as there were still rough spots here and there. I mainly got things smoothed out so the walls didn't look wrinkled. Once you go over the walls briefly with the Scotch-Brite you see all kinds of small rough spots...

I hope I haven't messed it up by being too thorough...

[mlinder]

That intake looks plenty rough for keeping fuel and air mixed.

[MRieck]

that's lookin sweet, but you need a little roughness in the intake to help swirl around the fuel and air mix and keep it from separating. The exhaust is where you want polished ports so carbon has less to stick to.

The ports aren't perfect, as there were still rough spots here and there. I mainly got things smoothed out so the walls didn't look wrinkled. Once you go over the walls briefly with the Scotch-Brite you see all kinds of small rough spots...

I hope I haven't messed it up by being too thorough...

You haven't messed anything up. You removed material from the right areas which is the most important thing. There all sorts of ideas regarding wall finishes, port sizes and even valve jobs (full radius vs. 5 angles). I've joked that real rough intake finishes are there because the porter didn't want to take the extra time to smooth it. Look at the 2006 Kawasaki ZX6 etc intake ports....they are very smooth.

[Jonesy]

Thanks for the reassurance, Mike. This was my very first time doing this kind of stuff, so naturally I worry about the outcome. (I commented to my wife, "Why is it when I learn a new procedure with these machines, someone else's bike is always the guinnea pig?")

That intake looks plenty rough for keeping fuel and air mixed.

By the time the head went back on, almost all of those rough spots were smoothed out. That was an "in progress" pic. Still wishing I had the camera available to get a final pic..

[mlinder]

If it's too smooth, you can rought it up a bit with your dremel. Basically, you don't want any polished surface. Fuel will stick to the polished surface and pool up. As long as you have an even, roughed up surface, you are fine.
Ive seen (cant remeber where) a spiral cut into the intakes, supposed to work well. Basically just cut very shallow, close together rings or spiral all the way down the intake.

[Jonesy]

I'll just have to ride it and see.

Briggs and Stratton used to put a twisted piece of sheet metal in the intake tract of the horizontal-crank small engines with side-draft carbs. I would love to know the thinking on that one!

As Mike said, there are many theories about port finish. I've seen some automotive heads that were highly polished, and some with the CNC marks still in them. Both perform well. One of the thoughts I found most interesting was about swirl. Some is beneficial to combustion, while too much can cause the fuel vapor to be flung into the cylinder walls, causing it to condense and wash the oil off the walls, speeding up wear of the cylinder.

GM built a cool engine years ago that used a synthetic sapphire crystal for the cylinder walls, so they could see the combustion process. Much of the study work went into the development of the new (at the time) LS-1 V8.

[kuyarico]

Great pics and writeup. I need to grow some balls and do this eventually.

[Bob Wessner]

I have no idea what the truth is when it comes to port work. I'm pretty much anchored in the school of, "if it's working, don't [fix] it, or in my case possibly break it.  I've read various pros and cons of port polishing, etc. One I recall was that the surface need not be of a mirror finish as the gases follow the rules of fluid dynamics and fill in the deep spots and create a smooth gas/fluid layer anyway. Came across this though, and thought I would toss it out for comment, interest, or whatever. Remember, I know zip about these things personally.

http://www.motorcycleproject.com/motorcycle/text/cows-porting.html

[paulages]

isn't the design of the port shape is self what creates the swirl?

[mlinder]

isn't the design of the port shape is self what creates the swirl?

A venturi is created there, or supposed to be anyway, yeah.
Mainly the swirl cut I saw was not to create a venturi, but to keep very high turbulence in the charge coming through, to keep air and fuel well mixed.

[Pinhead]

From the article posted above:

Furthermore, polish is not only unnecessary, it's actually harmful, in two ways. The first concerns the airflow itself. The experience of countless engine builders, plus research by Superflow, Boeing, and various members of the Society of Automotive Engineers, indicate that a smooth surface is not necessarily the slipperiest where air is concerned. Ever notice that an airplane's wings are not shiny smooth, but rough? The rough surface reduces air drag, and the wing glides through the air easier. Olympic bobsled teams stick sandpaper-like skateboard grip tape to the sides of the sled and the tops of their helmets for the same reason. Air tends to get lazy on a smooth surface. It's called the "boundary layer effect," and it refers to the fact that an ultra-smooth surface accumulates air pressure next to it. This pressure is really stagnant air, and it effectively obstructs airflow. A slightly roughened surface eliminates this boundary layer and increases airflow. The second way polish is bad concerns combustion. Intake tracts don't just flow air, remember. They flow an air/fuel mixture, whose behaviour is quite different from plain air. The same lazy air boundaries that constrict a polished port's airflow also make fuel "drop out" of suspension in that air. The mixture then enters the cylinder less thoroughly mixed, and poor combustion and reduced power result. For this reason, most builders glass-bead the port walls instead of polishing them. The slight roughness creates tiny eddy currects which keep fuel droplets suspended in the port airstream. Good combustion is thus ensured.

