Power Stumble. Not the Engine. By randall (Read 724 times)

[randall]

I've been getting my Diamo, 150 Gy6, ready to put into service and have finished dialing in the engine. Running great, quiet purr, perfect for this kind of bike. Anyway, with that done I've been turning my attention to the transmission. Here's what I'm experiencing.

When traveling at a constant speed on a smooth flat road, there is an occasional power stumble. Its subtle, only lasts for a quarter second or less, but it's noticeable. It's obvious that the motor is not missing a beat when this happens. It repeats intermittently but seems to occur more frequently when A. Accelerating up a slight hill, B. when hitting small bumps, and C. At midrange speeds between 25 and 35 mph, and only sometimes when taking off from a light.

With the bike stationary on the center stand, throttling it up to those speeds, it can also occur. The whole drivetrain bounces up a little when it occurs. The bike is quite drivable. As I say, it's very subtle.

Interestingly, it does not occur under heavy acceleration!

Here's what I've done....

Disassembled the variator, cleaned and inspected thoroughly, no flat spots on the rollers, ramps look good. I deglazed the pulley faces with sandpaper, greased the little posts, shaft, etc.

Pulled the clutch pulley bell, deglazed the shoes and bell, didn't disassemble the clutch though. Pads looked good, nice and thick. Did a little deglazing of the clutch pulley, reassembled everything and put on a brand new gates belt, even though the old one looked perfectly fine. Took out all that silly kick start stuff too. Hey, I got AAA!

The result? No change. Well, actually things seemed overall a little smoother, but the subtle stumble remains.

Logic is telling me it's in the clutch pulley. I'm leaning towards that big spring being weak or something. Any ideas?

[tvnacman]

Vaccine problem .
Spray some carb cleaner around the carb a short burst . Se if you get a stumble .

John

[randall]

Nope. Been all over the motor. Definitely not the problem. Rode with a precision tach hooked up too. Steady as a rock.

I've got a strobe tach here too. Might pull the tranny cover and maybe I'll be able to see something.

[alleyoop]

Since it also happens on the center stand take a Video of it with the CVT cover off. It could be the pins hanging on the SHEAVE Slots where the slots have a slight curve.
Alleyoop

[alleyoop]

Here is the sheave notice the curvature on the slots they maybe all dryed up and need a little grease on the pins that slide in the slots.
Alleyoop

[randall]

Jan 2, 2013 14:23:20 GMT -6 alleyoop said:

Here is the sheave notice the curvature on the slots they maybe all dryed up and need a little grease on the pins that slide in the slots.
Alleyoop

Thanks Alley. I'll give that a look. Makes sense that it might give the symptoms I'm having.

[randall]

Yeah Alley, this might be it. Not well greased at all, might have got some water ingress too. Also some uneven wear in the pin races. I'm going to file that a bit smoother, grease it all properly and reassemble. If that doesn't work I may just replace this whole clutch thing.

[alleyoop]

Hope that is it, per the symptoms and at the speeds it does it that is the only thing I can think of that would cause just a little hangup to make it skip a beat.
Alleyoop

[randall]

Haven't had a chance to test drive yet, but it's showing better signs on the center stand than it did. I noticed the pic you posted showed a sheave with 5 slots. Mine only has 3. I think when I eventually go clutch shopping I'll see if I can find one that has more spiral slots/pins. Better distribution of the load. You can see how mines worn. Doesn't show well in the pic, but there were a couple of worn depressions in the slot near its low speed end. Anyway, after filing those out and greasing it up with fresh amzoil, it's operation, by hand, feels very significantly smoother. Fingers crossed. Can't ride today, but maybe tomorrow.....

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[alleyoop]

Great, hope it takes away the stumble.

Here is the one with 6 slots, BUT you only use 3 slot at a time, the reason is has 6 is 3 slots are a little longer than the other 3 slots so it OPENs just a hair more to cause the belt to drop down a little more.

As you know BIGGER WHEEL WILL TURN A SMALLER WHEEL MORE TIMES PER REVOLUTION-- (Variator belt up high BIGGER WHEEL- Belt in Clutch pulley further down SMALLER WHEEL) little more top end speed.
Alleyoop
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[randall]

STUMBLE........... GONE!!!!!!

Nice call, alley. While I had planned on tearing down the clutch and sheaves as a possible next step, I doubt I would have given those slots the scrutiny I did had you not suggested them as the problem. So, I'm really glad you did. Also glad I got everything back there well lubricated now.

Along with that stumble being gone, my takeoffs have less vibration too. And interestingly, an apparent increase in rpms on takeoff. I think the sheaves are having an easier time coming together now. Just more confirmation that I need lighter variator rollers. Something I already knew but now it's worse. These bikes come with 13 gram, but 11.5 has been recommended to me by folks knowledgable with this model.

Thanks for the skinny on the 6 slot sheave. There's no end to how much you can tweak these things!

Enjoy your weekend.

[alleyoop]

Glad to hear it is running smooth with no hiccups.
Enjoy the ride and ride safe
Alleyoop