Topic: Splitting the cases on my CB750...first of many ?'s

[ron.cieri.313]

Well, step 1 is complete (i.e., my garage is relatively clean and organized) and I'm ready, gulp, to try and split the cases on the my Honda '76 CB750 K.  I'm hoping to fix my bike's inability to shift into 2nd gear which fixing the oil flow problem (oil not coming into the clutch through the shaft) and rebuilding the clutch (new plates and discs, and numerous other variations and manuevers) did not fix.

So, I'm looking for tips on how to begin...I've read available posts and plan on taking lets of pics and organizing/labeling etc...basically I understand that I have to get the engine out and then upside down in order to get at the trans gears and shift forks which I believe to be the problem.

I have the service manual which says to take off the cylinder head first but is that necessary for what I'm doing?  I was going to take off everything it says to but I don't know if the cylinder head, cylinder and cam chain tension need to be removed as indicated...thanks, ron.

[MCRider]

Well, step 1 is complete (i.e., my garage is relatively clean and organized) and I'm ready, gulp, to try and split the cases on the my Honda '76 CB750 K.  I'm hoping to fix my bike's inability to shift into 2nd gear which fixing the oil flow problem (oil not coming into the clutch through the shaft) and rebuilding the clutch (new plates and discs, and numerous other variations and manuevers) did not fix.

So, I'm looking for tips on how to begin...I've read available posts and plan on taking lets of pics and organizing/labeling etc...basically I understand that I have to get the engine out and then upside down in order to get at the trans gears and shift forks which I believe to be the problem.

I have the service manual which says to take off the cylinder head first but is that necessary for what I'm doing?  I was going to take off everything it says to but I don't know if the cylinder head, cylinder and cam chain tension need to be removed as indicated...thanks, ron.

I seem to recall we did this on an earlier thread. I don't blame you for wanting confirmation as its a big job. So I'll lay out my process and wait for someone else to confirm it.

First the main premise is No you do not have to remove any part of the top end to fix the transmission.

First you would remove the engine. Next, while on the floor, remove all of the bolts visible from the top that hold the cases together. Mostly 6mm bolts (with 10mm heads), including 2 or 3 in the countershaft area. and maybe one or 2 in the starter motor compartment.

Then get it on the bench upside down. Remove all the engine sidecovers. Remove the shifter linkage and the bearing carrier that crosses over the split between the cases.

Remove all the 6 mm bolts that hold the bottom case to the top. And the 3 along the back if you didn't take those out on the floor.  Finally, remove the 8mm main bolts (12mm heads).

Tap around the seam of the cases with a mallet, when it sounds hollow, the bottom case may be ready to come off.  Once the lower case half is off, the trans is exposed. The main shaft can come out with the clutch and you'll get enough slack in the primary chains to get it out. The crank does not need to be disturbed. But the lower crank main bearing shells are in the lower case, so treat them nice and be sure they are clean before reassembling.

While you are there, remove the oil pan and clean the pump screen. The oil pump will come out with the lower case and you won't see the screen if you don't remove the pan.

Hope someone else chimes in to confirm this, so I'll know I'm not crazy.  

PS: I seem to recall being taught to remove the mainbearing bolts last and install first.

[ron.cieri.313]

Exactly what I'm looking for...thanks MC...

...question...other than the cover, do I have to take out the alternator rotor which I think is referred to as the "AC generator rotor" in the service manual.

...and the clutch, same thing...just the cover?

thanks!

[MCRider]

Exactly what I'm looking for...thanks MC...

...question...other than the cover, do I have to take out the alternator rotor which I think is referred to as the "AC generator rotor" in the service manual.

...and the clutch, same thing...just the cover?

thanks!

On the alternator cover, the stator comes off with the cover, and its wires. No need to mess with anyhting else. The starter reduction gear will fall out in your hand. No big deal.

On the clutch cover, again its just the cover. The clutch stays with the main shaft and will not be in your way.

Only the shifter cover has things that span the seam of the cases and must be removed. The linkage and the bearing carrier.

The points plate behind the points cover spans the seam. And there are bolts behind the countershaft cover. But its off anyway to disconnect the chain.

[ron.cieri.313]

Thanks MC...I guess I would have figured out the chain needed to come off eventually...like when I tugged on the engine and it fell to ground cuz it was still attached.  I have new sprockets and a new chain so looks like a good time to take care of that too.