Don't polish your porst, do this:


http://fueleconomytips.com/2006/12/13/powre-lynz/

Those are screw threads in an intake port. They're called "PowreLynz" developed by Mike Holler at www.mpgresearch.com. For exactly what that article said about boundary layer adhesion and airflow. The rough texture actually increases airflow and also helps vaporise the fuel.

Powre Lynz work with several laws of fluidynamics to improve both power and economy. They:

- Work with the boundary layer of the intake ports to break up large liquid droplets into smaller droplets

- Act as a wick, holding liquid fuel against the heated port walls so the fuel vaporizes into the incoming air stream

- Liquid droplets will fall against the textured walls, the Powre Lynz will spread the fuel out radially increasing the surface area and make it easier to vaporize

- Powre Lynz add turbulence to the boundary layer to keep liquid fuel suspended in the air stream and prevent puddles and rivers of liquid fuel from forming

- Help create a cushion of air to improve flow and volumetric efficiency

[mlinder]

From the article posted above:

Furthermore, polish is not only unnecessary, it's actually harmful, in two ways. The first concerns the airflow itself. The experience of countless engine builders, plus research by Superflow, Boeing, and various members of the Society of Automotive Engineers, indicate that a smooth surface is not necessarily the slipperiest where air is concerned. Ever notice that an airplane's wings are not shiny smooth, but rough? The rough surface reduces air drag, and the wing glides through the air easier. Olympic bobsled teams stick sandpaper-like skateboard grip tape to the sides of the sled and the tops of their helmets for the same reason. Air tends to get lazy on a smooth surface. It's called the "boundary layer effect," and it refers to the fact that an ultra-smooth surface accumulates air pressure next to it. This pressure is really stagnant air, and it effectively obstructs airflow. A slightly roughened surface eliminates this boundary layer and increases airflow. The second way polish is bad concerns combustion. Intake tracts don't just flow air, remember. They flow an air/fuel mixture, whose behaviour is quite different from plain air. The same lazy air boundaries that constrict a polished port's airflow also make fuel "drop out" of suspension in that air. The mixture then enters the cylinder less thoroughly mixed, and poor combustion and reduced power result. For this reason, most builders glass-bead the port walls instead of polishing them. The slight roughness creates tiny eddy currects which keep fuel droplets suspended in the port airstream. Good combustion is thus ensured.

Don't polish your porst, do this:



Those are screw threads in an intake port. They're called "PowreLynz" developed by Mike Holler at www.mpgresearch.com. For exactly what that article said about boundary layer adhesion and airflow. The rough texture actually increases airflow and also helps vaporise the fuel.

A-ha, that was what I was talking about. Them lines raight thar.

[Jonesy]

Heck, I coulda just buzzed around with the coarse flap wheel and gotten nearly the same result. Oh well, I suppose I could rip the head off again if the performance suffers...

[paulages]

i'm not talking about the venturi, i'm talking about how the shape of the intake port itself affect the flow pattern. honda was quite ingenious in their intake design with the CVCC concept, and it should be noted that the CB750 was in production at the same time as the CVCC car engines. here's an exerpt from a (mazda) patent description, dated later than these bikes, but if i remember right from mechanic's school (over 10 years ago), honda's engineers led the field in the late 70's with intake engineering. this is describing a different intake design, but illustrates how intake shape can affect the flow pattern:

Various efforts have been made to configure the intake port in order to produce a swirl in a plane perpendicular to the axis of the cylinder and a vertical "tumble" in a plane parallel to the axis in a combustion chamber. One such effort is that described in Japanese Unexamined Utility Model Publication No. 4-137224. In order for the intake port to produce an enhanced tumble, the intake port is made, according to this publication, so as to be directed to and meet the outlet opening into the combustion chamber at a small angle (hereafter referred to as a directional angle). The intake port is further made to have an approximately straight center line intersecting the axis of an intake valve and a cross-section which is enlarged toward a location at which a tumble is produced.

[mlinder]

Sure, but a smooth bore there will still make the fuel pool on the metal.
Hence the bumps or grooves or whatever, to make the air closest to the walls of the bore more turbulent, decreasing the likelyhood of fuel and air separating.

[HondaMan]

Jonesy: beautiful work! You'll be pleased with the results. 

The things I have noticed over the years about "polish - don't polish - cut grooves" methods often involve "the latest thing" from some new engine out there, but it usually doesn't relate well to older technologies. In one picture above, the "cross-grooved" intake ports that some racers are using purport everything from better MPG to 25% more HP. I know 3 drag racers who have had this done to their engines, one of them a Keith Black engine, and they spent the (lots of) money again to remove them because the power was uneven and very peaky. One of these engines (the K.B. one) was blower-ed, one was turbo-ed with multi-port injection, and one had a single 4-bbl carb, all V-8s. That observation makes me very wary of this very specialized technology that was first debuted in some high-winding, computerized, fuel-injected, custom-tunable, Japanese car engines (Nissan). Then, suddenly, several Americans claimed to have invented it. I don't know who did it first, but all of the successful implementations use multi-port fuel injection tuning.

