OK, what / how does a jackshaft drive the crank ?

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4you2eat

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Oct 27, 2012
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OK, what / how does a jackshaft drive the crank . I've seen some vintage builds where the jackshaft appears to power the pedal / crank sprocket and there is only one chain going to the rear wheel. Is there a kit / part for that ? Do the pedals turn as long as the motor powers it ? It must have a slip like the rear wheels I'm guessing. I'd love any info from the pros here. The bike below is an example. I also see it has a 3 speed rear hub. I'm guessing they work OK w/ motoriized bikes too...thanxx for any help

 

BigBlue

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BarelyAWake

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Jul 21, 2009
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That's a SBP shiftkit second edition (they're on their third now) to a Sturmey Archer XL-RD3 on a 1943 Rollfast & at the time of that pic it had over 4500 miles on it.

As BigBlue linked to, it's a kit & the front sprockets are mounted to a (unidirectional) freewheel bearing on the pedal crank, so you needn't pedal along with the motor.

TBH, I do like the shiftkit & while I don't think I'd build another w/o one - that front freewheel bearing has proved somewhat problematic in the long run. I've destroyed three of them at this point (two cheapos and a quality) no matter the care & maintenance... remembering ofc the thousands of miles I got from them.

The additional maintenance requirements are not insignificant, with three chains just for the drive tensioning and adjustment becomes comparatively constant, not the easiest task as it's not well suited for it, the additional complexity something to be considered for a first time builder.

The Sturmey Archer XL-RD3 on the other hand has performed absolutely flawlessly as has it's mate, the front dynamo hub with 70mm drum brake Sturmey Archer X-FDD though I would recommend the XL-FDD for it's larger 90mm drum brake and greater stopping power.

Incidentally, the bike pictured can be found here;
The Rustoration Build Off
Rollfast Photo Album

 

The_Aleman

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Jul 31, 2008
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el People's Republik de Kalifornistan
Hey Barely, isn't your rear hub the X-RD3, not the XL? As you know, the X has 70MM and the XL has 90MM drums.

To the OP: as Barely said, these type of shifter configs are not easy to build, let alone keep going. I've had mine for over 2 years now, and while acceleration is great, it's a tough system to keep happy. It's very hard on chains. I had to eliminate the SBP chain adjustment system and am working on sprung tensioners for the crank chains instead.

I've never had problems with the stock crank freewheel, but I finally managed to wear one out after about 5200 miles. Running an HD version right now.
 

BarelyAWake

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Jul 21, 2009
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Yep, I stand corrected - meant to type that I've the X-RD3 & to recommend both the XLs front & rear.

Good eye Ale ;)