Topic: CB750F Cylinder Head Question

[akaRandakk]

Looking at a '76 CB750F that MAY have a later '77/'78 "improved" cylinder head with larger valves, etc.

Questions:

1. Are the later CB750F cylinder heads actually interchangeable onto the earlier CB750F engine?

2. Without disassembly to physically measure the valves, is there any definitive, external, non-invasive method to determine which type of cylinder head is actually on the engine.

Thanks

[madmtnmotors]

Looking at a '76 CB750F that MAY have a later '77/'78 "improved" cylinder head with larger valves, etc.

Questions:

1. Are the later CB750F cylinder heads actually interchangeable onto the earlier CB750F engine?

2. Without disassembly to physically measure the valves, is there any definitive, external, non-invasive method to determine which type of cylinder head is actually on the engine.

Thanks

1. You can use the later head, but only if you are willing to deal with the abandoned oil returns in the later head. There is more than one method for dealing with this.

2. You can pull the valve cover and count the oil returns. All the CB750K and A models all had eight oil returns, while the 77/78 F models only had four oil returns. Careful inspection between the fins on the exhaust side of the #2 and #3 cylinders should reveal exposed cylinder studs if you are looking at a 77/78 F model, but it may be difficult to tell if you don't know what you're looking at.

EZPZ 

[scottly]

The F2/F3 head has larger intake spigots (both OD and ID) than the other 750 heads. There *may* be a number on the top fin on the intake side between cylinders 2 and 3: 410 for F2/F3 and 392 for F0/F1 K7/K8.

[Don R]

 The 77/78 F engines came painted black. They are a "hemi" head with a bigger combustion chamber. Used with standard pistons make a lower compression ratio.
 The oil drains are also different, mismatched onto K cylinders or cases may result in oil seeping too.
 

[Tracksnblades1]

This may help.
Borrowed from Kenny @ Cycle Exchange X
Original black paint with 410 would be a dead giveaway.

[akaRandakk]

Thanks for the responses above.

I'm aware of most of the differences including valve size, domed pistons, increased combustion chamber volume, etc.  I would never undertake such a head swap myself. The "benefit" seems small for the hassle and complication.

What I'm looking at is:

1. '76 CB750F1 engine ...verified '76 F1 via serial number range.

2. It is a "silver" engine with silver cylinders.

3. But, it has a black cylinder head.

4. All other details match what you would expect for an F1 engine.

I'm inclined to believe that the black paint was just a cosmetic touch at some point.  Looking to verify this fact. I don't want to buy a mongrel engine and I"m relying on a 3rd party to do my inspection

Thanks.

[seanbarney41]

Scottly has it.  Have your friend measure the intake spigots.  F0/F1 should measure the same as any other K0-k6 engine...F2/F3 will be measureably bigger.

[Tracksnblades1]

Could slip the tank off.
After disconnecting gas cap area drain line ,
fuel line,  and rubber strap.
Then you could look right between 2&3 like scottly
Mentioned and remove all doubt.

1976 CB750F1 SS should be wearing a silver painted
“392” cylinder head..

Let us know what you find.

 If it’s wearing a 410, it may of had the pistons changed too.
But I’d be more concerned with the troublesome valve spring
retainers and locks the 410s were equipped with….

[scottly]

The early spigots have an ID of about 28.5mm, and an OD of about 33.75mm, not counting the flange on the end. The F2/F3 spigots are about 31mm ID, as far as I can remember.