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View Full Version : Clutch, or something more serious?



xwhatsit
22nd May 2008, 23:18
Hihi,

My clutch isn't very nice. It's always a struggle to set it up between slipping and dragging (in terms of cable slack), probably because of the excessive abuse it gets at the Traffic Light GP (compounded by the much taller geared sprockets I've put in).

Anyhow, it's started doing a new trick lately. Wind it up in first gear away from the lights, and a few thousand RPM before redline, suddenly the engine screams and I just about pitch forward over the handlebars. It's exactly like a gear jumping out; except, as soon as I back off on the throttle, it goes back to normal. It certainly doesn't go into neutral or anything (as far as I can tell with my left foot).

Now, that would seem to be a slipping clutch. But I'm a little confused. Limited prior experience with clutch slipping has been of a gentle sort of CVT scooter effect. This is a violent let-go; one moment it's holding on, next moment all hell is breaking loose. Also, why is it happening in first gear? Isn't this where the least stress is on the transmission? Wouldn't slipping like that happen in fourth or top as I'm winding it out on the motorway?

Of course, my curiosity will be satisfied whenever I have a spare moment to replace the clutch bits, but I'm rather anxious about this being a gearbox problem. I like to understand what's going on, rather than just throwing parts at the bike.

CookMySock
23rd May 2008, 08:41
I like to understand what's going on, rather than just throwing parts at the bike.hrm that pretty much sums up a full 50% of servicing anything 'mfraid dood. Many times we have no idea what the problem was.

DB

vifferman
23rd May 2008, 08:48
.... a few thousand RPM before redline
That would be when the turbo and Vtec kick in at the same time?
Don't you have it back-to-front - isn't first gear where the engine's doing the most revs relative to the wheels, so there's the most strain on the clutch? :spudwhat:
It sounds Eggs Zachary like the gearbox shifting into neutral or false neutral to me, but if it's not that, and is the clutch, then it's either worn / glazed plates, or tired springs (the most usual problem).

NOMIS
23rd May 2008, 08:48
My hornet does this if i load it up to hard taking off readlight gp style. But it usually not as bad as your sounds and normally when i change into 2nd gear it will go then loose 2nd back to neautral,
quite embarrasing hitting redline ringing the nut off it.

xwhatsit
23rd May 2008, 09:42
It sounds Eggs Zachary like the gearbox shifting into neutral or false neutral to me, but if it's not that, and is the clutch, then it's either worn / glazed plates, or tired springs (the most usual problem).
Yeah, I know it does sound like that, but it's different. That happens in second gear sometimes if you're not firm when selecting it (classic 250RS problem), but the difference is, is that it jumps out of gear and stays out of gear. This `slips' or jumps out or whatever in first, but then when I back off it engages again and everything's back to normal.

EDIT: And oh yes, it only happens when hot.

Magua
23rd May 2008, 10:28
http://www.davidsilverspares.co.uk/parts/genuine-spares/part_2582/ _b

vifferman
23rd May 2008, 10:33
Yeah, I know it does sound like that, but it's different. That happens in second gear sometimes if you're not firm when selecting it (classic 250RS problem)
No, classic Honda problem.
I've owned 7? 8? Hondas now, and every one has ended up with a crap gearbox. Yeah, I know I'm a serial gearbox wrecker, but even so, Honda gearboxes aren't great. The VFR had the best gearbox of any Honda I'd ridden (till I'd thrashed it a bit), and it's even better since I put a Factory Pro Evo Star shifter kit in it, innit? Now it generally behaves, except when the chains too loose/ tight / dirty or I'm especially sloppy on gearchanges.

CookMySock
23rd May 2008, 10:44
zounds like a worn gearbag part, like a selector or a dog.

DB

Ixion
23rd May 2008, 11:26
I'd say a worn selector. The torque load on the gear under heavy acceleration is enough to push the dog back against the selector fork. When you button off the fork reengages it.(Actually, it's probably wear in the snail groove and pin so that the fork can be pushed back a bit up the "ramp'. It's sort of hard to explain)

xwhatsit
23rd May 2008, 11:40
Ah, feck.

