Newbie help jackshaft question

[jeffsos3000]

hello all. totally new to forums so my apologies if im not doing things right.

I have a micargi slugo single speed fat wheel beach cruiser which i have purchased a 2 stroke engine for. I am wanting to run the sbp jack shaft setup on this bike to solve my tire and chain clearance issues without having to offset my motor. im just curious. can i simply install the jackshaft and run my bike still in its single speed configuration? i know everyone who is usually using these systems is running 3 speed hubs or multi speed cassettes. but im just wanting to keep mine a regular old single speed. is this going to be a problem at all? is there anything i should be aware of. or is iy not an issue at all and thngs will work out just fine staying with single speed configuration. im aware i wont be able to use my coaster brake and i have installed disc brakes front and back. im also running a high compression head with a motor thats ported and polished so i will be ordering the sbp hd kit.

I just havent found much information regarding using the jack shaft with single speed setup. everyone seems to run multiple gears ( which i understand is the main purpose of the jackshaft) but starting to wonder if running it in single speed causes problems or something

also if running in single speed configuration what kind of speed could i expect out of the jack shaft. im not building this bike for speed, my other motorized beach cruiser i have i only put around at about 19 mph. its more for joy riding around town more then commutting or travel.

i also currently dont know if my rear axle is steel or chromoly, im going to be looking into a chromoly axel as sbp suggests. but im also wondering is a chromoly axle a definite must have with the jack shaft if im not shifting any gears, i know its never been a requirement when direct drivingto rear wheel right from the motor.

any advice would be greatly appreciated

 

[FurryOnTheInside]

Shiftless shafter, eh?

 

[jeffsos3000]

Shiftless shafter, eh?

yeah prtty much, im just trying to keep the nice lines and asthetics of the bike so im wanting to keep the motor mounted centered in frame. so only way im aware of doing that is with the jack shaft. but i dont want multi speed gears just good old single speed. needless to say i havent been able to find much info on single speed applications using the jack shaft.

 

[FurryOnTheInside]

It's a lot of money to spend just to offset the chain and lose a little power. Not many shiftless shafters on the forum.
There's no reason you can't. It's the same as an IGH (internally geared hub) with the Shift Kit. Except you won't have the considerable advantage of the gears.
Just check the frame geometry and fat tyres still allow you the room needed to get the jackshaft in behind the seat tube.

 

[jeffsos3000]

It's a lot of money to spend just to offset the chain and lose a little power. Not many shiftless shafters on the forum.
There's no reason you can't. It's the same as an IGH (internally geared hub) with the Shift Kit. Except you won't have the considerable advantage of the gears.
Just check the frame geometry and fat tyres still allow you the room needed to get the jackshaft in behind the seat tube.

yeah i know its an ewxpense for sure, but in this case im taking a money is not an option approach. plus in the future if i ever chose to i would assume i could install a internally geared hub at some point and have a few gears if wanted. but just wanting to keep things simple and basic for now. im glad to hear this wont cause any issues for me.
as far as my wheel to seat tube clearance is concerned i have much more clearancthen the 1.5 inches sbp suggests, so everything is good there.

I keep hearing about power loss from the jack shaft. how much power loss are we actually talking? i understand that power loss is going to happen. but can anyone tell me what that power loss relates to in speed. i dont have to worry about climbing hills or anything at least as where i live is pretty flat aside from a couple over passes

 

[extremeodd]

I can't tell you exactly how much loss there would be, but I'd expect close to a 10% loss transmitting the power to the other side (roller chain drives are anywhere from 90-98% efficient, your adding 2 extra stages which we can assume to be roughly a 5% loss per stage). This could easily be offset with a few bolt-on parts such as a high compression head, an expansion chamber (an mz65, a cdh66/zeda88 would help a little but they aren't worth the money) and a wide bore intake.

The only other concern I've seen with running a jackshaft is the additional torque added to the axle VS running the power directly to the spokes/hub as you would with a standard setup. Everything I've read indicates that you need to upgrade the rear wheels axle to a stronger material to keep it from bending from the torque running through the gearset.

Ignore the naysayers, if you want a jackshaft on a single speed, go for it. If the power you have afterwards isn't acceptable then just buy either a good expansion chamber, port the jug (or buy a ported jug), or do both and have more power than a stock engine with no jackshaft. Or, since you're running the jackshaft, swap over to a multiple speed cassette and have multiple gear ratios so a lack of torque is never, ever an issue!

 

[jeffsos3000]

well my motor definitly isnt stock. it has the cnc machined high compression head, port and polish and the higher power lightning spark system. so im guessing itll be putting out more power then normal. one other thing im wondering about. the fellow i purchased the bike from installed front and rear disc brakes onto it. the front disc is mounted on the front wheel hub and the rear disc is mounted to a cnc hub adaptor along with an original 46 tooth sproket. the calipers however are attached with some sort of clamp that wraps around front fork on the front and around one of the rear wheel arms if i remember correctly. now i realize this probably isnt an optimal setup. but would it be good enough brake system to use for this application? right now i see it as my only option since i cant use a coaster brake with the jack shaft and the bike had no front brake originally

 

[GreasyChris]

Well I run a jackshaft and a 5 speed freewheel 28-14. I haven't noticed any loss of power and my bike regularly hits 80km/h. Any loss you may experience can be made up using different chainrings from sbp. I currently runa 44 tooth driven off the jackshaft and a 36 tooth drives my freewheel. Its has lots of torque and will lift the front wheel if i dump the clutch. You can run a single speed on the rear wheel with no issues. My bike originally came as a single speed. You can also get different size doubler speed freewheels with different teeth counts as well. There's lots of different gear ratios to choose from depending on your needs.

 

[Arty]

There's no doubt that a jackshaft uses up a bit of power (extra bearings, sprockets, chains), but any loss is more than made up for in the ability to keep the engine in the sweet spot using multiple gears. I don't think I'd do it for a single speed though, mainly due to the added complexity, and thus added wear and tear. - -For me though, I've used both single speed, and jackshaft multi-speed, and would go with the multi-speed every time unless it was a race bike.

 

[CrazyDan]

The only real reason for upgrading your rear axle is because of shifting gears. Normally people will have 1st gear at a frame twisting axle bending 30:1+ to make take off real easy and help with super crazy hills. If you run a single speed with normal gear reduction around 16-20:1, you won't have that big of a torque multiplier to the rear.