CBR125 Clutch/Gearbox(?) noise problem

[ThoughtContro...]

Bike: CBR125 RS6, Carbed model, 57 Reg, 9718 miles

Symptoms:

1. Ride at 60-70mph+ 8500-9000+rpm in 5th or 6th. Slow down and change down gears to 3rd and hear scraping sound when in 3rd, 2nd. "Tshshshshshsh" sound, like you were holding a piece of tin against the brake disc (thought it was first time I heard it, took out, cleaned and replaced pads as soon as I got in). Cant hear anything at speed above the general engine/wind noise.

2. Sound usually disappears when changing down to 1st and gear lever feels like gearbox has sorted itself out. If it doesn't (if you've been caning it for a while), then when you change down to first it feels like you kicked the lever down without disengaging the clutch.

3. Clutch feels/sounds "clattery" around biting point in first. If you try slow control in 1st you'll get a clattery sound and rough feel. 2nd is OK. If when slowing down you use engine braking in 1st or 2nd, and your slow about engaging the clutch you'll hear a clattery sound about biting point. If you're smoothly swift about the change down all is good, smooth as silk.

4. On the move above 9000rpm *maybe* very faint rattley sound. Sounds like something loose maybe. Hard to tell if I'm imagining it or not in all the general din. Phantom Ring Tone syndrome?

5. Problem only really apparent on motorways, NSL A roads. For commuting around town etc up to 50mph in 5th you'd never even really notice that the above occurs. Gear changes usually around 7500rpm. Engine never gets properly caned to redline. Redlined maybe twice when slipped out of gear changing at NSL speeds.

6. Engine sounds fine at standstill. Starts no problem. Ticks over like a sewing machine. Revs fine with no adverse noises. A bit vibey above 8500rpm. Rare occasional burp and cut out at tickover if engine cold (usually me giving cold engine a slight rev while bored at city lights - carb maybe needs cleaning?)

7. Valves clearances checked twice. Sept 09, adjusted intake valve clearance, on edge of out of spec, exhaust valve fine. May 2010, Adjusted exhaust valve clearance, gap slightly too large, Intake valve unchanged.

8. Oil changes - Dealer first service 1073 miles (May 08), 2186miles (Nov 08, bought Oct 08), ~4700miles, ~6700 miles, ~9,100 miles. Castrol Power1 10W 30 each time. Oil level checks fine.

9. Cleaned the oil strainer at last oil change (probably first time). Approx 4-5 tiny slivers of tinsel-like flakes of silver, maybe ~0.5mm x 0.5mm in size. No obvious marks inside clutch compartment, tho didn't remove clutch. Casting inside feels surprisingly a bit rough, some tiny spikey bits here and there.

So what is the probable diagnosis? Other than, "It's a CBR125, the gearbox is supposed to be crap"
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Prize cunt
--
"In a world of universal deceit telling the truth is a revolutionary act" - George Orwell

[Vincent]

Off the top of my head - drive shaft bearing? (ever overtightened the chain?), Loose chain? Although, from what you say about the engine lurching when changing to first, could be a clutch problem.

[monkeyking118]

How much freeplay is there on you're clutch lever? and is it still firmly in place at the gearbox end?
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Baimo RSR125(sold), Suzuki En-125 '06 (sold), Honda VFR400 NC-30 '92(sadly stolen), Kawasaki ZX6R Ninja '96 (sadly stolen), Kawasaki GPZ500s '93 (sold), KTM rc390 '16 (f***ing stolen), Kawasaki Z750R, Triumph Daytona 675

[0l0dom0l0]

Maybe take the clutch off and check that the plates are okay. might be that they have degraded over time? i initally thought it might be 'pinking' but when i read on the symptoms dont match. or atleast i dont think they do?

[ThoughtContro...]

As I last mentioned here,

https://www.bikechatforums.com/viewtopic.php?t=197589

I'd adjusted the clutch freeplay and still had the problem with occasional noise after long periods of high speed, especially louder when the clutch was pulled in.

So today I pulled the clutch cover off and checked things out.
I speculated that maybe it was the lifter plate bearing. Well it doesn't look like it. There's no real signs of wear, no play or lateral movement and it spins smoothly, sweet as a nut. Checked the lifter piece and shaft and there's no signs of wear there either.

Double checked the oil strainer and no signs of any metal, a couple of bits of fluff was the only thing in it.

I also checked the clutch guide and shaft and there's no wear on that either.

There is some minor marking and indentation wear on the clutch basket from the plain plates. Haynes says this can be dressed up using a fine file. Is this worth doing?

Checked the friction plates:

Outer fine, measures 3.59mm (spec 3.5-3.6)

Inner plates OK too, approx 3.02mm (2.92-3.08 spec, 2.85min)

Plain plate warpage seems OK, the most I measured was 0.08mm, 0.15 is allowed max.

The springs are no good tho. The free lengths vary from 37.52 - 38.63mm, 39.1 is the allowed minimum.

So it looks like I need some new springs, wemoto does an EBC set for under a tenner. I presume they can be used with the original Honda clutch plates, and not just the EBC heavy duty ones that Wemoto also sell?

I'll also need a set of lifter plate bolts. I was tightening the bolts up, criss cross fashion, a bit at a time, and it didn't feel like there was any tightness at all, when a bolt head shears off like toffee. Then PANG! and another bolt head flies across the yard when I'm untightening the remaining bolts so I could get the remains of the snapped bolt out. I inspected the 2 intact bolts and the thread look stretched near the head

So I'll order some stainless steel M6 x 25 flange bolts. A pack of 10 is only £4 or so. I'll be a lot more careful tightening em next time.

I'll see whether replacement springs cure the noise problem, but for this week my little bike is off the road and I'm relegated to the SV
____________________
Prize cunt
--
"In a world of universal deceit telling the truth is a revolutionary act" - George Orwell