Topic: what engine do I have?

[Jerry E.]

Hi all, I am a new member here, and I am doing my first total rebuild on a motorcycle. Am a longtime rider, but needed a project to tinker on. My question is: what motor do i have? Tha frame I.D. #2220995 shows a 1973 CB750K model I believe, but the motor is  #2509690, and I thought it should be a #22---- number. Does this make the motor a 1975 CB750F1 model? Or did I look it up wrong? Also, is this a better motor, or not, than the original? I need to know for ordering parts. I didn't realize the motor had been changed before buying the bike.

[Elan]

I assume your looking at the honda chopper timeline? link below.  I interpret it as that number falling into both the f and k categories, but the head number should seal the deal. assuming you dont have a hodgepodge engine..What number do you have on the head?

http://www.hondachopper.com/engine/engine_timeline/timeline.html

[Accolay]

Hi Jerry, welcome.

I don't have a 750, but seems to me that engines starting with 25 belong with the 1976 models, or 1975 Supersports (I'm assuming they bolt on the same).

[flybox1]

K6

[Elan]

K6

couldnt it be an F too just by the enging number?

Model   Sell Date  Prod. Code  Frame #                  Engine # 
750F0    1975        392            CB750F-1000002    CB750(*)-2500004 -
750K6    1976        341            CB750-2540001      CB750E-2428762 -

* = Number may contain
F and or E


But if it says 392 on the head its an F, and if it says 341 or 405 on the head its a K.
 

[flybox1]

couldnt it be an F too just by the enging number?

YES, you are correct...
K  - CB750E-250XXX
F - CB750FE-250XXX

[david 750f]

Looks like a 1975 CB750F motor. The serial number falls within the 75F motor numbers. (2500004-2515085). 

There should be a 392 cast into the cylinder head.

[Jerry E.]

Thanks for the info, I will check the head number to be sure. I have looked thru the info on the forums, and they are very helpful. If I figure out how to do it, I will post pics of my progress. Plan a motor rebuild, forks/swingarm rebuild, re-powdercoat the frame, etc. Going for the Cafe Racer look. Right now I have many small pieces, and lots of work ahead.

[Jerry Rxman Griffin aka MuthaF'er]

Never seen "FE" on a F engine, just "E" - I don't believe it. I think that was a mistake or a typo. My Honda parts manual agrees with me too. I have two 75 F's sitting in my garage now. CB750E-2501606 and CB750E-2507696. I'd love to hear from someone that has a "FE" engine and see a picture of the serial number.

The 392 on the head will be located on the top fin intake side between #2 and #3

[Jerry E.]

The serial number only has an "E" on it, not an "F". The head casting has a "392" on it, so I must have a 1975 CB750FO engine. Thanks for the help.

[Don R]

Some say it's the best 750 engine.

[BeSeeingYou]

Some say it's the best 750 engine.

+1  Think of it as an upgrade.