Author Topic: clutch slip with a knocking noise (Read 4643 times)

rev.buttons · « **on:** September 19, 2011, 06:54:35 AM »

So I just recently got my cb750 and was told the bike had no first gear. Well as I started futzing with it I found that it does go iknto first but when you just get going it made a horrible knock noise and then appeared to slip out of first and the bkike would die. So I went in and adjusted the clutch as per the manual and took it oujt. It appeard to be a little better, as in I didn't hear the noise just as it started pulling but I do believe it stated happening once the rpms got higher and then again it slipped out and the bike died. Do you think I need to replace the clutch plates? Or you think its something else?? Also as a side note how can I tell what modle my 76 is? The frame just says cb750(followed by other numbers ) and the eng says cb750e(numbers). I haven't seen anyrhing on an e modle so I don't know. Thx guys
Rev.

ekpent · « **Reply #1 on:** September 19, 2011, 08:26:26 AM »

Drum brake on back is a K and disc on back is an F model.2nd gear is usually the troublesome gear on the 750-worn shift dogs and forks.Usually don't clunk much though just slips into another type of neutral.Have you tried taking off in 2nd gear just to see what happens?When you say the engine dies do the electrics shutdown like from a clutch safety switch for instance.Did the PO mention if he had taken the clutch or shifting linkage apart recently?. PS-Welcome to the forum.

rev.buttons · « **Reply #2 on:** September 19, 2011, 09:01:32 AM »

Well it does have a drum in the rear. Well the bike has been hardtailed so no indicator lights bujt when the bike dies I still have a healight and the power switch light is on. I have tried takikng off in 2nd but same thing...it dies. The po said he ujsed to take off in 2nd all the time. I think/he was bsing me...too many indicators that he didn't actually ride the bike. He said he had never done anything to the clutch. I could. Tell someone had been in there though cause the adjujstment screw was messed up. If I take the clutch pack oiut what should I be looking for and do you have any rec as to what brand cluthes I should get. I'm tring to stay on the cheap but good quality since money is scarce

ekpent · « **Reply #3 on:** September 19, 2011, 09:37:44 AM »

Post up the engine serial numbers if you can to verify that it is a 76 engine. I think there is a slight variation in that clutch compared to the earlier years.Once you determine the exact year I would study-print out an exploded parts diagram of the clutch components and then compare to what you have if you think that is the cause of the problem. As for the engine dying-

? is it in a fairly good state of tune?

scottly · « **Reply #4 on:** September 19, 2011, 10:27:08 AM »

You might want to read this thread, Rev.

http://forums.sohc4.net/index.php?topic=86429.msg972479#msg972479

rev.buttons · « **Reply #5 on:** September 19, 2011, 11:42:45 AM »

Ok so complete eng # cb750e-2365690. I read the who thread there scotty. That kind of scares me. Never split the cases befor. Hmmmmm. Also as far as a tune up. I have no idea. I certianlly have not done anything to the bike since I got it 2 weeks ago other than try and trouble shoot it. I guess its time to stop dicking aRound and start taking crap apart...boy this is going to lead to a happy wife

ekpent · « **Reply #6 on:** September 19, 2011, 11:51:49 AM »

Looks like the engine is a late K4 or 1974. http://www.hondachopper.com/engine/engine_timeline/timeline.html

scottly · « **Reply #7 on:** September 19, 2011, 12:02:00 PM »

Before you split the case, you might try pulling off the shifter cover and taking a look the the shift mechanism.

ekpent · « **Reply #8 on:** September 19, 2011, 12:07:04 PM »

Quote from: scottly on September 19, 2011, 12:02:00 PM

Before you split the case, you might try pulling off the shifter cover and taking a look the the shift mechanism.

+1--I would check everything and throw at it what I had first before splitting the cases.Were all just guessing over here right now.

rev.buttons · « **Reply #9 on:** September 19, 2011, 01:17:46 PM »

And your guesses are much better than nothing. I'll try and pull that cover (left?) Later and see if I see anyrhing unusual.
--so I was going to do that now buttttt I now see manyh of the screws are striped out so I'll hace to get my remover from work befor I can pull thatg cover. What should I be looking for? It feels like it shiftrs from gear to gear fine

rev.buttons · « **Reply #10 on:** September 21, 2011, 05:54:43 PM »

Alreight so i got the cover removed and took a look and right off the back i found someything that didnt belong. about a 1 inch flathead screw. it definatly did not belong there. i inspected and found no "spare holes". I also checked the operation of the clutch and it seems like it is only going to third gear. When i have the gear in 1st the shift drum stopper??is just to the left of the notch on the gear shift side plate. then once in neutral it is in the notch. then it will go in 2nd just to the right on the notch and then it seems like it just goes in to third but then doesnt move any more. i dont see anything damaged from the screw that was in there, so...where to go now?? is it shifting right and i just dont see it?? thanks in advance for all yalls help so far. if it wasnt for you saying to pull that cover i would have never found that screw

MCRider · « **Reply #11 on:** September 21, 2011, 05:58:51 PM »

You will need to move the wheel to get it to shift into all the gears. Gotta mix up the gears and shafts to get them to mesh. Did you?

rev.buttons · « **Reply #12 on:** September 21, 2011, 06:08:20 PM »

no i didn't do that. i will have to try and put it up on a stand tomorrow and try that. so should i just spin the wheel by hand and then shift? i was also noticing that i was able to do the basic shifting to third ish without even pulling in on the clutch. is this normal when the eng is off?

