Grubee Freewheel Sprocket Failure


Irish John

I wonder has this happened to anyone else. My freewheel grubee sprocket failed after 150 kms. The whole assembly became loose and the ratchet mechanism failed. I took it apart - quite interesting to see how it's made - very fragile really and I wonder how the tiny ball bearings could last when they weren't sealed in place properly. I think when it came loose the grease must have come out and the whole think disintegrated.
Don't know how it came loose cos the sprocket is held together by a revers threaded flange on the inside and a bolt holds it onto the shaft.
Disappointing thing to happen to my lovely new Billinudgel Bullet. It's not quie as bulletproof as I thought and I'll have to make another key for it and they are tiny little things with rounded ends.
There is a tiny wire circlip that goes around the middle of the assembly but I can't figure out just how it should go back together.
Wow- sorry to hear that. I look forward to you reports on solving this problem....for when I have to.
This sprocket isn't fixable cos I think it's been mangled too much and lost a couple of ball bearings. I'm posting it back and he's posting me a replacement.
No I won't. I'll take it apart and photo it for MBc posterity cos I'm sure if the pics are good one of you guys will understand how it all works.
Then I'll post the info up here so we can study this little beast.
Then I'll post it.
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How the freewheel sprocket works

Here are pictures of the innards of the freewheel sprocket. I think I assembled it correctly but I could be wrong. I do know, however, that the ball race flange that holds the whole thing together should be loctited in very securely because it came loose and that is what caused this sprocket to fail at 150 kms. Those bearings fall out through a very small gap but I think they are easily available from a good bike shop.
I'm posting these pictures because I am sure they will be useful to other Grubee owners. Many suppliers will only supply a replacement sprocket attached to the rear gearbox casing, the final drive shaft, the engager and cable (but not the gearbox to engine gasket). This isn't very good service when you only want a freewheel sprocket.
Lastly, remove the old sprocket with small 3 jawed gear pullers (100mm size) and do not put it back on the keyed shaft with rubber hammer blows. I think it needs to be squeezed back on in a vice cos it won't just slide on using hand force. The key has to be a very good fit and that usually means it will be very tight.


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Thanks, great info
Could you please post a pic of the shaft that the freewheel goes on? ( with the freewheel removed)
And give the dimensions of the shaft?

Thanks again
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Very similar to Dicta construction. Which is also not bulletproof. To some extent it's the nature of a low resistance freewheel. (and trade off for cost vs. tolerance)

Good pictures.
Sprocket Shaft diameter & Keyway.

I seized mine up on a bonehead move by welding it to the output shaft without the bearing and rear cover. it still freewheels. I can't believe I did this, i've done this once before when the woodruff key broke. This time I was in a rush.

It's not a woodruff key Proboscis it's an ordinary straight key and it's 3mm wide. The shaft is 10.5mm dia.


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Irish John. I'm Portuguese :) Oh do I wish it held up on the first day, sheered right off that key.