Topic: First bike, first project. '76 750 Four S with pics

[andy750]

Looks like it might work..keep us updated on oil leaks or lack thereof.

And you were right that the two bolts at the back of the swingarm should NOT have been pointing down!!  Glad to hear you are figuring it out.

Good luck
Andy

[goon 1492]

You should also buy an impact screw driver set, home depot has em for about 25 bucks, you'll need it when you have to take the altenator cover or cam cover off etc. good to see the "weld" took like you planned.


Oh yeah since no one else said it yet you should tie that left side cover down so it doesn't fall off on you most of them do or have; I'm sure others can comment on this 

[Roach Carver]

if I were you, or if alternately you were me.... Maybe I (or you) could look for a good motor. quite often I see them here and on ebay for a little to nothing if they are close enough to go pick up. then you could just do an engine swap.

[trprbill]

I swear the one pic looked like a hole. The JB Weld should work fine, and I think that certain years the bikes came with steel case protectors to gaurd against the chain breaking the case. It might be a good thing to look into or if anybody knows about them? I think if your chain comes off again it might be a bigger problem.

[MrZxp]

You definitely have a "K". Follow this link to confirm for yourself - http://www.sohc4.net/index.php?title=CB750K.
Here is the link for the "F" model guide - http://www.sohc4.net/index.php?title=CB750F.

Good luck with your repairs!

Cheers, Phil

[Johnie]

I sure hope it works for you.  Have you downloaded a manual yet?  You will get a lot of info from that manual.  Nice pics...

[Gamma]

I did the same type of repair to my cases on a CB750 F1 in 1980.  The hole was bigger, in both cases, due to a chain break.  I used a product called Doublebond (2 part epoxy putty) and oversealed it all with Araldite 24 hour epoxy.  I remember using M.E.K. to degrease the area, and dropping the sump plate and changing the oil in an attempt to get the bits out.
I ran that bike hard on a daily basis, for another year, with no engine problems before it was stolen in Germany.  Then I bought an F2

[mystic_1]

OK, so I have had damage just like this on a 750 motor.  The biggest concern in that area is whether the crankcase has been pushed in enough to come into contact with the transmission gears, the clearance at that point is not very big and it only takes 1/2 inch or so before the case is in contact with the gears.  At this point your gears will begin to machine a nice arc into the inside of the case.  After a while of driving like that your oil will be a nice bright silver from all the aluminum shavings   Ask me how I know this

So, I can confirm that sealing this crack with JB Weld WILL in fact work.  I cut a piece of sheet steel into a patch and JB welded it in place.  It held up through a full riding season and then some, couple of thousand miles I figure.  Once I changed my oil and saw the aluminum particles I decided it was time to give it up and just rebuild the engine, and that's where I am now.  When I pulled the engine apart I had to chisel out the JB weld, it was still sealing the area just fine. 

Now, having said all that, I'd recommend trying to source a replacement motor if that's within your budget, it probably would be cheaper than trying to repair the existing one, and safer than the JB Weld routine.

cheers
mystic_1