Jackshaft Shift Kit Questions for anyone thats allready installed one


Well-Known Member
Sep 8, 2009
So Could something I didn't check prevented this?
There are three potential possibilities. Either you didn't make sure the air gap between magnet and magneto coil arms was correct; allowing the spinning magnet to hit the arms, thereby placing stress on the crank, or you didn't tighten up the magneto coil screws sufficiently, allowing the magneto arms to come into contract with the spinning magnet or you left something metallic (like a washer) in the magneto housing; allowing it to get trapped between the magnet and magneto arms.

From the severity of the damage in the photos, i'm suspecting that it was either a loose washer in the magneto housing or it was the woodruff key that keeps the magnet in alignment with crankshaft indexing slot.

I have had this situation happen to me before, when the woodruff key slips out behind the magnet as it's being installed it on the crankshaft. If you are aware that this can happen, you are paying attention that the woodruff key can slip out.

If the woodruff key did indeed slip out, there's a change it could become trapped in between the spinning magnet and the magneto arms. Considering that there is only 0.5mm air gap between magneto arms and magnet, the problem will become quite serious when a 4mm woodruff key tries to pass through a 0.5mm gap.

the replacement is going to be a slant plug if I go that way. Will it be better quality?
The slant plug design is the manufactures solution to allowing fitment of these engines into bicycle frames with restricted space. Because of the packaging requirements and henceforth the altered physical dimensions, the modified cylinder head design gives the engine higher compression than conventionally designed OEM cylinder heads.

Higher compression = higher engine torque, with some people also reporting that these engines produce increased power due to the slant cylinder head.


Jun 3, 2013
i apoligize it looked to my eyes like the seal had come partialy free to me/ thats what i was refering to. dont blame someone w a specialized diploma in the feild has some advice for clearifcation of a subject. unless you sir have ur diploma.....my statement was accurate for my engine but yours runs on warranties and guaranties so somebody else will pay for it.....jra-just ridng along.......

i probly saw what i wanted to see i apoligize again if the seal is in factory condition.

good luck
Whatever im the one thats going to eat this. Theres no user error on this at all!


New Member
Nov 16, 2018
I read through these questions and found most don't understand the basics but Jim Welch (Ghost0) did an excellent job of shedding truth on all the misunderstandings:
Ladies and Gentlemen, please STOP! As the designer of the Shift Kit and one who has dealt with both Fabian and KC extensively some of what is being throw out here is opinion. There is no need to run a 410 chain on the left side. I have never run a 410 chain on the left side. I did fit one up once and noticed that some engine output sprockets will accept them and some won't. Please follow the instructions. Use the chain that came with your engine for the left side chain no matter what size it is. Our 17 tooth sprocket is designed to work adequately with both. Second if you are having issue with getting the correct chain tension let me help. Send me your engine, chains, sprockets etc and let me fit them. Once this is done I would encourage you to report back to this group exactly what I did to resolve your issue. I will even pay to ship it back if you get it here. Send me a PM or email me on our website if you are interested.
I have had several e-mails with him in the past few days and he is an excellent, exacting designer and everything can be made to fix exactly.
As far as the 415 chain being too close to the SBP mount, I simply ground a few mm off of both the steel part and the aluminum braces. The big problem I had was with newer engines coming with 8mm 1.25mm threads instead of 6mm supplied with the kit so simply drilled out the steel mount to allow 8mm holes (center to center is also slightly wider) but now have everything modified (the newer kits come with thick medium and extremely thin spacers to get the exact alignment so the 6mm screw coming in from the large engine gear side fits exactly in the center of the adjustment slot on the side to get perfect 415 chain tension from the 10T engine sprocket.


Use the 415 chain supplied with the SickBikeParts shift kit.

My assembly required the use of 2 large washers and one thin washer to get perfect alignment with the 10 tooth sprocket, so i guess there must be 3 or 4mm between the chain and the jackshaft plate.

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thats great Fabian.....i bought a bike from a young man who made these mistakes..i found out by slowly working through ...
If i had known before,how these really require thinking through....!
Have read many of your posts and they are a great help....


Dec 19, 2008
thats great Fabian.....i bought a bike from a young man who made these mistakes..i found out by slowly working through ...
If i had known before,how these really require thinking through....!
Have read many of your posts and they are a great help....
I have always use 410 Bmx half link chains.I believe shift kit comes with 410 chain just not the half link type.