Vintage Dirt Bike Q & A

Quick rundown:

Installed everything 100% correct to manual.

When the clutch cable is installed, adjusted, and locked in... I can pull the cover off the clutch adjuster bolt (the aluminum screw cap) and see the clutch moving when I pull the lever.

That being said, the clutch does NOT disengage. I can put it in first gear, and push forward and the engine turns over whether I pull the clutch in or not.

If I start the bike... pull the clutch... and drop it into first... the bike jerks slightly and then the clutch slips.

If the rear wheel is off the ground... the rear tire will spin when put in 1st no problem.

With the wheel on the ground, I can sit on the bike running... pop it into first, and rev the motor up to about 1/2 throttle, shift into second, rev up, shift into third... as if it's driving... but it's just sitting there... making noise and not moving.

THERE IS ABSOLUTELY NO NOISE out of the transmission... No grinding, no whizzing, no hum... nothing sounds out of the ordinary.

It's almost as if both the clutch springs are too weak, and the clutch plates are stuck together.

I've tried removing the clutch cable completely and I get the same result... the clutch slips as soon as you pop it into first.

...

I've never dealt with a clutch this bad... so I don't know if it's 100% clutch or not. But there is definitely a disconnection between the clutch and the final drive shaft.... everything else in the transmission/engine is engaged as normal.

Any ideas?

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I drink your milkshake!

what oil do you filled in the gear?

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80 CR250Ra
80 CR250Ra
78 CR250R
80 CR80
82 Bultaco Sherpa 340
78 Bultaco Pursang 250 MK12
76 Bultaco Frontera 370 MK10
76 Bultaco Alpina 250
73 Bultaco Lobito 125 MK6
76 Suzuki RM125A
90 Kawasaki KX250

When troubleshooting, it helps me to keep in mind the possibility - however unthinkable - that I might have made a mistake. If I don't, I just run into dead end after dead end ("it can't be that, everything's correct"). I assume the clutch adjustment procedure on pp. 22-23 of the shop manual has been carried out to the letter?

If two steel plates got put in side by side, the existing plates are worn down to nothing and/or competely glazed, or the springs are super tired, you could get the symptoms you describe; I'm sure there must be other causes as well. Also as mentioned, the oil can have a very big effect on slippage, especially on vintage Honda clutches. I ruined a brand-new set of friction plates once with Mobil 1 synthetic, and now I only use Bel-Ray EXL 10W-40 conventional oil (or similar non-automotive oil) in my gearboxes.

If I pull apart a clutch these days, I always install new OEM plates and heavier Barnett springs if available. I've kicked myself too many times after a reassembled clutch started slipping in a short time.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Ray,

Before reading your post I actually had the clutch 100% apart. I re-installed everything 100% to the shop manual and still... there is slippage.

I backed the adjustment screw all the way out and had it just touching, tightened it back up, and then completely slacked the cable. Sure enough, it grabs SLIGHTLY at Low RPM, but once you rev it there's no go.
....

Time for a new clutch and springs.

I'm running SAE10w30 per the shop manual to the proper level... I even tried under filling and over filling slightly.

No affect.

Dan

_________________
I drink your milkshake!