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

[nobody]

So I'm having trouble splitting my cases. I feel like I must have missed some bolts but can't find them. I count 23 from the bottom half, got the three on the front, the one in the starter area, the three countershaft bolts. I think I've removed all the bits that I needed to... I'm at a loss.

Can anybody see anything that I've missed? (I flipped it back over and checked the top side as well)




Also, how do I get the clutch out? I removed that spring plate and tried to get it out but couldn't figure out a good way to lock the engine so I could get that nut off that hold the clutch plates in...

[MCRider]

On the transmission cover side, that piece with the 4 phillips head screws has to come off. Its a bearing holder and it spans the seam of the cases. It would keep the cases from coming apart, but you should still be able to at least loosen the seam so there may still be something else.

That nut holding the clutch on is locked in place with a lock tab folded up into one of the 4 grooves in the nut. Assuming you fold that tab down its still hard to turn that nut. There is a four prong tool, some cut the T handle off the tool and weld it to a socket so it can go on an impact wrench. I've had success with a hammer and punch, turning the nut but mangling it pretty bad too.

Holding the shaft now that its off the bike is hard. Usually loosening the nut is done while its still in the bike so you can put it in gear and lock the shaft.

[MCRider]

There are 3 big bolts across the back. They are pretty obvious.

I can't remember if there are any below the oil pan or not. Might as well take it off and look as you've got to clean the oil pump screen.

[754]

 Working witout a manual, is asking for problems, but hey some folks must know something we dont , or just plain rely on online help to get out of a jam..

 I dont know how many bolts, but I know where to look, and they are all pointed out in the manuals. And I always strip the trans cover side, before you undo casebolts, so you dont forget the bearing piece that spans the cases.

 The clutch.. if you are pulling trans shafts to inspect, its just much easier to do it with clutch off... and so much harder to remove clutch, once the cases are split..

[nobody]

I'm going by the Haynes manual, step by step, which tells me there are only 20 bolts on the bottom side. Also, the manual is assuming that the top end is completely disassembled so it instructs me to do things that simply cannot be done. For instance, it's telling me to lock the engine by sticking a rod through the most right piston rod, can't do that. Any other suggestions on how to lock the engine for clutch removal now that the engine is no longer in the bike?

It may just be the bearing spanner at this point that's holding me up.

[ron.cieri.313]

Yes, I think it is...you do not have to remove the entire clutch (i.e. friction disc, etc), just the outer clutch cover and the small lever arm.

[nobody]

Part of me feels like I should though so I can check it's condition. The bike's got 14k miles, not sure if the clutch is original or not. I didn't have any slippage or ill performance prior to tear down but I just figure since I'm in here already...

[MCRider]

I'm going by the Haynes manual, step by step, which tells me there are only 20 bolts on the bottom side. Also, the manual is assuming that the top end is completely disassembled so it instructs me to do things that simply cannot be done. For instance, it's telling me to lock the engine by sticking a rod through the most right piston rod, can't do that. Any other suggestions on how to lock the engine for clutch removal now that the engine is no longer in the bike?

It may just be the bearing spanner at this point that's holding me up.

Put a wrench on the alternator rotor nut and pin it to the floor or workbench. The crank is tied to the mainshaft by the primary chains so that should hold it.

[ron.cieri.313]

Alright...so back at ron's ranch...we have removed the shift forks...seems like on tip doesn't look like the others (see long tip of middle fork)?...abrnormal wear or is it designed that way?


Well if its abnormal wear, you would expect to see evidence of this cataclysmic event on the gears, no?...so I fishing around the gears and dogs and find a broken tooth on two different gears (don't know if you'll be able to see in the photos)..dogs looked fine.

See second gear from the left/top tooth...this is in the upper crankcase but upside in order to split the cases


and...the middle gear below...this is the lower crankcase...tooth up top:


...does this make any sense?...think I have found the problem?...thx...ron.

[mystic_1]

Your shift forks look normal, the center fork is cast with that longer finger on it.