These are 1960s engines with 2-jet carbs; keep that in mind.   

In engines with large, slow-moving intake tracts (Harleys, older V-8s, Briggs lawn owers, etc.), the roughness of the port walls help keep the fuel in atomization. Were it possible to open up an SOHC4 that big (MRieck comes close!), this "fuel wetting" problem would occur, no doubt. But, these little SOHC engines ALL suffer asthma because Honda was not the financial giant it is today, and they designed from the viewpoint of using as little metal as possible, for profit reasons. So, the engine walls are thin, the fins barely adequate (at times) and rust and corrosion are issues on these bikes that must be watched over and cared for. So, personally, I don't see any benefit of the roughness, and my experience has been that "smoother flows better" in these, even if the ports are not opened up. The castings were just too hastily done for accuracy in those production days.

From your pictures, I'd say you actually would have a long way to go, if you were racing, to maximize flow, but that would also bring some tuning headaches you don't want. I would estimate a seriously noticeable improvement from your work when the ice thaws there, based on what I see you've done. That flat "football" you fixed up causes a flow reversal at very low engine speeds, helping idle, sort of like that B&G "spiral mixer" in the otherwise unshaped intake tract. It also causes a serious restriction because of this reversal at engine speeds from about 2500-4500 RPM. Above that, it simply acts like something is "stuck" in the middle of the throat, restricting the ability of this great little 500-4 engine to rev. Typically, after this kind of work, the 500 becomes a real nice canyon racer, giving stronger midrange and longer RPM in every gear.

Just wait, you'll see!   

[HondaMan]

i'm not talking about the venturi, i'm talking about how the shape of the intake port itself affect the flow pattern. honda was quite ingenious in their intake design with the CVCC concept, and it should be noted that the CB750 was in production at the same time as the CVCC car engines. here's an exerpt from a (mazda) patent description, dated later than these bikes, but if i remember right from mechanic's school (over 10 years ago), honda's engineers led the field in the late 70's with intake engineering. this is describing a different intake design, but illustrates how intake shape can affect the flow pattern:

Various efforts have been made to configure the intake port in order to produce a swirl in a plane perpendicular to the axis of the cylinder and a vertical "tumble" in a plane parallel to the axis in a combustion chamber. One such effort is that described in Japanese Unexamined Utility Model Publication No. 4-137224. In order for the intake port to produce an enhanced tumble, the intake port is made, according to this publication, so as to be directed to and meet the outlet opening into the combustion chamber at a small angle (hereafter referred to as a directional angle). The intake port is further made to have an approximately straight center line intersecting the axis of an intake valve and a cross-section which is enlarged toward a location at which a tumble is produced.

etc.... 
Honda invented the CVCC concept and marketed it worldwide in the late 1960s. It consisted of a 4-cylinder engine (600cc, 700cc and 1000cc sizes) with 2 combustion chambers per cylinder, with 2 sparkplugs, and with 3 valves. The carb was a 2-bbl unit, with one smaller side running at 12:1 mixture and the other running at 16:1 mixture. The rich carb fed 4 tiny "pre-combustion" chambers thru a separate intake tract and a tiny intake valve. The other carb side fed the lean mix into a normal-sized chamber above a piston, like all of us are used to seeing. The dual-point, dual distributor and coil setup then fired the tiny chamber early, about 10-14 degrees ahead of the big one. A small passage from the tiny one entered the big one at a sharp angle, and the resulting burn pressure caused a strong swirl ("whirlwind", their manual called it...) in the bigger chamber. When the piston rose, it compressed and increased this spin, centrifugally forcing the richer part of the mix toward the outer walls of the cylinder. This created a cool, slow-burning outer shell of expanding gases while a lean center burn's higher heat made the burn last longer than normal, with less hydrocarbons in the exhaust. The result was increased torque through the whole range (you can't imagine how big that 1000cc engine felt in those cars!) and really good MPG. And, it was a waste-spark system, like our bikes, for lower emissions, too.

But, it suffered from mechanic's fear. Opening the hood, it looked like 2 engines had been rammed together at a very high speed, and the plumbing went everywhere. The timing (points type) was very hard to set right, didn't last any longer than on a 750-4, and when it was wrong, could blow the muffler clear off the car with powerful, rich backfires. It suffered in the American marketplace for those reasons, and Honda turned to "stratified charge" swirl, like all engines today, to get that swirl instead, with multiple valves, even multiple valve timing. By 1970 the whole concept disappeared, at least in the U.S.

But, unless you were wrenching in 1967, you might not remember those...