Topic: Alternator Rotor Removal in CB750A

[mberning]

Can anyone walk me thru the process of removing the alternator rotor and starter gear in the 76 CB750A.

I have the rotor removal tool but would like some hints on how to remove the bolt and eventually the rotor.  What direction do I turn the bolt to remove it and how do I keep the rotor from turning.

I need to replace the starter gear and maybe repair the starter clutch.

[MCRider]

Can anyone walk me thru the process of removing the alternator rotor and starter gear in the 76 CB750A.

I have the rotor removal tool but would like some hints on how to remove the bolt and eventually the rotor.  What direction do I turn the bolt to remove it and how do I keep the rotor from turning.

I need to replace the starter gear and maybe repair the starter clutch.

Hopefully the engine is still in the frame. Put it in 5th gear and tighten up the brake adjuster to where the brake is full on. Then hit the bolt with an electric impact or a socket with a 3 ft cheater bar. It's standard thread, righty tighty lefty loosie. That's to get the bolt out.

Then put your puller bolt in. Run it in with the impact. Then strike the head of the puller bolt with a 2.5lb ball/peen hammer. Nothing any lighter IMO. Tighten the bolt puller again, then smack it agiin. That should bust (shock) the alt rotor off its taper and it will just fall off in your hand.

If the engine is on the bench, you'll have a lot more trouble holding the crank still. Wedge something in the sprocket/ case region. But I didn't say that.

[mberning]

This is an automatic (i.e. CB750A Hondamatic) with just 2 gears.  So I assume you mean put it into second gear and set the parking brake to keep the tire from turning.

 

[MCRider]

This is an automatic (i.e. CB750A Hondamatic) with just 2 gears.  So I assume you mean put it into second gear and set the parking brake to keep the tire from turning.

Oops, that would be correct. And I also assumed that everything about the rotor on the A is the same as a K2, which is where i have my experience. I did not look at a fish to confirm this.

Holding the engine still in the frame is far easier than on the bench.

[raymond10078]

But - putting the bike in second will not hold the crank.  The Hondamatic clutch packs only engage when oil pressure exists (the bike is running).  No oil pressure - the clutches spin free.

I'd remove the alternator bolt with an impact wrench (since I have one).

In looking at the CB750A and a CB750K manual, neither mention how to hold the crank.  I suggest trying one of those strap wrenches to hold the alternator (they are cheap).

When putting it back together - the manual makes mention of keeping the taper (on both parts - the crank and the alternator) as clean and oil free as possible.  Some adjacent parts need oil as well.

[MCRider]

But - putting the bike in second will not hold the crank.  The Hondamatic clutch packs only engage when oil pressure exists (the bike is running).  No oil pressure - the clutches spin free.

I'd remove the alternator bolt with an impact wrench (since I have one).

I was thinking about that...

Any suggestions? Have you actually removed the bolt from the alternator? I have, several times from different motors and it was not possible with my electric impact without holding the crank. Perhaps your tool hits harder than mine?

[raymond10078]

My impact wrench puts out 600 ft-lb.

Well, another option that will without a doubt hold the crank is the rope in the cylinder trick.

Remove a plug, and with the cylinder down in the barrel, push in some nylon rope - fill it up, then turn the crank over (counter-clockwise when viewing the alternator) until the crank firms up/stops.  Then use a breaker bar/socket.  You just want the piston to be coming up on its compression stroke!

[jukku]

Use a chain oilfilter wrench to hold the crank!

[mberning]

A couple of additional questions?

1) Do I need to drain the oil to remove the alternator rotor

2) The starter gear and starter clutch are right behind the rotor. Is that correct? 

3) I dont need to remove the starter to change out tthe clutch parts and starter gear.  Is that correct?

Thanks for assistance.

[MCRider]

A couple of additional questions?

1) Do I need to drain the oil to remove the alternator rotor

2) The starter gear and starter clutch are right behind the rotor. Is that correct? 

3) I dont need to remove the starter to change out tthe clutch parts and starter gear.  Is that correct?

Thanks for assistance.

Oil: You don't need to drain it, but I suggest tilting the bike to the right and putting a shim under the pedal or foot of the centerstand. This will cause the oil that is in the alt cover to drain to the sump. Even with the shim, you'll want to use a catch pan to catch what drips out. Without the shim, for sure.
The gear will fall off the rotor. The clutch is screwed to the rotor and will require at least a hammer impact to loosen the screws. The clutch usually doesn't need to come off. The trifecta of springs, caps, and rollers can be replaced with the clutch in place.
No, the starter motor itself can stay put.

[mberning]

I was able to remove the alternator rotor bolt using a Kyobi One+ 18V impact driver.   All of the starter gear looks good so I suspect the problem is the clutch parts.

I screwed in a rotor puller tool but can not break the rotor loose from the drive shaft.

How hard does that screw need to be turned in to break the seal?  I dont want to mess anything up.   I am using a rubber holding strap while simultaneously turning the rotor puller bolt.  I have pounded on it with a hammer and tried tightening dont kow if its really tightening any further.

Any suggestions on what I need to do or additional hints?

[mberning]

Ok, used a little more elbow grease and it popped out.   I see that the alternator plate is slightly warped.  Would that have contributed to my starter slipping problem?


May have to locate a good uesd one since the part is obsoleter unless someone knows a source for it

[MCRider]

Ok, used a little more elbow grease and it popped out.   I see that the alternator plate is slightly warped.  Would that have contributed to my starter slipping problem?


May have to locate a good uesd one since the part is obsoleter unless someone knows a source for it

Alternator plate? Que es?

In my experience: Starter slipping = triple triple. 3 sets of caps, springs and rollers.

[mberning]

Im replacing the 3 (rollers, springs and pin ) but the clutch itself is warped in a section of one of the those 3 sets which is probably causing the rattling noise i hear when I try to engage the starter.   

So I think I have to replace the clutch as well as all 3 (rollers, springs and pins)

I dont know if its cheaper to buy a good used one or get it machined to be flat so the roller does not fallout of vibrate.

[MCRider]

Im replacing the 3 (rollers, springs and pin ) but the clutch itself is warped in a section of one of the those 3 sets which is probably causing the rattling noise i hear when I try to engage the starter.   

So I think I have to replace the clutch as well as all 3 (rollers, springs and pins)

I dont know if its cheaper to buy a good used one or get it machined to be flat so the roller does not fallout of vibrate.

Curious. That's a new one on me.

[mberning]

The plate that sits over the (roller, spring and pin) has an outward buldge over on of the 3 sets.  I think this outward buldge is causing some play.

See attached photo (area on top where metal is shiny) buldges upward.  Looks like its pried upward



 

[raymond10078]

If it were me, I'd try pounding the raised portion flat, and then re-using it.

But - I can't really see how bad it is from the pic . . . .

If you want or need to look for another to replace it, the interchange info is as follows:

1976 CB750A, F, K models
1977 CB750A, K models
1978 CB750A, K models

[mberning]

I found a good used rotor/clutch combo on Ebay.  On mine the rollers would fall out anytime you tilted it sideways.  The one I am installing they stay in place.

Hence I know what was causing the clanking sound.  It was kind of like having a bunch of marbles rolling around.