Topic: Senior project for high school - 78 CB750K

[mystic_1]

Yeah that's the roller clutch in the behind the alternator rotor slipping.  You can hear from the sound that the starter is just freewheeling and the crank is not turning.  You can confirm that by pulling the points cover and watching there while you crank.

You SHOULD totally be able to kick start it, but with the clunking sound I suspect you may have a missing or damaged roller or even possibly some parts gone walkabout inside the alternator cover.

You'll need a rotor puller to get the alternator rotor off the end of the crank in order to access this.

Items 3 and 6, plus three sets of (4, 5, 15) and three of 21 from the first diagram.  All mounted to the back of the rotor and with the rollers running against a machined part of the starter gear, item 4 from the second diagram.  These parts constitute a one-way clutch.  When crank speed exceeds starter gear speed, the rollers ride up into ramps on part #6 (I think of this as "the cage") which allows the gear to freewheel on the crank.  During starting, the springs and plungers push the rollers forward on the ramps which cause them to clamp down on the starter gear and spin the crank.

[edwardmorris]

I fully tore mine down checked them all and put it back together along with a new seal, there are some pix in my K2 thread if you want to see what they look like. Gordon/ilbikes makes a great rotor puller (very high strength material) that makes quick work of removing it (just did that on my K3 thread). Bill might have the factory puller too, but I doubt the rotor will come off just twisting by hand. While on the bike, you'll probably want to get it into the fifth gear, fully tighten the rear brake adjuster, have someone fully engage the rear brake, then use a cheater bar to remove the bolt.

An electrical impact driver will make things a lot easier.

[Restoration Fan]

We didn't pull the rotor on this build but I did go ahead and buy a puller, just in case we needed to do so.  And I have an air impact wrench.  So, we'll get to this this weekend and I'll be contacting my buddy Bill to see if he has some replacement parts for me.  Maybe then, we can get this thing to fire up.

[mark52]

Stella's fighting you and Logan at every turn, she's a real diva!!! I'm sure Bill can help out but I guess he is moving a little slow right now.  Keep on keeping on time is getting short. Trying to get up there in a couple of week so maybe I can help in the finally push, I will give you a call.

Mark

[knottedknickers]

<snip>
Items 3 and 6, plus three sets of (4, 5, 15) and three of 21 from the first diagram.  <snip>

mystic_1 wins for clearest ever parts diagrams! Could you share your source?

[Restoration Fan]

<snip>
Items 3 and 6, plus three sets of (4, 5, 15) and three of 21 from the first diagram.  <snip>

mystic_1 wins for clearest ever parts diagrams! Could you share your source?

I agree.  They appear to have come from CMSNL.
http://www.cmsnl.com/honda-cb750k8-four-usa_model14397/partslist/E10.html#results

[Stev-o]

Items 3 and 6, plus three sets of (4, 5, 15) and three of 21 from the first diagram. 

mystic_1 wins for clearest ever parts diagrams!

Was thinking that too!  Glad he's back...

[mystic_1]

Thanks guys, source is a Clymer manual from the 1971-1972 era.  This came with my bike when I bought it in the early 90's, I've since taken high resolution scans of every page in order to preserve it.

mystic_1

[mystic_1]

During starting, the springs and plungers push the rollers forward on the ramps which cause them to clamp down on the starter gear and spin the crank.

I guess it's the other way around, really, it's when the clutch is releasing than the plungers come into action, helping the rollers to ride up into the ramps so that the retract positively.

sorry, my bad.

mystic_1

[Restoration Fan]

When you're right, you're right!  You guys were spot on.  It was the starter clutch.

Despite the fact that the rotor itself looked really good


there were some hidden problems on the back side.


Turns out that 2 of the 3 screws were actually broken and one of the springs was missing. 
Got the old one off tonight and we'll put the new one on tomorrow and see what happens from there.

[edwardmorris]

I guess I shouldn't have prefixed the call with "long shot" 

Grab a rebuild kit here

http://www.cb750supply.com/products/5/electrical/49/batteries-and-starter-system-parts

[Restoration Fan]

Rafi,
I just went over to Bill's yesterday and bought a whole new rotor with the starter clutch assembly still on it.

[Restoration Fan]

OK....here are the problems du jour:
1.  The shifter mechanism has displayed issues before and I ended up pulling the neutral switch out the other day just so it would shift properly.  We shifted up to 5th gear before we started working with the rotor.  So it WAS in 5th gear....currently, we can't really tell what gear it's in.  But as you can see from the video, it will shift about twice but won't go all the way down to first gear and certainly can't get to neutral.  The mechanism that should only go around in a circular motion appears to be moving up and down as well.

