Rather than call this a tech page, lets call this a useful "tid-bits" page.
We do not see any reason to talk about Hondas timelines and changes they made unless its useful.
We do not see any reason to copy and paste a bunch of tech articles about theories that do not pertain to the Honda cb750 engine.

Under heavy construction.
More to come


The cylinder head:

Removing the valves can be done in a couple of ways.

The left photo shows a conventional spring compressor tool. Due to the fact we do not use the old valves because they are old technology (unleaded fuel unfriendly), the top is usually hammered and grinding the valve face is inaccurate for a couple of reasons. The valve stem is usually worn and the valve grinding chuck has a hard time finding a even place to hold on to. Also, most valve grinders in many shops are not as good as advertised. We will leave the hardness topic of the valve face after grinding to the forums and chat rooms.

Anyway, the photo on the right shows the quick and simple way to remove the valves. Take a deep well socket and place it on the top spring retainer and give it a quick, sharp tap with a hammer. The keepers, top spring retainers will pop right off.

The last photo shows a home-made tool to remove the springs with out removing the head. This tool would mainly be used by racing folks that realize springs are under severe stress and need to be changed occasionally, especially with over 200 pounds of pressure at full lift on some motors.

Part identification

Many Honda cb750 parts can be swapped and indentifying parts can be difficult at times. The above photo should help.

There seems to be typo on the photo of the valve stem keeper groove and the photo of the keeper identification.
It says, thru 1977. It is actually 69-76.

The 69-76 valves and keepers are the preferred choice when re-doing your Honda head.
Also, the 77-78 K and F2 upper retainers look the same. They are not.

F2 Upgrades


Because of the top spring retainer problems with the 77-78 Honda CB750 supersport that was mentioned above, we have these retainers for your consideration.
The first photo shows machined top retainers (not stamped steel) that will not fail.
The second photo shows our light weight retainers with holes to dribble oil on the guide area for extra cooling and lubrication.



New Parts Selection

Before starting work on the head, we should consider the choice of parts to be used.

Hard Chrome Plating vs KPMI® Black Diamond® Coating


"First and foremost I must point out that not everyone is qualified to make this comparison, unless they have access to and know how to use Vickers hardness testing equipment, and can take a specimen and view it with a high power microscope and then understand the matrix present. Further they must now how these two process are applied and react to the substrate material they are being used on."

"Hard chrome plating is an adhesive process which means the chrome is “laying on and sticking to” the surface of the substrate material. Hard chrome can trap foreign material within the chrome layer and virtually turn that surface into sandpaper, which also allows the surface to become larger than intended. There is such a thing as nearly perfect chrome, which requires a double cleaning process and the diode to be a tube, which helps to create a clean even-layer of chrome. None the less, chrome can come off and is known to gall and lacks lubricity."

"The KPMI® Black Diamond® coating is a process which impregnates the substrate and develops a 2-tenth layer below and above the surface that is 55-65Rc. What this means is a shell develops underneath and above the surface that is very hard and cannot come off under even the most extreme conditions. Further, there is a second process applied on top of this hard shell that produces a very low coefficient of friction, some very slippery stuff."

"In the world of application, you would be foolish to consider chrome as a superior valve stem coating when compared to the KPMI® Black Diamond® Coating."


Cycle X Cast Iron Valve Guides
Kibblewhite manufactured cast iron guides are made from the best hardened material available. The guides are 49.50 mm in length for added support and longevity.

Some people are fans of various types of bronze composition valve guides. We feel it depends on the motor geometry and other considerations. For example, many people would never use bronze guides on Harleys and others. They just do not last.

To us, Honda CB750's with cast guides last longer, lubricate just as well as bronze and experience after inspecting heads with X amount of miles tells us this.







Removal, Installation of Parts and Machining the Head

Removal of the valves guides can be done in several ways. But first, remove the carbon from the port side of the valve guide before removal...leaving the carbon on can rip aluminum with it on the way out.

This photo shows the budget or old way to remove valve guides.
Heat the head. (Approx. 300 degrees)
Drift the guide out with a bit of spray lubricant.
You can make a mental note of how easy the guide drifted out. You can measure the new guide and the guide bore to be accurate.
But, a virgin head with the carbon removed will generally be fine to install the new guides.
So, with the new guides in the freezer and the head heated to approx 300 degrees, install the guides. (Reverse the removal procedure)

The bad news!
Doing the above budget mentioned procedure can case a few problems if you are unlucky in life.
The guides can go in a bit off, cocked or not follow the same path causing more work when cutting the seats when doing a valve job.
Secondly, when installing the guides with a hammer and drift the valve guides can distort on the inside, kinda making an "S" bent looking bore. (Especially bronze guides)
The reaming process might be more of a struggle, inaccurate and making your valve job procedure an adventure.

Preferred Method

This photo shows the preferred method to remove and installing valve guides.
Our tool is installed and uses and 45 degree machined valve seat tool and machined shaft thru the center of the guide to pull the guide out perfectly.
When installing the guides using this tool the guides will be remarkably straight leaving your valve job a breeze. Be aware, any time new guides are installed a valve job will need to performed.

Reaming the Guides

The above photo shows a method of reaming. Low speed, Steel or carbide ream, well lubricated, followed up by honing. This method works great when the guides were installed with the preferred above mentioned method.

