24 inch Full sus. 6hp driving deraileur build up, pics and story

Discussion in 'Performance Mods' started by professor, Sep 18, 2009.

  1. professor

    professor Active Member

    This is for field use, no peddling- for street, it would need a second jackshaft rater than using the crank shaft, and would need a one way sproket deal.

    The bike is one I got at a curb sale (garbage day) and fixed up a couple of years ago:
    The engine mount is eighth inch steel straight back off the one side with a support bracket mounted where the electric starter was to the frame. Seems pretty solid, of course the frame itself will flex a bit since the notor is cantilevered back so far.
    Initally, i wanted to use the petalcrank to also power the bike so the motor does clear the back of my boots.
    I did not want the engine on the rear triangle bouncing around and adding lots of un-sprung weight, thus the rear frame mount, motor only weighs 10 pounds, have yet to add a muffler system and aircleaner- maybe 3 pounds.
    Ideally this would be a great set-up for a chainsaw motor and it's cent. clutch, gastank and muffler.
    So far I have had to actually buy a crank tool (Avner crank puller fromUSBIKEBARGANS- got it in a couple of days), a 9 tooth #41 sproket from McMaster carr another fast delivery) and a v-belt. Everything else I had.

    Here is a pic of the jackshaft (plain brgs. -had them for decades but ball would be better)- it is slotted for adjustment and mounted on a 1/4 inch bracket with small gussetts-
    Oh, here is a tip- if you have a jackshaft with no keyway, or sprockets/ pulleys without them, you can place the shaft on the item and drill the end so that one half of the hole is in the shaft and one half is in the pulley, then you tap it and put a long set-secrew (or 2 short ones) in the hole. They become a "Key" of sorts. Locking it both from turning and coming off. The downside is they become dedicated. I used quarter twentys in the 1/2 inch jack shaft.

    The concept is to reduce the gear ratio a real lot before it gets to the derailur, thus the 4.5 ratio from the engine to jackshaft and 5 or so to one down from the shaft to the large chain ring. I am hoping the small sproket to the derailer will be enough to kill the ratio some more - I am only looking for around 20 mph and down.

    The next pic shows how I drilled the rivets out of the ring in order to affix a big washer with other washers welded to it (my adapter) which will carry the small sprocket you see in my hand welded to the "adapter".

    The trick here wil be getting the little one to run true. Think I will weld studs to the adapter, measure the sprockets to center as much as I can then clamp and tack weld the sproket to the adaptor.
    Then, bolt them together lightly and set the ring sprocket in place (tight). Then spin it and make sure I can tap it true, go back and final weld the sproket to the adapter, re-mount, tap true and tighten down and tack weld the adaptor in several places.
    Was anyone un-able to follow that explaination?
    There is a lot yet to do. Gotta come up with footpegs, and a bunch of other things.
    Will do more updates as I go..........

  2. roddy4477

    roddy4477 Member

    very resourefull
  3. professor

    professor Active Member

    Thanks Roddy, that sproket was a bugger, lined it up with a bolt thru the middle then tapped it centered (measuring from between the teeth on the little one to the same zone on the big one- using a dial caliper, going back and forth across it). Tack, check runout on the bike, weld it up.

    PS - I found there was only one way the chain ring set would go on that would run true. The reason for the paint marks on the pic:

    I checked the final drive ratio by marking and spinning the jackshaft assembly v/s the tire in the lowest gear on the cassette X engine pulley ratio= 38 to 1. Horray! I think it is geared down enough. Of course there are 5 smaller sprockets back there, so I think this will go a lot faster than I am willing to go.
    By the way, if you do a project like this, be prepared to do things more than once because the first time isn't always right.
    I also had a small fire coming off the bike when welding.
    I should have grounded the welder to the main frame rather than the kickstand. I lifted my hood to find a plume of black smoke- the ground was going thru the brake and derailer cables!
    No wonder 75 amps seemed strangely low.
  4. jclo3313

