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Old 01-26-2011, 08:20 AM
buzbikebklyn1 buzbikebklyn1 is offline
Join Date: Jun 2009
Location: Brooklyn N.Y.
Posts: 208
Default Re: To jackshaft or not to jackshaft..

Its long been my stance that a properly set up jack shaft system and secondary dive (the bikes derailleur system) will always be superior to a left side sprocket set up for anything BUT all out racing.
I just got my hands on a S6-T Morini engine and I'm building a jack shaft based set up using 415 type primary drive cogs and chain-
Engine out put, left side jack shaft, right side jack shaft and driven chain ring will all be 415 pitch.
Then reaching back into the past for the inner derailleur drive chain ring, an old style(new old stock) 5 speed chain with a 5 speed rear cassette stacked up on a 9 speed shimano XT type disc hub using spacers.
I've tested this chain with a hydraulic ram and it took twice the amount of force to stretch and then break it than modern 7, 8 or 9 speed chain.
Remember, this is old coaster brake chain that was designed to take the forces of a coaster brakes.
The next weak link was the derailleur its self, I'm using an old XTR derailleur that I installed super heavy springs in, and I spaced out the pulley cage with slightly longer bolts with washers to take the thicker chain and used aluminum pulleys with roller bearings, I'm using a 10 speed quick click shifter pod that ill have to double click to shift.
The last potential weak spot would be the dreaded chain slap, which can happen in non motored bikes...
I've designed a lower chain tensioner with a sliding roller skate wheel on a longer shoulder bolt as an idler that will follow the chain as it moves up and down the cassette.
I cant over state the importance of proper chain line!
YES... the chain will stretch, but in a controlled manner.
Lastly, THROTTLE CONTROL! no power up shifts please!
even Shimano suggests that you back off (not stop!) on the peddles before up shifting. Use the peddles to shift, then eeeease into the throttle, just whacking it open will snap a chain.

Be not afraid of the jack shaft... its a good thing... really!

Last edited by buzbikebklyn1; 01-26-2011 at 08:31 AM.
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