Note: The key to this reaming process is to never let the ream stop turning like using a hand held holder. (You will ruin the ream)
Some people talk about honing the guides while the head is in a Serti machine. That's another method. Better? Not really.
It's not the machine or tools, but the user of the machine or tools.

Valve stems vary in diameter. But, a .259 ream and a 6mm guide hone is generally used. (Goodson has these items)


Valve Job

The above photo shows a method of doing a valve job. Stones have been used since the beginning of the internal combustion engine.
Like we said: It's not the machine or tools, Its the user of the machine and tools.
Serti valve machines are quick and can make each and every valve seat pretty close to the same. Many people that use Serti machines can struggle with the intake seats because they are very soft and can leave chatter marks. Many people in the industry start with Serti machines and follow up with stones for perfection.

F-2 Drain Hole Modification
As great as Honda is and was...
…a mistake was made.
4 cylinder studs are exposed through the fins in the head which could allow dirt and road debris to enter the lower end.
Honda tried to correct this problem by putting large “O” rings at the bottom of the studs to prevent water and debris from entering the motor.
Here is what we do, drain holes are drilled and honed to accept brass tubes. Brass tubes are pressed into place and problem solved.


          Free Performance Modification

These photos show where a bit performance gains can be found.
The first photo shows a "almost done" valve job. The pen is pointing at the 60 degree angle used by many. By machining the 60 degree area deeply (almost the depth of the seat) with a steeper angle cutter can be a performance gain. This technique commonly used with oversize valves because there is a bit more area to modify verses stock valves.

The second photo (bad photo) shows a valve with a lapping line. By chucking the valve into a valve grinder, you can grind the port side of the valve face with 35 degree set up right to the lapping line.

To be continued.



When assembling the head, the phrase "cleanliness is next to godliness" cannot be over emphasized.
Want your valves to malfunction? Leave dirt inside your guides when assembling.
This reminds me of a story.

Received a phone call and a customer mentioned that the black "stuff" on his valve peeled off. After inspecting the head (done by someone else) the guides were filthy on the inside acting like sandpaper.

There are many assembly lubes in the world when assembling the head. We like Lucas brand.

To be continued.

Valve Springs

Valve springs lead a hard life.
 Hot, cold, high RPM and father time all contribute to a motor not performing like it did years ago.
If you ride and putt around on your bike only on Sunday's to get a gallon of milk, we would still get new springs.

But, performance topics are more fun.
Due to the fact there are hundreds of tech articles about conical springs, bee-hive springs and dual springs, cam profiles etc., we will save ourselves time and simply state what works best for us on Honda CB750 motors because Honda CB750 valve train components are heavy and heavy is not good.

We recommend:

Bee-hive valve springs (Super light weight and superior quality)
Titanium adjustor jam nuts and lighten your rocker arms. Lightening your rocker arms can be done with various grinders and flap wheels. If you need a photo of a lightened rocker arm, the machine shop page has a photo.
Doing all three of these recommended valve train upgrades will insure you have the lightest and most beneficial bang for the buck.
The other reason we recommend light weight valve train and is especially important to high performance world is valve control.
Tighter valve to valve clearances and valve to piston clearances than recommended by manufactures can make engine builders pay very close attention.
In the olden days, builders would add enormous spring pressure for control and basically rob the motor of horsepower.

Generally speaking, static spring pressures are set up to 75 to 95 lbs. The higher side would be for big-boy camshafts.
To be continued.


Porting the Head

  Port clean-up can be a bit beneficial (a bit) meaning casting marks and protrusions.
Generally, with expenses involved we are working around the perimeters Honda has given us.
A few skilled and experienced cylinder head porting experts have managed to extract some power from the Honda head.
These skilled people need a lot of information about your build, parts being used, goals. So, if you ask a question about porting a head, the porting expert should ask you ten questions.

For extreme racing without expense in mind the Honda head can be modified to compete with many somewhat modern 4 valve per-cylinder DOHC makes and models.
We have raised the ports, angled the intake ports for a down draft situation and angled the exhaust ports upward. All of these modifications have helped.
Probably one of best and most time consuming modifications is straitening the angled ports.

Just for kicks, take a Honda CB750 DOHC 4 valve per cylinder head and stick a garden hose into the intake port and turn it on full blast.
You will notice only 1 of the 2 intake valves is doing all the work. (With the stock angled port)
Many people that have ported Honda DOHC ports have seen gains and then hit a brick wall.
The only way to knock down this brick wall is to straighten the intake ports.

The reason we mentioned DOHC Honda heads is because the garden hose thing is more obvious. But, SOHC heads are the same and can see the same benefits.
Anyway, if you are approaching 1000cc or using methanol you need to open the ports up enough to fill that big bore!

To be continued.


Useful Tid-Bits (Maybe)

Cylinder head thickness: 2.842
Cylinder thickness: 3.334
At full operating temperature the cylinder & head can grow .015 or more.
Conventional (paper) head gaskets can compress up to .016 after running X amount of miles.
Conventional (paper) base gaskets can compress around .004 after X amount of miles.
Cylinder head nuts can lose 5 to 12 lbs of torque after conventional head gasket compression.
Like a rear chain, the cam chain can stretch and lose about 3 degrees of cam timing or so. (Varies)
For every .001 of increased valve lash, 1 1/2 degrees of cam duration will be lost.




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