First time I rebuild my tranny my center fork was about half as thick as yours with quite obvious wear damage (read huge gouges).  You should verify clearances to the shift fork shaft and also the thickness of the contact pads but they look ok in the pics.

The gears with chipped teeth are obviously a problem.

Re your original problem, shifting into second gear is accomplished by moving countershaft gear C5, the end gear on the shaft closest to the shift mechanism.  See pic below and examine gears C5, C2, and their corresponding shift fork.

mystic_1

[ron.cieri.313]

Hi Mystic...I have tried reading that chart in the manual but can never make out the numbers shown as sub-text below the M or the C...perhaps you can help?

In the photo, moving from right to left, the M gears are...

M
M1
M2
M3
M4




and the C gears

C
C1
C2
C3
C4

?

thx

[HondaMan]

Alright...so back at ron's ranch...we have removed the shift forks...seems like on tip doesn't look like the others (see long tip of middle fork)?...abrnormal wear or is it designed that way?

See second gear from the left/top tooth...this is in the upper crankcase but upside in order to split the cases


and...the middle gear below...this is the lower crankcase...tooth up top:


...does this make any sense?...think I have found the problem?...thx...ron.

Wow, that's cool! Broken 750 gears are as rare as hen's teeth. Maybe you could sell it on eBay? 

It appears that some "foreign object" (as Honda's manuals used to call it) got caught in that gear tooth. I suppose it could have been a minor manufacturing defect (like a technician dropped it 30+ years ago, picked it up and put it on the assembly when it was being born...), which finally failed many miles later.

I have seen that sort of 'defect' in other areas on Hondas and Kawis, over the years.

[mystic_1]

Hi Mystic...I have tried reading that chart in the manual but can never make out the numbers shown as sub-text below the M or the C...perhaps you can help?

In the photo, moving from right to left, the M gears are...

M
M1
M2
M3
M4




and the C gears

C
C1
C2
C3
C4

?

thx

Reading Left to right, I make it as:


M5  M2  M3  M4  M

C5  C2  C3  C4  C1


mystic_1

[ron.cieri.313]

K...will give a more thorough examination to the C5 and C2 and the left shift fork and the M2 gear.

Sounds like the broken hen's teeth could then be unrelated damage or damage not at the root cause of my shifting problem?

[ron.cieri.313]

"Check the groove oin the 2/3 gear also. Shame to repalce the fork only if that groove is worn you'll be back in trouble after a while."

MC...what were you referring to here?...can you clarify...thx...ron.

[HondaMan]

K...will give a more thorough examination to the C5 and C2 and the left shift fork and the M2 gear.

Sounds like the broken hen's teeth could then be unrelated damage or damage not at the root cause of my shifting problem?

Don't be surprised to find the bushing(s) near that particular gear to be damaged from the chip being ground up into little pieces. The debris from that piece may have cause other damage in the rotating areas: look for that.

Honda's wear limit for these gears-on-shafts is measured by holding the assembly with one hand (while in the crankcase half) and rotating one gear at a time against the splines on the shaft. You measure the rotation with a dial indicator against a tooth. The spec limit is 0.008" of rotation: this works out ot 0.0035" of clearance between the shaft's splines and the inside splines of the gear itself, times the distance from the shaft to the dial indicator at the tooth. Usually, damage to the gears on the shafts is limited to either scars in the bronze bushings inside the free-spinning gears on those shafts: the ground-up bits of broken engine pieces can sometimes work their way down into those vulnerable bronze bearings.

Time was, you could buy just the bearing bushings. Today, not (although, I could probably make some on my lathe, using the dimpled 841 bronze). There's lots of used trannys around, though, for about $50 per set. Check each dog for squareness not the edges, with a magnifying glass, and make sure the receiving oval holes are square on their edges where the dogs butt in. If they are chipped or rounded, it can cause them to push the dogs back out after a shift, when the clutch is dropped closed. They do have a slight chamber on the dogs, which helps their engagement, from the factory. But, chips are not normal.

