Topic: Engine assembly advice? (CB750K2)

[ealanm]

I'm about to start the reassembly of my CB750K2 engine, which will be used in a vintage racing car (see avatar).  I'm looking for any advice from those with more experience, particularly on this engine.

I've rebuilt quite a few car engines, so I'm not a complete neophyte, but I've never done a bike engine before.  So I also have some specific questions about this engine.

I'm planning to use ThreeBond for the crankcase joint.  (Why do so many companies think it's cool to name their product as though it were a C function call?)  It's what my local Honda dealer recommended; they don't sell Hondabond, for some reason.  I'll be using plastigauge to trial fit the main bearings.  Will I get an accurate enough measurement if I don't use any ThreeBond on the cases when I do the trial fit?  The ThreeBond will put some space between the cases during final assembly, but I don't have a feel for whether it's enough to matter.

The procedure in the manual has the crankshaft going in first, and then the gearbox gets assembled.  I'm still waiting for my main bearings, so I thought I might assemble the transmission while I wait, and put the crankshaft in afterward.  There doesn't seem to be any reason that won't work, but I'd hate to get the transmission assembled and then discover a "gotcha."  Anybody know a reason why my plan won't work?

My installation doesn't need the kick starter.  In fact, to fit the old engine in the car I had to saw the spline off the kick-start shaft, because it interfered with the oil tank.  So I was thinking of leaving the entire kick-start assembly out and just plugging the holes with a dummy shaft made out of aluminum.  Any reason that won't work?

Thanks in advance for any answers.

[lucky]

I would use Gaskacinch for the case halves. Put a light coat on each side and let dry. Then assemble.

Gaskacinch was and is the industry standard. Yamabond and Hondabond are copies of Gaskacinch.

Do not use sealer made for car parts.

[Bodi]

The sealant is squeezed out of the gap on torquing the studs, it won't affect clearance and measuring can be done dry. Threebond is fine. Make sure the surfaces and the case area close to the sealing surfaces are csuper lean, you want the bead that gets squeezed out to stick well to the cases and not fall off easily. Use very little sealant so this bead is tiny.
I don't think there's any problem with assembling the transmission first with no crank, but I haven't done that.
Deleting the kick starter should be no problem. I don't think there are any oil issues as with the electric starter removal.

[MCRider]

The sealant is squeezed out of the gap on torquing the studs, it won't affect clearance and measuring can be done dry. Threebond is fine. Make sure the surfaces and the case area close to the sealing surfaces are csuper lean, you want the bead that gets squeezed out to stick well to the cases and not fall off easily. Use very little sealant so this bead is tiny.
I don't think there's any problem with assembling the transmission first with no crank, but I haven't done that.
Deleting the kick starter should be no problem. I don't think there are any oil issues as with the electric starter removal.

If you drop the trans in first, you will have to remove the mainshaft once again to thread it thru the primary chains. Much more difficult, maybe impossible to thread the crank with rods thru the chains second.

So from a convenience standpoint, the crank is first, hold up the chains, pass the mainshaft thru, set the chains.

Its, "you can't get there from here" kinda things.

You'll have to keep at least the KS shaft as it is the axle for the oil pump drive gear.

[ealanm]

Thanks to all. 

MCRider, good point about the crank and rods.  Not being used to bike engines, I have to keep reminding myself that the rods are already on the crank when it goes in.  Thanks for the tip on the oil pump drive, too.  I probably wouldn't have noticed that until waaaaay too late!

[MCRider]

Thanks to all. 

MCRider, good point about the crank and rods.  Not being used to bike engines, I have to keep reminding myself that the rods are already on the crank when it goes in.  Thanks for the tip on the oil pump drive, too.  I probably wouldn't have noticed that until waaaaay too late!

YW. The CB750 rods can go on after the crank is in, but I've never seen anyone do it that way. Too hard to manhandle everything.

[ealanm]

A related question:  What exactly is the doohickey in the photo, and how does it work?  It appears to be important to controlling the flow of oil to the bearings on the output shaft, and plugging the hole in that shaft.  But after examining the oil holes in the shaft it's still not clear to me how this thing works and how to properly install it.

[MCRider]

A related question:  What exactly is the doohickey in the photo, and how does it work?  It appears to be important to controlling the flow of oil to the bearings on the output shaft, and plugging the hole in that shaft.  But after examining the oil holes in the shaft it's still not clear to me how this thing works and how to properly install it.

That is the adjusting doohickey to the flow of oil to the chain oiler. If you screw the center screw all the way flush it comes as close to turning it off as possible, which is what most people do. If you have the engine apart you can remove a small plate that will disable the oiler all together. Or remove the adjuster and thread in a bolt that is long enough to cover the samll hole in the driveshaft from which the oil emerges.

It has nothing to do with the drive bearing or anything serious.

It is threaded into the drive shaft and held there with a tabbed lock washer, not in your picture.

[ealanm]

MCRider:

Thanks, that is extremely helpful.  Clearly, I had completely misinterpreted its purpose.  I don't need chain oiling at all in my application, so I'll probably just block it off completely.

Maybe that explains why I always had oil on the back of my engine, too!

[MCRider]

MCRider:

Thanks, that is extremely helpful.  Clearly, I had completely misinterpreted its purpose.  I don't need chain oiling at all in my application, so I'll probably just block it off completely.

Maybe that explains why I always had oil on the back of my engine, too!

The chain oiler could make a god-awful mess in the drive sprocket area. There is a small 1" x 1' or so plate that has a snout that feeds oil into the drive shaft. It is held in place by a 6mm bolt. Just leave it off, and screw a bolt in the end of the shaft. (proper thread).

[ealanm]

To clarify, you're talking about this little plate, right?  I leave that out altogether, and then block off the end of the shaft with a bolt (or just screw down the plug all the way).  No oil goes out to the chain, but lubrication of the bearings is not affected.  Correct?

[MCRider]

To clarify, you're talking about this little plate, right?  I leave that out altogether, and then block off the end of the shaft with a bolt (or just screw down the plug all the way).  No oil goes out to the chain, but lubrication of the bearings is not affected.  Correct?

Keerectomundo. That's it.

First hand knowledge, done it many times, not hearsay.

Take it off and bolo it into the ether.