...but I don't want to get distracted...anything else you can think of that needs to come off to get the engine out?

[Henning]

It's not that difficult, as long as you're comfortable with wielding a few spanners. You need space to lay out disassembled parts, and you need to work methodically. When you remove the kickstart and gear lever, rethread the bolt into the kickstart/gearlever and lay them aside; that makes reassembly easier. Similarly the sprocket cover has two screws; put them in where they belong and lay them aside. The primary sprocket has two bolts, the chain oiler bit, and two different locking bits. Reassemble lightly on the desk and lay it aside. Continue in that vein. It all makes reassembly easier and you don't need to make so many notes. But you do need a manual.

I last split the cases on a 750 over 25 years ago - to change the second gear fork - so it's not all that fresh in my mind. It took three long days and nights for a quick in/out operation, so expect to spend time above that when you need to find the fault. The hardest part will be to get the engine in and out, rather than splitting the cases. You don't need to touch the head/topend at all, as has been said before.

[ron.cieri.313]

Thanks H...I'm trying not to assume the obvious so adding to the list of things before the engine comes out:

...drain oil
...pull plugs
...remove tach cable
...drop exhausts

[Henning]

I don't know how far you've got with this project, but I suggest you start from the top and work down - at least as far as removing the engine goes. I had my engine out last summer (750 K1), so I can give advice on that.

Get the tank off. Remove the sidecovers. Remove the air filter. Disconnect the two cables to the carbs. Get the carbs off (can be difficult). Remove the breather hose to the valve cover. Disconnect the rev counter drive and tie out of the way. Disconnect the spark plug cables and tie out of the way (so they don't get in the way when you remove the engine). If you've more energy after this, remove the pipes, and, hey, the whole top end is ready for engine removal. And remember, lay out all disassembled parts from left to right in associated groups, which will all make reassembly in days/weeks/months easier.

- Henning

[ron.cieri.313]

Excellent..thanks Henning...haven't started yet cause I'm heading up to my cottage and getting ready to close her up for the winter...but I'm itching to get started...I appreciate the specific advice as I'm trying to be very organized about this as you suggest.

[heatvision]

My new 74 CB750 came with the exact same problem, and I'll also be attempting a fix later this fall.  Make sure to take lots of pictures!. 

Are you planning on replacing anything else while you're in there (cam chain, ect) ?

[ron.cieri.313]

Definitely will be taking lots of pics to help reassembly, to get answers to my stupid questions and to hopefully help anybody like me who has to try this and doesn't have a hundred years of experience like lots of these guys.

I am not going to mess with anything in the top end or extends into the top end unless I have to...so I will leave the cam chain alone.  I did read some posts about cleaner the cam chain tensioner which sounds like a good idea. 

I will probably work on the back end too..replacing drive and counter sprockets, chain, swingarm bushing, rear tire and rear brakes...but those will all probably wait until the engine is out and back on...I'm confident about all that stuff but I will have my fingers crossed on the tranny till its back on and tested.

[ron.cieri.313]

Well, hope to get begin teardown tomorrow...just putting up some pre tear down reference pics...here's hoping I get her back together...

[ron.cieri.313]

Okay, made good progress on destruction in order to remove the engine...stuck on the darn exhaust.  

Here's a list of everything I've taken off and some pics of its current state:
Gas tank
Plug wires pulled off plugs
Drain oil
Plastic side covers
Points cover
Drained oil in resevoir
Removed clutch covers
Remove carb bank (detachied throttle cable, drain carb bowls)
Remove clutch cable and corresponding lever mechanism on clutch
Gear shifter
Left rear cranckcase cover
Countershaft bearing cover
Left sprocket cover
Sprocket

[ron.cieri.313]

Question...does it take two people to safely move the engine to the floor?

I'm planning on moving from the bike to a padded gymnastics matt cover with towels on the floor...then turn it upside while its on the matt...sound like a plan?

[bryanj]

Depends on how strong and dextrous you are, I have done it on my own and with both good and bad help.
However you do it the engine is a tight fit and heavy

[myhondas]

You can always lay the bike over on its right side. engine justs falls out. I pulled my k4 mtr out by myself that way.

