Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: bucksfizz on September 14, 2019, 09:55:44 AM
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Engaging first gear on my 1973 CB 750 K3 always crunches.
Unless this is a known problem, which I doubt, then I'd like to have a look at the clutch plates for potential contamination.
I've bought a castellated nut removal tool to effect clutch removal.
Question is: does oil seep out when removing the clutch?
Any other "gotchas" when working on the clutch?
(I've read the manual and tried a search, but to no avail.)
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They all do that sir.
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Normal....dry clutch system. Plates may have stuck together or gone hard. Even if you strip clutch and inspect / overhaul, there will still be a noticeable crunch.
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Thanks for the replies - I still have a lot to learn about these machines.
I thought the clutch was a wet system...
From my other machines, I would've said that it was clutch drag, especially as the other gears are not particularly quiet in engagement.
I'll live with it for now if it's a peculiarity of the clutch system, and take a peek over winter.
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Well it's a wet clutch system in as much as oil is sprayed in the clutch but not a wet clutch system as in other SOHC/4's.
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If it's pulling away smoothly without snatching on takeup, that suggest the plates aren't in bad condition so maybe not the first point of attention.
They, along with many bikes, only just release when the lever is fully actuated with not much spare travel to play with.
Operating system worth verifying first. Clutch lever pivot should have no play radially else it'll just not pull the cable fully before touching bars. Originally they had a good quality cable with internal plastic lining that makes operation easier.
Clutch end should be adjusted first without cable hooked up, wind screw in until it touches, back out 1/8 to 1/4 turn ( manual says 1/4 to 1/2 turn) then leave it alone. The slack is to avoid the operator mech pushing the clutch when hot.
Finally, install the cable making sure you don't adjust out the slack you've just put into the operating arm.
It should now move the arm starting with just under 90degree angle between cable and arm, to just over when fully pulled. That setup should give you the most lift on the clutch plates and hence the best release available to you.
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Wow, thanks for the very comprehensive clutch setup routine, K2-K6.
The clutch take-up is smooth; it's first gear that graunches, and I can feel the shafts are moving, which is causing the noise.
Other gears can be noisy when shifting.
I was going to tackle this job first thing tomorrow morning, but I'm volunteering at Haynes Bikers' Ride-in.
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There has been a recent discussion about the mod on the US site if you look there.
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Correct me if i'm wrong, but wasn't that mod to stop the rattling not the gear crunch?
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Dunno, never owned a 750 to run
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To be honest...I have had many bikes that engage first with a bit of a clunk.
IF the gears shift smoothly on the road, and the only clunk is engaging forst from neutral...then it's probably normal.
If you get a crunch from second to first... then I would suspect an issue with the selectors. Had an issue with an old Kwak triple I overhauled. I had done a top end rebuild, but left the gearbox. First when in with a big clunk....and it was awkward going from second into first, and it needed firm pressure or the thing would fight back. Had to replace the gear clusters....but the reason was a bent selector. Had probably been like that for a while when I bought the thing as a cheap project..back when they WERE cheap projects. On the bench...it had seemed to change gear OK .... but with the engine running, Crunch...clunk....and we were away.
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Honda must like that crunch...
I have a 1992 blade with only 13k on the clock it does it too
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Wasn't there a clutch basket mod to get more oil to the plates in order to try and stop this?
I found this thread (http://forums.sohc4.net/index.php/topic,7190.0.html) on the US site, and it makes for interesting reading.
This post (http://forums.sohc4.net/index.php/topic,7190.msg1821867.html#msg1821867) reckons that the modification helps to reduce clutch drag, and clutch drag is what I feel when selecting first gear.
Methinks a clutch strip is in the offing.
BTW, I adjusted the clutch as per K2-K6's instructions, and it was a little better, but no cigar.
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I finally got round to removing the clutch.
Talk about a pain trying to remove the castellated nut securing the clutch basket.
Even with the correct tool and locking the clutch with the bike in 1st gear and the rear brake on, the nut refused to budge.
The problem was that I couldn't get enough purchase on the nut and hold the rear brake pedal down at the same time.
In the end, I locked the clutch with Mole grips/channel lock pliers butting up against a length of wood:
[attachimg=1]
The clutch plates were reasonably clean, but I cleaned them with petrol nonetheless.
With fresh oil in the oil tank, I fired her up, and selected 1st gear...
Hurrah! A noiseless gear selection - as I thought, it was clutch drag.
I'm just hoping the noisy gear selection won't return.
If it does, I'll try the clutch basket modification.
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We'll done 👍👍👍
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I did the clutch mod on mine, it still clunks into first, I’ve never seen one that doesn’t, it’s about 3 years ago that I did the mod but I seem to remember it was an improvement, if you really want to avoid the crunch buy a Carby 900ss, proper dry clutch set up on that , I can’t even tell it’s gone into first sometimes!
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Both my Hondas and Kawasaki's go crunch but my Guzzi goes with a BANG
They all make a lovely noise when you put them in gear while still reving a bit high on the choke ;D
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I did the clutch mod on mine, it still clunks into first, I’ve never seen one that doesn’t, it’s about 3 years ago that I did the mod but I seem to remember it was an improvement, if you really want to avoid the crunch buy a Carby 900ss, proper dry clutch set up on that , I can’t even tell it’s gone into first sometimes!
The clutch mod is only for the early clutches as, they did not have any drain holes.
Bucksfizz, that is the worst way to lock a clutch up. It is very easy the break the alloy parts, you can lock a clutch with only 4 washers ;)
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The clutch mod is only for the early clutches as, they did not have any drain holes.
Bucksfizz, that is the worst way to lock a clutch up. It is very easy the break the alloy parts, you can lock a clutch with only 4 washers ;)
OK, thanks for the tip - the K3 does have some drain holes.
Oops - it looks like I was lucky then, even though the clutch vane looked strong enough to take the mole grips.
Out of interest, how do you lock up the clutch with four washers? TIA
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Very easy, 4 washers under the bolts that will compress the springs and lock the clutch ;)
[attachimg=1]
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Brilliant - it's easy when you know how.
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FWIW, old Brits used to crunch into 1st (Honda don't have the monopoly on this), usually after starting from cold. Kicking over with clutch held down freed the plates and helped. Don't know if this would help on a Honda, as mu old 750 used to do it.
Maybe selecting 2nd before 1st would help....
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Yes, same mod that I did, as above I think it made it better but it’s easy to kid yourself with such things, and it’s 3 years ago so I can’t remember how bad it was before, I think the “they all do that sir” is the best philosophy with Honda first gear selection.
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My K1 has a horrendous crunch when engaging 1st gear on cold start up after no use of about a week, my solution to this is before starting the bike, i select 5th gear, pull the clutch lever in and rock the bike back and forth untill it frees, usually no more than one rocking, then engage 1st gear, kill switch to off and turn the engine over on the starter motor with the clutch in and brakes on, and that does the trick, no need to do it again untill the next short lay up.
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Clunk Click Every Trip, as someone who shall remain nameless used to say in an advert.
My CB750 had one finger clutch operation but still made a loud clank has going into first.
My Harley is worse, it sounds like one of those .22 shooting galleries you get at fairgrounds.
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Clunk Click Every Trip, as someone who shall remain nameless used to say in an advert.
Now then, now then, now then, jingle jangle :D
Before starting, and with both wheels on the ground, put it in 1st gear, hold front brake and kickstart to turn motor. Should free any dragging clutch plates first, then into neutral and fire it.
Most Japanese bikes drive the motor from the kickstart via primary drive so you can kickstart them in gear rather than through the gearbox.