Oh well, I've got a 6-speed gearbox sitting in the garage, and two other mangled engines. I'm sure I can put something together eventually before it all turns to custard. Splitting the cases on my existing engine is not something I am relishing.

Hmmph. Wear in the selector drum seems funny, how fast do those things rotate at the end of the day? 1 rpm?

xwhatsit
23rd May 2008, 11:57
Oh, I should probably ask as well, if it is such a gearbox issue, am I causing any more damage by riding it like this (just not giving it heaps in first)? I drained the oil out a couple of days ago and can't recall seeing any metal bits floating around...?

Ixion
23rd May 2008, 12:50
Ah, feck.

Oh well, I've got a 6-speed gearbox sitting in the garage, and two other mangled engines. I'm sure I can put something together eventually before it all turns to custard. Splitting the cases on my existing engine is not something I am relishing.

Hmmph. Wear in the selector drum seems funny, how fast do those things rotate at the end of the day? 1 rpm?

Only rotate when you change gear. But it's quite heavily loaded, depending on how delicate you are with the clutch. Remember, the bike is how many years old?

xwhatsit
23rd May 2008, 13:22
Only rotate when you change gear.
My point -- then again, for its quarter-century lifespan it has done a lot of communting. *Bang* first gear, up into second -- 20 seconds later, red light, *bang* down into first and click into neutral.

Dropping those aluminium shavings in the sump from the cam sprocket affair probably didn't help, either :D

Maybe changing down to standard sprocket ratio will help alleviate the symptoms somewhat; shorter first gear means less stress on the transmission (@Vifferman -- my theory is that it's easiest for the engine to accelerate/do wheelies/spin rear wheel in lower gears, so there's less stress, whereas in top gear the engine is struggling to push against the rear wheel to accelerate. Dunno).

Monster 6-speed bored-out lumpy-cam CB275RS time.

Ixion
23rd May 2008, 13:33
It could also be wear on the little hooky thing that turns the selector drum. So it's not *quite* indexing. In which case you might be able to fettle it. The hooky thing is often accessible without splitting the cases (though that's not really a big job on a single)

avgas
23rd May 2008, 13:47
how tight are your springs - i had a similar issue with one of the GB's. Drained oil and went to pull clutch plates out and noticed that one of the bolts holding the spring was a bit loose.

xwhatsit
23rd May 2008, 13:54
how tight are your springs - i had a similar issue with one of the GB's. Drained oil and went to pull clutch plates out and noticed that one of the bolts holding the spring was a bit loose.
Causing this sort of unusual `false neutral' style slipping though? Limited to first gear?

It'd be nice if it was just the clutch, but I'm a negative fellow :Pokey:

Ixion
23rd May 2008, 16:21
To prove the point, if it's reasonably predictable, try keeping your foot on the gearlever while accelerating. If it doesn't do it it's almost certainly selectors. If it still does it, may or may not be.

erik
23rd May 2008, 19:40
if it was the dogs disengaging, wouldn't there be a thunk noise when it re-engaged when you throttled off?

The clutch is going to be subjected to the most force when the engine is at it's highest output, maybe since first gear lets the engine accelerate harder, it subjects the clutch to higher force than the slow acceleration in 6th? I'm just guessing, haven't thought about it enough.

How worn is the clutch? I've heard you can put washers behind the clutch springs to increase the force, maybe you could try that and see if it still does it (assuming it's the clutch slipping).

xwhatsit
23rd May 2008, 21:35
Yeah I dunno, it's all very confusing. Will try holding down the pedal, Ixion. Maybe that trick will let me once again reign supreme at the Traffic Light GP for a little while longer until I've built a new engine :D

The clutch isn't the best. I think, Ixion, you said a while that the steels are likely warped. I was complaining about the clutch `clicking' and engaging/disengaging/engaging/disengaging with half-clutch and inching forward at the same time. I can disengage clutch, the bike will happily sit there; roll the bike forward a little with my feet keeping the clutch lever in same position, then it will bite and start to pull me forward. Go a little further and it's entirely disengaged.