[nobody]

I'm extremely glad I stumbled upon this thread. I've got a 74 750k with a hard shifting issue with the engine ready to come out of the frame. I'll be watching/posting in this thread frequently.

[Henning]

So far so good, 'though it would have been better to wait with actual motor disassembly until you got it out of the frame. You need to get those pipes off, obviously! On the left side disconnect the big white connector from the alternator, as well as the cable to the starter solenoid, located near the fuses.

Get the oil filter off and then disconnect the two hoses from the oil tank where they go into the engine. You probably need to remove the right footpeg to do that. I loosened the bolt for the outer pipe at the oil tank as well, so that I could swing it rearwards and out of the way. I removed the three bolts holding the tank to the frame as well, just to give a bit more room to work with. Also at the oil tank, disconnect the hose from the back of the tank where it enters the back of the engine. You also need to disconnect the wiring from the points, also behind the oil tank somewhere.

Oh yeah, brake pedal off.

Then you are about ready to start removing the engine bolts. Get it on the centrestand. A cheapo scissors jack or compatible with a block of soft wood under the pan is great to lift the motor slightly, so you can rock the motor back and forth to get the (long) bolts out.

You really need a buddy to help you get the motor out. It's heavy and you need to juggle it about to get exhaust flanges etc. past the frame. Wear some heavy gloves, and it's useful if you have a crate the same height as the bottom frame rails to lift the motor onto. On the left side, lift on the no. 1 exhaust flange and the drive shaft, on the right lift on the no. 4 flange and the kickstart shaft (no, can't do that). You need to lift it halfway out so the pan rests on the frame, and then your buddy comes round to the right hand side to lift it onto the crate.

Be prepared for having forgotten something!

Good luck, Henning

[ron.cieri.313]

Thanks Henning...I've been battling the flu so I was slow to reply...appreciate the specifics...if i get the engine out without breaking a hand, foot or finger, I'll be quite pleased...ttyl...ron.

[ron.cieri.313]

Okay, i think what is affectionately referred to as the arse rape fairy was visiting southeastern MI (warning to all others in the Midwest U.S.), and my garage in particular...the only proof I have is this freakin' screw (see pic below), the only one of eight that just refused to come out in order for me to take off my my exhaust....it resisted seafoam spraying, impact wrenching, screw removal bits...nothing, finally it could not resist the power of the drill and dremel.



But it is off now, see below, and i can continue with the steps Henning outlined above...well, no one said it would be easy!

[Henning]

The good news is: you got the exhaust off. The bad news is: you made it a lot more difficult than it needed to be. Take a look at the diagram below (here's hoping it shows):

You loosen the bolt (28) on each of the four exhaust collars (1), as well as removing any rear exhaust bolts/mounts. Then you wiggle the exhaust up and down, left and right, curse, until you get it off the flanges (3). They can very well be rusted tight.

What it looks like you did is to remove the screws (31) which hold the flange (3) into the head. You don't need to do that, and those screws are notoriously difficult to remove. Next time round it will all be easier  . You probably want to get the flanges out of the exhausts before reassembly; it will be easier that way. A plastic hammer should do the job.

[ron.cieri.313]

Yep...thought that maybe was the case...and boy was I was wiggling and cursing till I decided it had to be easier removing the screws (wrong!)...but yeah, now that they are off I will have better leverage to finish the job and get the pipes of the flanges.

The pipes are pretty corroded but are pretty cool aftermarket pipes...think I will just paint them black or silver with engine paint because I don't want to replace until I know the tranny is fixed.

[ron.cieri.313]

http://www.gadgetjq.com/transmission.htm

If some are following this post for help down the road, I found these animations which helped me at least finally visualize how the transmission gears, dogs and "stuff" all move together to shift our bikes.

I do not have second gear any longer on my beast, so I assuming the gear dogs are worn down and not allowing the shift fork to grabe them on the gear or my shift fork is bent is a direction that allows it to engage with the gears necessary for 1st but not 2nd.

...hopefully we'll see...teardown to continue this weekend!

[754]

Take your crashbars off, And I would remove Dyno cover and Clutch cover before flipping over the motor. When you flip it shim up the back so it is  near level.

[ron.cieri.313]

Will do...also but two small hydralic jacks to shim up the back when flipped.