2.  The neutral light hasn't wanted to go out.  We took the switch out and confirmed that it works with the electrical tester.  Also, we took the neutral switch and connected it to the wire, then turned on the lights.  With the wire connected, when we ground the unit to the exhaust, the light comes on while the ball is extended.    With the unit still touching the exhaust or frame, if you push the ball in, the light goes out.  So the unit seems to be working.  I'm assuming that this problem has something to do with the shifting issue and there is some type of issue that's causing it not to get fully seated in the bottom of the unit and press the ball in enough to make the light go out.  But I welcome any comments that might explain why that is.  (By the way, we ended up taking the o-ring out just as a test, to make sure it wasn't the problem but it still doesn't go far enough in to depress the button even without the o-ring.)

3.  The rotor itself doesn't want to go back on the tapered shaft.  We put a tiny bit of grease on the inside of the new rotor and gear.  Then we slide it onto the shaft and insert the bolt and run it up tight.  With the bike in what we believe is 5th gear still, Logan holds down the rear brake and I use the air impact wrench to try and use the bolt to pull the assembly onto the shaft.  It turns a bit but soon stops and won't turn any more but it isn't pulling it onto the shaft...proof of which comes when we unscrew the bolt and are able to just pull the assembly off the shaft by hand with no trouble.

Is there some other something that we're missing that we should be doing here?  The manual just says, "Reassemble the following...." and has the AC Generator as one of the things to reassemble. 

[Johnie]

If the drive chain is on the bike try rotating the back wheel a little. Sometimes rotating that small sprocket a little helps when I run a bike through the gears while not running.

[madmtnmotors]

If the drive chain is on the bike try rotating the back wheel a little. Sometimes rotating that small sprocket a little helps when I run a bike through the gears while not running.

+1

[Restoration Fan]

You guys are awesome!  That fixed the shifting issue.  Any ideas on getting the rotor back on?

[Restoration Fan]

The rotor will go onto the shaft and the screw will go in and tighten up until the air wrench can't turn it anymore.  But when I back the screw out, you can remove the rotor by just pulling lightly on it.  I'm thinking that probably isn't good.

However, we did try to putting it on as far as it would go and trying to see if it would crank.  The good news is that the starter clutch issue is now fixed.  You can hear it trying to turn over.  It's now either just not getting spark or gas because it isn't firing and cranking.

Also, we got the shifter issue fixed; it was indeed something that just needed to be bumped on that rear wheel and let it remove the binding on the front and turning the wheel while it was in gear would make it move slightly and then the gear shift was freed up. 

And we also got the neutral light issue fixed.  Now when you put it in neutral, we get a light; when we shift into gear, there's no light. 

Small steps.  Now it seems we need to see what's going on with the carbs and/or spark.

[madmtnmotors]

>Make sure the kill switch is set to "run"
>Make sure the petcock is set to "on" (or reserve if you're only using a splash of fuel)

[Stev-o]

>Make sure the kill switch is set to "run"
>Make sure the petcock is set to "on" (or reserve if you're only using a splash of fuel)

>Confirm spark by pulling plug, reconnect plug wire, set plug against head and cranking motor.

[Restoration Fan]

That's a great tip, Steve-o.  Had to go out of town all day so just getting back home at the moment.  Going to try that tomorrow though. 

I'm wondering if the issue with getting the rotor back onto the shaft is that my air impact driver isn't strong enough?  I'm thinking maybe I should go get a bigger one, just in case?

[madmtnmotors]

Oh yeah! Bigger hammer fix everything!   

The starter gear isn't hanging up on the reduction gear is it? You might remove the reduction gear while installing the rotor, then reinstall the reduction gear...

just in case. 

[martin_uk]

That's a great tip, Steve-o.  Had to go out of town all day so just getting back home at the moment.  Going to try that tomorrow though. 

I'm wondering if the issue with getting the rotor back onto the shaft is that my air impact driver isn't strong enough?  I'm thinking maybe I should go get a bigger one, just in case?

Hi Ron,I have never tried removing rotor immediatly after fitting, so not sure about how tight they are to get off after recent fitment.

I have removed 6 rotors on different CB750's using large puller  bolt and some are very tight and others come off easily.

If there is no play when tightened and it is gripping the crankshaft it is probably OK.

I always use an impact wrench to do these up and providing you have good air pressure, should be OK.

You can try putting in gear with rear brake on and check tighteness with a long socket bar/torque wrench.

[Restoration Fan]

Wilbur,
Did your badges come in from Down Under yet?  Mine arrived today.

[danyo]

^^^ those are from F model. Did they send you wrong ones or you just don't care??

[Restoration Fan]

^^^ those are from F model. Did they send you wrong ones or you just don't care??

They sent me the wrong ones and I didn't notice until you said that.

Ron