So it's not really a happy clutch anyway. Might just rebuild it anyway and see where I get.

Thanks for all the advice guys!

Ixion
23rd May 2008, 21:47
Hm. Could be worn/collapsed gearbox bearings. They could cause the clutch effect and also push the gears out of mesh. But I'd expect to hear some noise from a shot bearing.

Bottom line, it's had 30 hard years. They've taken their toll. A rebuild is unlikely to cost all that much.

xwhatsit
23rd May 2008, 21:54
But I'd expect to hear some noise from a shot bearing.
You'd be hard pressed to hear it over all the other noises she makes :laugh:

I'm well aware of the `30 hard years' and am by no means complaining that she's falling apart now; I think I'm the first owner to change the oil regularly :pinch: Stuff like this is expected, in fact, since putting her back together after that top-end carnage she's been remarkably solid, aside from the oil leaks.

I'm sure this engine will stay together while I build up another one out of my spare bits. Ground-up engine build, make sure everything's right to begin with. Last another 30 years :niceone:

FJRider
23rd May 2008, 22:01
I would say replace clutch plates FIRST, then go from there. Its the simpler CHEAPER option for a first step to find problem.

Ixion
23rd May 2008, 22:03
Of course, since it only does it in first, and only a few thou rpm short of redline ("Wind it up in first gear away from the lights, and a few thousand RPM before redline,"), you COULD always just change up a little earlier. Just a wild thought.

xwhatsit
23rd May 2008, 22:15
Of course, since it only does it in first, and only a few thou rpm short of redline ("Wind it up in first gear away from the lights, and a few thousand RPM before redline,"), you COULD always just change up a little earlier. Just a wild thought.
Oh I've been doing that of course, but remembering a few thou short of redline is 6,000-6,500rpm, and that's where the power comes in, it becomes a limiting factor on an RS :eek:

Stop giving me reasons to not attempt building up a complete second engine! You're just worried about all the questions I'm going to ask you again and again :bleh:

TygerTung
24th May 2008, 01:01
Mine jumps out of first, but at about 5-6k rpm, so when you are up at pole position, go to do a really good launch, revving it hard, dump in first, then boom, into neutral, so ya go into second and it's only doing about 4000 and everyone blasts past you.... damn.

It might be a common problem, I might see if if holding the lever down works, that would be great if it did!

xwhatsit
25th May 2008, 01:13
Alright, not sure about this.

It seems holding down the lever stops it from happening almost all the time. However I'm not 100% sure -- my subconscious stops me from winding it out very hard in 1st gear, at least without immediately shifting to second (hard to do with your foot on top of the lever), it just feels like a nasty thing to do to the engine and my brain won't let me. (Perhaps that's why I ended up fouling the plug on Pippi the A100? Not hard-hearted enough to thrash the bikes I ride?)

So I'm not sure if I was giving it the full treatment when testing this out. It did slip/pop out once however with my foot on the lever, but that was going up a hill at even higher RPM/throttle than it popped out before, and my foot may not have been hard down on the lever.

I mentioned before that it only happens when engine is hot. It also only seems to happen when using the clutch from a standing start (of course I've let off the clutch completely by the time it pops out); if I'm already in gear rolling along at 5kph then give it heaps it doesn't seem to want to happen. But yet again, limited testing data.

So really, not very good testing, and who knows. Probably best to ignore all the above and order clutch plates, maybe rebuild one of my spare clutches with new friction plates. Measure springs, see if steels are flat. Take a look at that `little hooky thing that turns the selector drum' while I'm at it, then go from there.

At the end of the day, it's not a huge problem (yet, hopefully doesn't get worse). Just have to avoid filtering to the head of the lights unless I can see only Grandpa in his Morrie Thou and a refridgeration truck are at the front.

motorbyclist
25th May 2008, 04:39
i would just post a link to a cheap TM auction for an XR500 or 650 motor, but for some reason i can't find any:(

xwhatsit
25th May 2008, 10:05
i would just post a link to a cheap TM auction for an XR500 or 650 motor, but for some reason i can't find any:(
Haha do tell me if you find a 500 :D