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Author Topic: HELP! THIS CLUTCH HAS GONE MAD!!  (Read 771 times)

Offline SwingKid1

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HELP! THIS CLUTCH HAS GONE MAD!!
« on: Jan 09, 2018, 22:54:59 »
 I'm having some difficulty with the clutch. First, a little intro about the bike.

I first bought this 1976 KZ400D 3 years ago from a used motorcycle parts warehouse, with open title. I later found the original owner (who still lived in the area! small world!), and he graciously wrote me a bill of sale, so all legit at the DMV. I have since ripped apart the bike and rebuilt everything, apart from inside the engine itself. I also did some custom work, chopping, welding, and painting the frame, restoring, filling, and painting the gas tanks, new muffler, heat wraps, mikuni carburetors, wiring harness, chopped fenders, custom seat I built, rebuilt front and rear brakes, rebuilt forks with new seals, respoked rims, new tires, new signal lights, hand painted side covers, the works. She is now a beautiful brat/cafe style bike (see attached photo).


Among the technical issues I have run into, one of the biggest were the keihin carbs. Although I had started the bike up with the keihins before, I bought two rebuild kits and rebuilt them five or so times before deciding to buy a pair of mikuni MK30 carburetors, which came with these puffy pod filters and 2-in-1 throttle cables. After slapping them on, the bike started after only a few kicks. Luckily, it was on it's center stand, and here's where we come to the problem. Before attaching the new carburetors, I had to take the engine out and send it to a machinist to fix some stripped plugs/mounting holes which were just too far gone for me to re-tap myself. After getting the engine back, installing, hooking up electronics, new carburetors, and chain, I noticed that when I turned on the bike, the neutral light wasn't coming on. I found this odd as when on the center stand, I could feel the clutch was in neutral when I kicked the shifter half a click up from 1st, the wheel spun freely. Also before remounting the engine the neutral light and gear shifting worked fine. I tried starting the bike up, and lo and behold, only a few kicks with the choke (it was around 25 F outside) and she started up. However, the rear wheel immediately started spinning, fast. I tried pulling in the clutch lever, but the wheel kept spinning. After fiddling for a bit, I shifted half a click up from 1st, felt that it was in neutral, but the light still wasn't coming on, and the wheel was still spinning. I tried to stop the rear wheel by hand and it did. When I shifted down into first, even with the clutch lever pulled in, the gears would not disengage and the wheel kept spinning. Stopping it by hand was a no go, though the rear brake DID stop it. Additionally, when I pulled in the clutch lever and kicked the kick-starter, the shaft moved completely smoothly with no resistance or feeling of compression, which leads me to believe that that part of the clutch disengages properly. What the hell is going on? Has anyone run into this problem before? Before anyone suggests something involving the plates or springs, I drained the oil out and took off the clutch cover, and disassembled the whole clutch assembly. I checked the spring sizes with calipers, as well as inspected the plates for wear or damage, and both were in very fine condition. I should note that the bike is a '76, but the registration tag from the DMV on the forks says 1981, and the guy who it belonged to didn't even remember owning it (fun time explaining that one), plus there was only 5,400 miles on the display. My conjecture from this and the fact that apart from some flash rust and worn seals the bike was in very fine condition overall (basically no wear on rubbers in rear brake hub and perfect compression in both cylinders) is that the bike was very lightly ridden for a few years, then sat in a barn for about 30 years.

Offline teazer

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Re: HELP! THIS CLUTCH HAS GONE MAD!!
« Reply #1 on: Jan 10, 2018, 00:34:28 »
Wheel spinning in neutral is not uncommon and is caused by drag in the transmission or where the clutch drum spins on the input shaft.

It may be rust on some gears or the shafts they turn on.  the "right" answer is probably to pull the engine out and strip it.  But before you do that, what oil is in there and is it the correct level? If you have decent oil in there, I might be tempted to roll the bike onto its wheels and fire it up and run it through the gears with low load and see if that's enough to free it up.

If it is, flush the oil out and replace with good fresh oil and have fun. if it still has a major issue, the trans has to come out.

Offline SwingKid1

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Re: HELP! THIS CLUTCH HAS GONE MAD!!
« Reply #2 on: Jan 10, 2018, 11:05:10 »
The problem is when I shift down into 1st, the wheel automatically starts turning, even if I have the clutch pulled in, so I'm worried that if I try doing this with the rear wheel on the ground, the bike will just rocket away, as opposed to me easing off the clutch lever and making a smooth transition to movement.