    jclo3313 New Member

    It's not very pretty, but it's scary cool!
  5. roddy4477

    roddy4477 Member

    thanks for sharing and the pics. I admire the ingenity you used to make and solve the problems that comes with any build that is out of the box. we who have gone down the same path salute you.
  6. professor

    professor Active Member

    I wanted footpegs because it is safer, but this is what I had (and could come up with), I made the pieces out of 1/4 inch x 2 scrap metal mostly.
    There is a loop out of 1/2 round stock joining each side for stregnth.
    Plates go back to the lower triangle tube (hard to see), up to the top and down- around to a plate next to the kickstand- three point mounting.
    They unbolt to get at the bottom bracket (odd name for the crank brg). I cut the crank arms off to get the ends that the pedals thread into and welded them to the mounts. Threads are an odd size- not sae. and not met.
    Lots of fitting and checking with a level /tacking for the pedals/ breaking off re-fitting/re tacking until they were on the same plane both ways.

    After sitting on the bike, the pedals are really in the same basic place widthwise as a normal bike, and my legs go out board of them quite a bit to get to the ground.
    Bike wt. so far- 62#

  7. professor

    professor Active Member

    Clutch details-
    I made a clutch lever up on the handlebars under the left brake lever, with a catch to hold it in a "Freewheel" position like what I have seen here (what a pain-I reccomend buying one).
    Down below, I was surprised at how close to the pivot bolt (from the snowblower) the cable needed to be for correct action. You are looking at a 8" pulley off a riding mower transaxle and a flanged idler off some little tractor:

    Being that this engine was set with a governor, I needed to make a little arm as a throttle stop, with a real light spring to hold it at idle speed. I wanted to retain the governor feature so I would never over rev the engine. So another spring connected to the bell crank I made actually pulls it open. Haven't tested this yet, but am sure details will work out:
    I made a carb flange and some tube braised to it (3/4 inch tube, with a strip taken out to make it a wee bit smaller) to accept a Techumseh air filter from a run-of the mill 3horse).
    I wanted a throttle like a motorcycle but the one I had was some weird design that I could not figure out after I took the little "Clicker" spring out.
    But I did have a shift control that would operate like a snowmobile throttle. It had too much travel, so I braised a stop on it- seems fine.

    How about that red paint? Buick engine red. Found a qt. on my weekly treasure hunt ride.
  8. professor

    professor Active Member

    Here is the good, bad and ugly-
    Gearing was 'way off, so slow in first gear I wondered if it was moving at all. Took off my small sproket I adapted to behind the crank sproket and went to the standard smallest sproket that came on the thing. So the jackshaft just drives that one and the gearing from there to the wheel in low gear is about 1 to 1. Low gear is now around 23 to one, idle is walking speed. Fine.

    The ugly- offsetting the engine like it is, has one big unforseen issue" I managed to bump the bike over and it landed with a crash on the motor fan shroud. Driving the pull start into the fan. Banged it out with a rope attached to a big hammer.
    It is difficult to protect the engine.
    Unless it was in the frame like the HT, OR was solidly mounted a hard tail with a roll-bar to keep it from getting smashed.
    Maybe I can make a bar that goes around under the engine- looping back to the frame:tt1:
    This Tehumseh seems like a solid motor. 25 years old and runs fine. I think it is 144ccs. It probably makes the 6 hp rating at 3500 rpm.
    Wt. is 67#
  9. Hawaii_Ed

    Hawaii_Ed Member

    Wow! That is too wild LOL!
  10. professor

    professor Active Member

    Final update- riding around the yard, gearing is good, power is OK.
    BUT it needs a cent. clutch badly. There are just too many controls at hand. Very confusing. I remember why I stuck the motor out back- so I could pedal. With that option deleted, the engine should be down in the main frame. Bike is put away.
    Now, I am concentrationg on the gas/electric conversion to my Mongoose.