Topic: 1976 CB750F and 76 CB750K Engine Case Swaps?

[Bigsam302]

Sorry if this has been asked already, but I been searching all over for an answer.

I have a 76 CB750F Super Sport that I’m in the process of converting into a café racer.  As I started taking parts off, I noticed a small crack in the engine case right above the points cover.  I plan on rebuilding the engine in the future.  This guy has a 1976 CB750K upper engine case that he is willing to sell to me.  The lower case is rusted and cracked, so I can’t use it.  The upper case looks to be in good condition.  Is it possible to use this K engine case on my F?  They both are the same year and I was wondering if anyone has had any experience with this?

[afkrejci90]

If the crack is right around the points cover, you could just have it welded?  I have a crack in mine in the same area and I'm just getting it welded up.

[Bigsam302]

Thanks!  I just may go this route.  The crack is really small and I'll look around for a good welder here in San Diego

[scottly]

Sorry if this has been asked already, but I been searching all over for an answer.

I have a 76 CB750F Super Sport that I’m in the process of converting into a café racer.  As I started taking parts off, I noticed a small crack in the engine case right above the points cover.  I plan on rebuilding the engine in the future.  This guy has a 1976 CB750K upper engine case that he is willing to sell to me.  The lower case is rusted and cracked, so I can’t use it.  The upper case looks to be in good condition.  Is it possible to use this K engine case on my F?  They both are the same year and I was wondering if anyone has had any experience with this?

If you're asking if you can swap the upper case from another motor onto your lower case, the answer is no, regardless of years. The cases are precision machined together as a unit.
How bad is the crack? It may not need to be welded, depending on where it is and how bad. Sometimes what appears to be a crack to a newbie is actually a mark caused during the casting process as the metal cools. Can you post a pic of the crack?

[splitt]

Yep, scottly is correct. Upper and lower cases must go in pairs. You can't mix and match.

[James T Kirk]

the initial discussion in this link i've provided is about cam caps, however the same details of construction apply to the main bearings:

http://www.cb750c.com/modules.php?name=Forums&file=viewtopic&p=222549#222549

kirk out

[Bigsam302]

Ok, thanks for the info.  The crack is very small.  But I am going to wait until I crack the engine open and see how big the crack is.

[Bigsam302]

Another question...do you think if I go ahead and get the complete crankcase, I can put all of my F parts on it?  ie. head, crankshaft, transmission?