[ron.cieri.313]

thanks HMan...I think I reached a similar but less informed conclusion just prior to reading your post...time to buy a set of gears of ebay and replace these assemblies as who knows what could be damaged.

You might know before I go checking every part number, I have a '76 CB750...what other years can I use for my replacements...here's a few...if you got the time...suggestions on picking from the lot would be much appreciated.

http://cgi.ebay.com/ebaymotors/TRANSMISSION-GEARS-HONDA-CB750-1976-CB-750-76-75_W0QQcmdZViewItemQQhashZitem5883986d54QQitemZ380164926804QQptZMotorcyclesQ5fPartsQ5fAccessories

http://cgi.ebay.com/ebaymotors/HONDA-CB750-CB750F-TRANSMISSION-GEAR-SET-FREE-SHIPPING_W0QQcmdZViewItemQQhashZitem5189939ca7QQitemZ350200503463QQptZMotorcyclesQ5fPartsQ5fAccessories

http://cgi.ebay.com/ebaymotors/1974-Honda-CB750-transmission-gears-set_W0QQcmdZViewItemQQhashZitem2a0261935eQQitemZ180428575582QQptZMotorcyclesQ5fPartsQ5fAccessories


http://cgi.ebay.com/ebaymotors/TRANSMISSION-GEAR-77-78-HONDA-CB750F-CB750-CB-750-FOUR_W0QQcmdZViewItemQQhashZitem255568cb69QQitemZ160346721129QQptZMotorcyclesQ5fPartsQ5fAccessories

[ron.cieri.313]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=380164926804&viewitem=&sspagename=STRK%3AMEWAX%3AIT

...think I'm going with this one...a little expensive (man, not confident about putting more $$$ into this thing) but the seller assures me the part is good and he has other one available.

[ron.cieri.313]

k...parts are order along with shift forks already ordered...nothing to do but wait and replace when they come in...and then I can starting putting the beast back together.

Well, guess I clean all the freakin' parts i took of in the meantime...ttyl...ron.

[ekpent]

Eric in Kazoo watching your post. Got a spare running motor - minus 2nd gear and to many gears and cases around but have been watching your post to see how you throw it all together. Good move,I know it hurts the pocketbook but you did good by keeping the years consistnet and good luck on the rest of the rebuild. Eric in Kazoo

[ron.cieri.313]

Thanks Eric...I figured at this point, in for a dime, in for the dollar...I was just in Kzoo on Sunday...my daughter goes to WMU (violin major)...go Broncos!

[HondaMan]

After full repairs, these are long-haul bikes. Many I have fixed have done 10k miles the next year, more the next, and so on. I'd expect 50k miles, minimum, with 80k being pretty common.

Whatever happened to that tranny is pretty rare.

[MCRider]

After full repairs, these are long-haul bikes. Many I have fixed have done 10k miles the next year, more the next, and so on. I'd expect 50k miles, minimum, with 80k being pretty common.

Whatever happened to that tranny is pretty rare.

For sho' !

[ron.cieri.313]

Inspired by your support, I went out to do some mundane task like cleaning left over gasket goo from the crankcase halves...and I'm think, hmmm, better not let this crap fall into the case...yes, maybe I better check around...

Holy cow, er, Dogs???!!!...are these what I think they are?..sorry the pic is kinda of crappy but its late.

I found them about around here where they are shown in this photo


see them in the starter area...only they were more in the corners.

I found the first one a few months back when I dropped the oil pan to fix the oil flow problem...didn't know what it was, that and these two, make 3.  If they are, I can't see which gear is missing all three yet.  I was looking for a damage one, or a gear missing one, but all 3?!

I was keeping the gears on till the new ones arrive so I knew better how to re-install but this must drive me crazy enough to remove tomorrow.

[754]

Bad DOGS..  very..VERY BAD DOGS...

 gonna stray from the pack, we gonna take you away from the rest of the pack...............................................