Topic: What is it?

[Jinxracing]

I finally found a (I hope) suitable engine for my 1970 K1 cafe project. The fact that the engine came with a '70s chopper frame and rear wheel still attached was just part of the deal. Hopefully I can make a little bit of money from the frame and 16" rear wheel.  It turns over nicely with the kickstarter and doesn't make any scary noises so my fingers are crossed that I have a runner.

My question for the brain trust is, can anyone tell me what year this engine is? Is it a K or an F? I was TOLD that it was a '76 K motor, but I don't know enough to be able to tell visually, the serial number isn't there, and the guy I bought it from inherited it from his Dad and isn't really sure about any of the details. It doesn't appear as though the serial was filed off...just a blank field in the box on top of the case where it should be.  Is there any other place on the engine where I'd be able to find a serial number or any details to check that would give me more of a clue?

Thanks in advance! 

[Roach Carver]

as far as there being no serial no's, I have a 69 model with the same thing. I was told here, that back then the motors that were changed for waranty had no serial no's on the plaque. thats all I got.

[Jinxracing]

Wow, thanks for that piece of information...VERY interesting.  Gonna have to investigate further.

[Roach Carver]

a sandcast will stand out like a sore thumb. a lot of the bosses will be square and rough. more than likely it is not a sandcast. I will look for a pick.

[Jinxracing]

I just went to CB750sandcast.com and took a look at their gallery. Mine's definitely not a sandcast motor. You're right, they stand out like a BIG sore thumb. 

So if it was in fact delivered with no serial, the assumption is that it's a warranty replacement engine for a sandcast? Did yours have any other identifying numbers anywhere?

[Roach Carver]

To be honest I have not really looked at it. it is about three or four deep in my list of projects. my bike was built 11/69 so it is technically a k0.  I assume if mine is a warranty engine that it was not because of the sandcast case failures. As far as other places to get no's I dont know. I am sure one of the old timers will chime in with some useful info.

[Magpie]

The early 750's broke a lot of drive chains which would in turn smash the cases in the primary sprocket area. Honda then placed a shield there to help prevent this and went to a larger drive sprocket I bellieve.  These were then warrantied with new cases, perhaps this is one of them. The broken cases went on for some time. I have a '76 motor with welded together cases.
Cliff.

[crazypj]

If cases were changed due to accident or warranty Honda doesnt stamp them, the dealer should re-stamp with original numbers (the original cases are scrap or they wouldnt be changed)
It looks early to me, the head/block looks a bit 'square' I'm sure the later ones were more rounded?
PJ

[bryanj]

Without a number totaly impossible to date, Honda never supplied complete engines and as already said the dealer that changed the case was supposed to restamp the original number onto the new cases. just for information same thing if you bought a new frame as a spare part---comes with NO NUMBER

[ElCheapo]

My guess is that the exhaust flanges have not been changed. If they are Spigot style it is pre 76 (I think this was the cut off date was) After that (76 and later) they are the clam shell fastener type.

You will have to print out the list of Factory Revisions - (Some one please provide a link if you know of one.) And pick the easiest one that you can tear into. Also pre 75 and older had only 4 bolts in the clutch throwout bearing. The later ones had like 8 or 9? You may have to pull the head to figure this one. There was a thread here before about each of the heads K to F having different cc chambers.

Also the output shaft for the front spocket is different from a K to an F. They will not interchange I know this as I have a F motor in my K. Can't remember off hand what the difference was but there was something.

I hope this helps: maybe I am just blowing smoke. I invite corrections here