With ignition off and bike in neutral, it kicks over fine, and pulling in the clutch frees up the kicker so the pistons won’t rise ( as it should). However, after selecting first gear, pulling in the clutch no longer disengages the drive train.
I've examined the clutch plates and measured the spring heights on the clutch basket and all checks out. This is a very low mileage machine that sat for a long time. I can’t figure out why the clutch disengages in neutral but not in gear. Even if a selector fork were bent, shouldn’t the clutch disengage?

I've replaced the oil a few times on this project, using the correct amount and type.

Offline Tim

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Re: HELP! THIS CLUTCH HAS GONE MAD!!
« Reply #3 on: Jan 10, 2018, 11:28:42 »
If you can stop the rear wheel spinning with your hand while it is in N, there's not much to worry about.  Drag is normal.

When you kickstart the bike, I'm assuming it is on the ground with the rear wheel planted.  It has resistance to counter the drag on the clutch while in N.

When you pull the clutch in while in N and kickstart the engine, nothing happens, as both the pistons in the cylinder and the rear wheel have enough resistance to counter the clutch drag.

The fact you can shift from N into 1 without lots of clunky drama suggests any motion in the transmission is minimal.

While on the centre stand have you shifted through the other gears (without the engine running, just turn the rear wheel by hand as needed to align the transmission cogs)?

All of this sounds perfectly normal, but when you say the rear wheel is spinning 'fast' that's a little concerning.  Just how fast is fast?  Video would help.  Take a vid, upload to Youtube and post here.
"Quality . . . you know what it is, yet you don't know what it is. But that's self-contradictory. But some things are better than others, that is, they have more quality. But when you try to say what the quality is, apart from the things that have it, it all goes poof! There's nothing to talk about. But if you can't say what Quality is, how do you know what it is, or how do you know that it even exists? If no one knows what it is, then for all practical purposes it doesn't exist at all. But for all practical purposes it really does exist."

Offline SwingKid1

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Re: HELP! THIS CLUTCH HAS GONE MAD!!
« Reply #4 on: Jan 10, 2018, 12:13:27 »
I've been kick starting on the center stand for fear of the bike rocketing away when it automatically shifts into 1st. Still, when it's in 1st and I pull the clutch in it's not disengaging, which is more concerning than anything. Here is a video of the bike running in N.

https://www.youtube.com/watch?v=IOTnzGQtnh4&feature=youtu.be

(please excuse the high RPMs, I hadn't adjusted the mikunis yet, this is how they came)

Offline jpmobius

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Re: HELP! THIS CLUTCH HAS GONE MAD!!
« Reply #5 on: Jan 10, 2018, 13:45:34 »
1) slow the engine down to something like an idle.  If you have not cleaned the carbs, and it has set for 30 years, this will be a requirement.  Cleaning the carbs requires a 100% comprehensive disassembly, but likely will need no parts.  Do not use an aftermarket rebuild kit!!!  If you need parts (unlikely unless you break something or tear a gasket) order OEM parts only!
2)  Start it on the centerstand, put it in neutral.  Hold the wheel stationary with the rear brake.  Pull in the clutch lever and put it in gear.  If the clutch disengages the kick starter, it is working and will also disengage the transmission, though it may drag.  This should not be the case if you have had it apart and separated the plates and correctly adjusted the throw-out mechanism.  Very commonly the drive and friction plates glue themselves together when allowed to sit for a long time, but usually there is no damage and once separated the clutch is fine.  If you have not had all the plates out and separated and cleaned, do so and make sure the throw-out mechanism is properly adjusted.
Mobius


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Offline doc_rot

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Re: HELP! THIS CLUTCH HAS GONE MAD!!
« Reply #6 on: Jan 10, 2018, 15:02:58 »
make sure the throw-out mechanism is properly adjusted.

I would double check this. you cannot tell if its adjusted properly from the clutch lever. Also I wouldn't worry about the bike "rocketing" away when you put in in first, if the clutch is engaged and you dont give it throttle the bike will just die.
« Last Edit: Jan 10, 2018, 15:05:25 by doc_rot »

Offline Tim

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Re: HELP! THIS CLUTCH HAS GONE MAD!!
« Reply #7 on: Jan 11, 2018, 13:43:12 »
Sheesh - you said you stopped the rear wheel with your hand?  At that speed?

Take the chain off the bike and get the engine running properly.  Then move on and deal with the clutch.
"Quality . . . you know what it is, yet you don't know what it is. But that's self-contradictory. But some things are better than others, that is, they have more quality. But when you try to say what the quality is, apart from the things that have it, it all goes poof! There's nothing to talk about. But if you can't say what Quality is, how do you know what it is, or how do you know that it even exists? If no one knows what it is, then for all practical purposes it doesn't exist at all. But for all practical purposes it really does exist."