MCRider · « **Reply #13 on:** September 21, 2011, 06:23:22 PM »

That's good news actually, as you are lucky to get 3 gears without moving the wheel. You won't need to spin it, just 1/4 turn back and forth should get the other gears shifted.

And you do not need to pull in the clutch to do this, that's OK.

scottly · « **Reply #14 on:** September 21, 2011, 06:34:42 PM »

That flat head screw goes into the center of the shift drum, and locks the plates and pins to the drum. The shift pawl engages the pins to rotate the drum. With that screw missing, the pins flex around, and the drum doesn't rotate as far as it should.

MCRider · « **Reply #15 on:** September 21, 2011, 06:54:44 PM »

Quote from: scottly on September 21, 2011, 06:34:42 PM

That flat head screw goes into the center of the shift drum, and locks the plates and pins to the drum. The shift pawl engages the pins to rotate the drum. With that screw missing, the pins flex around, and the drum doesn't rotate as far as it should.

Wow you're probbably right.

That screw is torqued and staked into place at the end of the drum. I can't imagine it coming loose without someone else being in there. Removed it then didn't get it tight enough on reassembly.

To the OP. Get hold of a diagram to see what scottly is saying.

MCRider · « **Reply #16 on:** September 21, 2011, 06:56:18 PM »

With the cover on I wonder if there is enough room for that screw to back out?

scottly · « **Reply #17 on:** September 21, 2011, 07:03:12 PM »

I'm sure there is now!

rev.buttons · « **Reply #18 on:** September 21, 2011, 07:22:51 PM »

Yes, that screw is installed. Its a flat head phillips. The screw that I took out was "shiny and new" with a rounded top to be screwed in with a flat head driver not phillips. My drum is good. It looks like someone just pujt a screww in there.

MCRider · « **Reply #19 on:** September 21, 2011, 07:55:24 PM »

Again that's good to hear. Wonders of the world where that came from, could've been jammed in the linkage keeping it from going into first.?

Keep us informed.

scottly · « **Reply #20 on:** September 21, 2011, 08:54:51 PM »

Quote from: rev.buttons on September 21, 2011, 07:22:51 PM

The screw that I took out was "shiny and new" with a rounded top

So the loose screw you found was not a flat-head??...

Still, I would focus on the shift drum, and the assembly of the pins and plates. It is a bit of a jig-saw puzzle, and is often assembled incorrectly.

rev.buttons · « **Reply #21 on:** September 22, 2011, 03:07:53 AM »

I will look into that to make sure its done correwctly. Other than the outter cover screws that were compleatly stripped, it had a gasket made of silicone (which I would believe is not stock) and ik see a cover behind the drum that the screws appear to have been tampered with...hmmm I wander what the po was doing/thinking.

rev.buttons · « **Reply #22 on:** October 03, 2011, 03:18:39 AM »

Well finally after what seems like ages I was finally able to take the bike out and ride. It still has a bad clank/skip when in first. Once I get it out of first it seems to be good. So any thoughts? Do you think I should go ahead and remove the clutch and insp. I would just love to get this bike going. Thx ya'll

wrenchmuch · « **Reply #23 on:** October 03, 2011, 11:59:36 AM »

I can't see how the clutch could produce the problem you are having . If the problem is only in first then its more likely a transmission problem . The shifter cover is a strange place to find a slotted screw . I can't think of anywhere on the bike that you could find such a screw . A P.O. could have used it as a replacement for another bolt . Maybe the shaft holder .
http://www.cmsnl.com/honda-cb750-four-k3-usa_model481/partslist/E++19.html
#1 in the pic above . Its fastened with 4 Phillips flat head screws . Is one of them missing ?
You might try pulling the oil pan in order to look for debris . Take pics and post them if you can .
If you find bits in the pan and they are magnetic they could be bits from the tranny .
Hope this helps .
Mike

rev.buttons · « **Reply #24 on:** October 04, 2011, 05:17:32 PM »

Hey mike,
Your the 1st to say it might be trany, and then it wasz double comfermed by another shop around town, that they believe its yhe trans also. So it looks like a nice eng tear down and a complete insp of the trans. Yeah!!!

I'm still gonna pull the pan tomorrow, just to see.

News:

Author Topic: clutch slip with a knocking noise (Read 4643 times)